Translation and Protein Synthesis

Comprehensive vocabulary flashcards covering the mechanisms of the genetic code, bacterial and eukaryotic translation, elongation, termination, mRNA surveillance, and differential gene expression.

1. Front: What is the one gene-one enzyme hypothesis?

Back: The idea proposed by Beadle and Tatum that each gene encodes a separate enzyme. It was later modified to the one gene-one polypeptide hypothesis.

2. Front: What is an auxotroph?

Back: An organism with a mutation that prevents it from synthesizing an essential biological molecule, so it cannot grow on minimal medium unless the needed substance is supplied.

4. Front: What is the relationship between genes and proteins?

Back: Genes contain information that specifies polypeptides, which form proteins. Proteins perform many functions, including catalysis, structure, transport, regulation, communication, and defense.

5. Front: What is a polypeptide?

Back: A chain of amino acids joined by peptide bonds.

6. Front: What is the primary structure of a protein?

Back: The sequence of amino acids in the protein.

7. Front: What is the genetic code?

Back: The set of rules by which the nucleotide sequence of mRNA specifies the amino acid sequence of a protein.

8. Front: What is a codon?

Back: A sequence of three nucleotides in mRNA that specifies an amino acid or a translation stop signal.

9. Front: Why is the genetic code a triplet code?

Back: One or two nucleotides provide only 4 or 16 possible combinations, which is not enough to encode 20 amino acids. Three nucleotides provide 64 possible codons.

10. Front: How many possible codons are there?

Back: 64 total codons.

12. Front: What is a degenerate genetic code?

Back: A code in which more than one codon can specify the same amino acid.

13. Front: What are synonymous codons?

Back: Different codons that specify the same amino acid.

14. Front: Which two amino acids have only one codon each?

Back: Methionine and tryptophan.

15. Front: What is wobble?

Back: Flexibility in base pairing between the third nucleotide of an mRNA codon and the corresponding position of a tRNA anticodon.

16. Front: Why is wobble important?

Back: It allows some tRNAs to pair with more than one codon.

17. Front: What is a reading frame?

Back: One of the three possible ways to divide a nucleotide sequence into groups of three nucleotides.

18. Front: Why must translation use the correct reading frame?

Back: Each reading frame produces a different set of codons and can specify a different amino acid sequence.

19. Front: What establishes the reading frame?

Back: The start codon establishes the reading frame. The following nucleotides are read in successive groups of three.

20. Front: What is the usual start codon?

Back: AUG, which also specifies methionine.

21. Front: Which other codons can sometimes serve as start codons?

Back: GUG, UUG, and some other codons.

24. Front: What are the three stop codons?

Back: UAA, UAG, and UGA.

27. Front: What is translation?

Back: The process in which ribosomes use the codon sequence of mRNA to assemble amino acids into a polypeptide.

28. Front: What is the difference between transcription and translation?

Back: Transcription produces RNA from a DNA template. Translation uses mRNA to assemble a polypeptide.

29. Front: Where does translation take place?

Back: On ribosomes.

30. Front: In which direction does a ribosome move along mRNA?

Back: From the 5′ end toward the 3′ end.

31. Front: In which direction does a polypeptide grow during translation?

Back: From the amino (N) end toward the carboxyl (C) end, with new amino acids added to the carboxyl end.

32. Front: What are the four stages of protein synthesis described in the textbook?

Back: tRNA charging, initiation, elongation, and termination.

33. Front: What is an aminoacyl-tRNA?

Back: A tRNA attached to its appropriate amino acid; it is also called a charged tRNA.

34. Front: What is the function of aminoacyl-tRNA synthetases?

Back: They attach the correct amino acid to its appropriate tRNA.

35. Front: How many aminoacyl-tRNA synthetases does a cell have, according to the textbook?

Back: 20, one for each of the 20 common amino acids.

36. Front: How do aminoacyl-tRNA synthetases recognize the correct amino acid and tRNA?

Back: They recognize amino acids based on properties such as size, charge, and R group, and recognize tRNAs based on their nucleotide sequences.

37. Front: How do some aminoacyl-tRNA synthetases improve accuracy?

Back: Their editing or proofreading activity detects and removes incorrectly attached amino acids.

38. Front: What are the two ribosomal subunits in bacteria?

Back: The small 30S subunit and the large 50S subunit.

41. Front: What are initiation factors?

Back: Proteins that help assemble the components needed to begin translation.

45. Front: What is the Shine-Dalgarno sequence?

Back: A sequence in the bacterial mRNA 5′ UTR that pairs with a complementary sequence near the 3′ end of 16S rRNA, positioning the ribosome over the start codon.

46. Front: How does the bacterial ribosome locate the start codon?

Back: The small subunit binds the mRNA through base pairing between the Shine-Dalgarno sequence and 16S rRNA, positioning it at the start codon.

47. Front: What amino acid does the bacterial initiator tRNA carry?

Back: N-formylmethionine (fMet).

48. Front: What is the first major difference between bacterial and eukaryotic translation initiation?

Back: Bacteria use the Shine-Dalgarno sequence to position the ribosome; eukaryotes use the 5′ cap and scan the mRNA to find a start codon.

49. Front: How does a eukaryotic ribosome locate the start codon?

Back: The small ribosomal subunit, initiation factors, and initiator Met-tRNA form a complex that binds at the 5′ cap and scans the mRNA until it finds an AUG start codon.

50. Front: What is the Kozak sequence?

Back: A consensus sequence surrounding the eukaryotic start codon that helps the translation machinery identify it.

51. Front: How many initiation factors are required for eukaryotic translation, according to the textbook?

Back: At least 12.

