Biology Chapter 15 review (2)

Genes & Proteins

What you need for Translation

• Ribosome: machine that makes the protein (large and small subunit)

• mRNA: carries the code (codon) to make the protein

• tRNA: carries amino acid

What you need for translation

• Ribosome: machine that makes the protein (large and small subunit)

• mRNA: carries the code (codon) to make the protein

• tRNA: carries amino acid

What you need for Translation

Translation is the process of decoding an mRNA (messenger RNA) sequence into a polypeptide chain (protein)

• mRNA Template: the single-stranded message transcribed from DNA that contains the triplet codon sequence (read in 5'→ 3' direction). It begins with the start codon AUG (methionine) and ends with a stop codon (UAA, UAG, or UGA)

• Ribosomes: macromolecular machines composed of rRNA (ribosomal RNA) and proteins. They consist of a small subunit (which binds the mRNA) and a large subunit (which catalyzes peptide bond formation). Ribosomes contain three active tRNA-binding sites:

• Transfer RNA (tRNA): Adaptor molecules that bridge nucleic acids to amino acids. Each tRNA has:

• An anticodon loop (3'→ 5' triplet) complementary to the mRNA codon (5'→ 3')

• An amino acid attachment site at the 3' end

• Ribosome: machine that makes the protein (large and small subunit)

• mRNA: carries the code (codon) to make the protein

• tRNA: carries amino acid

What you need for Translation:

Translation is the process by which a cell's ribosomes read the nucleotide sequence of a messenger RNA (mRNA) molecule and assemble a corresponding polypeptide (protein) chain of amino acids

• mRNA (Messenger RNA) Template: the single-stranded transcript containing the coded genetic message read in triplet codons

• Ribosomes: macromolecular machines composed of ribosomal RNA (rRNA) and proteins, divided into a small subunit (which binds mRNA) and a large subunit (which catalyzes peptide bond formation). They contain three critical active sites

• tRNA (Transfer RNA) Molecules: adaptor molecules featuring a 3-nucleotide anticodon complementary to an mRNA codon on one end and a specific amino acid attachment site on the other

• Ribosome: machine that makes the protein (large and small subunit)

• mRNA: carries the code (codon) to make the protein

• tRNA: carries amino acid

What you need for translation:

Translation is the process by which a cell's ribosomes read the nucleotide sequence of a messenger RNA (mRNA) molecule and assemble a corresponding polypeptide (protein) chain of amino acids

• Specific molecular components, energy, and a set of sequential steps to convert an mRNA template into a polypeptide chain

• mRNA (Messenger RNA): the template carrying the genetic code read in triplet sequences called codons (starting with the start codon AUG, which codes for methionine)

• Ribosomes: macromolecular complexes made of rRNA (ribosomal RNA) and proteins, consisting of a small and large subunit

• tRNA (Transfer RNA): adaptor molecules that have a 3-nucleotide anticodon complementary to an mRNA codon on one end and a specific amino acid attached to the other

Ribosome

A non-membrane-bound molecular complex composed of ribosomal RNA (rRNA) and proteins. It serves as the physical site of translation in both prokaryotic and eukaryotic cells, decoding messenger RNA (mRNA) sequences into polypeptide (protein) chains

• A non-membrane-bound molecular complex composed of ribosomal RNA (rRNA) and proteins that serves as the site of protein synthesis in all living cells

• Ribosomes: machines that make the protein

• A ribosome is a non-membrane-bound cellular structure composed of ribosomal RNA (rRNA) and proteins that serves as the molecular machine for translation

Structure: Consists of two distinct subunits (a large subunit and a small subunit) that assemble around an mRNA strand

• Prokaryotes: 70S ribosomes

• Eukaryotes: 80S ribosomes

Ribosome

A non-membrane-bound molecular complex composed of ribosomal RNA (rRNA) and proteins. It serves as the physical site of translation in both prokaryotic and eukaryotic cells, decoding messenger RNA (mRNA) sequences into polypeptide (protein) chains

• A non-membrane-bound molecular complex composed of ribosomal RNA (rRNA) and proteins that serves as the site of protein synthesis in all living cells

• Ribosomes: machines that make the protein

• A ribosome is a non-membrane-bound cellular structure composed of ribosomal RNA (rRNA) and proteins that serves as the molecular machine for translation

Structure: Consists of two distinct subunits (a large subunit and a small subunit) that assemble around an mRNA strand

• Prokaryotes: 70S ribosomes

• Eukaryotes: 80S ribosomes

Contains three vital tRNA-binding slots:

• A site (Aminoacyl): receives the incoming charged tRNA

• P site (Peptidyl): holds the tRNA carrying the growing polypeptide chain

• E site (Exit): where the uncharged (empty) tRNA exits the ribosome

Ribosome

A non-membrane-bound molecular complex composed of ribosomal RNA (rRNA) and proteins. It serves as the physical site of translation in both prokaryotic and eukaryotic cells, decoding messenger RNA (mRNA) sequences into polypeptide (protein) chains

• Ribosomes: machines that make the protein

• A ribosome is a non-membrane-bound cellular structure composed of ribosomal RNA (rRNA) and proteins that serves as the molecular machine for translation

Structure: Consists of two distinct subunits (a large subunit and a small subunit) that assemble around an mRNA strand

• Prokaryotes: 70S ribosomes

• Eukaryotes: 80S ribosomes

Contains three vital tRNA-binding slots:

• A site (Aminoacyl): receives the incoming charged tRNA

• P site (Peptidyl): holds the tRNA carrying the growing polypeptide chain

• E site (Exit): where the uncharged (empty) tRNA exits the ribosome

Large ribosomal subunit

The larger half of a ribosome responsible for catalyzing peptide bond formation during protein synthesis (translation). Made of ribosomal RNA (rRNA) and proteins, it joins with the small ribosomal subunit around a strand of messenger RNA (mRNA) to build polypeptide chains

• the larger half of a ribosome responsible for joining amino acids together into a polypeptide chain during protein synthesis (translation). Made of ribosomal RNA (rRNA) and proteins, it acts as a ribozyme (an RNA enzyme) by catalyzing the formation of covalent peptide bonds

• the large ribosomal subunit is the bigger of the two ribonucleoprotein complexes that make up a ribosome. Its primary role during translation is to catalyze the formation of peptide bonds between amino acids to build a polypeptide chain

