Gene Expression (Chapter 20)

Question 1

Define Substitution Mutation

Answer 1

Replacement of a base by a different base

Question 2

Define Mis-Sense Mutation

Answer 2

Incorrect amino acid inserted

Question 3

Define Nonsense Mutation

Answer 3

Stop codon produced early

Question 4

Define Silent Mutation

Answer 4

Same amino acid coded for due to degenerate code

Question 5

Define Deletion Mutation

Answer 5

A base is deleted which causes a frame shift which alters the following triplet codes so there are incorrect codons and an incorrect amino acid sequence.

Question 6

What happens when there is a change in amino acid sequence?

Answer 6

Change in H, Ionic bonds and disulphide bonds so tertiary structure is altered so a non functional protein/enzyme is formed (no enzyme-substrate complex formed)

Question 7

What are stem cells?

Answer 7

Undifferentiated cells

Question 8

Why are stem cells used in treatment?

Answer 8

• Produce normal/healthy polypeptide
• No faulty or defective polypeptide produced
• Stem cells continuously divide

Question 9

Define Epigenetics

Answer 9

Heritable changes in gene function without changes to the base sequence of DNA.

Question 10

How does SIRNA prevent translation?

Answer 10

• SiRNA binds to/destroys mRNA
• Prevents translation of CENP-W
• Reduces protein production

Question 11

What is a tumour?

Answer 11

Mass of unspecialised cells formed by uncontrolled cell division.

Question 12

How do tumours cause harm?

Answer 12

Damage organ concerned, form blockages or place pressure on other organs.

Question 13

Why is cancer more common in older people?

Answer 13

Cancer takes time to develop and immune system is less effective on older people.

Question 14

What is a benign tumour?

Answer 14

Cannot spread to other parts of the body and cannot invade neighbouring tissues.

Question 15

How does methylation cause cancer?

Answer 15

1) Methyl group can be added to both copies of a tumour suppressor gene.
2) The transcription of tumour suppressor genes is inhibited.
3) Protein is not produced which prevents cell division.
4) Uncontrolled cell division/no control of mitosis

Question 16

How does sunbathing cause cancer?

Answer 16

Suns radiation contains ultra violet radiation (mutagenic agent) that causes the mutation of genes which controls division.

Fair skin has less melanin that protects against UV radiation.

Question 17

Why is it important to destroy all cells of a tumour?

Answer 17

Cells can break off (metastasise) and remaining cells can divide and form new tumour.

Question 18

Describe the stages of altered DNA leading to cancer

Answer 18

1) DNA altered by mutation
2) Changes base sequence of gene controlling cell growth/oncogene or of tumour suppressor gene
3) Change protein structure of protein they code for
4) Tumour suppressor gene produces protein which inhibits cells division, therefore cannot do if mutated
5) Leads to mitosis so uncontrolled cell division.

Question 19

Describe totipotent cells

Answer 19

Can divide and produce any type of body cell by only translating part of their DNA.

Question 20

Where are pluripotent cells found?

Answer 20

Embryos

Question 21

Where are multipotent cells found?

Answer 21

Adult mammals

Question 22

Where are unipotent cells found?

Answer 22

Adult mammals

Question 23

Describe pluripotent cells

Answer 23

Can self-renew and differentiate into any type of cell except the cells that make up the placenta.

Question 24

Describe multipotent cells

Answer 24

Can only differentiate and divide into a limited number of cell types​

Question 25

Describe unipotent cells

Answer 25

Can only differentiate into a single type of cell e.g. cardiomyoblasts can only differentiate into cardiomyocytes.

Question 26

Describe induced pluripotent cells

Answer 26

Unipotent stem cells that have been reprogrammed to become pluripotent by using protein transcription factors to express genes associated with pluripotency