Control Of Gene Expression

Question 1

What are totipotent cells?

Answer 1

Cells with the ability to develop into any other cell in the organism

Question 2

What are the 2 ways in which gene expression can be prevented?

Answer 2

• breaking down mRNA before it can be translated

- preventing transcription and therefore production of mRNA

Question 3

Can specialised cells still develop into any other cell?

Answer 3

It depends; some cells (RBC) become so specialised they lose their nucleus , therefore they no longer contains genes to differentiate further

Question 4

What totipotent cells exist in mature animals and where are they found?

Answer 4

• adult stem cells

- found in lining of small intestine, skin and bone marrow

Question 5

Give examples of totipotent cells in animals

Answer 5

• adult stem cells

- embryonic stem cells

Question 6

What are transcriptional factors?

Answer 6

Molecules that move from cytoplasm into the nucleus, and stimulate gene for transcription

Question 7

How does oestrogen enter cells?

Answer 7

It diffuses across phospholipid bilayer, as it is lipid-soluble

Question 8

Explain how oestrogen affects transcription once inside the cell

Answer 8

1. Binds to receptor molecule on transcriptional factor (shapes are complimentary)
2. This changes shape of molecule, inhibitor is released
3. Transcriptional factor can now enter nucleus via pore and combine with DNA
4. Transcription is stimulated

Question 9

What is siRNA?

Answer 9

• small interfering RNA

- small double stranded sections of RNA

Question 10

Explain how siRNA prevents gene expression

Answer 10

1. Enzyme breaks double stranded RNA into small sections (siRNA)
2. One of strands combines with enzyme, and pairs with complimentary bases on mRNA strand
3. Enzyme cuts mRNA into small sections, therefore preventing translation