Large ribosomal subunit

The larger half of a ribosome responsible for catalyzing peptide bond formation during protein synthesis (translation). Made of ribosomal RNA (rRNA) and proteins, it joins with the small ribosomal subunit around a strand of messenger RNA (mRNA) to build polypeptide chains

• the larger half of a ribosome responsible for joining amino acids together into a polypeptide chain during protein synthesis (translation). Made of ribosomal RNA (rRNA) and proteins, it acts as a ribozyme (an RNA enzyme) by catalyzing the formation of covalent peptide bonds

• the larger of the two macromolecular complexes that form a functional ribosome, composed of ribosomal RNA (rRNA) and proteins. Its primary role during protein synthesis (translation) is to catalyze the formation of peptide bonds between adjacent amino acids to build a polypeptide chain

Small ribosomal subunit

The smaller of the two molecular complexes—composed of ribosomal RNA (rRNA) and proteins—that make up a functional ribosome. Its primary role during protein synthesis (translation) is to bind to messenger RNA (mRNA) and decode its genetic sequence so that the correct amino acids are assembled

• the smaller of the two molecular complexes—composed of ribosomal RNA (rRNA) and proteins—that make up a functional ribosome. Its primary role during protein synthesis (translation) is to bind messenger RNA (mRNA) and decode the genetic message by ensuring accurate base-pairing between mRNA codons and transfer RNA (tRNA) anticodons

• Initiation of Translation: the small subunit is the first component to bind to the mRNA transcript. It scans the mRNA (or uses specific rRNA-mRNA interactions in prokaryotes) to locate the start codon (AUG) and establish the correct reading frame

• Decoding Genetic Information: once the initiator tRNA binds to the start codon and the large subunit joins to form a complete ribosome, the small subunit acts as the "decoding center". It verifies that each incoming tRNA anticodon matches the exposed mRNA codon before a peptide bond is formed

Small ribosomal subunit

The smaller of the two molecular complexes—composed of ribosomal RNA (rRNA) and proteins—that make up a functional ribosome. Its primary role during protein synthesis (translation) is to bind to messenger RNA (mRNA) and decode its genetic sequence so that the correct amino acids are assembled

• the smaller of the two molecular complexes—composed of ribosomal RNA (rRNA) and proteins—that make up a functional ribosome. Its primary role during protein synthesis (translation) is to bind messenger RNA (mRNA) and decode the genetic message by ensuring accurate base-pairing between mRNA codons and transfer RNA (tRNA) anticodons

• Initiation of Translation: the small subunit is the first component to bind to the mRNA transcript. It scans the mRNA (or uses specific rRNA-mRNA interactions in prokaryotes) to locate the start codon (AUG) and establish the correct reading frame

• Decoding Genetic Information: once the initiator tRNA binds to the start codon and the large subunit joins to form a complete ribosome, the small subunit acts as the "decoding center". It verifies that each incoming tRNA anticodon matches the exposed mRNA codon before a peptide bond is formed

Ribosome tRNA binding sites

During protein translation, the ribosome contains three tRNA-binding sites located in the large subunit that coordinate the delivery of amino acids and the growth of a polypeptide chain

• A site (Aminoacyl site): the entry point where an incoming charged tRNA (aminoacyl-tRNA) first binds, matching its anticodon to the current mRNA codon

• P site (Peptidyl site): the location holding the peptidyl-tRNA, which is the tRNA attached to the growing polypeptide chain. Here, a peptide bond forms between the new amino acid in the A site and the existing chain

• E site (Exit site): the final site where the empty (uncharged) tRNA resides briefly before it detaches from the ribosome and returns to the cytoplasm to pick up another amino acid

Ribosome tRNA binding sites

During translation in protein synthesis, the ribosome contains three tRNA binding sites located on the large subunit that coordinate the movement of transfer RNA (tRNA) and the growth of the polypeptide chain

During protein translation, the ribosome contains three tRNA-binding sites located in the large subunit that coordinate the delivery of amino acids and the growth of a polypeptide chain

• A site (Aminoacyl site): the entry point where an incoming charged tRNA (aminoacyl-tRNA) first binds, matching its anticodon to the current mRNA codon

• P site (Peptidyl site): the location holding the peptidyl-tRNA, which is the tRNA attached to the growing polypeptide chain. Here, a peptide bond forms between the new amino acid in the A site and the existing chain

• E site (Exit site): the final site where the empty (uncharged) tRNA resides briefly before it detaches from the ribosome and returns to the cytoplasm to pick up another amino acid

Large vs. Small ribosomal subunit

Ribosomes are made of two main parts: a small ribosomal subunit and a large ribosomal subunit. They work together to turn messenger RNA (mRNA) into proteins during a process called translation

Small Ribosomal Subunit

• Primary Role: decodes the genetic message by reading the mRNA codons and matching them with the right transfer RNA (tRNA) anticodons

• Prokaryotes (Bacteria & Archaea): known as the 30S subunit

• Eukaryotes: known as the 40S subunit

Large Ribosomal Subunit

• Primary Role: Acts as the catalytic center that forms peptide bonds between amino acids to build a growing protein chain.

• Prokaryotes (Bacteria & Archaea): known as the 50S subunit

• Eukaryotes: known as the 60S subunit

Large vs. Small ribosomal subunit

Ribosomes are made of two main parts: a small ribosomal subunit and a large ribosomal subunit. They work together to turn messenger RNA (mRNA) into proteins during a process called translation

Small Ribosomal Subunit

• Primary Role: decodes the genetic message by reading the mRNA codons and matching them with the right transfer RNA (tRNA) anticodons

• Prokaryotes (Bacteria & Archaea): known as the 30S subunit

• Eukaryotes: known as the 40S subunit

Large Ribosomal Subunit

• Primary Role: Acts as the catalytic center that forms peptide bonds between amino acids to build a growing protein chain.

