20. Gene Expression

Question 1

Describe what is meant by substitution of bases.

Answer 1

• nucleotide is ‘swapped’
• may cause STOP codon stopping translation of polypeptide
• ## may result in a change in one amino acid, may not - degenerative code

Question 2

What is meant by frame shift?

Answer 2

• entire sequence moves to left (or right)
• sequence from that point on is wrong

Question 3

When does frame shift occur?

Answer 3

• deletion of base
• addition of base
• duplication of base

Question 4

What is meant by inversion mutation?

Answer 4

Group of bases separates from one sequence of DNA and rejoin in inverse order.

Question 5

What is meant by translocation mutation?

Answer 5

Bases separate and join a different one.

Question 6

What is meant by mutagenic agents?

Answer 6

Something that increases rate of mutation

Question 7

Name two types of mutation agents, give examples.

Answer 7

High energy ionising radiation
- a/b partials
- X-ray
- UV

Chemicals
- nitrogen dioxide
- benzopyrene, inhibits tumour suppressor gene

Question 8

Give 5 types of mutations

Answer 8

• substitution
• addition/ deletion
• duplication
• inversion
• translocation

Question 9

What is meant by cell differentiation

Answer 9

The process of cells becoming specialised, suited for specific role

Question 10

What are the four types of stem cells?

Answer 10

• totipotent
• pluripotent
• multipotent
• unipotent

Question 11

Where are totipotent cells found

Answer 11

Early embryos (no later that 16 days)

Question 12

Where are pluripotent cells found?

Answer 12

Embryos

Question 13

What two types of stem cells are found in bone marrow?

Answer 13

Multipotent
Unipotent

Question 14

What are ethical issues with using pluripotent cells in research and treating human disorders?

How are they overcome?

Answer 14

Use of pluripotent involves killing of embryos

Induced pluripotent cells (IPC)
- genes that have been ‘switched off’ during differentiation are switch back on using transcription factors

Question 15

What is a carcinogen?

Answer 15

chemicals that can alter the structure of DNA and interfere with transcription.

Question 16

What is the role of transcription factors?

Answer 16

‘switches on gene’ binding of TS factor and DNA initiates transcription

Question 17

What is the role of hormones in the action of transcription factors?

give an example.

Answer 17

Activate DNA binding site of transcription factors

oestrogen

Question 18

How is oestrogen specific to its function? (activating transcription factor)

Answer 18

• lipid soluble, enter cytoplasm easily
• complementary shape to receptor on transcription factors

Question 19

Describe how a hormone can switch on a gene and start transcription.

Answer 19

• oestrogen diffuses into cytoplasm
• oestrogen binds to receptor on transcription factor
• DNA binding site changes shape, now complementary to DNA
• transcriptional factor can now enter nucleus through nuclear pore
• binding of transcriptional factor with DNA stimulates transcription of gene.

Question 20

What is meant by epigenetics?

Answer 20

Environmental factors cause changes in gene function without altering DNA base sequence.

Question 21

What is meant by epigenome?

Answer 21

shape of DNA-histone complex, describes ‘tags’ (acetyl and methyl)

Question 22

Explain the impact that decreased acetylation has on transcription.

Answer 22

Decreased acetylation inhibits transcription.

• Histones become more positive, more attracted to the phosphate group of DNA
• Histones are strongly associated with DNA, transcription factors unable to bind

Question 23

How does methylation inhibit transcription?

Answer 23

• Methyl group prevents transcription factors from binding to cytosine group
• Attracts proteins that condense DNA-histone complex

Question 24

Cancer is caused by…

Answer 24

mutations is genes that regulate mitosis.

Question 25

What are oncogenes?

Answer 25

mutated proto-oncogenes, can be permanently activated, cells divide continuously.

Question 26

What do proto-oncogenes code for?

Answer 26

proteins involved in initiation of DNA replication and mitosis

Question 27

What is the role of tumour-suppressor genes?

Answer 27

• slow down division
• cell death
  … if DNA copying error is detected, identifying and destroying mutated cells

Question 28

Describe benign tumours. (3)

Answer 28

• grow at slow rate
• non-cancerous
• adhesion keeps cells together in capsule, remains localised

Question 29

Describe malignant tumours. (4)

Answer 29

• grow rapidly
• cancerous
• metastasis occurs due to no adhesive, spreads across body
• recurrence likely

Question 30

Explain how the menopause can be linked with breast cancer.

Answer 30

No oestrogen being produced in ovaries, fat cells in breast produce it instead. High (localised) concentration can lead to breast cancer.

Oestrogen can bind to genes to initiate transcription, if proto-oncogene is activated, (= oncogene), tumour will develop.

knock on effect larger tumour = more oestrogen

Question 31

Genome

Answer 31

entire genetic material of an organism (contained in nucleus)

Question 32

What is meant by ‘sequencing genomes’?

Answer 32

working out entire base sequence for all DNA in cell

Question 33

Why are simpler organisms’ genomes easier to sequence?

Answer 33

does not have introns or regulatory genes,

Question 34

How can DNA sequencing be used to fight disease?

Answer 34

genome of simple organisms can be used to sequence their proteome.

proteome can be used to identify potential antigens to use in vaccines

Question 35

How can translocation be inhibited by siRNA

Answer 35

• enzyme breaks down RNA into siRNA
• siRNA binds to enzyme
• siRNA takes enzyme to mRNA and attaches to it (complementary base pair)
• enzyme breaks down mRNA, cannot be translocated