Control of Gene Expression

Question 1

What are transcriptional factors (TF’s)?

Answer 1

Proteins that bind to a specific sequence on the DNA near their target genes, thus regulation transcription initiation.

Question 2

What are the 2 ways transcriptional factors may work?

Answer 2

• Activators: up-regulate gene expression of a particular gene by helping RNA polymerase to bind to target gene.
• Repressors: they work to inhibit the gene expression by preventing the binding of RNA polymerase to particular genes.

Question 3

How do transcriptional factors lead to gene expression?

Answer 3

Transcriptional factors are proteins which are complimentary to specific DNA sequences in the promoter region. Activators form a complex with the promoter region and lead to the recruitment of RNA polymerase to initiate transcription.

Question 4

What is cancer?

Answer 4

Rapid, uncontrolled growth and division of cells.

Question 5

What are the properties of benign tumours?

Answer 5

• Can grow large at slow rate
• Non-cancerous because they produce adhesion molecules sticking them together and to a particular tissue
• Often surrounded by capsule, so they remain compact + can be removed by surgery

Question 6

What are the properties of malignant tumours?

Answer 6

• Cancerous and grow large rapidly
• Cell nucleus becomes large + cell can become unspecialised again
• Do not produce the adhesive, so instead metastasis occurs meaning the tumour breaks off + spreads to other parts of the body (invades secondary tissues / organs)

Question 7

What are the 2 types of genes that control cell division?

Answer 7

Tumour-suppressor genes and proto-oncogenes

Question 8

When functioning normally, what do tumour suppressor genes do?

Answer 8

Tumour suppressor proteins which slow / arrest cell division when DNA is damaged. If the cell can’t be fixed, the gene triggers apoptosis.

Question 9

What is the two hit hypothesis?

Answer 9

Cancer due to tumour suppressor gene mutation results from a loss of function to the protein, which prevents cell cycle regulation. As a person has 2 copies of each gene, both must be “knocked out” to cause cancer / stop tumour suppressor proteins being produced.

Question 10

When functioning normally, what do proto-oncogenes do?

Answer 10

Cause the expression of proteins which upregulate cell division (vital for mitosis)

Question 11

When proto-oncogenes are mutated, what happens?

Answer 11

They form oncogenes which are overactive and stimulate uncontrollable cell division.

Question 12

What are the 3 ways mutation in proto-oncogenes can result in uncontrollable cell division?

Answer 12

• Mutation of proto-oncogene to form oncogene to form hyperactive protein
• Multiple copies of gene, normal protein in excess
• Gene moved to new DNA locus / under new controls, so a normal protein is in excess (new promoter may have more readily available TFs)

Question 13

What are they key properties of cancerous cells?

Answer 13

• Evading apoptosis
• Self-sufficiency in growth signals
• Insensitivity to anti-growth signals
• Sustained angiogenesis
• Limitless replicative potential
• Tissue invasion + metastasis

Question 14

What are the 4 types of stem cells?

Answer 14

• Unipotent (differentiate into 1 type of cell) [foetus onwards]
• Multipotent (different into many types of cells) [foetus onwards]
• Pluripotent (differentiate into most types of cells, not placenta) [blastocyst: 3-5 day embryo]
• Totipotent (can differentiate into any type of cell, including placenta) [early embryo: 1-2 days]

Question 15

What is chromatin?

Answer 15

It consists of DNA wrapped around / associated with histone proteins.

Question 16

When is chromatin “transcriptionally active”?

Answer 16

When histones are less closely associated with one another so the promoter region of a gene is available for the binding of transcription factors.

Question 17

What does methylation do?

Answer 17

• Addition of a methyl group to DNA (occurs on cytosine)
• Prevents binding of transcriptional factors
• Attracting proteins that condense the DNA-histone complex so is inaccessible to transcription factors
• Down-regulates transcription

Question 18

What does acetylation do?

Answer 18

• Addition of an acetyl group to histone
• Makes DNA-histone complex less condensed so more accessible to transcription factors
• Up-regulates transcription

Question 19

Describe how oestrogen upregulates gene expression (oestrogen-oestrogen receptor complex)

Answer 19

Oestrogen receptors are proteins that are in an inactive site. When oestrogen binds to it, it forms an oestrogen-oestrogen receptor complex. This causes a conformational change to the tertiary structure and results in it becoming an active transcriptional factor. It then binds to specific promoter regions as it moves into the nucleus and upregulates gene expression.