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MCBM Exam 5 > Translation > Flashcards

Translation Flashcards

1
Q

What is a codon?

A

Triplet of DNA that encodes amino acids

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2
Q

How many codons are there?

A

64

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3
Q

How many stop codons are there?

A

3

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4
Q

How many amino acid encoding codons are there?

A

61

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5
Q

What is the initiation codon?

A

AUG

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6
Q

What else does AUG encode for, other than being the initiation codon?

A

Met

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7
Q

What is degeneracy?

A

More than one codon for some amino acids

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8
Q

What does UUU code for?

A

Phe

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9
Q

What does CCC code for?

A

Pro

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10
Q

What does GGG code for?

A

Gly

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11
Q

What does AAA code for?

A

Lys

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12
Q

What are the three stop codons?

A

UGA
UAG
UAA

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13
Q

What is the open reading frame (ORF)?

A

The in-frame sequence between the initiation codon and the termination codon

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14
Q

What does the 5’ end of the mRNA correspond to?

A

The N-terminal of the protein (amino terminus)

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15
Q

What does the 3’ end of the mRNA correspond to?

A

The C-terminal (carboxy terminus)

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16
Q

Who discovered that protein synthesis begins at the amino terminal end of the nascent proteins?

A

Dintzis (1961)

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17
Q

What serves as the adapter molecules for specific amino acids, since mRNA templates can’t directly line up amino acids for protein synthesis?

A

tRNA - bind to specific codons on the RNA template

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18
Q

How are amino acids linked to tRNA molecules before being incorporated into the protein?

A

Amino acids are enzymatically to tRNA

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19
Q

Which undergoes more proofreading, translation, transcription or replication?

A

Replication

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20
Q

How many bases are found in tRNA?

A

73-93 (small)

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21
Q

All cells have at least ___ tRNAs.

A

32

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22
Q

What forms the wobble in the “wobble rules”?

A

The fact that some tRNAs can recognize more than one codon

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23
Q

What do most tRNAs have at the 5’ end?

A

G

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24
Q

What does the D arm of tRNA contain?

A

Dihydrouridine

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25
Q

What does the TpsiC arm contain?

A

The sequence ribothymidine (T) pseudouridin (psi) cytosine (C)

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26
Q

What is the anticodon? Where is it found?

A

A 3 base sequence

In the anticodon loop of tRNA

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27
Q

What does the anticodon of tRNA base pair with?

A

The codon in mRNA

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28
Q

What base does inositate contain?

A

Hypoxanthine

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29
Q

Some tRNAs contain what different nucleotide?

A

Inositate

30
Q

Hypoxanthine can base pair weakly with which bases?

A

U, C, A

31
Q

How many subunits make up ribosomes?

A

2 - a large and a small subunit

32
Q

What is each ribosomal subunit made of?

A

An assembly of one or more rRNA molecules and many different proteins

33
Q

What 3 sites do the ribosomal subunits form?

A
  1. Peptidyl (P) site
  2. Aminoacyl (A) site
  3. Exit (E) site
34
Q

What occurs at the aminoacyl site?

A

It is the site where the amino acids come in

35
Q

How big is a large bacterial ribosomal subunit?

A

50S

36
Q

How big is a large eukaryotic ribosomal subunit?

A

60S

37
Q

What size is the small bacterial ribosomal subunit?

A

30S

38
Q

What size is the small eukaryotic ribosomal subunit?

A

40S

39
Q

What are the 5 major stages of protein synthesis?

A
  1. Activation of amino acids
  2. Initiation
  3. Elongation
  4. Termination and ribosome recycling
  5. Folding and posttranslational processing
40
Q

What occurs in stage on o protein synthesis?

A

The tRNA is “charged” with the proper amino acid

41
Q

How and where are amino acids attached to the corresponding tRNA?

A

Via ester bonds to the 3’ OH

42
Q

What is the reaction that attaches the amino acid to the tRNA?

A

Aminoacylation of the 3’ OH

43
Q

What catalyzes the aminoacylation of the amino acid to the tRNA?

A

Amino acyl-tRNA synthetase

44
Q

tRNA charging is highly ___.

A

Specific

45
Q

Why is tRNA charging irreversible?

A

It uses 2 high-energy bonds

46
Q

T or F: The identity of the amino acids attached to the tRNA are checked by the ribosome.

A

False

47
Q

How do aminoacyl-tRNA synthetases recognize correct tRNAs? (4 ways)

A

Some recognize the anticodon
Some recognize 10 or more bases in tRNA
Some recognize one specific base pair

48
Q

After tRNA is charged by a snthetase, the aminoacyl tRNA forms a complex with what molecule that will also bind one GTP molecule?

A

EF-Tu (elongation factor)

49
Q

How many tRNAs do all organisms have for methionine?

A

2 - one for initiation, one for methionines within the polypeptide chain

50
Q

In bacteria, how many components are required for initiation?

A

7

51
Q

How many steps does it take for the 7 bacterial initiation factors to assemble?

A

3 steps

52
Q

How is the initiation codon distinguished in step 1 of bacterial protein initiation?

A

By proximity to the Shine-Dalgarno sequence

53
Q

In bacteria protein initiation, where is the P site placed?

A

Right over the AUG of the start site

54
Q

What is the first step in bacterial mRNA initiation?

A

Small (30S) subunit positions itself on the mRNA template

55
Q

What is step 2 in the initiation of protein synthesis in bacteria?

A

Initiator tRNA binds to the P site

56
Q

What is step 3 in protein synthesis initiation in bacteria?

A

Large (50S) subunit binds to the complex

57
Q

How many initiation factors or involved in the initiation of protein synthesis in eukaryotes?

A

At least 9

58
Q

What is the Kozak sequence, that is found at many initiation sites?

A

5’-CCACCAUGG-3’

59
Q

Do eukaryotes have a Shine-Dalgarno sequence?

A

No

60
Q

How many ribosomes are found bound to each mRNA molecule?

A

10-100

61
Q

What are the 3 steps of elongation?

A

Bind next aminoacyl-tRNA
Peptide bond formation
Translocation

62
Q

Why are 2 steps used to move tRNAs?

A

Anchors one of of tRNA with the other moves

Prevents premature release of peptidyl-tRNA, enhances processivity

63
Q

Proofreading on ribosomes is limited to what?

A

Codon-anticodon interactions

64
Q

In termination, how is the peptide chain released from the ribosome?

A

Induce peptidyl transferase to transfer peptide chain to water

65
Q

How many termination factors do eukaryotes have?

A

1

66
Q

How much energy does protein synthesis take?

A

At least 4 high-energy bonds per peptide bond

67
Q

Why is so much energy used in protein synthesis?

A

To maintain proper alignment of codon, tRNA and the growing end of the chain

68
Q

Tetracycline and chloramphenicol are two drugs that do what?

A

Inhibit translation

69
Q

What side affects can tetracycline have? (used to treat perio-disease)

A

Stain teel

70
Q

How do tetracyclines inhibit translation?

A

Bind the A site

Block aa-tRNA binding

71
Q

How does Ricin inhibit translation?

A

Inactivates the 60S subunit by depurinating the A residue of 28S rRNA - can’t bind TF

MCBM Exam 5 (11 decks)

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