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Translation & the Genetic Code

Tier 3 · #19 of 33 · moderate yield · topic 2.3 — every high-yield fact from the book chapter, exam-ready.

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  1. Front
    How many nucleotides specify a single amino acid in the genetic code?
    Back
    Three (the code is triplet )
  2. Front
    How many possible codons exist, and why that number?
    Back
    64 — because there are 4 nucleotides read in triplets ( 4³ = 64 )
  3. Front
    The genetic code property meaning most amino acids are encoded by more than one codon is called ______.
    Back
    Degenerate ( redundant )
  4. Front
    Does "degenerate" mean a single codon can specify more than one amino acid ?
    Back
    No — each codon still specifies only ONE amino acid; degenerate ≠ ambiguous
  5. Front
    Which two amino acids are each encoded by only a single codon ?
    Back
    Methionine and tryptophan
  6. Front
    Which two amino acids each have six codons ?
    Back
    Leucine and serine
  7. Front
    A point mutation in the third ( wobble ) position of a codon that leaves the amino acid unchanged is what type of mutation?
    Back
    Silent mutation
  8. Front
    The genetic-code property describing reading in continuous triplets with no gaps or punctuation is called ______.
    Back
    Comma-free ( non-overlapping, read continuously )
  9. Front
    Why does a single nucleotide insertion or deletion produce a non-functional protein?
    Back
    It causes a frameshift — every downstream codon is read in a new wrong frame
  10. Front
    What does it mean that the genetic code is "nearly universal"?
    Back
    Almost every organism uses the same codon table (minor exceptions in mitochondria /some microbes)
  11. Front
    The near-universality of the genetic code is what makes which technology possible?
    Back
    Recombinant DNA technology (a human gene expressed in a bacterial ribosome yields human protein)
  12. Front
    Name the three stop codons.
    Back
    UAA, UAG, UGA
  13. Front
    What recognizes stop codons , since no tRNA reads them?
    Back
    Protein release factors
  14. Front
    What is the start codon , and which amino acid does it encode?
    Back
    AUG — methionine (formyl-methionine in bacteria)
  15. Front
    Which enzyme family matches each amino acid to its correct tRNA ?
    Back
    Aminoacyl-tRNA synthetases (one per amino acid )
  16. Front
    Why is aminoacyl-tRNA synthetase fidelity called the "second genetic code"?
    Back
    An error here is invisible to the ribosome — it inserts the wrong amino acid uncorrectably
  17. Front
    What intermediate forms in the first step of tRNA charging, and what is released?
    Back
    Aminoacyl-AMP intermediate; pyrophosphate (PPi) is released and hydrolyzed
  18. Front
    What is the total energy cost of charging one tRNA (amino acid activation)?
    Back
    2 ATP equivalents (1 ATP used + PPi hydrolysis consumes the second high-energy bond)
  19. Front
    On the tRNA , the three-nucleotide sequence complementary and antiparallel to the mRNA codon is the ______.
    Back
    Anticodon
  20. Front
    The hypothesis explaining how one tRNA can recognize more than one codon is the ______.
    Back
    Wobble hypothesis
  21. Front
    At which codon position does wobble base-pairing occur?
    Back
    The third codon position ( never the first )
  22. Front
    Ribosomes are made of what two classes of molecule?
    Back
    rRNA and protein (ribonucleoprotein)
  23. Front
    Which ribosomal component carries the catalytic peptidyl transferase activity, making the ribosome a ribozyme ?
    Back
    The rRNA (of the large subunit )
  24. Front
    What is the size of the eukaryotic ribosome and its two subunits?
    Back
    80S = 60S (large) + 40S (small)
  25. Front
    What is the size of the prokaryotic ribosome and its two subunits?
    Back
    70S = 50S (large) + 30S (small)
  26. Front
    Why don't ribosomal subunit Svedberg values add up (e.g., 60S + 40S = 80S, not 100S)?
    Back
    S (Svedberg) units measure sedimentation rate and are not additive
  27. Front
    Which ribosomal site accepts the incoming aminoacyl-tRNA ?
