protein synthesis

Question 1

what is the start codon?

Answer 1

AUG = methionine

Question 2

what are the stop codons?

Answer 2

UAA
UAG
UGA

Question 3

what is the wobble base position?

Answer 3

3rd position

Question 4

how is it that each tRNA can bind to more than one codon?

Answer 4

tRNA binds using either watson-crick binding or wobble base binding
wobble bases are made by modification using enzymes
allows the use of fewer tRNAs for the 64 codons

Question 5

what is an some example of wobble base modification?

Answer 5

A ——> inosine
(by deamination)
- inosine can bind to A, U or C

Question 6

how is an amino acid coupled to a tRNA during protein synthesis?

Answer 6

1. AMP added to c-terminus of amino acid
2. adenylated amino acid used to attach tRNA to amino acid - high energy ester linkage formed. aminoacyl-tRNA formed.
   enzyme used = aminoacyl-tRNA synthetase

Question 7

how does the correct amino acid pair with the correct tRNA?

Answer 7

amino acid has to fit into 2 different pockets in the synthetase (before and after AMP addition)
tRNA nucleotides in the acceptor stem, anticodon etc. fits into pockets in the synthetase

Question 8

what is the function of the large ribosomal subunit?

Answer 8

catalyses polymerisation (of amino acids)

Question 9

what is the function of the small ribosomal subunit?

Answer 9

facilitates amino acid/tRNA interaction

Question 10

what is the function of EF-1 and how does it work?

Answer 10

1. anticodon on tRNA binds to codon on mRNA
2. EF-1 prevents peptidyl transferase from working -> causes delay allowing time for incorrectly bound tRNAs to fall off
3. EF-1 hydrolyses GTP to GDP
4. EF-1 dissociates from tRNA

Question 11

DEFINE: ribozyme

Answer 11

an RNA that catalyses a reaction

Question 12

how are eIFs involved in translation

Answer 12

1. mRNA with a 5’ cap and 3’ poly A tail bound by eIF-4G and eIF-4E + forms a loop
2. methionine tRNA and eIF-2 bound to small subunit
3. complex binds to 5’ cap and associated eIFs
4. complex scans mRNA to search for first AUG for tRNA to bind to
5. methionine tRNA forms base pairs –> signals for release of eIF and binding of large subunit
6. translation begins

Question 13

what are release factors

Answer 13

• recognise stop codons

- look like charged tRNAs + enter A site –> facilitates dissociation of ribosome

Question 14

what is a molten globule

Answer 14

protein initially folded into roughly the correct conformation with hydrophobic side chains put in the middle to achieve a lower energy state

Question 15

what is misfolding

Answer 15

reaching low energy state creating an uphill battle to get to its properly folded state

Question 16

hsp70

Answer 16

no atp required

binds to hydrophobic side chains on proteins to protect them from sticking together to give time to fold properly

Question 17

hsp60

Answer 17

large chamber with hydrophobic amino acids on surface of entrance = recognises proteins with hydrophobic amino acids on their surface
misfolded proteins pulled into chamber and partially unfolded
groES cap seals protein inside to allow refolding . atp required.

Question 18

what are protein aggregates?

Answer 18

cluster of proteins without a functional morphology

Question 19

which diseases are associated with protein aggregates?

Answer 19

CJD
huntington’s disease
alzheimer’s disease

Question 20

what are prions?

Answer 20

protein aggregates converting normal proteins into misfolded proteins
amyloid plaques formed = made up of cross-beta filaments