3.8.2 Gene expression is controlled by a number of features

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 3 types of stem cell

Answer 2

1. Totipotent = can develop into any cell including 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 eg bone marrow transplants, treating blood disorders
Drug testing on artificially grown tissues
Research eg on formation of organs and embryos

Question 8

How are induced pluripotent stem cells produced

Answer 8

From mature, fully specialied (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, eg 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 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 complexes with ER alpha receptor in cytoplasm
3. Complex enters the nucleus and acts as a 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 a CH3 group to cytosine bases which are next to guanine. Prevents transcription factors from binding. Therefore gene transcription is suppressed

Question 14

How does decreased acetylation of histones affect gene transcription

Answer 14

Positively charged histones bind to negatively charged DNA. Decreasing acetylation increases positive charge of histones. Binding becomes too 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 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
Dont spread easily
Easy to treat
Non cancerous

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 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 ie 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 non-functional 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 concentration, such as adipose tissue in the breasts, cell division can become uncontrolled