    Back
    The A site ( aminoacyl site )
  28. Front
    Which ribosomal site holds the tRNA bearing the growing peptide chain?
    Back
    The P site ( peptidyl site )
  29. Front
    Which ribosomal site is where uncharged tRNA exits?
    Back
    The E site ( exit site )
  30. Front
    In which 5'→3' direction does the ribosome move along the mRNA?
    Back
    5' to 3' , one codon at a time
  31. Front
    During eukaryotic initiation, what mRNA feature do the eIFs first recognize?
    Back
    The 5' cap
  32. Front
    After binding the 5' cap , how does the pre-initiation complex find the start codon ?
    Back
    It scans from the 5' end to the first AUG in a favorable Kozak context
  33. Front
    Which tRNA is brought to the P site during initiation?
    Back
    The initiator Met-tRNA
  34. Front
    Which elongation factor delivers aminoacyl-tRNA to the A site in eukaryotes, and at what cost?
    Back
    eEF1A ; costs 1 GTP
  35. Front
    Which enzymatic activity forms the peptide bond between the A-site and P-site amino acids?
    Back
    Peptidyl transferase (the large-subunit rRNA )
  36. Front
    Which elongation factor drives translocation , and at what cost?
    Back
    eEF2 ; costs 1 GTP
  37. Front
    During translocation , the peptidyl-tRNA moves from the A site to which site?
    Back
    The P site
  38. Front
    How many GTP are consumed per elongation cycle ?
    Back
    2 GTP (1 for A-site delivery + 1 for translocation)
  39. Front
    During termination, which eukaryotic factor recognizes all three stop codons ?
    Back
    eRF1
  40. Front
    At termination, what does peptidyl transferase add instead of an amino acid to release the chain?
    Back
    Water (hydrolyzing the peptide off the P-site tRNA )
  41. Front
    What is the total energy cost of adding one amino acid to the growing chain?
    Back
    4 ATP equivalents
  42. Front
    Break down the 4 ATP-equivalent cost per amino acid added.
    Back
    2 ATP (tRNA charging) + 1 GTP (A-site delivery) + 1 GTP (translocation)
  43. Front
    Tetracycline blocks aminoacyl-tRNA binding to which ribosomal site/subunit?
    Back
    The A site of the prokaryotic 30S subunit
  44. Front
    Which antibiotic causes mRNA misreading (codon-anticodon mismatch) at the 30S subunit ?
    Back
    Streptomycin
  45. Front
    Which antibiotic blocks peptidyl transferase on the prokaryotic 50S subunit ?
    Back
    Chloramphenicol
  46. Front
    Which drug blocks peptidyl transferase on the EUKARYOTIC ( 60S ) subunit?
    Back
    Cycloheximide
  47. Front
    Erythromycin stalls elongation by blocking what part of the large subunit ?
    Back
    The output/exit channel (peptide cannot thread through)
  48. Front
    Which inhibitor works in BOTH prokaryotes and eukaryotes by mimicking aminoacyl-tRNA ?
    Back
    Puromycin
  49. Front
    How does puromycin halt translation once incorporated into the A site ?
    Back
    It forms a peptide bond but cannot translocate , causing premature chain release
  50. Front
    Diphtheria toxin fragment A carries what enzymatic activity?
    Back
    ADP-ribosyltransferase
  51. Front
    Diphtheria toxin ADP-ribosylates which translation factor, on which modified residue?
    Back
    eEF2 , on its diphthamide (modified histidine) residue
  52. Front
    Functionally, what does ADP-ribosylation of eEF2 prevent?
    Back
    Translocation (translation is permanently blocked )
  53. Front
    Why is a single molecule of diphtheria toxin enough to kill a cell?
    Back
    Fragment A is catalytic — one enzyme inactivates the entire eEF2 pool
  54. Front
    Ricin is what type of enzyme?
    Back
    An RNA N-glycosidase
  55. Front
    Ricin removes a single adenine from which rRNA , in which subunit?
    Back
    The 28S rRNA of the 60S (large) subunit
  56. Front
    Roughly how many ribosomes does one ricin molecule destroy per minute?
