Gene expression

Question 1

What is a stem cell?

Answer 1

Undifferentiated cells, that can divide indefinitely and turn into other specific cell types.

Question 2

Name and define the three types of stem cell.

Answer 2

1. Totipotent = can develop into any cell type including the placenta and embryo.
2. Pluripotent = can develop into any cell type excluding the placenta and embryo.
3. Multipotent = can only develop into a few different types of cell.

Question 3

What happens to totipotent cells during embryonic

development?

Answer 3

Certain parts of the DNA are selectively translated so that only some genes are ‘switched on’, in order to differentiate the cell into a specific type and form the tissues that make up the foetus.

Question 4

Give a unique feature of pluripotent cells and the use

of this feature.

Answer 4

They can divide in unlimited numbers, and can therefore be used to repair or replace damaged tissue.

Question 5

What is a unipotent cell? Give an example.

Answer 5

A cell that can only develop into one type of cell.
This happens at the end of
specialisation when the cell can only propagate its own type.
An example is cardiomyocytes (heart cells).

Question 6

Which types of stem cell are found in embryos?

Answer 6

Totipotent and pluripotent.

Multipotent and unipotent cells are only found in mature mammals.

Question 7

Give some uses of stem cells.

Answer 7

Medical therapies e.g. bone marrow transplants, treating blood disorders.
Drug testing on artificially grown tissues.
Research e.g. on formation of organs and embryos.

Question 8

How are induced pluripotent stem cells produced?

Answer 8

From mature, fully specialised (somatic) cells.
The cell regains capacity to
differentiate through the use of proteins, in particular transcription factors.

Question 9

What is a transcription factor?

Answer 9

A protein that controls the transcription of genes so that only certain parts of the
DNA are expressed, e.g. in order to allow a cell to specialise.

Question 10

How do transcription factors work?

Answer 10

1. Move from the cytoplasm into nucleus.
2. Bind to promoter region upstream of target gene.
3. Makes it easier or more difficult for RNA polymerase to bind to gene.
4. This increases or decreases rate of transcription.

Question 11

Give an example of a hormone that affects

transcription and explain how it works.

Answer 11

1. Steroid hormone oestrogen diffuses through cell membrane.
2. Forms hormone-receptor complex with ER 𝛼 receptor in the cytoplasm.
3. Complex enters the nucleus & acts as transcription factor to facilitate binding of RNA polymerase.

Question 12

What is meant by epigenetics?

Answer 12

A heritable change in gene function without change to the base sequence of DNA.

Question 13

How does increased methylation of DNA affect gene transcription?

Answer 13

1. Involves addition of a CH3 group to cytosine bases which are next to guanine.
2. Prevents transcription factors from binding.
3. Therefore gene transcription is suppressed.

Question 14

How does decreased acetylation of DNA affect gene transcription?

Answer 14

1. Positively-charged histones are positively charged bind to negatively-charged DNA.
2. Decreasing acetylation increases positive charge of histones.
3. Binding becomes too tight and prevents transcription factors from accessing the DNA.
4. Therefore gene transcription is suppressed.

Question 15

How might epigenetic changes affect humans?

Answer 15

They can cause disease, either by over activating a gene’s function (such as in
cancer) or by suppressing it.

Question 16

Give an application of epigenetics.

Answer 16

Treatments of various diseases.

Development of ways to reverse epigenetic changes.

Question 17

Describe the process of RNA interference, including the organisms in which it occurs.

Answer 17

RNA molecules act to inhibit gene expression, usually by destroying mRNA so that it cannot be translated. Occurs in eukaryotes and some prokaryotes.

Question 18

Give some characteristics of benign tumours.

Answer 18

● Slow growth
● Defined by a clear boundary due to cell
adhesion molecules
● Cells retain function and normal shape
● Don’t spread easily
● Easy to treat

Question 19

Give some characteristics of malignant tumours.

Answer 19

● Rapid, uncontrollable growth.
● Ill-defined boundary (finger-like projections).
● Cells do not retain function and often die.
● Spreads quickly and easily (metastasis).
● Difficult to treat.

Question 20

Describe the role of tumour-suppressor genes.

Answer 20

-Code for proteins that control cell division; in particular, stopping the cell
cycle when damage is detected.
-They are also involved in programming apoptosis i.e. ‘self destruction’ of the cell.

Question 21

Explain how tumour suppressor genes can be

involved in developing cancer.

Answer 21

A mutation in the gene could code for a nonfunctional protein. Increased methylation or
decreased acetylation could prevent transcription.
Cells will divide uncontrollably resulting in a
tumour.

Question 22

Describe the role of proto-oncogenes.

Answer 22

Control cell division; in particular, code for proteins that stimulate cell division.

Question 23

Explain how proto-oncogenes can be involved in developing cancer

Answer 23

Mutation in the gene could turn it into a permanently
activated oncogene. Decreased methylation or
increased acetylation can cause excess transcription.
This results in uncontrolled cell division and formation
of a tumour.

Question 24

Explain how abnormal methylation of genes can

cause cancer.

Answer 24

Hyper-methylation of tumour -suppressor genes or oncogenes can impair their
function and cause the cell to divide uncontrollably.

Question 25

Explain how oestrogen can be involved in developing breast cancer.

Answer 25

We already know oestrogen is an activator of RNA polymerase.
Therefore in areas of
high oestrogen conc, such as adipose tissue in the breasts, cell division can become uncontrolled.