lec 2

genetic code

The genetic code is the rule system that tells the cell which 3-letter RNA sequence corresponds to which amino acid during protein synthesis. It is basically the "dictionary" that translates nucleic acid language into protein language. For example, one codon may mean methionine, while another may mean leucine, and some codons mean stop. It is important because without the genetic code, the cell would have no way to convert information in mRNA into a real protein

codon

A codon is a sequence of 3 RNA bases on mRNA that tells the ribosome what to do during translation. Most codons specify one amino acid, but some codons tell the ribosome to stop translation. Codons are read in order, one after another, from the 5' end toward the 3' end of mRNA. They are important because the protein sequence depends directly on the codon order

RNA bases

The four RNA bases are A, U, G, and C, which stand for adenine, uracil, guanine, and cytosine. These are the "letters" used to write codons in RNA. Because there are 4 choices for each of the 3 positions in a codon, there are 4³ = 64 possible codons. These bases are important because all translation language is built from them

A in codons

A stands for adenine, one of the four nitrogenous bases in RNA. It can pair with U during normal RNA-DNA or RNA-RNA base pairing. When you see a codon like AUG or AUU, the A is simply one letter in that 3-letter instruction. It matters because changing even one letter can change the amino acid or create a stop signal

U in codons

U stands for uracil, the RNA base that replaces thymine found in DNA. Uracil pairs with adenine during base pairing. When you see codons like UUG, UAG, or UGA, that first letter is uracil. It is important because RNA uses U instead of T, so codons are always written with U, not T

G in codons

G stands for guanine, one of the four RNA bases. Guanine normally pairs with cytosine. In codons like UUG or UGA, the G is simply part of the 3-letter code being read by the ribosome. It matters because different placements of G can completely change the meaning of a codon

C in codons

C stands for cytosine, one of the four RNA bases. Cytosine pairs with guanine. Codons containing C may code for very different amino acids depending on the full 3-letter combination. This is important because the ribosome reads the whole codon, not just one base

64 codons

There are 64 total codons because each codon has 3 positions and each position can contain 1 of 4 RNA bases, so 4 × 4 × 4 = 64. Out of these, 61 code for amino acids and 3 are stop codons. This means the code has more codons than amino acids, which is why multiple codons can specify the same amino acid. This is important for understanding degeneracy of the genetic code

61 sense codons

The 61 sense codons are the codons that actually code for amino acids. They are called "sense" because they carry amino acid meaning in translation. Since there are only 20 standard amino acids, many amino acids are encoded by more than one codon. This matters because mutations in the third base may sometimes leave the amino acid unchanged

stop codons

Stop codons are codons that do not code for any amino acid and instead tell the ribosome to stop translation. In standard genetic code, the stop codons are UAA, UAG, and UGA. When the ribosome reaches one of them, release factors bind and the finished protein is released. They are important because they define where the protein ends

UAG

UAG is one of the three stop codons in the genetic code. It does not code for an amino acid, so when the ribosome reads it, translation stops instead of adding another amino acid. This prevents the protein from becoming too long. It is important because if a normal amino acid codon mutates into UAG, translation may stop too early

UGA

UGA is another stop codon in the standard genetic code. Like UAG and UAA, it signals termination of translation rather than amino acid insertion. When it enters the A site of the ribosome, release factors recognize it and end protein synthesis. It is important because proper protein length depends on correct stop codon recognition

UAA

UAA is the third standard stop codon. It tells the ribosome that the coding sequence has ended and that the completed polypeptide should be released. It does not recruit a tRNA carrying an amino acid. It is important because without stop codons, translation would continue into noncoding regions

AUG

AUG is the main start codon used to begin translation. It codes for methionine, and in bacteria the initiating methionine is usually formyl-methionine. AUG is important because it sets the reading frame, meaning it determines how all the later codons will be grouped. If translation starts at the wrong AUG, the whole protein sequence can be wrong

UUG

UUG is a normal codon that codes for leucine in the standard genetic code. It is not a stop codon, so the ribosome would add leucine if this codon appears in the correct reading frame. This shows why every codon has to be memorized by meaning, not guessed from one letter. It is important because similar-looking codons can mean completely different things

