Genetic Code, Transcription, and Translation Overview Wk10

What is the Central Dogma of molecular biology?

The flow of genetic information from DNA to RNA to protein.

How is a gene defined in biology?

A gene is a discrete unit of inheritance, a region of specific nucleotide sequence in a chromosome, or a DNA sequence that codes for a specific polypeptide chain.

What hypothesis did Beadle and Tatum propose in the 1940s?

They proposed the one gene - one enzyme hypothesis, showing a connection between genes and metabolic enzymes using Neurospora crassa.

What is the role of proteins in genetics?

Proteins link genotype to phenotype and are synthesized based on the information encoded in genes.

What are alleles?

Alleles are different versions of genes.

What are the two stages of gene expression?

Transcription and translation.

Where does transcription occur in eukaryotic cells?

Transcription occurs in the nucleus.

What is produced during transcription?

Pre-mRNA is synthesized from the DNA template.

What is RNA processing?

RNA processing involves modifying pre-mRNA into mature mRNA before it is translated.

What is the role of mRNA in translation?

mRNA carries the genetic information from the DNA to the ribosome, where it is translated into a polypeptide.

What is a codon?

A codon is a triplet of nucleotides in mRNA that codes for a specific amino acid.

How many codons are there, and what is their significance?

There are 64 codons; 61 code for amino acids, and 3 are stop signals that end translation.

What is meant by the redundancy of the genetic code?

Redundancy means that more than one codon can specify the same amino acid.

What does it mean that the genetic code is not ambiguous?

No codon specifies more than one amino acid.

What is the significance of Uracil in RNA?

Uracil replaces Thymine in RNA.

What is the difference in translation between prokaryotes and eukaryotes?

In prokaryotes, translation can begin before transcription has finished.

What is the final product of translation?

The final product of translation is a polypeptide.

What is the relationship between DNA and traits?

DNA inherited from parents dictates the synthesis of proteins, which leads to specific traits.

What are the components of the flow of genetic information?

DNA -> Transcription -> mRNA -> Translation -> Polypeptide.

What is the role of ribosomes in translation?

Ribosomes facilitate the synthesis of polypeptides by translating mRNA into amino acid chains.

What does the term 'gene expression' refer to?

Gene expression refers to the process by which information from a gene is used to synthesize a functional gene product, typically a protein.

What must codons be read in to produce the specified polypeptide?

The correct reading frame.

What initiates and terminates the process of translation?

Start and stop codons.

What is transcription?

The DNA-directed synthesis of RNA, the first stage of gene expression.

What role does RNA polymerase play in transcription?

It pries the DNA strands apart and adds RNA nucleotides.

How is RNA related to the DNA template strand?

RNA is complementary to the DNA template strand.

What is the difference between the template strand and the non-template (coding) strand?

The non-template strand specifies the amino acid sequence of the encoded protein, while the template strand provides the template for RNA transcription.

What are the three stages of transcription?

Initiation, elongation, and termination.

What occurs during the initiation stage of transcription?

Promoters signal the transcription start point, and transcription factors mediate the binding of RNA polymerase.

What is the TATA box?

A transcription factor binding site in eukaryotic promoters.

What is the role of Transcription Factor IID?

It binds to the TATA box and initiates the binding of other transcription factors.

What happens during the elongation stage of transcription?

RNA polymerase moves along the DNA, untwisting the double helix and adding nucleotides to the 3′ end of the growing RNA molecule.

How can a gene be transcribed in eukaryotes?

Simultaneously by several RNA polymerases.

What happens during the termination of transcription in bacteria?

The polymerase stops transcription at the terminator.

What occurs after transcription termination in eukaryotes?

Other processing occurs before and after termination.

What is pre-mRNA?

The initial RNA transcript that undergoes processing before becoming mRNA.

What modifications occur to pre-mRNA in eukaryotic cells?

Both ends are altered, and certain interior sections are cut out and spliced together.

What are the functions of the modifications made to mRNA ends?

They facilitate the export of mRNA to the cytoplasm, protect mRNA from hydrolytic enzymes, and help ribosomes attach to the 5′ end.

What is the flow of genetic information from DNA to polypeptide?

Transcription (DNA to pre-mRNA), RNA processing (pre-mRNA to mRNA), and translation (mRNA to polypeptide).

What happens when RNA polymerase hits the stop codon?

It dissociates, the RNA transcript is released, and the DNA helix zips back up.

What is the role of transcription factors in gene expression?

They help direct and regulate gene expression.

What is the significance of the transcription initiation complex?

It is the completed assembly of transcription factors and RNA polymerase II necessary for transcription to begin.

What is the purpose of RNA splicing?

RNA splicing removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence.

What are introns and exons?

Introns are non-coding regions, while exons are expressed regions.

How can introns contribute to gene expression regulation?

Some introns contain sequences that may regulate gene expression.

What is alternative RNA splicing?

Alternative RNA splicing allows some genes to encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing.

What is the role of the spliceosome in RNA splicing?

The spliceosome facilitates RNA splicing by excising introns and uniting exons in mature mRNA.

What are small nuclear ribonucleoproteins (snRNPs)?

snRNPs are components of the spliceosome that consist of various proteins and small nuclear RNAs that recognize splice sites.

What are ribozymes?

Ribozymes are catalytic RNA molecules that can splice RNA.

What is an example of a self-splicing ribozyme?

Group I introns are examples of self-splicing ribozymes.

How does transcription differ between prokaryotes and eukaryotes?

In prokaryotes, there is no mRNA processing needed, and translation can begin before transcription finishes, while in eukaryotes, transcription occurs in the nucleus and is separated from translation in the cytoplasm.

