8.2 Gene Expression

Question 1

What is a stem cell?

Answer 1

Undifferentiated cells that can divide indefinitely 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 placenta and embryo

Question 4

What is a pluripotent stem cell?

Answer 4

Can develop into any cell type excluding 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 DNA are selectively translated so that only some genes are “switched on” to differentiate the cells into a specific type & form the tissue that make up the foetus

Question 7

Give a unique feature of pluripotent cells.

Answer 7

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

Question 8

What is a unipotent cell?

Answer 8

A cell that can only develop into one type of cell

Question 9

When do cells become unipotent?

Answer 9

The end of specialisation when the cell can only propagate its own type

Question 10

Give an example of a unipotent cell.

Answer 10

Cardiomyocytes (heart cells)

Question 11

Which types of stem cell are found in embryos?

Answer 11

Totipotent & pluripotent

Question 12

What types of stem cell are found in mature mammals?

Answer 12

Multipotent & unipotent

Question 13

Give examples of stem cell use.

Answer 13

Medical therapies
Drug testing on artificially grown tissue
Research

Question 14

How are induced pluripotent stem cells produced?

Answer 14

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

Question 15

What is a transcription factor?

Answer 15

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

Question 16

How do transcription factors work?

Answer 16

Move from cytoplasm into nucleus
Bind to promoter region for target gene
Makes it easier/harder for RNA polymerase to bind to gene
Increases/decreases rate of transcription

Question 17

Give an example of a hormone that affects transcription.

Answer 17

Oestrogen

Question 18

Explain how oestrogen affects transcription.

Answer 18

Diffuses through cell membrane
Forms hormone-receptor complex with ER alpha receptor in the cytoplasm
Complex enters the nucleus & acts as transcription factor to facilitate binding of RNA polymerase

Question 19

Define epigenetics.

Answer 19

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

Question 20

How does increased methylation of DNA affect gene transcription?

Answer 20

Addition of a methyl (CH₃) group to cytosine bases
Prevents transcription factors from binding to promotor region

Question 21

How does decreased acetylation of DNA affect gene transcription?

Answer 21

Positively charged histones bind to negatively charged DNA
Increases charge of histones
Binding becomes too tight & prevents transcription factors from accessing promotor region

Question 22

How can epigenetic changes affect humans?

Answer 22

Can cause disease by over activating or suppressing a genes function

Question 23

Give two applications of epigenetics.

Answer 23

Treatments of disease
Development of epigenetic change reversal

Question 24

Which organisms experience RNA interference?

Answer 24

Eukaryotes & some prokaryotes

Question 25

Describe the process of RNA interference.

Answer 25

RNA molecules act to inhibit gene expression, usually by destroying mRNA so that it cannot be translated

Question 26

Give some characteristics of benign tumours.

Answer 26

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 27

Give some characteristics of malignant tumours.

Answer 27

Rapid, uncontrollable growth Ill-defined boundary Cells do not retain function and often die Spreads quickly and easily (metastasis) Difficult

Question 28

Describe the role of tumour-suppressor genes.

Answer 28

Code for proteins that control cell division - stops the cell cycle when damage is detected Involved programming apoptosis

Question 29

What is apoptosis?

Answer 29

Cell death/self destruction

Question 30

Explain how tumour-suppressor genes can be involved in the development of cancer.

Answer 30

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 31

Describe the role of proto-oncogenes.

Answer 31

Control cell division Code for proteins that stimulate cell division

Question 32

Explain how proto-oncogenes can be involved in the development of cancer.

Answer 32

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

Question 33

Explain how abnormal methylation of genes can cause cancer.

Answer 33

Hyper-methylation of tumour-suppressor genes or oncogenes can impair their function & cause uncontrollable cell division

Question 34

Explain how oestrogen can be involved in development of breast cancer.

Answer 34

Oestrogen is an activator of RNA polymerase Cell division can become uncontrolled in areas of high oestrogen concentration High concentration in adipose tissue in the breasts