AUU

AUU is a codon that codes for isoleucine in the standard genetic code. It is one of several codons for isoleucine, showing that the genetic code is degenerate. Even though AUU looks similar to AUG, it does not function as the usual start codon. This is important because one-base differences can change the translation instruction

degenerate genetic code

Degenerate means that more than one codon can code for the same amino acid. For example, one amino acid may have 2, 3, 4, or even 6 codons. This does not mean sloppy coding

it means redundancy. It is important because some mutations become "silent" and do not change the protein sequence

not ambiguous genetic code

Not ambiguous means that each codon has only one meaning in the standard code. A codon may have sibling codons that code for the same amino acid, but one codon itself does not mean two different amino acids at the same time. This makes translation reliable. It is important because protein synthesis would fail if codons had multiple meanings

nearly universal genetic code

Nearly universal means that the same codons usually mean the same amino acids in almost all organisms. For example, AUG usually means methionine in bacteria, plants, animals, and humans. There are small exceptions, especially in mitochondria and some microbes, which is why we say "nearly" universal rather than absolutely universal. This is important because it shows how conserved biology is across life

mRNA

mRNA stands for messenger RNA, the RNA molecule that carries the coding information copied from DNA to the ribosome. The ribosome reads mRNA codon by codon to build a protein. You can think of mRNA as the temporary working copy of a gene. It is important because translation cannot occur without the message to read

translation

Translation is the process of making a protein by reading the codons on mRNA. The ribosome reads each codon, tRNAs bring the matching amino acids, and those amino acids are joined into a polypeptide chain. Translation turns nucleic acid information into a functional protein sequence. It is important because proteins carry out most cellular work

reading frame

The reading frame is the way the ribosome groups RNA bases into sets of three during translation. If the frame starts at the correct place, the codons make biological sense and produce the intended protein. If the frame shifts, the codons change and the protein becomes abnormal. It is important because AUG usually helps establish the correct frame

5' to 3' direction

5' to 3' describes the direction in which nucleic acids are read or synthesized, based on the numbering of carbons in the sugar. During translation, the ribosome reads mRNA codons from the 5' end toward the 3' end. During nucleic acid synthesis, new nucleotides are also added in the 5'→3' direction. This is important because many exam questions test directionality

tRNA

tRNA stands for transfer RNA, the adapter molecule that connects the codon on mRNA with the correct amino acid. One end of tRNA carries the amino acid, and another part contains the anticodon that base-pairs with the codon. This lets the ribosome insert the correct amino acid at the correct time. It is important because amino acids cannot recognize codons by themselves

anticodon

The anticodon is a 3-base sequence on tRNA that is complementary to the codon on mRNA. For example, if the codon is AUG, the anticodon on the matching tRNA pairs with it according to base-pair rules. This pairing ensures that the correct amino acid is delivered. It is important because anticodon-codon matching is central to translation accuracy

aminoacyl-tRNA

Aminoacyl-tRNA is a tRNA that has been loaded with its correct amino acid. It is the "charged" form of tRNA used in translation. The amino acid is attached to the 3' end of the tRNA before it enters the ribosome. It is important because the ribosome uses aminoacyl-tRNA as the direct substrate for protein synthesis

ribosome

The ribosome is a ribonucleoprotein complex made of rRNA and proteins that performs translation. It binds mRNA, positions tRNAs, and catalyzes peptide bond formation. In bacteria it has a small 30S and large 50S subunit that form the 70S ribosome. It is important because it is the machine that actually builds proteins

30S and 50S ribosomal subunits

In bacteria, the small ribosomal subunit is 30S and the large subunit is 50S, together forming the 70S ribosome. The S stands for Svedberg unit, which reflects sedimentation behavior, not simple arithmetic size. The small subunit mainly helps decode mRNA, while the large subunit performs peptide bond formation. This is important because prokaryotic translation questions often test these numbers

A site

The A site of the ribosome is the aminoacyl site where the incoming charged tRNA first binds. The codon currently being read is positioned here. If the anticodon matches correctly, that amino acid becomes the next one added to the growing chain. It is important because the A site is where decoding of the next codon happens

P site

The P site is the peptidyl site of the ribosome. It usually holds the tRNA carrying the growing polypeptide chain. During peptide bond formation, the chain is transferred from the tRNA in the P site to the amino acid on the tRNA in the A site. It is important because it anchors the growing protein during elongation