What modifications do eukaryotic RNA transcripts undergo?

Eukaryotic RNA transcripts are modified through RNA processing to yield the finished mRNA.

What is the function of transfer RNA (tRNA) in translation?

tRNA transfers amino acids to the growing polypeptide in a ribosome.

What is the structure of tRNA?

tRNA is a single RNA strand that is about 80 nucleotides long.

What are the two key features of tRNA?

Each tRNA carries a specific amino acid on one end and has an anticodon on the other end to pair with a complementary codon on mRNA.

What is required for charging the tRNA?

Charging the tRNA requires a match between a tRNA and an amino acid, facilitated by the enzyme aminoacyl-tRNA synthetase, and a correct match between the tRNA anticodon and an mRNA codon.

What is the role of aminoacyl-tRNA synthetase?

Aminoacyl-tRNA synthetase catalyzes the covalent bonding of an amino acid to its corresponding tRNA.

What happens during the charging of tRNA?

Amino acid and tRNA enter the active site of the enzyme, and using ATP, the enzyme catalyzes the formation of an aminoacyl-tRNA.

What is the significance of the nuclear envelope in eukaryotic cells?

The nuclear envelope separates transcription from translation, allowing for RNA processing.

What is the relationship between the number of genes and the number of proteins an organism can produce?

The number of different proteins an organism can produce is much greater than its number of genes due to processes like alternative splicing.

What is the end product of transcription in eukaryotic cells?

The end product of transcription in eukaryotic cells is mature mRNA after RNA processing.

What is the role of the ribosome in translation?

The ribosome is the site where translation occurs, synthesizing polypeptides from mRNA.

What is the initial step of translation?

Translation begins with the binding of tRNA carrying an amino acid to the ribosome, matching its anticodon with the mRNA codon.

What is the function of ribosomes in protein synthesis?

Ribosomes couple tRNA anticodons with mRNA codons.

What are the three binding sites of a ribosome for tRNA?

The three binding sites are the P site, A site, and E site.

What does the P site of a ribosome hold?

The P site holds the tRNA that carries the growing polypeptide chain.

What is the role of the A site in a ribosome?

The A site holds the tRNA and the next amino acid to be added.

What happens at the E site of a ribosome?

The E site is the exit site, where discharged tRNAs leave.

What are the three stages of translation?

The three stages of translation are Initiation, Elongation, and Termination.

What is required for all three stages of translation?

All three stages require protein factors that aid in the translation process.

What is the direction in which amino acids are added during elongation?

Amino acids are added to the C-terminus of the growing chain along the mRNA in a 5′ → 3′ direction.

What are the three steps involved in the elongation cycle of translation?

The three steps are codon recognition, peptide bond formation, and translocation.

What signals the start of translation?

The start codon (AUG) signals the start of translation.

What is the role of initiation factors in translation?

Initiation factors bring in the large subunit to complete the translation initiation complex.

What occurs during the termination of translation?

The ribosome reaches a stop codon, a release factor promotes hydrolysis, and ribosomal subunits and other components dissociate.

What is the function of the release factor in translation termination?

The release factor causes the addition of a water molecule instead of an amino acid.

What is meant by 'tRNA third position wobble'?

The third nucleotide base pairing rules in tRNA are not strictly observed.

How many different tRNAs recognize the 61 different codons?

There are 32 different tRNAs that recognize 61 different codons.

What does it mean that the genetic code is redundant?

It means that several different codons can code for the same amino acid.

What is the role of GTP in the translation process?

GTP provides energy for some steps in the translation process.

What is the function of peptidyl transferase during translation?

Peptidyl transferase catalyzes peptide bond formation during elongation.

What happens during codon recognition in the elongation cycle?

The ribosome is ready for the next aminoacyl tRNA to enter the A site.

What is the structure of the translation initiation complex?

The translation initiation complex includes the small ribosomal subunit, mRNA, and initiator tRNA.

What are the stop codons in mRNA?

The stop codons are UAG, UAA, or UGA.

What is a polyribosome?

A structure formed by multiple ribosomes translating a single mRNA simultaneously.

What advantage do polyribosomes provide to bacterial cells?

They enable a cell to make many copies of a polypeptide quickly.

How do bacteria streamline the process of polypeptide synthesis?

By coupling transcription and translation.

What is the role of RNA polymerase in bacteria?

It synthesizes mRNA from the DNA template during transcription.

What separates the processes of transcription and translation in eukaryotic cells?

The nuclear envelope.

What must happen to RNA before it leaves the nucleus in eukaryotic cells?

RNA must undergo processing.

Where does polypeptide synthesis begin?

In the cytosol.

What type of ribosomes make proteins for the endomembrane system?

Bound ribosomes on the endoplasmic reticulum (ER).

What marks polypeptides destined for the ER or secretion?

A signal peptide.

What is often required for a polypeptide to become a functional protein?

Modification or movement.

What happens to a polypeptide chain during its synthesis?

It coils and folds spontaneously into a specific shape.

What are post-translational modifications?

Chemical modifications that may be required before a protein is functional.

How does the process of polypeptide synthesis contribute to protein diversity?

Through chemical modification, resulting in more proteins than there are genes.

What is the significance of the 5′ and 3′ ends of mRNA in translation?

They indicate the directionality for ribosomes during translation.

What is the size of a polyribosome in bacterial cells as seen in TEM?

Approximately 0.25 µm.

What is the function of signal peptides in polypeptide synthesis?

To direct polypeptides to their correct cellular destinations.