• Prokaryotes (Bacteria & Archaea): known as the 50S subunit

• Eukaryotes: known as the 60S subunit

Large vs. Small ribosomal subunit

A ribosome consists of two separate subunits (a large and a small subunit) made of ribosomal RNA (rRNA) and proteins that lock together during translation to synthesize proteins

• Ribosomes are made of two main parts: a small ribosomal subunit and a large ribosomal subunit. They work together to turn messenger RNA (mRNA) into proteins during a process called translation

Small Ribosomal Subunit

• Primary Function: acts as the decoding unit. It binds to the mRNA template and matches mRNA codons with the correct incoming tRNA anticodons to ensure accurate genetic information flow

  • Eukaryotes: 40S subunit

  • Prokaryotes: 30S subunit

Large Ribosomal Subunit

• Primary Function: acts as the catalytic unit. It holds the tRNA molecules and contains the peptidyl transferase center (acting as a ribozyme) to catalyze peptide bond formation, linking amino acids into a growing polypeptide chain. It also features the A, P, and E sites for tRNA movement

  • Eukaryotes: 60S subunit (combines with 40S to form an 80S ribosome)

  • Prokaryotes: 50S subunit (combines with 30S to form a 70S ribosome)

Large vs. Small ribosomal subunit

A ribosome consists of two separate subunits (a large and a small subunit) made of ribosomal RNA (rRNA) and proteins that lock together during translation to synthesize proteins

• Ribosomes are made of two main parts: a small ribosomal subunit and a large ribosomal subunit. They work together to turn messenger RNA (mRNA) into proteins during a process called translation

Small Ribosomal Subunit

• Primary Function: acts as the decoding unit. It binds to the mRNA template and matches mRNA codons with the correct incoming tRNA anticodons to ensure accurate genetic information flow

  • Eukaryotes: 40S subunit

  • Prokaryotes: 30S subunit

Large Ribosomal Subunit

• Primary Function: acts as the catalytic unit. It holds the tRNA molecules and contains the peptidyl transferase center (acting as a ribozyme) to catalyze peptide bond formation, linking amino acids into a growing polypeptide chain. It also features the A, P, and E sites for tRNA movement

  • Eukaryotes: 60S subunit (combines with 40S to form an 80S ribosome)

  • Prokaryotes: 50S subunit (combines with 30S to form a 70S ribosome)

mRNA

A single-stranded RNA molecule that is transcribed from a DNA template and carries genetic information out of the nucleus to the ribosome in the cytoplasm, where its sequence of codons is translated into a polypeptide chain

• mRNA: carries the code to make the protein

• a single-stranded RNA molecule transcribed from a DNA template that carries genetic instructions out of the nucleus to a ribosome for protein synthesis

• Codons: the nucleotide sequence is read by ribosomes in non-overlapping, 3-letter units called codons, where each codon specifies a particular amino acid

mRNA

A single-stranded RNA molecule that is transcribed from a DNA template and carries genetic information out of the nucleus to the ribosome in the cytoplasm, where its sequence of codons is translated into a polypeptide chain

• mRNA: carries the code to make the protein

• a single-stranded RNA molecule transcribed from a DNA template that carries genetic instructions out of the nucleus to a ribosome for protein synthesis

• Codons: the nucleotide sequence is read by ribosomes in non-overlapping, 3-letter units called codons, where each codon specifies a particular amino acid

Messenger RNA (mRNA)

A single-stranded RNA molecule transcribed from a DNA template during transcription that carries genetic protein-building instructions from the nucleus out to the ribosomes in the cytoplasm for translation

• Structure: single-stranded nucleic acid containing ribose sugar, a phosphate backbone, and four nitrogenous bases (adenine, cytosine, guanine, and uracil instead of thymine)

• Central Dogma Role: acts as the mobile intermediary in the flow of genetic information: DNA → mRNA → Protein

• Eukaryotic Processing: In eukaryotes, raw pre-mRNA undergoes post-transcriptional modifications before leaving the nucleus—including adding a 5' cap, a poly-A tail, and splicing out non-coding introns while keeping coding exons

• Codons: read by the ribosome in non-overlapping, 3-nucleotide sequences called codons, which correspond to specific amino acids

• mRNA: carries the code to make the protein

• a single-stranded RNA molecule transcribed from a DNA template that carries genetic instructions out of the nucleus to a ribosome for protein synthesis

Messenger RNA (mRNA)

A single-stranded RNA molecule transcribed from a DNA template during transcription that carries genetic protein-building instructions from the nucleus out to the ribosomes in the cytoplasm for translation

• Structure: single-stranded nucleic acid containing ribose sugar, a phosphate backbone, and four nitrogenous bases (adenine, cytosine, guanine, and uracil instead of thymine)

• Central Dogma Role: acts as the mobile intermediary in the flow of genetic information: DNA → mRNA → Protein

• Eukaryotic Processing: In eukaryotes, raw pre-mRNA undergoes post-transcriptional modifications before leaving the nucleus—including adding a 5' cap, a poly-A tail, and splicing out non-coding introns while keeping coding exons

• Codons: read by the ribosome in non-overlapping, 3-nucleotide sequences called codons, which correspond to specific amino acids

• mRNA: carries the code to make the protein

• a single-stranded RNA molecule transcribed from a DNA template that carries genetic instructions out of the nucleus to a ribosome for protein synthesis

tRNA

A small RNA molecule that acts as a molecular "adapter" or "translator" during protein synthesis (translation). It connects the nucleotide language of messenger RNA (mRNA) to the amino acid language of proteins

• Anticodon: a specific three-nucleotide sequence at one end of the tRNA that base-pairs with a complementary codon on the mRNA strand

• Amino Acid Attachment Site: the opposite end of the tRNA molecule carries the specific amino acid that corresponds to its anticodon

• Shape: It forms a classic cloverleaf secondary structure that folds into a compact 3D L-shape

• Charging Enzyme: the enzyme aminoacyl-tRNA synthetase links each tRNA to its correct amino acid

• tRNA carries the amino acid

• a small, folded RNA molecule that acts as an adapter/translator during protein synthesis (translation) by linking messenger RNA (mRNA) codons to specific amino acids

tRNA

A small RNA molecule that acts as a molecular "adapter" or "translator" during protein synthesis (translation). It connects the nucleotide language of messenger RNA (mRNA) to the amino acid language of proteins

• Anticodon: a specific three-nucleotide sequence at one end of the tRNA that base-pairs with a complementary codon on the mRNA strand

• Amino Acid Attachment Site: the opposite end of the tRNA molecule carries the specific amino acid that corresponds to its anticodon

• Shape: It forms a classic cloverleaf secondary structure that folds into a compact 3D L-shape

• Charging Enzyme: the enzyme aminoacyl-tRNA synthetase links each tRNA to its correct amino acid

• tRNA carries the amino acid

• a small, folded RNA molecule that acts as an adapter/translator during protein synthesis (translation) by linking messenger RNA (mRNA) codons to specific amino acids

