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MOL BIO Exam #1- Lo > Lec 08- Transcription and Translation 2 > Flashcards

Lec 08- Transcription and Translation 2 Flashcards

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1
Q

Where does protein synthesis occur?

A

on ribosomes

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2
Q

In what direction is a protein synthesized?

A

in the amino-to-carboxyl direction

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3
Q

What end of the growing peptide do amino acids add to?

A

the carboxyl end

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4
Q

What kind of bond is formed when amino acids are added to the carboxyl end of the growing peptide?

A

dipepdityl bond

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5
Q

What is the genetic code?

A
  • a set of rules
  • converts the nt sequence of a gene into the amino acid sequence of a protein
  • uses mRNA as an intermediary
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6
Q

The sequence of ______ nucleotides in the mRNA molecule is read consecutively in groups of _______

A

4 nucleotides

groups of 3

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7
Q

How many total codons are possible?

A

4^3 = 64

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8
Q

How many of the codons are stop codons?

A

3 stop codons

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9
Q

How many codons are there for the 20 amino acids?

A

61 codons

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10
Q

What does the adaptor hypothesis postulate?

A

that the genetic code is read by molecules that can recognize a codon and carry the corresponding amino acid

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11
Q

What serves as the adaptor that binds to a specific codon and brings with it an amino acid for incorporation into the polypeptide chain?

A

tRNA

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12
Q

What does the tRNA structure look like?

A

a cloverleaf

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13
Q

tRNA folds up into a defined 3D structure and contains ____ short double-helical segments

A

4 short double-helical segments

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14
Q

What are the 2 regions of unpaired nucleotides that are crucial to the functions of tRNA?

A
  • Anticodon loop

- 3’ CCA terminal region

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15
Q

What is the anticodon loop?

A
  • set of 3 consecutive nucleotides

- pairs with a complementary codon in an mRNA molecule

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16
Q

What is the 3’ CCA terminal region?

A
  • region on the 3’ end

- binds the amino acid that matches the corresponding codon

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17
Q

How many tRNAs are there for most amino acids?

A

more than 1 tRNA for most amino acids

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18
Q

What is the wobble hypothesis?

A
  • some tRNAs require accurate base-pairing only at first 2 positions of the codon
  • can tolerate mismatch/wobble at the 3rd position
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19
Q

What does the wobble base-pairing explain?

A

why so many of the alternative codons for an amino acid differ only in their 3rd nucleotide

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20
Q

What catalyzes recognition and attachment of the correct amino acid to the corresponding tRNA?

A

aminoacyl-tRNA synthetases

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21
Q

Where does the aminoacyl-tRNA synthetase covalently couple an amino acid to on the ribose residue of its corresponding tRNA? What does this form?

A

the 3’ terminal

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22
Q

What is an aminoacyl-tRNA made of?

A

an amino acid covalently coupled to the 3’ terminal ribose residue of its corresponding tRNA

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23
Q

What drives the process of aminoacyl-tRNA formation?

A

ATP hydrolysis

produces a high energy bond between tRNA and the amino acid

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24
Q

Most cells have ____________________ for each amino acid.

A

a different synthetase enzyme

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25
Q

Where does the editing (hydrolytic) site cleave?

A

cleaves activated species that are smaller than the correct one

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26
Q

What is the result of hydrolytic editing?

A

raises the overall accuracy of tRNA charging to 1 mistake in 40,000 couplings

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27
Q

What are the 2 adaptors that translate the genetic code?

A
  • aminoacyl-tRNA synthetase

- tRNA molecule

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28
Q

What kind of activation sites does aminoacyl-tRNA synthetases contain?

A

highly discriminating amino acid activation sites

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29
Q

What has the highest affinity for the active-site pocket of the tRNA synthetase?

A

the correct amino acid

-therefore favored over the other 19 amino acids

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30
Q

Which amino acids of not bind to the active site of the tRNA synthetase?

A

amino acids that are larger than the correct one

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31
Q

What does the aminoacyl-tRNA use for proofreading?

A

an editing site

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32
Q

What are the general size differences between PRO and EUK ribosomes?

A

PRO = small subunit (70S)

EUK = large subunit (80S)

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33
Q

What is a ribosome and what does it consist of?

A
  • a complex catalytic machine

- consists of 2 subunits

34
Q

What does each ribosomal subunit contain?

A
  • different ribosomal proteins

- several rRNAs

35
Q

What is the function of rRNAs?

A

Determines:

  • overall ribosome shape
  • ability to position tRNAs on the mRNA
  • catalytic activity in forming peptide bonds
36
Q

What does the small subunit provide?

A

a framework on which the tRNAs are accurately matched to the codons of the mRNA

(binding sire for mRNA strand)

37
Q

What does the large subunit do?

A

catalyzes the formation of the peptide bonds that link the amino acids together into a polypeptide chain

38
Q

Why does protein synthesis occur on the ribosome?

A
  • ensures accuracy

- maintains correct reading frame

39
Q

When are the 2 ribosomal subunits separated?

A

when they are not synthesizing proteins

40
Q

Where do the 2 ribosomal subunits join together?