    Back
    About 1,500 ribosomes per minute
  57. Front
    Actinomycin D appears on the inhibitor table but is actually what kind of inhibitor?
    Back
    A transcription inhibitor (intercalates DNA, blocking RNA polymerase )
  58. Front
    Group 1 proteins (cytoplasmic/nuclear/mitochondrial) are synthesized where?
    Back
    On free polysomes in the cytoplasm
  59. Front
    Group 2 proteins (secretory, membrane, ER/Golgi/lysosomal) are synthesized where?
    Back
    On ribosomes docked to the rough endoplasmic reticulum (RER)
  60. Front
    What binds the emerging ER signal sequence , pauses translation, and docks the ribosome to the RER ?
    Back
    The signal recognition particle (SRP)
  61. Front
    What is the default trafficking pathway for proteins entering the ER ?
    Back
    ER → Golgi → secretion or membrane
  62. Front
    What is the lysosomal targeting signal added to lysosomal enzymes?
    Back
    Mannose-6-phosphate (M6P)
  63. Front
    In which Golgi compartment is the M6P tag ADDED, and by which enzyme ?
    Back
    The cis Golgi ; by N-acetylglucosamine phosphotransferase
  64. Front
    In which Golgi compartment is M6P RECOGNIZED by its receptor for packaging?
    Back
    The trans Golgi
  65. Front
    If N-acetylglucosamine phosphotransferase is defective, where do lysosomal enzymes end up?
    Back
    Secreted into the plasma (not delivered to lysosomes )
  66. Front
    What disease results from defective N-acetylglucosamine phosphotransferase (failed M6P tagging)?
    Back
    Mucolipidosis type 2 ( I-cell disease )
  67. Front
    Which gene is mutated in I-cell disease ?
    Back
    GNPTAB (encodes the alpha/beta subunits of the phosphotransferase)
  68. Front
    What is the characteristic lab fingerprint of I-cell disease ?
    Back
    Elevated plasma lysosomal enzymes + deficient intracellular lysosomal activity
  69. Front
    Which chaperone family dominates cytosolic and ER protein folding in eukaryotes?
    Back
    Hsp70 (heat shock protein 70)
  70. Front
    What energy source does Hsp70 use to cycle between binding and releasing substrate?
    Back
    ATP hydrolysis
  71. Front
    Which two ER -only lectin chaperones bind incompletely folded glycoproteins?
    Back
    Calnexin (membrane-anchored) and calreticulin (soluble)
  72. Front
    Which ER -only enzyme forms and rearranges disulfide bonds?
    Back
    Protein disulfide isomerase (PDI)
  73. Front
    What does peptidyl-prolyl isomerase do?
    Back
    Rotates peptide bonds at proline between trans and cis configurations
  74. Front
    Which vitamin is the cofactor for proline/lysine hydroxylation in collagen, and what deficiency results?
    Back
    Vitamin C (ascorbic acid) ; deficiency causes scurvy
  75. Front
    N-glycosylation attaches oligosaccharides to which residue and consensus sequence?
    Back
    Asparagine , in an Asn-X-Ser/Thr sequence
  76. Front
    O-glycosylation attaches sugars to the hydroxyl of which residues?
    Back
    Serine or threonine
  77. Front
    What is the key difference between glycosylation and glycation?
    Back
    Glycosylation is enzyme-mediated and site-specific ; glycation is non-enzymatic and random
  78. Front
    Non-enzymatic attachment of glucose to hemoglobin (as in diabetes ) produces what measured marker?
    Back
    Hemoglobin A1c (HbA1c)
  79. Front
    How many amino acids long is ubiquitin?
    Back
    76 amino acids
  80. Front
    A polyubiquitin chain linked through which ubiquitin lysine signals proteasomal degradation?
    Back
    Lysine-48 (K48)
  81. Front
    What non-degradative functions does K63 -linked ubiquitin serve?
    Back
    DNA repair signaling and endocytosis
  82. Front
    Which barrel-shaped protease complex degrades polyubiquitinated proteins?
