Translation

Question 1

What is translation?

Answer 1

The synthesis of a protein from a transcribed sequence into mRNA

Question 2

Where does translation occur?

Answer 2

cytoplasm

Question 3

In prokaryotes (70S), translation is __-_________

Answer 3

co-transcriptional

Question 4

In eukaryotes (80S), translation occurs after _______

Answer 4

transcription

Question 5

How big is a ribosome?

Answer 5

10nm

Question 6

The different units of ribosome are characterised based on the rate at which they sediment (measured in S) in a _______

Answer 6

centrifuge

Question 7

What does the small ribosomal subunit contain?

Answer 7

Decoding centre needed for reading mRNA

Question 8

What does the large ribosomal subunit contain?

Answer 8

Catalytic RNA-peptidyl transferase centre

Question 9

What is a polyribosome?

Answer 9

Multiple ribosomes on an mRNA strand

Question 10

tRNA carries amino acids that occupy A,P and E sites that occur mostly in the large/small subunit, but are completed in the large/small subunit

Answer 10

large

small

Question 11

What is the A site?

Answer 11

acceptor site where amino-acyl tRNA lands

Question 12

What is the P site?

Answer 12

Peptidyl tRNA site occupied by the last amino acid

Question 13

What is the E site?

Answer 13

exit site where tRNA leaves

Question 14

What is tRNA?

Answer 14

Adaptor molecules that deliver amino acids to the ribosome

Question 15

What is the secondary structure of tRNA?

Answer 15

• clover leaf shape

- contains intra-tRNA H-bonding sites

Question 16

The specific sequence of the anticodon is ________ to a sequence on mRNA

Answer 16

complementary

Question 17

What are codons?

Answer 17

3 nucleotide triplets

Question 18

Describe the method of the Nirenberg experiment

Answer 18

• They synthesised mRNA with repeating nucleotides, and they added these to a test tube containing E.coli lysate.
• The proteins were isolated to see which amino acids were incorporated

Question 19

What were the results of the Nirenberg Experiment

Answer 19

UUU is an mRNA codon for phenylalanine
AAA is an mRNA codon for lysine
CCC is an mRNA codon for protine

A triplet codon based on 3 base codons determines amino acids

Question 20

List the 3 stages of translation in prokaryotes

Answer 20

• Initiation
• Elongation
• Termination

Question 21

Define translocation

Answer 21

Movement of a ribosome along mRNA

Question 22

What does the initiation complex of translation include?

Answer 22

• ribosome
• mRNA
• initiator tRNA

Question 23

Initiator tRNA recognises the ____ codon and enters the __- site, and the following tRNA’s only enter the __-site

Answer 23

AUG
P
A

Question 24

What else is required for initiation?

Answer 24

• 3 initiation factors

- GTP

Question 25

What 3 steps are involved in elongation?

Answer 25

- Peptide bond formation - Translocation - Aminoacyl-tRNA delivery

Question 26

After initiation, the __-site is occupied whilst the __-site is empty

Answer 26

P | A

Question 27

3 elongation factors are recruited to the initiation complex and they can all bind to ___ or ___

Answer 27

GTP or GDP

Question 28

What do elongation factors do?

Answer 28

- delivers aminoacyl-tRNAs - generates release of EF-Tu-GDP complex - Translocation uses energy from GTP hydrolysis to eject tRNA from P-site, and move peptidyl-tRNA into the P-site from the A-site

Question 29

How is frameshifting prevented?

Answer 29

The ribosome complex maintains a 6bp contact with the mRNA

Question 30

When does elongation stop?

Answer 30

When a termination codon appears at the A-site

Question 31

What is the process called in which the ribosome dissociates from the mRNA?

Answer 31

Termination

Question 32

Protein release factors (RF) interact with these termination codons to release the polypeptide chain. Describe what each RF does

Answer 32

- RF 1 - recognises UAA + UAG - RF 2 - recognises UAA + UGA - RF 3 - facilitates RF 1 + RF 2

Question 33

RF causes ____________ to transfer the polypeptide to water so the protein is released

Answer 33

peptidyltransferase

Question 34

RF dissociates the ribosome complex from the _____ and removal of tRNA from __-site

Answer 34

mRNA | P

Question 35

What is co-translation?

Answer 35

When transcription and translation occur simultaneously.

Question 36

What is an example of a co-translational control?

Answer 36

Tryptophan operon (trp operon)

Question 37

What is the trp operon?

Answer 37

Group of genes that encode enzymes for Tryptophan

Question 38

When is the trp operon expressed?

Answer 38

When tryptophan levels are low

Question 39

When is the trp operon repressed?

Answer 39

When tryptophan levels are high

Question 40

What regulates the trp operon?

Answer 40

trp repressor

Question 41

How does the trp repressor work?

Answer 41

When bound to tryptophan the trp repressor blocks expression from the operon

Question 42

What is attenuation used as?

Answer 42

A control mechanism when tryptophan levels are high and stops ribosome progressing along the mRNA

Question 43

The attenuator polypeptide contains 2 tryptophan residues. What happens if there is NO tryptophan?

Answer 43

The ribosome stalls and an anti-terminator hairpin follows allowing transcription and translation to proceed

Question 44

What happens if there is a lot of tryptophan?

Answer 44

The mRNA stalls and stops due to the terminator hairpin

Question 45

What are the sequences needed to generate anti-terminator and terminator?

Answer 45

anti-terminator - 2 +3 | terminator - 3 + 4

Question 46

List the properties of proteins

Answer 46

- contain C,H,O,N - can absorb light in the UV range - contain charged/uncharged/hydrophilic/hydrophobic amino acids