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Y2S2 - Adv. Molecular Biology > MolBio8 - 45 > Flashcards

MolBio8 - 45 Flashcards

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1
Q

What is the total number of codons?

A

61

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2
Q

What is the start codon?

A

AUG - methionine

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3
Q

What are the three possible stop codons?

A

UAA, UAG, UGA

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4
Q

What is the ORF?

A

Open reading frame

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5
Q

What is the region of tRNA that binds with the codon called?

A

The anti-codon

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6
Q

What gives tRNA its structure?

A

Intramolecular base pairing

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7
Q

Name two modified tRNA nucleotides

A

Pseudouridine, dihydrouridine

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8
Q

How many possible nucleotide modifications are there?

A

> 50

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9
Q

What do modified nucleotides facilitate?

A

Interaction with other proteins, enzymes etc

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10
Q

Why is there not a 1:1 ratio of tRNA to codon?

A

Wobble pairing allow same anticodon to bind more than one codon

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11
Q

Name one instance of wobble pairing

A

Deamination of G to create inosine, which can apri U C or A

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12
Q

How is coupling of amino acid to tRNA achieved?

A

By aminoacyl-tRNA synthetases

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13
Q

How to synthetases work?

A

First primes amino acid by adding AMP to c-terminus, then uses adenylated amino acid to form aminoacyl-tRNA

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14
Q

Why is aminoactyl-tRNA known as charged?

A

Energy of the ATP hydrolysis is still contained within the ester linkage

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15
Q

What does translation of mRNA into precise amino acid sequence require?

A

Two adapters: the synthetase that binds a/a to tRNA, and tRNA that pairs correct a/a to the correct codon

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16
Q

Which terminus is the protein built on?

A

C-terminus

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17
Q

What performs protein synthesis?

A

50 ribosomal proteins and several ribosomal RNAs

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18
Q

What are the functions of the two rRNA subunits?

A

Large - catalyzes polymerisation; small - facilitates tRNA/mRNA interaction

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19
Q

What are the three sites of rRNA?

A

A-P-E

20
Q

Outline protein construction by rRNA

A

tRNA enters A-site, peptidyl-transferase catalyses amino acid addition, tRNA moves to P-site, rRNA moves small subunit 3 nucleotides, tRNA leaves E-site

21
Q

What are elongation factors?

A

Factors that help translation and improve accuracy

22
Q

Describe the function of EF-1

A

Thought only to bind correctly to tRNA that have correct amino acid coupling, it adds a checkpoint to translation, as before peptidyl transferase works, it must hydrolyse GTP to GDP and dissociate

23
Q

What is the purpose of the EF lag?

A

Allow time for incorrectly bound tRNAs to fall off. Some correct ones also fall off, but at a slower rate

24
Q

What is a ribosome also known as, and why?

A

Ribozyme - RNA that catalyses a reaction

25
Q

In which rRNA segment is the bulk of enzymatic activity?

A

Larger subunit

26
Q

Outline translation initiation

A

mRNA with cap and tail bound by eIF-4G/E to form loop, which binds to small rRNA, methionine tRNA scans for AUG, EF hydrolyse and dissociate, so does eIF-2, and large rRNA binds, translation ensues

27
Q

What does eIF stand for?

A

eukaryotic Initiation Factor

28
Q

What is the Kozak sequence?

A

ACCAUGG - helps initiate translation

29
Q

What is a polysome?

A

Multiple ribosomes binding one mRNA

30
Q

How far apart are ribosomes on polysomes?

A

80 nucleotides or so

31
Q

What are stop codons recognised by?

A

Release factors

32
Q

Describe release factors

A

Look like charged tRNAs - molecular mimicry - and enter the A-site

33
Q

When does protein folding commence?

A

Immediately after leaving ribosome

34
Q

Describe initial protein folding

A

Puts hyrophobic side chains in the middle to achieve a lower energy state, creating a molten globule - roughly the correct folding

35
Q

Describe the correct protein folding pathway

A

Multistep process and it is important that the steps occur in the correct order - incorrect folds may reduce the energy state, but blocks further folding

36
Q

What rescue proteins by reversing incorrect folding steps?

A

Chaperones

37
Q

What are the two major classes of protein chaperones?

A

hsp60 and hsp70

38
Q

What does hsp stand for, and why?

A

Heat shock proteins, because their expression is elevated when the temperature is above normal so they can mop up temperature-denatured proteins

39
Q

Where do hsp70s work?

A

Directly on proteins as they exit the ribosome, binding to exposed hydrophobic amino acids

40
Q

What do hsp60s do?

A

Put misfolded proteins into isolation

41
Q

How do hsp60s work?

A

Hyrdophobic entrance binds to the protein partially unfolding it, with a GroES cap that seals the protein inside for 15s to allow refolding

42
Q

What happens to incorrectly folded, irretrievable proteins?

A

Polyubiquinated to mark these for destruction in the proteosome - almost 1 in 3 immediately!

43
Q

How can incorrect folding cause disease?

A

If they aggregate - they become large and protease resistant, sometimes causing a chain reaction by causing well folded proteins to change (prions)

44
Q

What diseases implicate aggregate placques?

A

CJD, Huntington’s and Alzheimer’s - amyloid placques made up of cross-beta filaments

45
Q

What are prions?

A

Misfolded proteins that can convert normal proteins to the same cross-beta filament

Y2S2 - Adv. Molecular Biology (14 decks)

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