    Back
    The proteasome
  83. Front
    Which reversible post-translational modification is the most ubiquitous regulatory switch in cell biology?
    Back
    Phosphorylation (added by kinases , removed by phosphatases )
  84. Front
    Regulatory phosphorylation is added to which three amino acid residues?
    Back
    Serine, threonine, and tyrosine
  85. Front
    Which enzymes ADD versus REMOVE a regulatory phosphate group on a protein?
    Back
    Kinases add the phosphate; phosphatases remove it
  86. Front
    Reversible acetylation of which residues on histones controls gene expression?
    Back
    Lysine residues
  87. Front
    At termination, which eukaryotic factor is a G protein that promotes release of the finished chain?
    Back
    eRF3
  88. Front
    Termination: eRF1 recognizes the stop codons ; what is eRF3 's distinct role?
    Back
    eRF3 (a GTP-binding G protein ) promotes the actual release of the peptide
  89. Front
    Why do the costs of translation sum to '4 ATP EQUIVALENTS' rather than just ATP ?
    Back
    GTP hydrolysis is thermodynamically equivalent to ATP hydrolysis , so 2 ATP + 2 GTP = 4 ATP equivalents
  90. Front
    Every protein begins with methionine — what often happens to that initiator Met afterward?
    Back
    It is frequently cleaved off post-translationally
  91. Front
    Diphtheria toxin is produced by which organism?
    Back
    Corynebacterium diphtheriae
  92. Front
    Where does the gene encoding diphtheria toxin actually come from?
    Back
    A lysogenic bacteriophage (the toxin gene is phage-derived)
  93. Front
    At the lysosome , what triggers the M6P receptor to release its bound enzyme?
    Back
    The low pH of the lysosome
  94. Front
    After releasing the enzyme at the lysosome , what does the M6P receptor do?
    Back
    Recycles back to the Golgi for reuse
  95. Front
    Several eIFs (and several elongation/release factors) belong to what class of protein?
    Back
    G proteins (GTP-binding proteins)
  96. Front
    A translation G protein switches between an ACTIVE and an INACTIVE conformation depending on whether it is bound to ______ vs ______.
    Back
    GTP (active) vs GDP (inactive)
  97. Front
    Which two regulators switch a translation G protein on and off? (Define each by function.)
    Back
    GEFs (guanine nucleotide exchange factors) reload GTP to turn it ON ; GAPs (GTPase-activating proteins) trigger GTP hydrolysis to turn it OFF
  98. Front
    Beyond providing energy, what else does GTP hydrolysis supply at each step of translation?
    Back
    A conformational switch that drives each step forward and makes it irreversible
  99. Front
    Besides causing mRNA misreading at the 30S subunit , what second step does streptomycin block?
    Back
    The initiation-to-elongation transition
  100. Front
    Classify these PTMs as reversible or irreversible: phosphorylation, collagen proline hydroxylation, heme attachment, lysine acetylation.
    Back
    Reversible: phosphorylation and acetylation . Irreversible: collagen proline hydroxylation and heme attachment
  101. Front
    Which signal routes a Group 1 protein into the nucleus , and through what structure does it pass?
    Back
    A nuclear localization signal (NLS) ; through nuclear pores
  102. Front
    What signal directs a cytosolically-made Group 1 protein into the mitochondrion ?
    Back
    A mitochondrial targeting sequence (directs it into the matrix )
  103. Front
    Hsp70 clamps its substrate tightly in which nucleotide-bound state?
    Back
    ADP-bound (closed, high-affinity) state — the ATP -bound state is open/low-affinity and releases substrate
  104. Front
    Is tetracycline bactericidal or bacteriostatic?
    Back
    Bacteriostatic
  105. Front
    After the initiator Met-tRNA and start codon are set in eukaryotic initiation, what completes the 80S ribosome ?
    Back
    The 60S large subunit joins (and the initiation factors are released)
  106. Front
    In which organelles does glycosylation of proteins occur?
    Back
    The ER and the Golgi
  107. Front
    Ricin is isolated from which plant?
    Back
    The castor bean (Ricinus communis)

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