Biology: Control of gene expression

Question 1

what is base substitution and what can happen as a result?

Answer 1

-a nucleotide in a section of DNA is replaced by another.

POSSIBLE CONSEQUENCES:

• formation of a stop codon, polypeptide formation stops prematurely.
• formation of a different amino acid

Question 2

what is base deletion and what can happen as a result?

Answer 2

-a nucleotide in a section of DNA is removed

POSSIBLE CONSEQUENCES:

• frameshift: bases move by 1 to the left, can result in the formation of a completely different polypeptide.
• can form a stop codon

Question 3

what is base addition and what can happen as a result?

Answer 3

-a nucleotide is added to a section of DNA.

POSSIBLE CONSEQUENCES:

• can cause a frameshift as bases move to the right.
• can form a stop codon.

Question 4

what is base inversion and what can happen as a result?

Answer 4

-a group of bases detach from the DNA sequence and rejoin in reverse order. can effect the amino acid formed.

Question 5

what is base translocation and what can happen as a result?

Answer 5

-a group of bases detach from the DNA sequence and attach to a different chromosome. can lead to an abnormal phenotype, can cause infertility and other health problems.

Question 6

what are some causes of mutations? explain each

Answer 6

• ionizing radiation: can disrupt the structure of DNA

- chemicals: some chemicals can disrupt DNA structure or interfere with transcription.

Question 7

how do cells differentiate from an embryo?

Answer 7

• as an embryo, cells are the same, but totipotent.
• totipotent cells have the potential to develop into any type of cell.
• not all embryo cells go towards developing the foetus, some are used to make the placenta and umbilical cord.
• because the cells are totipotent, they take a number of different forms and differentiate, this means that the foetus can develop organs etc.

Question 8

what are stem cells?

Answer 8

cells which retain the ability to differentiate into other cells (not many in mature mammals).

Question 9

where can stem cells originate from in mammals?

Answer 9

embryonic stem cells: come from the embryo in early stages of development.

umbilical cord blood stem cells: derived from umbilical cord blood and are similar to adult stem cells.

placental stem cells: found in the placenta and develop into specific types of cells.

-adult stem cells: specific to a particular tissue or organ, not totipotent.

Question 10

what are pluripotent stem cells and how can they be used to treat disorders?

Answer 10

• found in the embryo and can differentiate into almost any type of cell.
• can be used to regrow damaged tissue or to cure paralysis.

Question 11

what is the effect of oestrogen on transcription?

Answer 11

• it’s a liquid-soluble molecule, it diffuses early through the phospholipid bilayer.
• once inside the cytoplasm, it binds with a site on a receptor molecule of the transcriptional factor. the shape of this site and the shape of oestrogen complement one another.
• it changes the shape of the DNA binding site on the transcriptional factor.
• the transcriptional factor can now enter the nucleus, binding to specific base sequences on DNA.
• this stimulates the transcription of a gene that makes up the portion of DNA.

Question 12

define epigenetics

Answer 12

environmental factors causing heritable changes in gene function without changing the base sequence of DNA.

Question 13

What is the epigenome?

Answer 13

chemical tags surrounding histones. determines the shape of the DNA-histone complex. these chemical tags respond to environmental changes.

Question 14

what is the chromatin made up of?

Answer 14

DNA and histones.

Question 15

what does deacetylation of histones cause?

Answer 15

increases attraction between histones and DNA, making it inaccessible to transcription factors. the gene is ‘switched off’.

Question 16

what is increased methylation of DNA and what does it cause?

Answer 16

• methyl group added to cytosine in DNA.
• prevents binding of transcription factors of DNA.
• does this by attaching proteins that condense the DNA-histone complex.

Question 17

what is the link between epigenetics and disease?

Answer 17

• altering epigenetic processes can cause abnormal silencing or activation of genes.
• genes which should be active can be switched off and vice versa.

Question 18

how can epigenetic therapy be used to treat diseases?

Answer 18

• treatment can be used to inhibit enzymes which cause DNA methylation/acetylation
• other treatments can be used to analyse the extent of DNA methylation at an early stage of disease.

Question 19

what are proto-oncegenes?

Answer 19

• stimulate cell division by producing growth factors which bind to the cell membrane, stimulating DNA replication and cell division.
• it has the ability to switch itself on and off.

Question 20

what are oncogenes?

Answer 20

• mutated proto-oncogenes
• permanently activated as the receptors on the cell surface can be permanently activated, even without the presence of growth factors.
• the oncogene can code for growth factors to be made in excessive amounts.
• causes uncontrolled cell division.

Question 21

what are tumour suppressor genes? what happens if they become mutated?

Answer 21

• slow down the rate of cell division
• repair faulty cell DNA
• cause apoptosis (cell death)

MUTATED:
-inactivated, stops inhibiting cell division and causes cell to divide out of control.

Question 22

how can tumour suppressor genes be silenced?

Answer 22

• hypermethylation happens in the promoter region.
• this leads to the gene being deactivated
• transcription of the promoter regions is inhibited.
• the tumour suppressor genes are silenced.
• nothing to control cell division, cells divide out of control.

abnormal methylation of this type is thought to occur in BRCA1 gene.

Question 23

how can increased oestrogen cause cancer in post-menopausal women?

Answer 23

• lots of oestrogen produced at this stage.
• binds to oestrogen receptors which in turn binds to DNA sequence, increasing rate of cell division.
• happens very rapidly, causing cell division to speed out of control, causes tumour which further stimulates cell division