Cellular Control - Module 6

Question 1

Definition of a gene mutation

Answer 1

A random change to genetic material/ a change to the DNA

Question 2

What are possible causes of mutations?

Answer 2

• Tar in tobacco smoke
• Ionising radiation e.g. UV light, x-rays and gamma rays

Question 3

What are somantic mutations?

Answer 3

Mutations occuring in mitosis that are not passed on to offspring

Question 4

What may mutations in mitosis be associated with?

Answer 4

Cancerous tumours

Question 5

When do mutations tend to occur in the cell cycle?

Answer 5

During DNA replication

Question 6

What is a point mutation?

Answer 6

Base subsitutions during transcription
- Including silence, missence and nonsense mutations

Question 7

What are silent mutations?

Answer 7

When the triplet codes for the same amino acid, primary structure remains the same so the tertiary structure has no chnage

Question 8

Where is it best for a silent mutation to take place and why?

Answer 8

Best for a change to occur on last letter of a triplet as it reduces the effect
- Amino acids are degenerate and have more than one base triplet code except Methionine

Question 9

Which amino acid is not degenerative?

Answer 9

Methionine

Question 10

What is a missence mutation?

Answer 10

When a change in the base sequence leads to a change in the amino acid sequence of a protein. Alters the primary structure leading to change in tertiary structure.

Question 11

When may a missence mutation not matter?

Answer 11

Where the tertiary structure of a protein isn’t related to it’s function or when the change in protein has a similar structure

Question 12

Give an example of something caused by a missence mutation

Answer 12

Sickle cell anemia

Question 13

What is a nonsense mutation?

Answer 13

An alter to the base triplet so it becomes a termination (stop) to a peptide chain resulting in a truncated protein

Question 14

Give an example of something cause by a nonsense mutation

Answer 14

Duchenne muscular dystophy

Question 15

What is an indel mutation?

Answer 15

Insertion or deletion of bases which can cause a frameshift so after amino acid sequence is disrupted primary and tertiary structureds are changed

Question 16

What do insertions and deletions cause and why?

Answer 16

A frameshift as nucleotide base pairs (not in group of 3) are inserted or deleted from a gene all the base triplets after alter which is a frameshift resulting in addition or loss of an amino acid

Question 17

What are expanding triple nucleotide repeats?

Answer 17

Some genes contain a repeating triplet like CAG. The number of triplets increases at meiosis and again from generation to generation. If numbers go above a critical number then the person with that genotype will develop symptms of Huntington disease

Question 18

4 reasons not all mutations are harmful

Answer 18

1) Many mutations are benficial and occured for evolution through natural selection
2) Mutation of blue eyes may be harmful in areas of high sunlight intensity but in temperate zones it can lead to seeing better in less light
3) Early humans in Africa would of had black skin to protect them from sunburn and skin cancer. When humans migrated paler skin enabled vitamin D to be produced with lower light intensities
4) some mutations are neither harmful or beneficial e.g. differently shaped ear lobes or inability to smell different flowers

Question 19

What does the lac operon consist of?

Answer 19

Regulatory gene - codes for a ropressor protein
Promoter gene (p) - RNA polymerase binds so that transcription of structural genes lacZ and lacY begin
lacO - part of promoter region and binds to ropressor protein
lacZ - produces B galactosidase
lacY - produces lactose permease

Question 20

What happens when E coli are grown on glucose?

Answer 20

Repressor protein coded fro by regulatory gene. When regulatory gene is expressed the repressor protein produced binds to lacO preventing RNA polymerase from binding to the promoter region. So srtructural genes are turned off. LacZ and lacY cannot be transcribed so translation doesnt happen and enzymes for lactose metabolism are not made

Question 21

What happens when E coli are grown on lactose?

Answer 21

Lactose binds to the repressor protein altering it’s shape. So the repressor protein won’t bind to the lacO (operator) RNA polymerase can bind to promoter region. Structural genes can be transcribbed into MRNA that is then transcribed into enzymes.
lactase permease - impermeable uptake of lactose
B galactosidase - hydrolyses lactose into glucose and galactose

Question 22

How is gene expression in Eukaryotic cells regulated?

Answer 22

• for gene to be transcribed, enzyme RNA polymerase (needed to produce MRNA) must attach to control site of the gene. It attaches to the promoter.
• In prokaryotes, RNA polymerase attaches to DNA of the promoter
• In humans and other eukaryotes RNA can only attach to promoter with help of a transcription factor
• Once bound to the promoter it makes it easier or harder for RNA polymerase to bind to promoter of the gene
• The transcription factor/factors therefor either activate or supress transcription of the structural gene

Question 23

What is a transcription factor?

Answer 23

A protein or short non-coding piece of RNA that can bind to a specific length of DNA