8.2 - Gene expression

Question 1

What is a stem cell?

Answer 1

Indifferentiated 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 the only some genes are ‘switched on’, in order to differentiate the cell into a specific type and form the tissues that makeup the foetus.

Question 4

Give a uniques 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 induces pluripotent stem cells produced?

Answer 8

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

Question 9

What is a transciption 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. This increases or decreases rate od transcription.

Question 11

Give an example of a hormone that affects trascription and explain how it works.

Answer 11

1. Steroid hormone oestrogen diffuses through cell membrane.
2. Forms hormone-receptor complex with ER a receptor in the cytoplasm.
3. Complex enters the nucleus and 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 increases methylation of DNA affect gene transcription?

Answer 13

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

Question 14

How does decreased acetylation of DNA affect gene transcription?

Answer 14

Positively-charged histones are positively charged to bind to negatively-charged DNA. Decreasing acetylation increases positive charge of histones. Binding becomes to tight and prevents transcription factors from accessing the DNA. 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 functions 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 benighn tumours.

Answer 18

• Slow growth
• Defined by a clear boundary due to cell adhesion molecules
• Cells etain 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
• Cells do not retain function and often die.
• Spreads quickly and easily
• Difficult to treat.

Question 19

Describe the role of tumour-suppressor genes.

Answer 19

Code for proteins that contol 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 20

Explain how tumour-suppressor genes can be involved in developing cancer.

Answer 20

A mutation in the gene could code for a non-functional protein. Increases methylation or decreased acetylation could prevent transcription.
Cell will divide uncontollably resulting in a tumour.

Question 21

Describe the role of proto-oncogenes.

Answer 21

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

Question 22

Explain how proto-oncogenes can be involved in developing cancer.

Answer 22

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

Question 23

Explain how abnormal methylation of genes can cause cancer.

Answer 23

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

Question 24

Explain how oestrogen can be involved in developing breast cancer.

Answer 24

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