Gene expression

Question 1

Mutation definition

Answer 1

Change in the DNA base sequence

Question 2

When in the cell cycle are mutations most likely to occur?

Answer 2

Interphase - DNA replication

Question 3

Name 2 mutagens

Answer 3

1. High energy radiation e.g. UV
2. Chemicals e.g. asbestos

Question 4

What are the 5 types of mutation?

Answer 4

1. Deletion/addition
2. Substitution
3. Inversion
4. Duplication
5. Translocation

Question 5

Translocation mutation definition

Answer 5

Sequence of bases moves from one location on the genome to another

Question 6

What is a frame-shift mutation?

Answer 6

All triplet codes change from the point of mutation

Question 7

What are the 3 types of substitution mutation?

Answer 7

1. Mis-sense mutation: base change leads to a new amino acid produced
2. Silent mutation: degenerate
3. Nonsense: base change leads to a stop

Question 8

How does a cell differentiate?

Answer 8

Certain genes for specific proteins are expressed

Question 9

Stem cell definition

Answer 9

Unspecialised cell which can keep dividing and differentiate into specialised cells

Question 10

What are the 4 types of stem cell?

Answer 10

1. Totipotent - can divide and differentiate into ANY type of cell
2. Pluripotent - MOST
3. Multipotent - LIMITED
4. Unipotent - ONE

Question 11

When are the different stem cell types present in an organisms lifetime?

Answer 11

Totipotent: first 4 days of embryo
Pluripotent: after 4 days (embryo)
Multipotent: mature mammals
Unipotent: mature mammals

Question 12

How can stem cells be used in the treatment of disease?

Answer 12

Can be transplanted to divide and differentiate into the cell type required

Question 13

What are the advantages and disadvantages of adult stem cells?

Answer 13

Advantages: no ethical issues, less chance of rejection

Disadvantages: multipotent, difficult to isolate

Question 14

What are the advantages and disadvantages of embryonic stem cells?

Answer 14

Advantages: Pluripotent, easy to isolate

Disadvantages: unethical?, high chance of rejection

Question 15

What are induced pluripotent stem cells?

Answer 15

Normal cells which were removed and had factors added to them to make them pluripotent

Question 16

What are the advantages of induced pluripotent stem cells?

Answer 16

• No ethical issues
• Can differentiate into most cell types
• Less chance of rejection

Question 17

How do transcription factors cause transcription?

Answer 17

Proteins which bind to a promotor of a gene which stimulates RNA polymerase to transcribe the gene and produce mRNA

Question 18

What are the 2 types of transcription factor?

Answer 18

1. Activators - activate transcription
2. Recessors - inhibit transcription

Question 19

How does oestrogen act as a transcription factor?

Answer 19

Lipid so crosses phospholipid bilayer by diffusion and binds to complementary protein receptor in cytoplasm. Receptor-oestrogen complex binds to promotor which stimulates RNA polymerase etc.

Question 20

How can oestrogen cause cancer?

Answer 20

Can cause breast cells to divide more so more likely that mutations occur when DNA replicates so can produce tumours

Question 21

How does siRNA prevent translation?

Answer 21

1. siRNA has specific complementary base sequence to target mRNA
2. Binds to RISC protein which acts as an enzyme
3. One of siRNA strands becomes single-stranded
4. siRNA binds to mRNA molecule by complementary base pairing
5. mRNA destroyed
6. Can’t be used in translation

Question 22

How is miRNA different to siRNA?

Answer 22

Not fully complementary to one mRNA so targets more than one type of mRNA

Question 23

What is the difference between benign and malignant tumours?

Answer 23

Cells in benign tumours can’t metastasise whilst in malignant tumours they can

Question 24

What do tumour suppressor genes do?

Answer 24

Code for proteins which prevent cell division

Question 25

What do proto-oncogenes do?

Answer 25

Code for proteins which stimulate cell division

Question 26

How can mutations of tumour suppressor genes cause cancer?

Answer 26

Changes DNA base sequence, amino acid sequence, tertiary structure which stops production of proteins which prevent cell division --> uncontrolled cell division

Question 27

How can mutations of proto-oncogenes cause cancer?

Answer 27

Changes DNA base sequence changes amino acid sequence changes tertiary structure --> become oncogenes which produce more proteins which stimulate cell division --> uncontrolled cell division

Question 28

Epigenetics definition

Answer 28

Heritable changes in gene function without a change in DNA base sequence

Question 29

How does the methylation of DNA affect gene expression?

Answer 29

Methyl groups added to DNA so transcription factors can't bind to promotor. RNA polymerase not activated so gene is not transcribed

Question 30

How does acetylation of histone proteins affect gene expression?

Answer 30

Addition of acetyl groups makes chromatin less condensed so transcription factors can bind to the promotor. RNA polymerase is activated so gene is transcribed

Question 31

The DNA of which cells needs to be methylated/acetylated in order for offspring to 'inherit' their parents environmental effects?

Answer 31

Gametes

Question 32

How can the methylation of a tumour suppressor gene lead to cancer?

Answer 32

Methyl groups added to tumour suppressor gene so transcription factor can't bind to the promotor so no transcription so no proteins which prevent cell division --> uncontrolled cell division

Question 33

How can the demethylation of a proto-oncogene lead to cancer?

Answer 33

Methyl groups removed from proto-oncogene so transcription factor can bind to promotor so more transcription and more proteins which stimulate cell division --> uncontrolled cell division