Topic 7.2 Gene Expression

Question 1

What is the significance of coiling of histones?

Answer 1

Coiling makes DNA less accessible

Question 2

What are enhancer regions

Answer 2

They are found further away from gene
And tend to make DNA more or less condensed = accessible for transcription(affect binding with DNA/RNA polymerase)

Question 3

What are transcription factors? (1 mark)

Answer 3

Protein That Controls transcription of genes (by binding to DNA)
That enhances/suppress DNA expression

Question 4

How do transcription factors work?

Answer 4

Enter nucleus from cytoplasm
Bind to DNA near target gene
Either increase or decrease rate of transcription

Question 5

What is the promoter region

Answer 5

Found closer to gene
Enable binding of RNA polymerase - promote transcription

Question 6

What is epigenetic modification? (1 mark)

Answer 6

Heritable changes in the phenotype without altering the DNA / gene

Question 7

How can a transcription factor increase rate of glycolysis? (3 marks)

Answer 7

• switch on gene expression
• bind to promoter region - stimulate protein synthesis
• for enzymes involved in glycolysis

Question 8

What are nucleosomes?

Answer 8

Cluster of histones(8 of them)

Question 9

How to enhance transcription?

Answer 9

• DNA demethylation
• histone acetylation

Question 10

How does DNA methylation work? How?

Answer 10

• silences sequence of genes
• by adding methyl group (by phosphodiester bond) (usually to Cytosine on CpG site)
• histones are more packed = less accessible for transcription
• stops transcription factors from binding to promoter region

So opposite promotes transcription

Question 11

How does histone acetylation increase transcription?

Answer 11

• reducing positive charge of histone proteins, reduce histone acetylation
• (dna is negative charge)
• less charge difference hence attraction
• so more available for transcription

Question 12

State the meaning of the term DNA methylation. (1 mark)

Answer 12

A methyl group added to a CpG site (usually cytosine next to a guanine)

Question 13

Why is DNA methylation essential in growth of embyro? What happens when? (3 marks)

Answer 13

• level of DNA methylation increases after blastocyst stage
• because genes are switched off, cannot be transcribed
• causing cells to become differentiated

Question 14

What is splicing?

Answer 14

Removing introns and joining exons (from pre-mRNA)
Cutting mRNA for gene to be synthesised into protein

Question 15

State the meaning of term epigenetic modification. (1 mark)

Answer 15

Change in phenotype without change to base sequence DNA

Question 16

What is a CpG site?

Answer 16

Cytosine next to Guanine
Where methyl group can attach to for methylation to silence gene expression

Question 17

Why can different polypeptide products (proteins) result from the same gene?

Answer 17

Post transcription modification of mRNA

Question 18

What enzyme performs splicing of pre mRNAs?

Answer 18

Spliceosomes

Question 19

How does the addition of transcription factor / hormone causes the human gene to be switched on?

Answer 19

• interaction on cell membrane
• TF activated after binding to specific gene sequences
• mRNA produced, RNA polymerase used

Question 20

Explain how a cell differentiates into either X cell or Y cell. (4 marks)

Answer 20

• by epigenetic modification
• like DNA methylation or histone acetylation
• genes needed in both cell types turn on
• genes needed in one but not the other cell type switches off
• causing proteins to be made that are specific to the cell type

Question 21

Explain why stem cells are used to produce vaccines rather than bone marrow cells. (2 marks)

Answer 21

• stem cells are pluripotent
• so can divide into wider range of cell types

Question 22

Where are pluripotent cells obtained from?

Answer 22

Late embryo

Question 23

Describe how iPS cells can be produced. (3 marks)

Answer 23

• fibroblasts are used
• specific genes are put into cells
• eg Oct4, Sox2
• using vector / virus

Question 24

How can iPS cells be used to cure a genetic disease in the retina involving dysfunctional cells? (2 marks)

Answer 24

• replace dysfunctional cells with funcitonal cells derived from iPS cells
• iPS cells are injected into the retina then develops into normal retinal cells

Question 25

The tissue formed by an embryonic cell is called the 'fate' of the cell. Explain how the scientist could identify the fate of the repositioned cell. (2 marks)

Answer 25

- examine cells from different tissues under a **microscope** - cells descended from repositioned cell are fluorescent due to traces of dye injected

Question 26

The tissue formed by an embryonic cell is called the 'fate' of the cell. Explain how a scientist can figure out if a cell has changed its fate. (2 marks)

Answer 26

- cell would still be pluripotent (if fate hasn’t changed) - so cell signalling in the new position could determine the fate of the cell - causing activation of TF for transcription of genes (relevant to the new position) - leading to synthesis of proteins into diff tissues

Question 27

Describe the differences between totipotent, multipotent and pluripotent stem cells **during the development of an embryo**. (3 marks)

Answer 27

- zygote/morula are totipotent stem cells as they give rise to all cell types - blastocyst contain pluripotent cells, they give rise to most cell types - cells in developing embryo are multipotent, can only become some cell types

Question 28

Why is DNA methylation involved in the development of an embryo? (2 marks)

Answer 28

- genes silenced, cannot be transcribed - so cells become differentiated

Question 29

How is DNA demethylation involved in a conversion of cells? (2 marks)

Answer 29

- demethylation results in gene being **activated** - so transcription gene takes place, producing protein that causes change in fibroblast cells