MolBio8 - 45

Question 1

What is the total number of codons?

Answer 1

61

Question 2

What is the start codon?

Answer 2

AUG - methionine

Question 3

What are the three possible stop codons?

Answer 3

UAA, UAG, UGA

Question 4

What is the ORF?

Answer 4

Open reading frame

Question 5

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

Answer 5

The anti-codon

Question 6

What gives tRNA its structure?

Answer 6

Intramolecular base pairing

Question 7

Name two modified tRNA nucleotides

Answer 7

Pseudouridine, dihydrouridine

Question 8

How many possible nucleotide modifications are there?

Answer 8

> 50

Question 9

What do modified nucleotides facilitate?

Answer 9

Interaction with other proteins, enzymes etc

Question 10

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

Answer 10

Wobble pairing allow same anticodon to bind more than one codon

Question 11

Name one instance of wobble pairing

Answer 11

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

Question 12

How is coupling of amino acid to tRNA achieved?

Answer 12

By aminoacyl-tRNA synthetases

Question 13

How to synthetases work?

Answer 13

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

Question 14

Why is aminoactyl-tRNA known as charged?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Which terminus is the protein built on?

Answer 16

C-terminus

Question 17

What performs protein synthesis?

Answer 17

50 ribosomal proteins and several ribosomal RNAs

Question 18

What are the functions of the two rRNA subunits?

Answer 18

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

Question 19

What are the three sites of rRNA?

Answer 19

A-P-E

Question 20

Outline protein construction by rRNA

Answer 20

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

Question 21

What are elongation factors?

Answer 21

Factors that help translation and improve accuracy

Question 22

Describe the function of EF-1

Answer 22

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

Question 23

What is the purpose of the EF lag?

Answer 23

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

Question 24

What is a ribosome also known as, and why?

Answer 24

Ribozyme - RNA that catalyses a reaction

Question 25

In which rRNA segment is the bulk of enzymatic activity?

Answer 25

Larger subunit

Question 26

Outline translation initiation

Answer 26

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

Question 27

What does eIF stand for?

Answer 27

eukaryotic Initiation Factor

Question 28

What is the Kozak sequence?

Answer 28

ACCAUGG - helps initiate translation

Question 29

What is a polysome?

Answer 29

Multiple ribosomes binding one mRNA

Question 30

How far apart are ribosomes on polysomes?

Answer 30

80 nucleotides or so

Question 31

What are stop codons recognised by?

Answer 31

Release factors

Question 32

Describe release factors

Answer 32

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

Question 33

When does protein folding commence?

Answer 33

Immediately after leaving ribosome

Question 34

Describe initial protein folding

Answer 34

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

Question 35

Describe the correct protein folding pathway

Answer 35

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

Question 36

What rescue proteins by reversing incorrect folding steps?

Answer 36

Chaperones

Question 37

What are the two major classes of protein chaperones?

Answer 37

hsp60 and hsp70

Question 38

What does hsp stand for, and why?

Answer 38

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

Question 39

Where do hsp70s work?

Answer 39

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

Question 40

What do hsp60s do?

Answer 40

Put misfolded proteins into isolation

Question 41

How do hsp60s work?

Answer 41

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

Question 42

What happens to incorrectly folded, irretrievable proteins?

Answer 42

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

Question 43

How can incorrect folding cause disease?

Answer 43

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

Question 44

What diseases implicate aggregate placques?

Answer 44

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

Question 45

What are prions?

Answer 45

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