Topic 3C - Differentiation and Variation

Question 1

EQ. State what is meant by the term stem cell. (3 marks)

Answer 1

• an undifferentiated
• can give rise to specialised cells
• can divide to produce more stem cells

Question 2

What are totipotent cells

Answer 2

Can produce all specialised cells including extraembryonic cells

Question 3

What are pluripotent cells

Answer 3

Can produce all specialised cells excluding extraembryonic cells

Question 4

When do totipotent cell occur in mammals

Answer 4

Occur for a limited time in early mammalian embryos

Question 5

When do pluripotent cell occur in mammals

Answer 5

After the first few cell divisions of a cell embryo

Question 6

What are multipotent cells

Answer 6

Can produce a limited number of different cell types

Question 7

Describe what happens when histones are acetylated

Answer 7

The chromatin is less condensed, so RNA polymerase can bind to the DNA and it can be transcribed. That gene will be expressed.

Question 8

Describe what happens when acetyl groups are removed from histones

Answer 8

The chromatin is more condensed, so RNA polymerase cannot bind to the DNA and it will not be transcribed. The gene will not be expressed.

Question 9

EQ. Explain how methylation of DNA represses a gene. (4 marks)

Answer 9

• When a methyl group is attached to the CpG site on the DNA
• This changes the structure of the DNA
• Stops transcription factors and RNA polymerase from binding to the DNA
• Prevents the expression of the gene

Question 10

Identify two examples of factors that cause epigenetic changes to our genes.

Answer 10

• diet
• environmental pollutants
• physical activity

Question 11

EQ. Explain why the cooler regions of a Siamese cat have dark coloured fur and the warmer regions have lighter coloured fur. (3 marks)

Answer 11

• tyrosinase is active in cooler areas
• so more melanin is made in cooler areas
• in warm areas tyrosinase is denatured which changes the active site
• so it cannot bind to tyrosine to make melanin

Question 12

EQ. Suggest how the ‘p53 tumor suppressor gene’ could stop a potential tumour cell forming. (2 marks)

Answer 12

• product of the p53 gene stops development of tumour cells
• inhibits protein synthesis
• lead to apoptosis

Question 13

EQ. Explain how transcription factors could activate insulin gene expression in beta cells. (3 marks)

Answer 13

• the transcription factor interacts with the promotor region on the gene
• RNA polymerase binds to the promotor region
• transcription occurs and mRNA is produced for the insulin gene