E site

The E site is the exit site of the ribosome. After a tRNA has given up its amino acid and becomes uncharged, it moves to the E site before leaving the ribosome. This helps make room for the next tRNA cycle. It is important because orderly movement through A, P, and E sites keeps elongation organized

amino acid activation

Amino acid activation is the step where an amino acid is prepared for translation by being attached to its correct tRNA. This is done by aminoacyl-tRNA synthetase and requires ATP. The process makes an aminoacyl-AMP intermediate before the amino acid is transferred to tRNA. It is important because peptide bond formation depends on amino acids being activated first

ATP in amino acid activation

ATP provides the energy needed to activate amino acids before they are attached to tRNA. The amino acid reacts with ATP to form aminoacyl-AMP, which is a high-energy intermediate. This energy is then used to form the bond between the amino acid and tRNA. It is important because translation fidelity and efficiency depend on this activation step

aminoacyl-AMP

Aminoacyl-AMP is the activated intermediate formed when an amino acid reacts with ATP during tRNA charging. It contains a high-energy bond that helps drive transfer of the amino acid to tRNA. This is not the form used directly in the ribosome, but it is a necessary step before aminoacyl-tRNA is made. It is important because it explains how ATP is used in translation before the ribosome even starts elongating

aminoacyl-tRNA synthetase

Aminoacyl-tRNA synthetase is the enzyme that attaches the correct amino acid to the correct tRNA. Each amino acid has its own synthetase or a very specific one, and these enzymes are critical for fidelity. If the wrong amino acid is attached, the ribosome usually cannot detect the mistake later. This is important because synthetases, not the ribosome, are the real guardians of amino acid accuracy

Shine-Dalgarno sequence

The Shine-Dalgarno sequence is a purine-rich sequence in bacterial mRNA upstream of the start codon. It helps align the mRNA correctly on the 30S ribosomal subunit so AUG is placed in the right spot for initiation. You can think of it as a bacterial ribosome-positioning signal. It is important because bacterial initiation depends on proper start-site alignment

IF-1, IF-2, IF-3

These are bacterial initiation factors that help assemble the initiation complex. IF-3 helps keep the 30S and 50S subunits from joining too early, IF-1 helps organize the small subunit, and IF-2 uses GTP to bring the initiator tRNA. Together they ensure translation starts correctly. They are important because initiation is highly controlled and errors here shift the whole protein sequence

fMet

fMet stands for N-formylmethionine, the modified methionine used to initiate translation in bacteria. It is carried by a special initiator tRNA and used specifically at the beginning of the new polypeptide. Later internal AUG codons usually insert regular methionine, not formyl-methionine. This is important because bacterial initiation is distinguished by this special first amino acid

elongation factors

Elongation factors are helper proteins used during the elongation stage of translation. In bacteria, the main ones discussed here are EF-Tu, EF-Ts, and EF-G. They help deliver charged tRNA, recycle factor activity, and move the ribosome along mRNA. They are important because elongation is not just the ribosome alone

it depends on regulated protein helpers and GTP

EF-Tu

EF-Tu is a bacterial elongation factor that binds GTP and escorts the incoming aminoacyl-tRNA to the A site of the ribosome. After correct codon-anticodon pairing, GTP is hydrolyzed and EF-Tu leaves. This helps make sure only properly matched tRNAs are accepted efficiently. It is important because it improves elongation accuracy and timing

EF-Ts

EF-Ts is the elongation factor that helps regenerate EF-Tu back to its active GTP-bound form after EF-Tu has released GDP. In other words, EF-Ts recycles EF-Tu so it can bring another aminoacyl-tRNA. This keeps elongation going repeatedly. It is important because without recycling, EF-Tu activity would quickly run out

EF-G

EF-G is the bacterial elongation factor responsible for translocation, the step where the ribosome moves one codon forward on the mRNA. It uses GTP hydrolysis to drive this movement. After translocation, the peptidyl-tRNA shifts from A to P site and the empty tRNA shifts toward E site. This is important because without EF-G the ribosome would stall after each peptide bond

peptide bond

A peptide bond is the covalent bond that links one amino acid to the next in a protein. During translation, the ribosome forms this bond between the growing chain in the P site and the new amino acid in the A site. This is how a polypeptide lengthens one residue at a time. It is important because protein structure is literally built from repeated peptide bonds

translocation

Translocation is the step in elongation where the ribosome moves one codon along the mRNA toward the 3' end. This shifts tRNAs from A to P and from P to E site, opening the A site for the next aminoacyl-tRNA. EF-G and GTP are needed for this in bacteria. It is important because elongation must physically advance codon by codon