Transfer RNA (tRNA)

A small, functional RNA molecule that acts as a molecular "adaptor" or "translator" during protein synthesis (translation). It bridges the gap between the nucleotide sequence of messenger RNA (mRNA) and the amino acid sequence of a growing polypeptide chain

• tRNA carries the amino acid

• Dual Function: tRNA has two crucial sites that allow it to translate the genetic code

  • Anticodon Loop: a specific sequence of three unpaired nucleotides that base-pairs with a complementary mRNA codon (triplet) at the ribosome

  • Amino Acid Attachment Site: the 3' end (always terminating in the sequence CCA) which binds a specific amino acid corresponding to that anticodon

• Structure:

  • Forms a characteristic cloverleaf shape in two dimensions due to internal base-pairing

transfer RNA (tRNA)

A small RNA molecule that acts as a molecular "adapter" or "translator" during protein synthesis (translation). It connects the nucleotide language of messenger RNA (mRNA) to the amino acid language of proteins

• Anticodon: a specific three-nucleotide sequence at one end of the tRNA that base-pairs with a complementary codon on the mRNA strand

• Amino Acid Attachment Site: the opposite end of the tRNA molecule carries the specific amino acid that corresponds to its anticodon

• Shape: It forms a classic cloverleaf secondary structure that folds into a compact 3D L-shape

• Charging Enzyme: the enzyme aminoacyl-tRNA synthetase links each tRNA to its correct amino acid

• tRNA carries the amino acid

• a small, folded RNA molecule that acts as an adapter/translator during protein synthesis (translation) by linking messenger RNA (mRNA) codons to specific amino acids

Anticodon

An anticodon is a sequence of three adjacent nucleotides on a transfer RNA (tRNA) molecule that base-pairs with a complementary three-nucleotide sequence—called a codon—on a messenger RNA (mRNA) strand during translation

• Location: located on the anticodon loop of a tRNA molecule, while the matching codon is located on the mRNA strand at the ribosome

• Function: acts as the physical and molecular "adapter" or bridge that ensures the correct amino acid is delivered and added to the growing polypeptide chain

• Base Pairing: follows standard complementary rules (A pairs with U, C pairs with G) via hydrogen bonds. For example, if the mRNA codon is 5'-AUG-3', the complementary tRNA anticodon is 3'-UAC-5'

• Always use the mRNA codon—never the tRNA anticodon—when reading a genetic code / codon chart to determine amino acid sequences. Looking up an anticodon directly on a standard mRNA codon chart will yield the wrong amino acid

Anticodon

A sequence of three nucleotides located on a transfer RNA (tRNA) molecule that binds to a complementary codon on a messenger RNA (mRNA) strand during translation

• a sequence of three adjacent nucleotides on a transfer RNA (tRNA) molecule that binds to a complementary codon on a messenger RNA (mRNA) strand during translation

• Location: found on the loop of a tRNA molecule, while the matching codon is on the mRNA molecule

• Function: acts as the physical and molecular bridge ensuring translation fidelity by delivering the specific amino acid corresponding to the mRNA instruction

• Base-Pairing Rules: follows complementary base pairing (A pairs with U, C pairs with G) in an antiparallel orientation (5' → 3' vs. 3' → 5')

• When determining which amino acid is added to the polypeptide chain using a codon chart, you must always look up the mRNA codon, never the tRNA anticodon

Anticodon

An anticodon is a sequence of three adjacent nucleotides on a transfer RNA (tRNA) molecule that base-pairs with a complementary three-nucleotide sequence—called a codon—on a messenger RNA (mRNA) strand during translation

• Location: located on the anticodon loop of a tRNA molecule, while the matching codon is located on the mRNA strand at the ribosome

• Function: acts as the physical and molecular "adapter" or bridge that ensures the correct amino acid is delivered and added to the growing polypeptide chain

• Base Pairing: follows standard complementary rules (A pairs with U, C pairs with G) via hydrogen bonds. For example, if the mRNA codon is 5'-AUG-3', the complementary tRNA anticodon is 3'-UAC-5'

• Always use the mRNA codon—never the tRNA anticodon—when reading a genetic code / codon chart to determine amino acid sequences. Looking up an anticodon directly on a standard mRNA codon chart will yield the wrong amino acid

Anticodon on tRNA

A sequence of three nucleotides on a transfer RNA (tRNA) molecule that is complementary to a specific codon on messenger RNA (mRNA). During translation at the ribosome, the anticodon base-pairs with the mRNA codon to ensure that the correct amino acid is added to the growing polypeptide chain

• An anticodon is a sequence of three adjacent nucleotides on a transfer RNA (tRNA) molecule that base-pairs with a complementary three-nucleotide sequence—called a codon—on a messenger RNA (mRNA) strand during translation

• Structure and Location: a tRNA molecule folds into a cloverleaf-like shape with two functional ends. The anticodon loop sits at one end, while the amino acid attachment site sits at the opposite 3' end

• Antiparallel Base Pairing: codons and anticodons bind in an antiparallel orientation. The ribosome reads the mRNA codon in the 5' to 3' direction, so the complementary tRNA anticodon aligns in the 3' to 5' direction. RNA base-pairing rules apply, meaning adenine (A) pairs with uracil (U) and cytosine (C) pairs with guanine (G)

• Translation Example. If an mRNA strand has the start codon 5'-AUG-3', the matching tRNA carries the anticodon 3'-UAC-5' and delivers the amino acid methionine

Codon

A sequence of three consecutive nucleotides in messenger RNA (mRNA)—or DNA—that specifies a particular amino acid, a start signal, or a stop signal during protein synthesis

• The Triplet Code: the genetic code is read in non-overlapping, continuous groups of three bases (ex; 5'-AUG-CCU-GAA-3'), known as a triplet code

• Start Codon: AUG is the universal start codon. It establishes the reading frame and codes for the amino acid methionine (though AUG later in a sequence just adds methionine)

• Stop Codons: UAA, UAG, and UGA signal the termination of translation. They do not code for any amino acid and are recognized by release factors rather than tRNA

• Number and Redundancy: There are 4^3 = 64 possible codon combinations:

  • 61 codons code for the 20 standard amino acids

  • 3 codons are stop signals

  • The code is redundant (degenerate)—meaning multiple different codons can specify the same amino acid—which can help protect against silent mutations

