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Genetics > Genetic Code > Flashcards

Genetic Code Flashcards

1
Q

who used fungus Neurospora to work out the relation of genes to protein

A

Beadle and Tatum

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2
Q

protein are polymers consisting of amino acids are linked by

A

peptide bonds

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3
Q

the linear sequence of amino acid is

A

the primary structure

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4
Q

how is the secondary and tertiary structure developed

A

primary structure folds

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5
Q

two or more polypeptide chains associate to form

A

quartenary structure

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6
Q

level of structural organization of protein

A

1, primary
2. secondary
3. tertiary
4. quaternary

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7
Q

what determines how the nucleotide sequence specifies the amino acid sequence

A

genetic code

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8
Q

what are the examples of breaking the genetic code

A
  1. use of homopolymers
  2. use of random copolymers
  3. use of ribosome-bound tRNAs
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9
Q

what amino acid are specifies by codons composed of only one type of base?

A

UUU=phenylalanine

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10
Q

Nirenberg and Matthaei developed a method for identifying amino acid specifies by

A

a homopolymer

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11
Q

the use of poly (U) directs

A

incorporation of phenylalanine

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12
Q

the use of poly (A) directs

A

incorporation of lysine

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13
Q

use of poly (C) directs

A

incorporation of proline

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14
Q

use of poly (G) directs

A

did not yield interpretable results

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15
Q

effect of using random copolymers

A

synthesized RNAs containing 2 or 3 nucleotides which gives info about the base composition but not EXACt sequence

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16
Q

what does ribosome-bound tRNAs do

A

provide information about genetic code

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17
Q

codon GUU specifies

A

valine

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18
Q

out of 64 codons, how many encode amino acids

A

61 called sense codons

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19
Q

what is the initiation codon

A

AUG=methionine

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20
Q

what are stop codons

A

UAA
UAG
UGA

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21
Q

Why can an aminoacid be specified by more than one codon

A

because they are degenerate

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22
Q

how is codon in an mRNA decoded

A

it is decoded by base pairing with its anticodon in tRNA

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23
Q

what are isoaccepting tRNAs?

A

different tRNAs that accept the same amino acid but have different anticodons

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24
Q

where is the wobble position

A

third (3’) position of the codon
first (5’) position of anticodon

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25
Q

who proposed the wobble hypothesis

A

Francis Crick

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26
Q

THE first codon of an open reading frame is called

A

initiation codon or start codon

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27
Q

which sequence is used for initiation in a few bacterial mRNAs and encode for methionine

A

GUG or UUG

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28
Q

which sequence is used for initiation codon in eukaryotes

A

CUG

29
Q

In bacteria, translation begina with

A

N-formylmethionine (fMet)

30
Q

fMET is delivered to the ribosome by

A

a special tRNA (tRNAi Met)

31
Q

initaiton codon establishes the correct or incorrect reading frame

A

correrect reading frame

32
Q

eukaryotes begin translation with

A

methionine

33
Q

tRNA Met is used for

A

elongation

34
Q

genetic code is generally overlapping or non overlapping

A

non overlapping

35
Q

alternate names for termination codons are

A

stop codons or nonsense codons

36
Q

exceptions of each codon encodes the same amino acid is found in

A

Mitochondrial genes

37
Q

how are amino acid are assembled into a protein through

A

translation

38
Q

translation of an mRNA molecule takes place where

A

on a ribosome

39
Q

protein is synthesized from which terminus

A

N to C

40
Q

what is the first stage of translation

A

the attachment of a tRNA to its amino acid

41
Q

—— attaches an amino acid to the 3’ end of a tRNA to form an aminoacyl-tRNA

A

Aminoacyl-tRNA synthetase

42
Q

certain positions on tRNA are recognized by the appropriate aminoacyl-tRNA synthetase. TRUE/FALSE

A

TRUE

43
Q

step of charging tRNA

A
  1. Amino acid reacts with atp TO PRODUCE aminocyl-AMP and 2 Pi
  2. Amino acid is transfered to the tRNA forming aminoacyl-tRNA. AMP is released
44
Q

what is the second step of translation

A

initiation

45
Q

which components assemble during intiation

A
  1. mRNA
  2. the large and small ribosomal subunits
  3. the initiator aminoacyl-tRNA
  4. Initiation factors
  5. GTP
46
Q

Initiation occurs in 3 steps

A
  1. mRNA binds to the small ribosomal subunit
  2. The initiator aminoacyl-tRNA base pairs to the initiation codon
  3. The large ribosomal subunit joins the initiation complex
47
Q

what sequence in bacterial mRNA is required for the attachment of the small lsubunit of the ribosome

A

Shine-Dalgarno sequence

48
Q

Eukaryotic mRNAs do not have Shine-Dalgarno sequence, so what is the alternate

A

5’ cap play a role in initiation

49
Q

describe initiation in eukaryotes

A
  1. the small ribosomal subunit, IFs, and Met-tRNAi Met form a complex that binds to the 5’cap
  2. initiation complex scan down the mRNA until reaching the initiation codon
  3. Kozak sequence helps identify the initiation codon in eukaryotic mRNAs
50
Q

what affects initiation of mRNA in eukaryote

A

The proteins that attach to the poly A tail interact with cap-binding protein and enhance binding of ribosome to 5’end of the mRNA

51
Q

what is the third stage of translation

A

elongation

52
Q

what do elongation require

A

70s initiation complex, Aminoacyl-tRNAS, elongation factors & GTP

53
Q

tRNAs occupy which sites on ribosome

A

3 sites
‘Exit (E) site
Peptidyl (P) site
Aminoacyl (A) site

54
Q

3 steps in elongation stage of translation comprises

A
  1. fMET-tRNA fMet occupies the P site of the ribosome
  2. Ef-Tu, GDP and charged t-RNA form a complex that enters the A site
  3. Peptide bond form between the P and A sites, and the tRNA in the P site is released. Ribosome moves down the mRNA and A is ready to receive another t-RNA
55
Q

function o fRelease Factors (RF) in termination

A

Binds to ribosome when stop codon is reached and terminate translation

56
Q

an mRNA molecule may be translated simultaneously by several ribosomes. this is called

A

Polyribosomes

57
Q

examples of Messenger RNA surveillance

A

Nonsense-mediated mRNA decay (NMD)
Stalled ribosomes and nonstop mRNAs
No go decay

58
Q

what do messenger RNA surveillance do

A

they detect and correct errors in mRNA

59
Q

what results in the rapid degradation of an mRNA containing a premature stop codon

A

Nonsense mediated mRNA decay (NMD)

60
Q

what does bacteria use to remove stalled ribosomes

A

transfer-messenger RNA (tmRNA)

61
Q

how does eukaryote degrade abnormal RNA from the 3’end

A

process called nonstop RNA decay

62
Q

what removes stalled ribosomes resulting from secondary structures or chemical damage to the mRNA, premature stop codons

A

NGD no-go decay

63
Q

tmRNA is charged with —- and binds to

A

Ala and binds to A site

64
Q

which antibiotic blocks binding of aminoacyl-tRNA to A site of ribosome

A

Tetracycline

65
Q

which antibiotic prevents the transition from initation complex to chain elongation and also causes miscoding

A

streptomycin

66
Q

which antibiotic blocks tehpeptidyl transferase reaction on ribosomes

A

chloramphenicol

67
Q

which antibiotic bloxks teh translocation reaction on ribosomes

A

cycloheximide

68
Q

which antibiotic blocks initiation of transcription by binding to RNA Polymerase

A

Rifamycin

Genetics (20 decks)

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