release factors

Release factors are proteins that recognize stop codons in the ribosomal A site and trigger termination of translation. Since stop codons do not have matching tRNAs, release factors take over instead. They promote hydrolysis of the bond linking the completed polypeptide to the final tRNA. They are important because they end translation properly and free the new protein

posttranslational modification

Posttranslational modification means a protein is chemically changed after it has already been synthesized on the ribosome. Examples include phosphorylation, glycosylation, cleavage, acetylation, disulfide bond formation, and prosthetic group addition. These changes often determine whether the protein becomes active, stable, or correctly localized. This is important because the ribosome usually makes only the raw starting version of many proteins

phosphorylation

Phosphorylation is the addition of a phosphate group, usually to serine, threonine, or tyrosine residues in proteins. It commonly changes protein activity, interactions, or signaling behavior. Because it is reversible, it acts like a molecular on/off or tuning switch. It is important because many enzymes and signaling pathways are controlled this way

glycosylation

Glycosylation is the covalent addition of carbohydrate chains to proteins. This often happens during or after protein synthesis and helps with folding, stability, recognition, and secretion. Glycoproteins and proteoglycans rely on these modifications. It is important because many membrane and secreted proteins are nonfunctional without proper carbohydrate attachment

proteolytic processing

Proteolytic processing means a larger inactive precursor protein is cut into a smaller active form. This is common for hormones and digestive enzymes such as proinsulin, trypsinogen, and chymotrypsinogen. The cleavage activates or matures the protein. It is important because many proteins are deliberately made inactive first for safety and control

zymogen

A zymogen is an inactive enzyme precursor that must be activated later, usually by proteolytic cleavage. Digestive proteases are classic examples because producing them in active form would damage the cells that synthesize them. Zymogens allow safe storage and transport before activation. This is important because pancreatic and gastric self-protection depends on this strategy

pepsinogen

Pepsinogen is the inactive zymogen form of pepsin made by chief cells in the stomach. In the acidic stomach environment, it is converted into active pepsin. Pepsin then starts protein digestion by cleaving peptide bonds, especially near aromatic amino acids. It is important because stomach proteolysis begins with this protected precursor system

trypsinogen

Trypsinogen is the inactive pancreatic precursor of trypsin. It is activated in the intestine by enteropeptidase, and then trypsin can activate more trypsinogen plus other pancreatic zymogens. This creates a powerful enzyme activation cascade. It is important because premature activation inside the pancreas can cause acute pancreatitis

enteropeptidase

Enteropeptidase is an intestinal enzyme that activates trypsinogen into trypsin. It is located where pancreatic proteases are supposed to become active, which helps protect the pancreas from self-digestion. Once trypsin is formed, it amplifies activation of other zymogens. This is important because it is the physiological trigger for pancreatic protease activation

acute pancreatitis

Acute pancreatitis is inflammation and self-digestion of the pancreas caused by premature activation of pancreatic digestive enzymes inside pancreatic tissue. Instead of being activated in the intestinal lumen, zymogens become active too early and start digesting the organ itself. This causes severe pain and can be life-threatening. It is important because it is a classic clinical consequence of failed zymogen control

protein digestion

Protein digestion is the breakdown of dietary proteins into absorbable amino acids and small peptides. It begins in the stomach with acid denaturation and pepsin, then continues in the small intestine with pancreatic proteases and brush-border enzymes. Different proteases have different cleavage preferences, making digestion efficient. It is important because proteins must be broken down before their amino acids can be absorbed and reused

transamination

Transamination is the transfer of an amino group from one amino acid to an alpha-keto acid. Usually the amino group is transferred to alpha-ketoglutarate to form glutamate. This lets the body collect nitrogen from many amino acids in a common form. It is important because most amino acid degradation starts this way rather than by direct free-ammonia release

deamination

Deamination is the removal of an amino group as free ammonia or through reactions that effectively release it from the amino acid skeleton. In human amino acid metabolism, glutamate dehydrogenase is especially important because glutamate acts as the main nitrogen collector. The released ammonia can then enter urea synthesis. This is important because nitrogen must be removed safely before carbon skeletons can be used for energy

trans-deamination

Trans-deamination is the combined process where amino groups are first transferred to glutamate by transamination, and then glutamate undergoes oxidative deamination to release ammonia. This two-step system is efficient because many amino acids can funnel nitrogen through glutamate. It links amino acid breakdown to urea production. It is important because it explains why glutamate sits at the center of nitrogen metabolism