Codon vs. Anticodon

Codon vs. Anticodon

• Codon: a sequence of three nucleotides on mRNA (messenger RNA) that codes for a specific amino acid or a stop signal during translation

• Anticodon: a complementary sequence of three nucleotides on tRNA (transfer RNA) that binds to the mRNA codon and delivers the corresponding amino acid

Codon

A sequence of three consecutive nucleotides in messenger RNA (mRNA)—or DNA—that specifies a particular amino acid, a start signal, or a stop signal during protein synthesis

• a sequence of three consecutive nucleotides on a messenger RNA (mRNA) molecule that specifies a particular amino acid or a stop signal during translation

• The Triplet Code: the genetic code is read by the ribosome three nucleotides at a time

• Directionality: mRNA codons are read by the ribosome in the 5' to 3' direction

• Start Codon: AUG is the universal start codon. It codes for the amino acid methionine and establishes the reading frame for translation

• Stop Codons: UAA, UAG, and UGA signal the termination of translation. They do not code for amino acids or bind to tRNAs; instead, release factors bind to them to release the polypeptide chain

• Redundancy (Degeneracy): there are 64 possible unique codons (4³), but only 20 standard amino acids. This means multiple codons can code for the same amino acid, which can protect against silent mutations

Anticodon

A sequence of three nucleotides on a tRNA (transfer RNA) molecule that is complementary and antiparallel to a specific codon on an mRNA (messenger RNA) strand

• a sequence of three nucleotides on a tRNA (transfer RNA) molecule that is complementary and antiparallel to a specific codon on an mRNA (messenger RNA) strand

• Location: found on a specific loop (the anticodon loop) of a tRNA molecule

Translation

The process in gene expression where the nucleotide sequence of a messenger RNA (mRNA) molecule is decoded by a ribosome to assemble a specific sequence of amino acids, forming a polypeptide chain (protein)

• the biological process in which a ribosome reads the nucleotide sequence of messenger RNA (mRNA) in triplet units called codons to assemble a corresponding chain of amino acids (a polypeptide)

• It represents the "protein synthesis" stage of the Central Dogma (DNA → RNA → Protein) and occurs at the ribosome in the cytoplasm or rough endoplasmic reticulum

The Three Main Stages:

1. Initiation: the ribosome assembles around the target mRNA, meeting the AUG start codon

2. Elongation: tRNAs deliver amino acids matching each codon; peptide bonds form between them as the ribosome shifts (translocates) along the mRNA

3. Termination: a stop codon is reached, a release factor binds, and the completed polypeptide chain is freed

Translation

The process in gene expression where the nucleotide sequence of a messenger RNA (mRNA) molecule is decoded by a ribosome to assemble a specific sequence of amino acids, forming a polypeptide chain (protein)

• the biological process in which a ribosome reads the nucleotide sequence of messenger RNA (mRNA) in triplet units called codons to assemble a corresponding chain of amino acids (a polypeptide)

• It represents the "protein synthesis" stage of the Central Dogma (DNA → RNA → Protein) and occurs at the ribosome in the cytoplasm or rough endoplasmic reticulum

The Three Main Stages:

1. Initiation: the ribosome assembles around the target mRNA, meeting the AUG start codon

2. Elongation: tRNAs deliver amino acids matching each codon; peptide bonds form between them as the ribosome shifts (translocates) along the mRNA

3. Termination: a stop codon is reached, a release factor binds, and the completed polypeptide chain is freed

Types of Ribosomes in eukaryotes vs. porkaryotes

Ribosomes are non-membranous, RNA-protein complexes found in all living cells that translate mRNA into polypeptide chains

Prokaryotic Ribosomes (70S)

• Size/Type: 70S ribosomes (measured by Svedberg units of sedimentation rate).

• Subunits: consist of a large 50S subunit and a small 30S subunit

• Location: free-floating in the cytoplasm

Eukaryotic Ribosomes (80S)

• Size/Type: 80S ribosomes

• Subunits: consist of a large 60S subunit and a small 40S subunit

• Location & Functional Types:

  • Free ribosomes: suspended in the cytosol; synthesize proteins that function inside the cytosol

  • Bound (or fixed) ribosomes: attached to the outside of the rough endoplasmic reticulum (rough ER) or the nuclear envelope; synthesize proteins destined for insertion into membranes, packaging into organelles (like lysosomes), or export/secretion from the cell

Types of Ribosomes eukaryotes vs. prokaryotes

Ribosomes are non-membranous, RNA-protein complexes found in all living cells that translate mRNA into polypeptide chains

Prokaryotic Ribosomes (70S)

• Size/Type: 70S ribosomes (measured by Svedberg units of sedimentation rate).

• Subunits: consist of a large 50S subunit and a small 30S subunit

• Location: free-floating in the cytoplasm

Eukaryotic Ribosomes (80S)

• Size/Type: 80S ribosomes

• Subunits: consist of a large 60S subunit and a small 40S subunit

• Location & Functional Types:

  • Free ribosomes: suspended in the cytosol; synthesize proteins that function inside the cytosol

  • Bound (or fixed) ribosomes: attached to the outside of the rough endoplasmic reticulum (rough ER) or the nuclear envelope; synthesize proteins destined for insertion into membranes, packaging into organelles (like lysosomes), or export/secretion from the cell

Types of ribosomes in Eukaryotes

Eukaryotic ribosomes are classified based on their size/structure and their cellular location

1. Classification by Size and Structure (80S vs. 70S)

• Eukaryotic Cytosolic Ribosomes (80S):

  • Found in the cytosol and on the rough endoplasmic reticulum (RER)

  • Composed of a 40S small subunit and a 60S large subunit (totaling 80S in Svedberg units)

• Endosymbiotic / Organellar Ribosomes (70S):

  • Found inside mitochondria and chloroplasts

  • Structurally smaller (a 30S small subunit and a 50S large subunit, totaling 70S) and more closely resemble prokaryotic ribosomes, which serves as key evidence for the endosymbiotic theory

Types of ribosomes in Prokaryotes

Prokaryotes contain 70S ribosomes in their cytoplasm, which are smaller than the 80S ribosomes found in eukaryotes

Structure of Prokaryotic (70S) Ribosomes

• Whole Ribosome: 70S (Svedberg units measure sedimentation rate/size)

• Large Subunit: 50S subunit, which contains 5S and 23S rRNA molecules plus about 31 protein subunits. It houses the peptidyl transferase activity that forms peptide bonds

