Control of gene expression

Question 1

Properties of Stem cells

Answer 1

• Will keep replicating, hence replacing themselves;
• Undifferentiated so can differentiate into other cells (totipotent)

Question 2

How can injecting stem cells to patients with heart disease help improve muscle contraction

Answer 2

• stem cells would develop into heart muscle cells;
• the relevant genes would be expressed

Question 3

Explain how unspecialised cells can develop into different types of tissue

Answer 3

• cells are totipotent meaning they can develop into any cell type
• different genes expressed
• so different enzymes and proteins produced

Question 4

Why should a person’s stem cells be used in an experiment

Answer 4

• Own stem cells used to minimise risk of rejection
• Totipotent so can divide into ‘required cells’ and fight appropriate issue

Question 5

Describe the role of oestrogen in protein synthesis

Answer 5

1. Oestrogen is a lipid, so crosses the cell membrane by lipid diffusion and enters the cytoplasm.
2. Oestrogen binds to its receptor protein** in the cytoplasm to form a **hormone-receptor complex.** Receptors changes shape and the inhibitor molecules is released, **exposing the binding site
3. This complex is now a transcription factor.
4. The activated transcription factor diffuses into the nucleus through a nuclear pore.
5. Complex can act as an activator or repressor so it can inhibit RNA P or facilliate it
6. In the nucleus the transcription factor binds to the DNA promoter,
7. This binding stimulates RNA polymerase to transcribe genes and so stimulates protein synthesis.

Question 6

Structure of siRNA

Answer 6

• small as it consists of only 20–25 nucleotides;
• double-stranded RNA

Question 7

How does siRNA interfere with gene expression

Answer 7

• single siRNA strand;
• binds to mRNA;
• by complementary pairing;
• enzyme cuts up mRNA
• this prevents translation

Question 8

How can addition/ deletion of DNA cause cancer?

Answer 8

• Inactivates tumour suppressor gene;
• Unable to control cell division
• Rate of cell division increased

Question 9

Role of transcriptional factors in making proteins

Answer 9

• Binds to DNA** at specific region (**promoter );
• Activates RNA polymerase
• Stimulate transcription
• It can turn on gene

Question 10

How can siRNA be used in treating diseases?

Answer 10

• Some diseases are genetic
• siRNA will stop non-functional protein of this gene being made

Question 11

Why doesn’t siRNA only affect the expression of other genes

Answer 11

• base sequence of siRNA complementary to one mRNA;
• will only bind to and destroy this mRNA

Question 12

What is a transcriptional factor

Answer 12

• A Protein** that moves from **cytoplasm to nucleus;
• TF binds to promoter
• They can allow/prevent RNA polymerase to bind to DNA;
• Leads to/prevents pre mRNA production