PLP

PLP stands for pyridoxal phosphate, the active coenzyme form of vitamin B6. It is required by aminotransferases and many amino acid-related reactions such as decarboxylation. PLP helps stabilize intermediates and transfer amino groups. It is important because many amino acid metabolism reactions fail when vitamin B6-dependent chemistry is impaired

decarboxylation of amino acids

Decarboxylation removes the carboxyl group from an amino acid, usually releasing CO2 and producing an amine. Many important neurotransmitters are made this way from amino acid precursors. These reactions usually require PLP. This is important because amino acid metabolism is directly tied to brain signaling molecules

dopamine

Dopamine is a catecholamine neurotransmitter derived ultimately from tyrosine. It is important in movement, reward, and several central nervous system pathways. Low dopamine is associated with Parkinson disease, while dysregulation may contribute to psychiatric disease. It is important because it shows how amino acid-derived molecules become crucial signaling compounds

GABA

GABA, gamma-aminobutyrate, is the major inhibitory neurotransmitter in the brain and is formed by decarboxylation of glutamate. It helps reduce neuronal excitability. Low GABA activity can contribute to seizures. It is important because it is a direct example of amino acid metabolism producing neurotransmitters

histamine

Histamine is formed by decarboxylation of histidine. It acts as a vasodilator, participates in allergic responses, and also stimulates gastric acid secretion. Because one molecule has roles in immunity and digestion, it is commonly tested from both angles. It is important because it shows how amino acid-derived amines can have diverse physiological functions

serotonin

Serotonin is a neurotransmitter derived from tryptophan through a multistep pathway that includes decarboxylation. It is involved in mood, gut function, sleep, and other regulatory processes. It is another example of an amino acid becoming a signaling molecule. It is important because tryptophan metabolism often appears in both normal physiology and disease questions

Which statement(s) explain the genetic code and how codons translate into amino acids

The genetic code is the system that converts RNA sequences into amino acids during protein synthesis. A codon is a sequence of 3 RNA bases (A = adenine, U = uracil, G = guanine, C = cytosine) read on mRNA, where mRNA is the messenger RNA carrying genetic information from DNA. Each codon corresponds to one amino acid or a stop signal, meaning it tells the ribosome what building block to add. This is important because without this code, the cell cannot translate nucleic acid information into functional proteins

Which compound(s) determine initiation and termination of translation and how specific codons function

AUG is the start codon, meaning it signals where translation begins and codes for methionine, the first amino acid. UAA, UAG, and UGA are stop codons, meaning they do not code for amino acids but instead signal the ribosome to stop protein synthesis. These codons are read by the ribosome, which is the protein-making machine made of rRNA and proteins. This is important because starting or stopping at the wrong codon changes the entire protein structure

Which statement(s) is/are correct regarding RNA bases and how codon combinations are formed

RNA bases include adenine (A), uracil (U), guanine (G), and cytosine (C), which are nitrogen-containing molecules that form genetic sequences. A codon is made of three of these bases, meaning there are 4³ = 64 possible codons. Out of these, 61 code for amino acids and 3 are stop codons. This is important because it explains degeneracy, where multiple codons can code for the same amino acid

Which compound(s) participate(s) in translation and why amino acids cannot directly read codons

tRNA (transfer RNA) acts as an adapter molecule that carries amino acids and matches them to codons using an anticodon. The anticodon is a 3-base sequence on tRNA that pairs with the codon on mRNA through base pairing. Amino acids themselves cannot recognize RNA sequences, so tRNA is required. This is important because without tRNA, translation from RNA to protein would not be possible

Which statement(s) explain the structure of tRNA and how it enables its function

tRNA has a cloverleaf structure with an anticodon loop and a 3' end where the amino acid attaches. The 3' end contains a hydroxyl (-OH) group that binds the amino acid. This structure allows one side of tRNA to read mRNA while the other carries the amino acid. This is important because it physically links genetic code to protein building

Which compound(s) belong(s) to ribosomal sites and how they function during translation

The ribosome has three sites: A (aminoacyl), P (peptidyl), and E (exit). The A site receives the incoming aminoacyl-tRNA, meaning a tRNA carrying an amino acid. The P site holds the growing polypeptide chain, which is the developing protein. The E site releases empty tRNA. This is important because proper movement through these sites ensures correct protein elongation

Which enzyme(s) is/are responsible for amino acid activation and why ATP is required