A

at the 5’ end of an mRNA

41
Q

What initiates protein synthesis?

A

the 2 ribosomal subunits joining together at the 5’ end of an mRNA

42
Q

What direction is the mRNA pulled through the ribosome?

A

5’&raquo_space; 3’ direction

43
Q

What happens to the mRNA sequence as the codons enter the core of the ribosome?

A

the mRNA sequence is translated into amino acid sequence using tRNAs as adaptors

44
Q

When does the ribosome release the protein?

A

when it encounters a stop codon

45
Q

How many binding sites for RNA does the ribosome contain?

A

4 binding sites

46
Q

What are the 4 ribosomal binding sites for RNA?

A

3 sites for tRNA:

  • A site = aminoacyl
  • P site = peptidyl
  • E site = exit

1 site for mRNA

47
Q

The rRNA from which subunit dorms the APE sites?

A

the rRNA of the large subunit

48
Q

Which subunit binds the mRNA?

A

the small subunit

49
Q

When are the tRNA molecules held in the AP sites?

A

only if their anticodon forms base pairs with complementary codon in mRNA threaded through the ribosome

50
Q

What is the fundamental reaction of protein synthesis?

A

formation of peptide bond between amino acids

51
Q

Where does the peptide bond occur?

A

between the carboxyl group at the end of the polypeptide and an amino group of the incoming amino acid

CO-NH

52
Q

A protein is synthesized stepwise from its ______ terminal to its ______ terminal end

A

N-terminal to C-terminal end

53
Q

Steps of peptide bond formation

A

1) peptidyl-tRNA attached to C-terminus of the growing polypeptide chain
2) aminoacyl-tRNA
3) tRNA molecule freed from its peptidyl linkage
4) peptide bond formed
5) new peptidyl-tRNA molecule attached to C-terminus of the growing polypeptide chain

54
Q

What are the 4 steps of mRNA translation?

A

1) tRNA binding
2) peptide bond formation (peptidyl transferase)
3) large subunit translocation
4) small subunit translocation

55
Q

What is very crucial for EUK translation initiation?

A

the site at which protein synthesis begins

56
Q

What does the site of protein synthesis determine?

A

the reading frame for the whole length of the message

57
Q

What do all known mRNA molecules contain?

A

signals that define the beginning of each encoded poylpeptide chain

58
Q

What codon starts translation?

A

AUG (methionine)

59
Q

What carries the amino acid methionine?

A

a special initiator tRNA

60
Q

What is the initiator tRNA-methionine complex loaded onto?

A

the small subunit of ribosomes on the P-site

61
Q

What other things, besides the initiator tRNA-methionine complex, are added for EUK translation initiation?

A

EUK initiation factors (eIFs)

62
Q

What subunit binds to the 5’ end of the mRNA?

A

the small ribosomal subunit

63
Q

How is the 5’ end of the mRNA recognized?

A
  • its 5’ cap

- the bound initiation factors

64
Q

What are the 2 bound initiation factors to EUK mRNA?

A

eIF4E

eIF4G

65
Q

What is ahead of the AUG of EUK mRNA?

A

a recognition consensus site

5’-ACCAUGG-3’

66
Q

What happens after EUK translation initiation?

A
  • the factors drop off
  • the large submit joins the small subunit
  • protein synthesis starts
67
Q

What makes EUK translation more efficient and accurate?

A

elongation factors

68
Q

What are the 2 PRO elongation factors and 2 EUK elongation factors?

A

PRO = EF-Tu & EF-G

EUK = EF1 & EF2

69
Q

What does EF-Gu bind to?

A
  • GTP

- the aminoacyl-tRNA

70
Q

What does EF-Gu do after binding GTP and the aminoacyl-tRNA?

A
  • escorts it to the ribosome

- checks whether the amino acid-tRNA match is correct

71
Q

What do elongation factors monitor?

A

interaction between anticodon of incoming aminoacyl-tRNA and the codon of mRNA

72
Q

What introduces critical proofreading steps into protein synthesis?

A

interactions of:

  • EF-Tu
  • tRNA
  • ribosome
73
Q

What brings conformational changes in the ribosomes to greatly increase efficiency?

A

GTP hydrolysis

74
Q

What are the 3 stop codons?

A

UAA
UGA
UAG

75
Q

What recognizes the stop codons?

A

release factors (RFs)

76
Q

What are release factors?

A

proteins that promote the release of the completed protein from the tRNA

77
Q

What happens when the RFs bind to the A site containing the stop codon?

A
  • catalyzes the addition of a water molecule instead of an amino acid
  • frees the carboxyl group of the polypeptide from tRNA
  • completed protein released from ribosome into cytoplasm
  • protein folded into 3D structure
78
Q

What are many effective antibiotics made by?

A

fungi that inhibit bacterial protein synthesis

79
Q

What do antibiotics do?

A

exploit structural and functional differences between bacterial and eukaryotic ribosomes

80
Q

Where do many antibiotics bind?

A

to ribosomes

81
Q

What happens when antibiotics bind to ribosomes?

A

interfere with protein synthesis by blocking ribosomal function

MOL BIO Exam #1- Lo (8 decks)

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