Gene Products and Protein Synthesis

Question 1

How many codons exist for the 20 different AA’s?

Answer 1

X64

Question 2

How many of the X64 AA codons are stop codons?

Answer 2

X3

Question 3

What triplet of bases is the start of every protein?

Which AA does this codon code for?

What is the name given to this codon?

Answer 3

AUG

Methionine

The initiation codon

Question 4

What is a frameshift mutation?

Answer 4

The addition or deletion of a base pair/s which alters the reading frame of the base pair sequences

Question 5

What is a point mutation?

Answer 5

The alteration (addition or removal) of a single base pair

Question 6

What are the x3 different types of point mutation?

Answer 6

1) silent
= the alteration in base pairs still codes for the same amino acid

2) missense
= the alteration in base pairs codes for a different amino acid

3) nonsense
= the new codon produced by altering the base pairs is a stop codon

Question 7

What is the point mutation in sickle cell anaemia?

Answer 7

An A goes to a T in the 6th AA

GAG —> GTG

GLUTAMINE —> VALINE

POLAR —> NON-POLAR

This occurs on the beta chains and creates hydrophobic regions on their outsides

Question 8

What is the shape or tRNA?

Answer 8

Clover leaf due to internal base pairings

Question 9

What is the name for the site on the middle tRNA loop that is specific for each AA?

Answer 9

The anticodon

Question 10

What is the sequence at the end of the 3 prime end of tRNA?

Answer 10

CCA-OH

Question 11

What is the name of the process whereby the last base on the anticodon loop can form non-Watson/crick base pairs?

Answer 11

Wobble base pairing

Question 12

Does amino acid attachment to tRNA require energy?

Answer 12

Yes - ATP

Question 13

How does the tRNA bind amino acids and where?

Answer 13

It binds them to the terminal adenosine from then CCA-OH complex at the 3-prime end of the tRNA.

It does this via aminoacyl-tRNA-synthetases

Question 14

What are the X2 safety mechanisms the tRNA-synthetases have when loading AA’s into tRNA?

Answer 14

1) the amino acid fits

2) the tRNA fits

Question 15

What is the name of the X3 binding sites of ribosomes?

Answer 15

1) A site = acceptor site
2) P site = polymerisation site
3) E site = exit site

Question 16

What is the first set of binding in initiation of translation?

What other factors need to bind?

Answer 16

The smaller subunit binds mRNA and the first tRNA in the central (P) position and then the larger subunit binds on top

The first tRNA is fmet-tRNA

(Fmet in prokaryotes = met in eukaryotes)

The initiation actors IF1, 2 and 3 also bind (2 requires GTP)

Question 17

Where do IF1 and 3 bind in initiation?

Answer 17

The small ribosomal subunit

Question 18

Where does IF2-GTP bind during initiation?

Answer 18

To the met-tRNA

Question 19

In the elongation phase of translation, what is an aminoacyl-tRNA?

Answer 19

tRNA with an amino acid bound

Question 20

How does elongation occur?

Answer 20

Elongation factor (EF) binds to GTP and aminoacyl-tRNA and enters the A site of the ribosome

GTP is hydrolysed as proof reading occurs

Question 21

Which enzyme links the amino acids in the elongation process?

Where is this enzyme found?

Answer 21

Peptidyl transferase

In the large ribosomal subunit

Question 22

How does the A site become free again to carry on elongation?

Answer 22

EF-G binds to the complex causing the ribosome to translocate.

The existing AA chain is added to the newest tRNA in the P-site, and the A site is free again for a new aminoacyl-tRNA complex to join

Question 23

How does termination occur within translation?

Answer 23

When the top codon on the mRNA reaches the A-site of the ribosome release factors 1 and 2 (RF 1 and 2) bind to the A-site why hydrolyses the newly formed protein.

The ribosome complex then disassembles

Question 24

What does monocistronic mean?

Answer 24

For eukaryotes, it means mRNA can code for only a single protein

Question 25

What happens to hnRNA to mature it into mature RNA in eukaryotes?

Answer 25

Capping and splicing

Question 26

What is the shine-dalgarno sequence

Answer 26

A sequence of base pairs upstream of the start codon which acts to re riot ribosomes to align in the correct place

Question 27

How does actinomycin work?

Answer 27

Binds to DNA at the transcription initiation complex to prevent transcription and rRNA elongation via RNA polymerase

Question 28

What type of RNA polymerase does mRNA use?

Answer 28

2

Question 29

What type of RNA polymerase does tRNA use?

Answer 29

1

Question 30

What type of RNA polymerase does rRNA use?

Answer 30

3

Question 31

How does rifamycin work?

Answer 31

It inhibits transcription by binding to prokaryotic RNA polymerase

Question 32

How does streptomycin work?

Answer 32

It affects the 30s subunit

Question 33

How does erythromycin work?

Answer 33

Affects the 50s subunit by preventing translocation

Question 34

How does chloramphenicol work?

Answer 34

It affects the 50s subunit by inhibiting peptidyl transferase

Question 35

How does tetracycline work?

Answer 35

Inhibits binding of aminoacyl-tRNA’s to the A-site of ribosomes

Question 36

How does puromycin work?

Answer 36

It prematurely terminates the chain

Question 37

How does alpha-aminitin work?

Answer 37

It inhibits RNA polymerase 2

Question 38

How does cyclohexamide work?

Answer 38

It interferes with translocation to prevent protein biosynthesis

Question 39

How does diphtheria toxin work?

Answer 39

It inactivates EF-2