52. Front: What role does the 5′ cap play in eukaryotic translation initiation?

Back: It helps recruit the initiation complex and small ribosomal subunit to the mRNA.

53. Front: What role does the poly(A) tail play in eukaryotic translation initiation?

Back: Proteins attached to the poly(A) tail interact with proteins bound to the 5′ cap, enhancing small-subunit binding and helping form a closed-loop mRNA structure.

54. Front: What is an important difference between bacterial and eukaryotic transcription and translation?

Back: In bacteria, transcription and translation can occur simultaneously. In eukaryotes, transcription occurs in the nucleus and translation occurs in the cytoplasm, so they are separated in time and space.

55. Front: What is elongation?

Back: The stage of translation in which amino acids are added one at a time to the growing polypeptide chain.

56. Front: What are the ribosome's A, P, and E sites?

Back: A site: aminoacyl-tRNA entry site. P site: holds the tRNA carrying the growing polypeptide. E site: exit site for tRNA.

57. Front: Which ribosome site does the initiator tRNA occupy first?

p site

58. Front: Which site do other charged tRNAs enter first?

a site

59. Front: What are the three steps of elongation?

Back: 1. A charged tRNA enters the A site. 2. A peptide bond forms between the amino acids in the A and P sites. 3. The ribosome translocates to the next codon.

62. Front: What is a ribozyme?

Back: An RNA molecule with catalytic activity. During translation, rRNA in the large ribosomal subunit catalyzes peptide-bond formation.

64. Front: What is translocation?

Back: The movement of the ribosome along the mRNA in the 5′ to 3′ direction to position it over the next codon.

66. Front: How do tRNAs move through the ribosome during elongation?

Back: They generally move from the A site to the P site to the E site, then exit into the cytoplasm.

67. Front: What happens to the ribosome's A site after translocation?

Back: It becomes empty and ready to receive the next charged tRNA.

68. Front: How is eukaryotic elongation similar to bacterial elongation?

Back: Both use charged tRNAs, peptide-bond formation, and ribosome translocation to extend the polypeptide chain.

70. Front: What is termination in translation?

Back: The stage when the ribosome reaches a stop codon, releases the completed polypeptide, and the translation components separate.

71. Front: What happens when a stop codon enters the ribosome's A site?

Back: No matching tRNA enters. Instead, a release factor binds to the ribosome.

72. Front: What are release factors?

Back: Proteins that recognize stop codons and promote release of the polypeptide from the tRNA and ribosome.

74. Front: How does a release factor cause the polypeptide to be released?

Back: Binding of RF-1 or RF-2 promotes cleavage of the polypeptide from the tRNA in the P site.

75. Front: How does eukaryotic translation termination differ from bacterial termination?

Back: Eukaryotes use eRF-1 to recognize all three stop codons and eRF-3, which binds GTP and stimulates polypeptide release.

76. Front: Is the stop codon at the very end of an mRNA?

Back: No. The stop codon is followed by the 3′ UTR.

77. Front: What is a polyribosome (polysome)?

Back: An mRNA molecule with multiple ribosomes translating it at the same time.

78. Front: Why can multiple ribosomes translate one mRNA at once?

Back: Ribosomes can attach successively near the 5′ end and move toward the 3′ end, each producing a polypeptide.

80. Front: How are transcription and translation coupled in bacteria?

Back: Ribosomes can begin translating an mRNA while RNA polymerase is still transcribing it.

81. Front: Why are transcription and translation separated in eukaryotes?

Back: Transcription occurs in the nucleus, while translation occurs in the cytoplasm.

82. Front: What is posttranslational modification?

Back: A change made to a protein after translation, such as cleavage, removal of an amino acid or group, attachment of carbohydrates, addition of chemical groups, or attachment of ubiquitin.

83. Front: What are molecular chaperones?

Back: Molecules that help some newly synthesized polypeptides fold into their correct shapes.

84. Front: What is mRNA surveillance?

Back: Quality-control mechanisms that detect and deal with faulty mRNAs, helping prevent wasted resources and production of potentially harmful abnormal proteins.

85. Front: What is nonsense-mediated mRNA decay (NMD)?

Back: A eukaryotic quality-control mechanism that rapidly eliminates mRNAs containing premature stop codons.

86. Front: Does nonsense-mediated mRNA decay occur in bacteria?

no

87. Front: What is a nonstop mRNA?

Back: An mRNA that lacks a termination codon, causing the ribosome to reach the end of the mRNA and stall.

88. Front: How can bacteria rescue ribosomes stalled on nonstop mRNAs?

Back: Transfer-messenger RNA (tmRNA) enters the ribosome, allows translation to continue using its own mRNA sequence, adds a tag to the incomplete protein for degradation, and helps release the ribosome.

89. Front: What is no-go decay (NGD)?

Back: A quality-control system that helps remove stalled ribosomes and degrade mRNAs that cause stalling, such as those with secondary structures or damage.

1. Front: Why can cells with identical DNA have different phenotypes?

Back: Different cells can express different genes. This causes them to produce different proteins, resulting in different characteristics and functions.

2. Front: How can bacteria with identical DNA have different phenotypes?

Back: Bacteria can turn different genes on or off depending on environmental conditions, producing different proteins and phenotypes.

3. Front: How can cells in a multicellular eukaryote have different phenotypes despite having identical DNA?

Back: Different cell types express different sets of genes, allowing them to produce different proteins and perform specialized functions.

4. Front: What is an example of different phenotypes in multicellular eukaryotes?

Back: Muscle cells and nerve cells contain essentially the same DNA but express different genes, giving them different structures and functions.