• Small Subunit: 30S subunit, which contains a 16S rRNA molecule plus about 21 protein subunits. It binds and decodes the mRNA sequence

Types of ribosomes prokaryotes vs. eukaryotes

Ribosomes are non-membranous, RNA-protein complexes responsible for protein synthesis (translation) in all living cells. The primary distinction between prokaryotic and eukaryotic ribosomes lies in their size, sedimentation rate (measured in Svedberg units, S), and subunit composition

Prokaryotic Ribosomes (70S)

• Size & Type: 70S ribosomes

• Subunits: composed of a 50S large subunit and a 30S small subunit

• Location: freely dispersed throughout the cytoplasm (cytosol)

Eukaryotic Ribosomes (80S)

• Size & Type: 80S ribosomes

• Subunits: composed of a 60S large subunit and a 40S small subunit

• Location & Function:

  • Free ribosomes: floating in the cytosol; synthesize proteins that function inside the cytosol

  • Bound ribosomes: attached to the exterior of the rough endoplasmic reticulum (rough ER); synthesize proteins destined for insertion into membranes, packaging into organelles (like lysosomes), or export (secretion) from the cell

Location of translation

Translation takes place on ribosomes in the cell cytoplasm (either floating freely or attached to the rough endoplasmic reticulum)

Key distinctions by cell type:

• Eukaryotes: transcription occurs inside the nucleus, and the messenger RNA (mRNA) must leave the nucleus to undergo translation on ribosomes in the cytoplasm or on the surface of the rough endoplasmic reticulum

• Prokaryotes (Bacteria): because prokaryotes lack a nucleus, transcription and translation happen simultaneously in the cytoplasm

Location of translation

Translation takes place on ribosomes in the cell cytoplasm (either floating freely or attached to the rough endoplasmic reticulum)

Key Location Details by Cell Type:

• Eukaryotes (plants, animals, fungi): translation occurs in the cytoplasm or on the membrane of the rough endoplasmic reticulum (rough ER), after the mRNA has been transcribed in the nucleus and exported out

  • Proteins made by free ribosomes generally function inside the cytosol

  • Proteins made by bound ribosomes on the rough ER are typically packaged for the endomembrane system, cell membrane secretion, or lysosomes

• Prokaryotes (bacteria): translation occurs in the cytoplasm. Because prokaryotes lack a nucleus, transcription and translation can happen simultaneously on the same mRNA strand

Location of translation

Translation takes place on ribosomes in the cell cytoplasm (either floating freely or attached to the rough endoplasmic reticulum)

Key distinctions by cell type:

• Eukaryotes: transcription occurs inside the nucleus, and the messenger RNA (mRNA) must leave the nucleus to undergo translation on ribosomes in the cytoplasm or on the surface of the rough endoplasmic reticulum

• Prokaryotes (Bacteria): because prokaryotes lack a nucleus, transcription and translation happen simultaneously in the cytoplasm

Translation diagram

The diagram illustrates translation. During this process, a ribosome reads an mRNA sequence to assmeble a specific chain of amino acids into a polypeptide

Key Components:

• mRNA strand (bottom letters): the continous sequence (AUG CUG CCC GUC) is messenger RNA (mRNA). It is read by ribosomes in groups of three nucleotides called codons, moving in the 5’ → 3’ direction

• tRNA molecules (blue cloverleaf shapes): transfer RNA (tRNA) molecules act as molecular adapters. Each tRNA carries a specific amino acid on one end and displays a three-base anticodon (shown in red) on the other

• Anticodons (red letters): the seuqences UAC, GAC, GGG, and CAG pair with complementary mRNA codons using standard RNA base pairing rules (A pairs with U, and C pairs with G)

• Growing polypeptide chain (top circles): the linked circles represent amino acids (Met - Leu - Pro - Val) joined together by covalent peptide bonds to form a primary protein structure

Translation diagram

The diagram illustrates translation. During this process, a ribosome reads an mRNA sequence to assmeble a specific chain of amino acids into a polypeptide

Key Components:

• mRNA strand (bottom letters): the continous sequence (AUG CUG CCC GUC) is messenger RNA (mRNA). It is read by ribosomes in groups of three nucleotides called codons, moving in the 5’ → 3’ direction

• tRNA molecules (blue cloverleaf shapes): transfer RNA (tRNA) molecules act as molecular adapters. Each tRNA carries a specific amino acid on one end and displays a three-base anticodon (shown in red) on the other

• Anticodons (red letters): the seuqences UAC, GAC, GGG, and CAG pair with complementary mRNA codons using standard RNA base pairing rules (A pairs with U, and C pairs with G)

• Growing polypeptide chain (top circles): the linked circles represent amino acids (Met - Leu - Pro - Val) joined together by covalent peptide bonds to form a primary protein structure

Translation diagram

The diagram illustrates translation. During this process, a ribosome reads an mRNA sequence to assmeble a specific chain of amino acids into a polypeptide

• The diagram depicts translation, the second major stage of protein synthesis. During this process, a cell decodes a messenger RNA (mRNA) sequence to assemble a specific chain of amino acids that will fold into a functional protein

Key Components:

• mRNA strand (bottom letters): the continous sequence (AUG CUG CCC GUC) is messenger RNA (mRNA). It is read by ribosomes in groups of three nucleotides called codons, moving in the 5’ → 3’ direction

• tRNA molecules (blue cloverleaf shapes): transfer RNA (tRNA) molecules act as molecular adapters. Each tRNA carries a specific amino acid on one end and displays a three-base anticodon (shown in red) on the other

• Anticodons (red letters): the seuqences UAC, GAC, GGG, and CAG pair with complementary mRNA codons using standard RNA base pairing rules (A pairs with U, and C pairs with G)

• Growing polypeptide chain (top circles): the linked circles represent amino acids (Met - Leu - Pro - Val) joined together by covalent peptide bonds to form a primary protein structure

Translation diagram

The diagram shows translation (protein synthesis). Translation is the process where a ribosome reads an mRNA sequence to build a polypeptide (protein) chain using tRNA molecules

Key Components:

• mRNA strand (bottom row): the continous seuquence AUG CUG CCC GUC represents messenger RNA (mRNA). It is read in groups of three bases called codons

• tRNA anticodons (middle row in red): the triplets UAC, GAC, GGG, and CAG represents transfer RNA (tRNA) anticodons. Each anticodon pairs with its complementary mRNA codon (A pairs with U, and C pairs with G)

