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L 211 > exam 3 (translation) > Flashcards

exam 3 (translation) Flashcards

1
Q

what material does translation use to make protein

A

DNA-encoded info

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2
Q

translation in what step of the central dogma

A

last step

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3
Q

where are proteins synthesized

A

ribosomes

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4
Q

describe the structure of a bacteria ribosome

A
  • large subunit has a short and long strand of rRNA and proteins L1, L2, L3
  • small subunit has strand of rRNA and proteins S1, S2, S3
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5
Q

how many proteins are in the large subunit of a bacteria ribosome? how many are in the small subunit?

A

large- 36

small- 21

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6
Q

how many proteins are in the large subunit of a eukaryotic ribosome? how many are in the small subunit?

A

large- 50

small- 33

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7
Q

what results in loss of ribosome function in yeast

A

cells grow slowly, can’t complete well with wild-type strains

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8
Q

what results in loss of ribosome function in Drosphila

A

a class of mutations (called minute)

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9
Q

what is Diamond-Blackfan anemia (DBA) and what is it a result of?

A

lack of red blood cells and congenital abnormalities. caused by mutations in 10-15 diff ribosomal protein genes (RPS19)

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10
Q

what is Treacher-Collins syndrome and what is it a result of?

A

craniofacial defects, hearing loss.

results from mutations of TCOF1, which participates in rRNA processing and genes that encode subunits of RNAPi

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11
Q

what programs ribosomes for protein synthesis

A

mRNA

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12
Q

mRNA is read in which direction

A

5’ –> 3’

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13
Q

what are codons

A

triplets of bases in mRNA that specify which amino acids are a part of the protein strand

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14
Q

what is the open reading frame (ORF)

A

portion of mRNA encoding a protein, that is a way the nucleotide sequence can be divided

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15
Q

reading frames start with which codon

A

ATG (AUG) methionine

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16
Q

what is the wobble in codon-anticodon pairing

A

the 5’ end of the tRNA anticodon can recognize multiple bases at the 3’ end of the codon

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17
Q

what provides the greatest flexibility for codon-anticodon pairing

A

inosine

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18
Q

what are the 3 codons that terminate translation

A

UAA
UAG
UGA

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19
Q

which of the stop codons can be repurposed to incorperate nonstandard amino acids into proteins

A

UGA

UAG

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20
Q

what is the 21st amino acids in proteins and is found in all domains of life

A

SEC- selenocysteine

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21
Q

selenocysteine is encoded by what codon

A

UGA codon

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22
Q

what is the function of the selenocysteine incorporation sequence (SECIS)

A

recoding of UGA as a U codon

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23
Q

what is the 22nd amino acid found in proteins of bacteria and archea

A

pyrrolysine

24
Q

what is pyrrolysine encoded by

A

UAG

25
Q

what is the adapter hypothesis

A

proposed by francis crick
states that there is some molecule that tells protein synthesis machinery which amino acids are specified by the mRNA
was later discovered that tRNAs are the adapters

26
Q

what is the function of the acceptor stem on tRNA

A

responsible for the interaction with an amino acid

27
Q

what is the function of the anticodon on the tRNA

A

responsible for the interaction with the mRNA codon

28
Q

the anticodon of the tRNA pairs with what during translation

A

codon on mRNA

29
Q

what are aminoacyl-tRNA synthetases

A

attach amino acids to their cognate tRNA (called=charging)

must be able to discriminate between amino acids with similar side chains

30
Q

explain the proofreading process of aminoacyl-tRNA synthetases

A

double-sieve model to only allow isoleucine
have course sieve on the activation site to reject larger amino acids
have fine sieve on editing site to reject smaller amino acids

31
Q

what can cause tRNA recognition by aminoacyl synthetases to be altered

A

mutation of the identity element alters the specificity of the tRNA for the synthetase

32
Q

what are the 4 mechanisms of translation

A

initiation
elongation
chain termination
recycling

33
Q

what other codons could start

A

GUG

UUG

34
Q

lacl has what starting codon

A

GUG

35
Q

lacA has what starting codon

A

UUG

36
Q

what is generally the first amino acid incorporated into a new protein

A

methionine

but can also occur in the middle

37
Q

what are the 2 methionine tRNAs in bacteria

A

initiator

elongator

38
Q

what hydrolyzes GTP to GDP during prokaryotic translation initiation

A

IF2

39
Q

what is the shine-dalgarno sequence

A
  • observations made by john shine and Lynn Dalgarno
  • many bacterial ORFs have purine-rich consensus sequence, 5-7 nt upstream of initiating AUG codon
  • the 16S rRAN has a complementary pyrimidine-rich sequence near its 3’ end
40
Q

how are eukaryotic translation initiation different that prokaryotic

A
  • mRNAs are much more highly processed
  • no shine-dalgarno sequence
  • ribosomes bind to the mRNA and scnas for a proper AUG
41
Q

what is the Kozak sequence

A

sequence that has AUG embedded, to start

42
Q

describe the 3 sites of the ribosome

A

A site: entry point for a charged tRNA
P site: where the peptidyl tRNA is located (tRNA is attached to the growing polypeptide chain)
E site: exit point for an uncharged tRNA

43
Q

when does translation termination occur

A

when a termination codon enters the A site

44
Q

translation termination requires 3 release factors

A
  • RF1 and 2 interact with the termination codon

- RF3 stimulates cleavage of the completed peptide from the last tRNA

45
Q

how does Diphtheria toxin target ribosomes

A

adds an ADP-ribose molecule to eEF2

46
Q

how does ADP-ribosylation and exotoxin A impair eEF2 function

A

inhibits protein synthesis

47
Q

What are and the functions of saponin, shiga toxin, adn ricin

A

they are ribosomal posions, of which each remove a single adenine base from the 28S rRNA

48
Q

where are many ribosomal toxins found

A

they are found in: staple crops–rice, maize, and barley because they aren’t toxic to humans

49
Q

how are ribosomes used in cancer therapy

A

they are a part of “immunotoxin”, where they are an antibody against cancer cell-specific proteins, where they inhibit protein synthesis

50
Q

what are chaperones

A

factors that mold disordered protein chains into proper shapes

51
Q

what is the bacterial chaperone’s role in it exit of a ribosome

A

the trigger factor associates with the nascent polypeptide chain

52
Q

what is the signal hypothesis

A
  • states that free and ER-asscoaited ribosomes are the same
  • it was originally hypothesized that all protein synthesis begins on free ribosomes and proteins were specifically functionized to be directed to ribosomes on the ER
53
Q

what is the function of proteasome

A

protein complex that gets rid of unnecessary/damaged proteins

54
Q

what is the structure of a proteasome

A

barrel-like structure that is capped by regulatory subunits

55
Q

explain the function of ubiquitin and ubiquitination with proteasomes

A
  • proteins that are to be degraded are tagged with ubiquitin
  • ubiquitination targets the protein to the proteasome
  • proteasomes hydrolyze peptide bonds, chopping proteins into small fragments

L 211 (12 decks)

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