Mutations, gene expression and cancer - A2

Question 1

Explain an insertion/deletion mutation.

Answer 1

where one or more nucleotide pairs are inserted or deleted from the sequence. This type of mutation alters the sequence of nucleotides after the insertion/deletion point known as a frameshift.

Question 2

Explain a duplication mutation.

Answer 2

On or more bases repeated causing a frameshift.

Question 3

Explain an inversion mutation.

Answer 3

A group of bases become separated from the DNA sequence and then re-join at the same position but in reverse order. Therefore affects the amino acid that is produced.

Question 4

Explain a translocation mutation.

Answer 4

A group of bases become separated from the DNA sequence on one chromosome and are inserted into the DNA sequence on another chromosome. This can often lead to significant effects on the phenotype.

Question 5

What 3 properties does the genetic code have?

Answer 5

• universal (same for all organisms)
• non-overlapping
• degenerate (more than one triplet codes for an amino acid)

Question 6

Give an example of a mutagenic agent. (increase rates of mutation)

Answer 6

X-ray
UV light
certain chemicals

Question 7

Define totipotent.

Answer 7

non specialised cell
can express all genes
can differentiate into any type of cell in organism (including embryonic cells)

Question 8

Define pluripotent.

Answer 8

Can form any cell type in the body
Except embryonic cells
Found in the early stages of an embryo
Often used in replacing damaged tissues in human disorders.

Question 9

Define multipotent.

Answer 9

Can differentiate into other cell types but more limited e.g. the cells in
the bone marrow and umbilical cord.

Question 10

Define unipotent.

Answer 10

Only give rise to one cell type.

Question 11

How do cells become specialised?

Answer 11

During the process, they switch on some genes ad other off, specialising the cell.
Differential gene expression.

Question 12

What can stem cells be used for in medicine?

Answer 12

• producing tissue for skin graft
• research in producing organs for transplants
• research into how cells become specialised
• research into cancer
• research into serious disease and the use of stem cells to cure such diseases as Parkinsons disease.

Question 13

Ethical concerns about the use of stem cells.

Answer 13

• some people believe embryos are human from conception
• some people believe the embryo is not a human being and is great for medicinal benefits
• some believe embryos have no moral rights at all
• use of animals for testing before trialed on humans
• patient donor should be able to give consent for cells to be used with iPs technology

Question 14

What is the promoter region?

Answer 14

One or more base sequences found upstream of a gene that control the expression of that gene.

Question 15

What is the transcription factor?

Answer 15

Proteins which when activated bind to the promoter region of a gene, stimulating RNA polymerase to transcribe the target gene.
These can also inhibit transcription by preventing RNA polymerase rom binding to DNA and transcribing the gene.

Question 16

How does oestrogen control transcription?

Answer 16

• the lipid soluble nature of oestrogen means it can diffuse across cell membrane where it binds to a receptor molecule on a transcription factor
• the binding alters the shape of DNA binding site on the transcription factor and makes it able to bind to the DNA
• therefore the transcription factor enters nucleus via nuclear pore where it binds to DNA
• this stimulates the transcription of the gene, by stimulating RNA polymerase, making up the DNA.

Question 17

Control of translation by small interfering RNA (siRNA).

Answer 17

• short term switching off of genes
• double RNA is hydrolysed into smaller fragments (siRNA) which is hydrolysed to become single stranded
• siRNA binds to complementary sequence of mRNA
• cell detects the now double strand (mRNA and siRNA) as abnormal
• mRNA is broken down by enzymes, preventing translation and gene expression.
• mRNA fragments further break down into RNA nucleotides

Question 18

Define epigenetics.

Answer 18

Change in organisms caused by modification of gene expression rather than altering the genetic code itself. (inheritable changes in genes function)

Question 19

Describe the process of methylation of DNA.

Answer 19

• a methyl group (CH3) is added to carbon atom 5 of cytosine residue
• this happens when cytosine is linked by a phosphodiester bond to a guanine base (CpG)
• Methyltransferase is the enzyme that catalyses this reaction
• repeated CpG sequences are common at 5’ end of genes so methylation of these silences effected genes by preventing activation of RNA polymerase

Question 20

Outline how acetylation of histones increases chance of gene transcription.

Answer 20

• the winding of chromosomes wrapped around histones may be too tight or too loose
• histone molecules have side branches called ‘tails’ which contain the amino acid lysine
• lysine has a positively changed R group and is attracted to negative charged phosphate backbone of DNA
• when lysine is acetylated, positive ion is removed causing DNA to be less tightly wrapped around histone
• so RNA polymerase and transcription factors can more easily bind to the DNA and gene expression is stimulated
• removal of acetyl groups (deacetylation) returns lysine to its positively charged state, gaining stronger connection to DNA and inhibiting transcription.

Question 21

Name the 2 types of cancer.

Answer 21

• Benign
• Malignant

Question 22

Describe a benign tumour.

Answer 22

• grows slowly and does not spread (metastasise)
• doesn’t cause much harm other that slight chemical damage from pressing against other cells/blood vessels

Question 23

Describe a malignant tumour?

Answer 23

• grows rapidly and does spread (metastasise)
• non-capsulated so will cause damage to other cells and spread
• metastasis is where it spreads through the bloodstream and lymphatic system to neighbouring cells
• difficult to treat

Question 24

What 2 genes control cell division and what do each do?

Answer 24

PROTO-ONCOGENES - stimulate cell division
TUMOUS SUPRESSOR GENES - slow cell division

Question 25

How do tumours develop?

Answer 25

• mutation occurs in proto-oncogene, altering it to become oncogene
• causes over-stimulation of cell division that is permanently switched on
• results in a mass of cells (tumour)
• if mutation occurs in tumour suppressor gene, it becomes inactivated so cell division increases
• if tumour suppressor gene becomes over methylated, gene becomes inactive so cell division increases
• if oncogene is undermethylated, gene becomes more active so cell division increases

Question 26

How can oestrogen concentrations cause development of breast cancer?

Answer 26

The cancer cells have ER receptor in the membranes, oestrogen stimulates them to divide.