Biological Molecules 4

Question 1

How is mRNA exported into the cytoplasm

Answer 1

Via the nuclear pore complex. This is an energy dependant process as it involves conformational changes from proteins within the central core.

Question 2

What are the four bases

Answer 2

Adenine
Thymine
Cytosine
Guanine

Question 3

What does a deletion or insertion of a base result in?

Answer 3

A frameshift affecting all subsequent amino acids. (nonsence mutation)

Question 4

What does a substitution of a base result in?

Answer 4

A point mutation which will only affect one amino acid. (Missense mutation)

Question 5

What is a silent mutation?

Answer 5

When there is a mutation but it doesn’t affect the amino acid produced due to the degenerate nature of genetic coding.

Question 6

What is polymorphism

Answer 6

A mutation that us not associated with any pathology. Seen as natural variation.

Question 7

What is the base sequence for a start codon?

Answer 7

AUG

Question 8

What are the three base sequences for a stop codon?

Answer 8

UAA
UAG
UGA

Question 9

What is the role of non-coding regions?

Answer 9

Provide stability.

Question 10

Describe some features of tRNA

Answer 10

They have a clover leaf shape with its 3’ end being the amino acid binding site. They also have an anticodon loop of tRNA base pairs that binds with the mRNA

Question 11

What ensures the correction amino acid binds to tRNA?

Answer 11

Aminoacyl-tRNA synthetases.

Question 12

What are the two steps that aminoacyl-tRNA synthetase is involved in?

Answer 12

1. Activation of amaino acid

2. Transfer of amino-acyl group to tRNA

Question 13

Describe the structure of a ribosome in humans

Answer 13

Contains a large 60S subunit and a small 40S subunit

Question 14

What are the three phases translation occurs in?

Answer 14

Initiation
Elongation
Termination

Question 15

Describe the first step (initiation) of translation

Answer 15

5’ cap is recognised by the cap-binding protein complex which then recruits ribsosomes. The ribosome scans through the 5’ non coding region until it reaches the initiation codon. Initiation factors are required..

Question 16

Describe the second step (elongation) in translation

Answer 16

Charged tRNAs bind and peptide bonds form between adjacent amino acids. Once formed, the ribosome move along one codon. The deacylated tRNA exits the complex and a new, charged tRNA binds.

Question 17

Describe the third step (termination) of translation

Answer 17

Termination codon encountered at the end of the open reading frame. Bond between the protein and last tRNA is broken to release the protein. Whole complex dissociates and this requires termination factors

Question 18

What is a polysome?

Answer 18

Multiple ribosomes moving along the same mRNA strand at the same time

Question 19

What occurs post-translation?

Answer 19

Translocation to relevant part of the cell, protein folding and post-translational modifications (e.g. Addition of sugars, OH groups and addition of a N atom to the amide group)