• Polypeptide chain (top connected circles): the linked circles labeled Met - Leu - Pro - Val represents amino acids joined together by peptide bonds to form a growing protein chain

Translation diagram

The diagram shows translation (protein synthesis). Translation is the process where a ribosome reads an mRNA sequence to build a polypeptide (protein) chain using tRNA molecules

Key Components:

• mRNA strand (bottom row): the continous seuquence AUG CUG CCC GUC represents messenger RNA (mRNA). It is read in groups of three bases called codons

• tRNA anticodons (middle row in red): the triplets UAC, GAC, GGG, and CAG represents transfer RNA (tRNA) anticodons. Each anticodon pairs with its complementary mRNA codon (A pairs with U, and C pairs with G)

• Polypeptide chain (top connected circles): the linked circles labeled Met - Leu - Pro - Val represents amino acids joined together by peptide bonds to form a growing protein chain

Peptide bonds

A peptide bond is a covalent chemical bond that links two amino acids together during protein synthesis

• A strong covalent bond formed between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of an adjacent amino acid

• Formation (Dehydration Synthesis / Condensation): the reaction releases a molecule of water (H2O) as a hydroxyl group (-OH) is removed from the carboxyl group and a hydrogen atom (-H) is removed from the amino group

• Breakdown (Hydrolysis): the reverse reaction breaks the peptide bond by consuming a water molecule, a process typically catalyzed by enzymes

• Protein Structure:

  • Linear chains of amino acids connected by peptide bonds form the primary structure of a protein

Peptide bonds

A peptide bond is a covalent chemical bond that links two amino acids together during protein synthesis

• a covalent chemical bond that links two amino acids together to form a protein's primary structure

• A strong covalent bond formed between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of an adjacent amino acid

• Formation (Dehydration Synthesis / Condensation): the reaction releases a molecule of water (H2O) as a hydroxyl group (-OH) is removed from the carboxyl group and a hydrogen atom (-H) is removed from the amino group

• Breakdown (Hydrolysis): the reverse reaction breaks the peptide bond by consuming a water molecule, a process typically catalyzed by enzymes

• Protein Structure:

  • Linear chains of amino acids connected by peptide bonds form the primary structure of a protein

Peptide bond

A peptide bond is a covalent chemical bond that links two amino acids together during protein synthesis

• a covalent chemical bond that links two amino acids together to form a protein's primary structure

• A strong covalent bond formed between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of an adjacent amino acid

• Formation (Dehydration Synthesis/ Condensation): the reaction releases a molecule of water (H2O) as a hydroxyl group (-OH) is removed from the carboxyl group and a hydrogen atom (-H) is removed from the amino group

• Breakdown (Hydrolysis): the reverse reaction breaks the peptide bond by consuming a water molecule, a process typically catalyzed by enzymes

• Protein Structure:

  • Linear chains of amino acids connected by peptide bonds form the primary structure of a protein

What type of bond links amino acids?

Amino acids are linked together by peptide bonds, which are a specific type of covalent bond

• A peptide bond is a strong covalent bond (specifically an amide linkage) that joins the carboxyl group (-COOH) of one amino acid to the amino group (-NH2) of an adjacent amino acid

Key Details:

• How they form: they are created through a dehydration synthesis (or condensation) reaction

• Which groups react: the carboxyl group (–COOH) of one amino acid reacts with the amino group (–NH₂) of another, releasing a molecule of water (H2O)

• Protein level: peptide bonds form the primary structure (the linear sequence) of a polypeptide chain or protein

Amino acids

An amino acid is the organic monomer (building block) used to construct proteins

Every standard amino acid shares a common backbone bonded to a central alpha (α) carbon

• A hydrogen atom (-H)

• An amino group (-NH₂)

• A carboxyl group (-COOH)

• A variable R group (side chain) that gives each amino acid its unique chemical identity

• The 20 Common Amino Acids: Cells use 20 different amino acids encoded by genetic information

• R Group Properties: amino acids differ only in their R groups, which dictate their chemical behavior

• Peptide Bonds: amino acids join together via dehydration synthesis (condensation reactions), forming covalent peptide bonds between the carboxyl group of one amino acid and the amino group of the next

Amino acids

An amino acid is the organic monomer (building block) used to construct proteins

Every standard amino acid shares a common backbone bonded to a central alpha (α) carbon

• A hydrogen atom (-H)

• An amino group (-NH₂)

• A carboxyl group (-COOH)

• A variable R group (side chain) that gives each amino acid its unique chemical identity

• The 20 Common Amino Acids: Cells use 20 different amino acids encoded by genetic information

• R Group Properties: amino acids differ only in their R groups, which dictate their chemical behavior

• Peptide Bonds: amino acids join together via dehydration synthesis (condensation reactions), forming covalent peptide bonds between the carboxyl group of one amino acid and the amino group of the next

Polypeptide chain

A polypeptide chain is a continuous, unbranched polymer of amino acids linked together by covalent peptide bonds

• Monomers: the building blocks are amino acids, each containing an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group) attached to a central alpha (α) carbon

• Peptide Bond Formation: chains are built via dehydration synthesis (condensation reactions) driven by ribosomes during translation. The carboxyl group of one amino acid joins the amino group of the next, releasing a molecule of water

• A polypeptide chain is a continuous, unbranched linear polymer of amino acids joined together by covalent peptide bonds

Polypeptide chain

A polypeptide chain is a continuous, unbranched polymer of amino acids linked together by covalent peptide bonds

• Monomers: the building blocks are amino acids, each containing an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group) attached to a central alpha (α) carbon

• Peptide Bond Formation: chains are built via dehydration synthesis (condensation reactions) driven by ribosomes during translation. The carboxyl group of one amino acid joins the amino group of the next, releasing a molecule of water

• A polypeptide chain is a continuous, unbranched linear polymer of amino acids joined together by covalent peptide bonds

Polypeptide

Alinear, unbranched polymer consisting of many amino acids linked together by covalent peptide bonds. It serves as the building block or precursor of a functional protein

• A polypeptide is a linear, unbranched polymer consisting of many amino acids linked together by covalent peptide bonds

• Monomers: the building blocks of polypeptides are amino acids. Each amino acid contains a central carbon attached to an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a variable R group (side chain)

