8A: Mutations and gene expression

Question 1

Describe a substitution mutation

Answer 1

1 or more bases are swapped for another

Question 2

Describe a deletion mutation

Answer 2

1 or more bases are removed

= frame shift

Question 3

Describe an addition mutation

Answer 3

1 or more bases are added

Question 4

Describe a duplication mutation

Answer 4

1 or more bases are repeated

Question 5

Describe an inversion mutation

Answer 5

A sequence of bases is reversed

Question 6

Describe a translocation mutation

Answer 6

A sequence of bases is moved from one location in the gene to another. This could be movement within the same chromosome or movement to a different chromosome

Question 7

What does the order of DNA bases in a gene determine?

What may happen if there’s a mutation?

Answer 7

The order of bases in a gene determines the sequence of amino acids in a particular polypeptide. If a mutation occurs in a gene, the sequence of amino acids in a polypeptide that codes for it could be changed (= change in functionality)

Question 8

What is a gamete?

Answer 8

A sex cell

Question 9

What can genetic disorders be caused by?

Answer 9

Inherited disorders, e.g cystic fibrosis, can be caused by mutations (abnormal genes or chromosomes)

Question 10

Some ______ can increase the likelihood of developing certain cancers.

Answer 10

Some mutations can increase the likelihood of developing certain cancers.

Question 11

What will happen if a gamete containing a mutation for a genetic disorder is fertilised?

Answer 11

The mutation will be present in the new fetus formed - called hereditary mutations because they are passed onto the offspring

Question 12

Why can some amino acids be coded for by more than one DNA triplet?

Answer 12

Because of the degenerate nature of genetic code

Question 13

What 3 types of mutation will almost always change the amino acid sequence of a polypeptide? Why?

Answer 13

Additions, duplications and deletions. Because, they all result in a frame shift so that the triplet code is read in a different way

Question 14

What are the base triplets that follow on from a mutation called?

Answer 14

They are said to be ‘downstream’ of the mutation.

Question 15

Give 3 examples of mutagenic agents

Answer 15

1. Radiation (UV, ionising)
2. Some chemicals
3. Some viruses

Question 16

What are mutagenic agents?

Answer 16

Things that can increase the rate of mutations

Question 17

What 3 ways can mutagenic agents increase the rate of mutation?

Answer 17

• Acting as a base
• Altering bases
• Changing the structure of DNA

Question 18

How do mutagenic agents ‘act as a base’?

Answer 18

Chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA.

Question 19

What are mutations that occur in individual cells after fertilisation called?

Answer 19

Acquired mutations

Question 20

How can mutations result in uncontrolled cell division?

Answer 20

If the mutation(s) occur in the genes that control the rate of cell division (mitosis)

Question 21

What is a tumour?

Answer 21

A mass of abnormal cells

Question 22

When are tumours called cancers?

Answer 22

If they invade and destroy surrounding tissue

Question 23

What are the 2 types of gene that control cell division?

Answer 23

Tumor suppressor genes and proto-oncogenes🙈

Question 24

What is the normal function of tumour suppressor genes?

Answer 24

They slow the rate of cell division by producing proteins that stop cells dividing or cause them to self-destruct (apoptosis)

Question 25

Describe how a mutation in tumour suppressor genes may result in a tumour.

Answer 25

The mutation may cause them to become inactivated, this means that the protein will not be produced and the cells will divide uncontrollably (the rate of cell division increases) resulting in a tumour.

Question 26

What is the normal function of proto-oncogenes?

Answer 26

They stimulate cell division by producing proteins that make cells divide

Question 27

Describe how a mutation in proto-oncogenes may result in a tumour.

Answer 27

The effect of a proto-oncogene can be increased if a mutation occurs, this stimulates the cells to divide uncontrollably (the rate of division increases) resulting in a tumour

Question 28

What is a mutated proto-oncogene called?

Answer 28

An oncogene

Question 29

Describe a malignant tumour

Answer 29

They are cancerous and grow rapidly, they invade other cells and destroy the surrounding tissues. Cells can break off and spread to other parts of the body in the bloodstream of lymphatic system

Question 30

Describe a benign tumour

Answer 30

They are not cancerous and usually grow slower than malignant tumours and are often covered in fibrous tissue that stops cells invading other tissues. They are often harmless but they can cause blockages that put pressure on organs. Some benign tumours can become malignant

Question 31

Describe how tumour cells are different to normal cells (6 ways)

Answer 31

• Irregular shape
• Larger and darker nucleus (sometimes more than one nucleus)
• Dont produce all the proteins needed to function properly
• Different surface antigen
• Don’t respond to growth regulating processes
• Divide by mitosis more frequently

Question 32

What does methylation mean?

Answer 32

Adding a methyl (-CH₃) group to something

Question 33

What does hypermethylation mean?

Answer 33

Too much methylation

Question 34

What does hypomethylation mean?

Answer 34

Too little methylation

Question 35

Describe what happens if tumour suppressor genes are hypermethylated.

Answer 35

The tumor suppressor genes are not transcribed - so the proteins they produce to slow cell division aren’t made
= Cells divide uncontrollably by mitosis and tumors develop

Question 36

Describe what happens if proto-oncogenes are hypomethylated.

Answer 36

Proto-oncogenes act as oncogenes - increasing the production of the proteins that encourage cell division
= stimulates cells to divide uncontrollably causing tumors to develop

Question 37

Increased exposure to oestrogen has been linked to some breast cancers.
Give 2 reasons why oestrogen might contribute to causing breast cancer.

Answer 37

1) Oestrogen can stimulate some breast cells to divide and replicate. More divisions = more likely mutations will occur, so increasing chance of cells becoming cancerous
2) Bc oestrogen stimulates cell division, this could also mean that if cells do become cancerous their replications would be faster = tumors would form quickly

Question 38

What type of hormone is oestrogen?

Answer 38

A steroid hormone

Question 39

What are 2 types of risk factors for cancer?

Give examples

Answer 39

Genetic - specific inherited alleles

Environmental - radiation, high fat diet, smoking

Question 40

Describe totipotent stem cells.

Answer 40

Totipotent cells can divide and produce any type of body cell.
- During development, totipotent cells translate only part of their DNA = cell specialisation.

Question 41

Where are totipotent stem cells found?

Answer 41

Totipotent cells occur only for a limited time in early mammalian embryos.

Question 42

Describe multipotent stem cells.

Give an example

Answer 42

Can differentiate into a few different types of cell

e.g red and white blood cells are formed from stem cells in bone marrow

Question 43

Describe unipotent stem cells.

Give an example

Answer 43

Can differentiate into one type of cell

e.g cardiomyocytes

Question 44

Describe pluripotent stem cells.

Answer 44

Pluripotent stem cells can divide in unlimited numbers and can be used in treating human disorders

Question 45

Where are pluripotent stem cells found?

Answer 45

Pluripotent cells are found in embryos

Question 46

How are induced pluripotent stem cells made?

Answer 46

iPS cells can be produced from adult somatic cells using appropriate protein transcription factors.

Question 47

Give 2 things stem cells can be used to treat

Answer 47

Leukemia and lymphoma