Aminoacyl-tRNA synthetase is the enzyme that attaches the correct amino acid to its corresponding tRNA. This process requires ATP (energy molecule) to form an aminoacyl-AMP intermediate, which is a high-energy activated form. The amino acid is then transferred to tRNA. This is important because incorrect pairing leads to wrong proteins

Which intermediate(s) is/are formed during amino acid activation and why this step ensures accuracy

Aminoacyl-AMP is formed when an amino acid reacts with ATP. This intermediate stores energy used to attach the amino acid to tRNA. The enzyme checks accuracy before transferring the amino acid. This is important because the ribosome cannot correct mistakes later

Which statement(s) explain initiation in bacteria and how the Shine-Dalgarno sequence functions

The Shine-Dalgarno sequence is a region on bacterial mRNA that helps align the ribosome with the start codon. It ensures AUG is positioned correctly in the ribosome. Initiation factors (IF-1, IF-2, IF-3) help assemble the ribosome and bring the initiator tRNA carrying fMet (formyl-methionine). This is important because correct alignment determines the reading frame

Which compound(s) participate(s) in elongation and how elongation factors function

EF-Tu delivers aminoacyl-tRNA to the ribosome using GTP, which is an energy molecule similar to ATP. EF-Ts regenerates EF-Tu, and EF-G drives translocation, which is movement of the ribosome along mRNA. This ensures continuous protein elongation. This is important because elongation requires coordinated movement and energy

Which process(es) explain peptide bond formation and how proteins grow

Peptide bonds are formed between amino acids by the ribosome's peptidyl transferase activity. This connects amino acids into a polypeptide chain. The chain grows from the N-terminus (start) to the C-terminus (end). This is important because protein structure depends on correct sequence formation

Which statement(s) explain termination and how proteins are released

When a stop codon (UAA, UAG, UGA) enters the A site, release factors bind instead of tRNA. They trigger hydrolysis, which releases the completed protein from the ribosome. The ribosome then dissociates into subunits. This is important because proteins must stop at the correct length

Which statement(s) explain why translation is energy-intensive and how ATP/GTP are used

ATP is used for amino acid activation, while GTP is used for initiation, elongation, and translocation. Translation consumes a large portion of cellular energy. This reflects how important protein synthesis is for cell function. Without energy, translation cannot proceed

Which statement(s) explain posttranslational modifications and why they are necessary

After synthesis, proteins undergo modifications like phosphorylation (adding phosphate), glycosylation (adding sugars), and cleavage. These changes affect activity, location, and stability. Many proteins are inactive until modified. This is important because the initial protein is often not functional yet

Which compound(s) belong(s) to zymogens and why they are produced inactive

Zymogens like trypsinogen and pepsinogen are inactive enzyme precursors. They prevent self-digestion of tissues. Activation occurs only in specific locations like the intestine or stomach. This is important because premature activation leads to diseases like pancreatitis

Which statement(s) explain amino acid degradation and how nitrogen is removed

Amino acids undergo transamination, where amino groups are transferred to alpha-ketoglutarate to form glutamate. Then oxidative deamination releases ammonia. This process allows safe nitrogen removal. This is important because ammonia is toxic and must be converted to urea

Which process(es) explain neurotransmitter synthesis from amino acids

Amino acids undergo decarboxylation, removing CO₂ to form neurotransmitters like dopamine (from tyrosine), GABA (from glutamate), and serotonin (from tryptophan). These reactions require PLP (vitamin B6 coenzyme). This is important because metabolism directly affects brain function

Which statement(s) explain the genetic code and how codons translate into amino acids

The genetic code is the system that translates RNA into proteins, where RNA is a molecule made of bases A (adenine), U (uracil), G (guanine), and C (cytosine). A codon is a sequence of 3 bases on mRNA, meaning messenger RNA that carries instructions from DNA. Each codon corresponds to one amino acid or a stop signal, allowing the ribosome to build proteins. This is important because without the genetic code, DNA information cannot become functional proteins

Which compound(s) determine initiation and termination of translation and what each codon means

AUG is the start codon, meaning it signals the beginning of translation and codes for methionine, the first amino acid. UAA, UAG, and UGA are stop codons, meaning they do not code for amino acids but signal the ribosome to stop. The ribosome is a cellular machine made of RNA and proteins that builds polypeptides. This is important because wrong start/stop leads to incorrect protein length