• Formation (Dehydration Synthesis): peptide bonds form between the carboxyl group of one amino acid and the amino group of the next through a dehydration synthesis (condensation) reaction that releases a water molecule. This is carried out by ribosomes during translation

Primary protein structure

The primary structure of a protein is the unique, linear sequence of amino acids in a polypeptide chain

The primary structure of a protein is its unique, linear sequence of amino acids linked together in a polypeptide chain

• Monomers & Building Blocks: proteins are polymers made of amino acid monomers. Each amino acid has a central (alpha) carbon attached to an amino group (-NH2), a carboxyl group (-COOH)), a hydrogen atom, and a variable side chain (R-group)

• Bond Type: amino acids are joined by peptide bonds, which are strong covalent bonds formed via dehydration synthesis (condensation reactions) between the carboxyl group of one amino acid and the amino group of the next

During the initiation phase of translation, the ribosome assembles around the messenger RNA (mRNA) to establish the correct reading frame before protein synthesis begins

Key Steps of Initiation

• Small Subunit & mRNA Binding: the small ribosomal subunit binds to the mRNA molecule

  • Eukaryotes: the ribosome recognizes and binds to the 5′ cap of the mRNA and scans downstream until it finds the start codon

  • Prokaryotes: the ribosome binds directly to a specific sequence upstream of the start codon called the Shine-Dalgarno sequence

• Start Codon Recognition: the ribosome locates the start codon AUG, which codes for the amino acid methionine

• Initiator tRNA: a transfer RNA (tRNA) carrying methionine and possessing the complementary anticodon binds to the AUG start codon in the P-site of the ribosome

• Large Subunit Assembly: the large ribosomal subunit joins the complex, completing the functional ribosome setup (initiation complex) so elongation can begin

Translation - initiation

During the initiation phase of translation, the cell assembles the molecular machinery required to read the messenger RNA (mRNA) and start building a polypeptide chain

• the ribosome assembles around the messenger RNA (mRNA) molecule and the first transfer RNA (tRNA) to establish the correct reading frame before synthesis begins

Key Steps in Initiation

• Ribosome Assembly: the small ribosomal subunit binds to the mRNA molecule

• Start Codon Recognition: the ribosome locates and aligns with the start codon AUG on the mRNA, which codes for the amino acid methionine

• Initiator tRNA: a specialized transfer RNA (tRNA) carrying methionine (with the complementary anticodon UAC) binds to the start codon in the ribosome's P site

• Large Subunit Joins: the large ribosomal subunit locks into place on top of the small subunit, completing the functional translation initiation complex (ready for elongation)

Initiation - Translation

The first stage of protein synthesis where the ribosome assembles around the target messenger RNA (mRNA) and establishes the reading frame to start building a polypeptide

Key Components:

• mRNA Strand: the messenger RNA (mRNA) carries the genetic code in three-base sequences called codons, starting with the sequence AUG

• Ribosomal Subunits: the small ribosomal subunits bind to the mRNA first, followed by the attachment of the large ribosomal subunit to form a functional ribosome

• Initiator tRNA: a transfer RNA (tRNA) molecule with the complementary anticodon UAC pairs with the start codon AUG on the mRNA

• Amino Acid (Met): the initiator tRNA carries the amino acid methionine (Met), which serves as the first amino acid in the growing polypeptide chain

Initiation - Translation

The first stage of protein synthesis where the ribosome assembles around the target messenger RNA (mRNA) and establishes the reading frame to start building a polypeptide

Key Components:

• mRNA Strand: the messenger RNA (mRNA) carries the genetic code in three-base sequences called codons, starting with the sequence AUG

• Ribosomal Subunits: the small ribosomal subunits bind to the mRNA first, followed by the attachment of the large ribosomal subunit to form a functional ribosome

• Initiator tRNA: a transfer RNA (tRNA) molecule with the complementary anticodon UAC pairs with the start codon AUG on the mRNA

• Amino Acid (Met): the initiator tRNA carries the amino acid methionine (Met), which serves as the first amino acid in the growing polypeptide chain

Initiation

The first stage of translation, where the ribosome assembles around the messenger RNA (mRNA) molecule and prepares to read the genetic code to build a polypeptide chain

• the first phase of translation (protein synthesis), where the ribosome, messenger RNA (mRNA), and the first transfer RNA (tRNA) assemble together to establish the correct reading frame

Key Events of Initiation

• Ribosome Assembly: the small ribosomal subunit binds to the mRNA strand

• Start Codon Recognition: the ribosome scans the mRNA until it reaches the start codon (AUG), which sets the correct reading frame for the rest of the sequence

• Initiator tRNA Binding: a special initiator transfer RNA (tRNA) carrying the amino acid methionine (with the anticodon UAC) pairs with the AUG start codon in the ribosome's P-site

• Large Subunit Joining: the large ribosomal subunit locks into place over the small subunit, completing the functional initiation complex ready for elongation

Initiation - translation

The first stage of translation, the process where a ribosome builds a polypeptide (protein) using the genetic instructions carried by an mRNA (messenger RNA) molecule

Key Events

• Small Ribosomal Subunit Binding: the small ribosomal subunit binds to the mRNA molecule

• Start Codon Recognition: the ribosome scans the mRNA until it locates the start codon, which is AUG

• Initiator tRNA Arrival: an initiator transfer RNA (tRNA) carrying the amino acid methionine (which pairs with the AUG codon via its complementary anticodon, UAC) binds to the start codon

• Large Subunit Assembly: the large ribosomal subunit joins the small subunit and the mRNA, placing the initiator tRNA into the P-site of the ribosome and completing the functional translation initiation complex

Translation-initiation complex

The assembled molecular structure that marks the starting point of protein synthesis, formed when the mRNA template, the small ribosomal subunit, the initiator tRNA, and ribosomal/initiation factor proteins come together at the start codon before elongation begins

• mRNA (Messenger RNA): provides the genetic code, specifically containing the start codon AUG (which codes for methionine)

• Small Ribosomal Subunit: scans the mRNA strand (in eukaryotes) or binds via the Shine-Dalgarno sequence (in prokaryotes) to locate the start codon

• Initiator tRNA: carries the first amino acid, methionine (or formylmethionine in bacteria), and binds directly to the AUG start codon via its anticodon (UAC) at the ribosome's P site

• Initiation Factors & GTP: protein helpers and GTP (energy source) that assist in bringing the components together and driving the attachment of the large ribosomal subunit to complete the functional ribosome

Transition-initiation complex