Gene Expression

Question 1

What is a stem cell?

Answer 1

Undifferentiatied cells that can divide indefinitely and turn into other specific cell types

Question 2

Name the three types of stem cell

Answer 2

• totipotent
• pluripotent
• multipotent

Question 3

What is a totipotent stem cell?

Answer 3

Can develop into any cell type including the placenta and embryo

Question 4

What is a pluripotent stem cell?

Answer 4

Can develop into any cell type excluding the placenta and embryo

Question 5

What is a multipotent stem cell?

Answer 5

Can only develop into a few different types of cell

Question 6

What happens to totipotent cells during embryonic development?

Answer 6

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 7

What is a unique feature of pluripotent cells?

Answer 7

Can divide in unlimited numbers and can therefore be used to repair or replace damaged tissue

Question 8

What is a unipotent cell?

Answer 8

• cell that can only develop into one type of cell
• happens at the end of specialisation when the cell can only propagate its own type
• e.g cardiomyocytes (heart cells)

Question 9

Which types of stem cell are found in embryos?

Answer 9

Totipotent and pluripotent

Question 10

Give some uses of stem cells

Answer 10

• medical therapies
• drug testing on artificially grown tissues
• research

Question 11

How are induced pluripotent stem cells produced?

Answer 11

From mature somatic cells

Cell regains capacity to differentiate through the use of proteins in particular transcription factors

Question 12

What is a transcription factor?

Answer 12

A protein that controls the transcription of genes so that only certain parts of the DNA are expressed

Question 13

How do transcription factors work?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

What is meant by epigenetics?

Answer 15

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

Question 16

How does increased methylation of DNA affect gene transcription?

Answer 16

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 17

How does decreased acetylation of histones affect gene transcription?

Answer 17

• • charged histones bind to - charged DNA
• decreasing acetylation increases positive charge of histones
• binding becomes too tight and prevents transciption factors from accessing the DNA
• therefore gene transcription is suppressed

Question 18

How might epigenetic changes affect humans?

Answer 18

They can cause disease either by over activating a gene’s function or by suppressing it

Question 19

Give an application of epigenetics

Answer 19

Treatments of various diseases

Development of ways to reverse epigenetic changes

Question 20

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

Answer 20

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

Question 21

What are some characteristics of benign tumours?

Answer 21

• slow growth
• clear boundary due to cell adhesion molecules
• cells retain function and normal shape
• don’t spread easily
• easy to treat

Question 22

What are some characteristics of malignant tumours?

Answer 22

• rapid uncontrollable growth
• ill-defined boundary
• cells do not retain function and often die
• spreads quickly and easily (metastasis)
• difficult to treat

Question 23

Describe the role of tumour-suppressor genes

Answer 23

• code for proteins that control cell division/stopping the cell cycle when damage is detected
• also involved in programming apoptosis

Question 24

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

Answer 24

• 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 25

Describe the role of proto-oncogenes

Answer 25

- control cell division | - code for proteins that stimulate cell division

Question 26

Explain how proto-oncogenes can be involved in developing cancer

Answer 26

- mutation in the gene could turn it into a permanently activated oncogene - decreased methylation or increased acetylation can cause excess transcription - results in uncontrolled cell division and formation of a tumour

Question 27

Explain how abnormal methylation of genes can cause cancer

Answer 27

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

Question 28

Explain how oestrogen can be involved in developing breast cancer

Answer 28

- oestrogen is an activator of RNA polymerase | - so in areas of high oestrogen concentration like in the breast, cell division can become uncontrolled