Which statement(s) explain what UUG and AUU are and how they differ from stop codons

UUG and AUU are codons, meaning 3-base sequences on mRNA that code for amino acids (leucine and isoleucine respectively). Unlike UAG or UGA, they do not signal stop but instead add amino acids to the chain. This shows that small changes in base sequence change meaning completely. This is important because misreading codons leads to wrong proteins

Which statement(s) explain degeneracy and why multiple codons code for the same amino acid

Degeneracy means that more than one codon can code for the same amino acid, such as several codons coding for leucine. This occurs because there are 64 codons but only 20 amino acids. It provides protection against mutations, as some changes do not alter the amino acid. This is important because it reduces the effect of genetic errors

Which compound(s) participate(s) in translation and why amino acids need tRNA

tRNA (transfer RNA) is a molecule that carries amino acids and matches them to codons using an anticodon. The anticodon is a 3-base sequence complementary to the codon on mRNA. Amino acids cannot bind codons directly, so tRNA acts as an adapter. This is important because it connects nucleic acid language to protein structure

Which statement(s) explain the structure of tRNA and how it enables binding

tRNA has a cloverleaf structure with an anticodon loop and a 3' end where amino acids attach. The 3' end contains a hydroxyl group (-OH) that binds amino acids. This allows one part of tRNA to interact with mRNA and another to carry the amino acid. This is important because structure determines function in translation

Which compound(s) belong(s) to ribosomal sites and what happens in each

The ribosome has three sites: A (aminoacyl), P (peptidyl), and E (exit). The A site receives incoming tRNA with amino acids, the P site holds the growing chain, and the E site releases empty tRNA. These sites ensure stepwise protein elongation. This is important because disruption leads to translation errors

Which enzyme(s) activate amino acids and how ATP is used

Aminoacyl-tRNA synthetase attaches amino acids to tRNA using ATP (energy molecule). ATP forms an aminoacyl-AMP intermediate, which activates the amino acid. The amino acid is then transferred to tRNA. This is important because incorrect activation leads to incorrect proteins

Which intermediate(s) is/are formed in amino acid activation and why irreversible

Aminoacyl-AMP is formed when amino acid reacts with ATP, storing energy for later transfer. The reaction releases pyrophosphate, making it irreversible. This ensures commitment to protein synthesis. This is important because reversibility would reduce efficiency

Which statement(s) explain initiation in bacteria and what Shine-Dalgarno is

The Shine-Dalgarno sequence is a region on mRNA that aligns the ribosome with AUG. It binds to the 30S ribosomal subunit, ensuring correct start position. Initiation factors (IF-1, IF-2, IF-3) help assemble the complex. This is important because incorrect alignment shifts the reading frame

Which compound(s) participate(s) in elongation and what EF-Tu, EF-Ts, EF-G do

EF-Tu brings aminoacyl-tRNA to the ribosome using GTP, EF-Ts regenerates EF-Tu, and EF-G moves the ribosome along mRNA (translocation). GTP is an energy molecule similar to ATP. These factors ensure smooth elongation. This is important because without them translation stalls

Which statement(s) explain peptide bond formation and how proteins grow

Peptide bonds link amino acids together in the ribosome. The ribosome catalyzes this reaction, not free enzymes. The chain grows from N-terminus to C-terminus. This is important because sequence determines protein structure

Which process(es) explain translocation and why it needs energy

Translocation moves the ribosome one codon forward on mRNA. EF-G and GTP provide energy for this movement. This shifts tRNAs from A to P to E sites. This is important because translation must proceed stepwise

Which statement(s) explain termination and role of release factors

Release factors recognize stop codons and trigger release of the polypeptide. No tRNA binds stop codons. The ribosome then dissociates. This is important because proteins must end correctly

Which statement(s) explain why translation uses large amounts of energy

ATP is used for amino acid activation and GTP for elongation steps. Translation consumes a large portion of cellular energy. This reflects protein importance. This is important because energy deficiency affects protein synthesis

Which statement(s) explain posttranslational modifications and examples

Proteins undergo modifications like phosphorylation (adding phosphate), glycosylation (adding sugars), and cleavage. These affect function and stability. Many proteins are inactive without modification. This is important because synthesis alone is not enough

Which compound(s) belong(s) to zymogens and why inactive

Zymogens are inactive enzyme precursors like trypsinogen. They prevent self-digestion of tissues. Activation occurs in specific locations. This is important because premature activation causes disease