control of gene expression

Question 1

mutation

Answer 1

any change to the quantity or structure of DNA

Question 2

gene mutation

Answer 2

any change to one or more nucleotide base, or any rearrangement of the bases

Question 3

inversion of bases

Answer 3

a group of bases becomes separated from the DNA sequence and rejoins at the same position but in reverse order

Question 4

translocation of bases

Answer 4

a group of bases becomes separated from the DNA sequence on one chromosome and becomes inserted into the DNA sequence of another chromosome

Question 5

what is a spontaneous gene mutation

Answer 5

a permanent change that arises during DNA replication and occurs without any outside influences.

Question 6

ionising radiation

Answer 6

Xrays

Alpha / Beta / gamma rays

Question 7

non ionising radiation

Answer 7

UV light
this is absorbed by the nitrogenous bases and has various effects including Thymine Dimers being produced. This is where adjacent Thymine bases in one DNA strand couple together instead of with the complimentary Addenine on the other strand.

Question 8

totipotent cells

Answer 8

cells that can mature into any body cell. This is the zygote and the first few divisions by an egg cell. Human embryonic stem cells.

Question 9

pluripotent cells

Answer 9

found in embryos and can differentiate into cells derived from any of the three germ layers.
eg. embryonic stem cells
fetal stem cells

Question 10

multipotent

Answer 10

these stem cells can produce only cells of a closely related family of cells eg. adult stem cells and. umbilical chord blood stem cells.

Question 11

unipotent cells

Answer 11

can only differentiate into one type of cell. Their ability for self renewal however makes them therapeutic in treating diseases (eg. skin transplants for burn victims).

Question 12

induced pluripotent stem cells (iPS cells)

Answer 12

can be produced by adult somatic cells (in the lab) using appropriate protein transcription factors. The fact that these cells are capable of being reactivated shows that adult cells retain the same genetic information that was present in the embryo.
Although iPS cells express many of the same genes as embryonic stem cells, they are not exact duplicates of them. However, one feature that they do have is of self renewal, meaning they can potentially indefinitely multiply and therefore provide a limitless supply, so could replace the use of embryonic stem cells in medical research thus overcoming many of the ethical issues surrounding the use of embryos .

Question 13

epigenetic

Answer 13

the heritable changes to gene expression in eukaryotic cells. (ie. genes can be switched on to off, and this on or off setting can be passed on when that cell divides).
Epigenetic changes are heritable but also reversible. So that genes that have been switched off can be switched back on again.
Epigenetic changes effect the phenotype of the cell without changing the underlying genotype of the DNA (so the DNA base sequence is unaffected).

Question 14

epigenome

Answer 14

the collective name for the chemical tags attached to DNA and histones.

Question 15

transcription factor

Answer 15

a protein that binds to a specific DNA sequence, thereby controlling the rate of transcription of genetic information from DNA to mRNA. They contain one or more DNA binding domains which attach to specific sequences of DNA adjacent to the genes that they regulate (they attach to promotor regions).

Question 16

promotor region

Answer 16

a sequence of about 100 genes upstream (before) the gene. This is where activated transcription factors bind to allowing RNA polymerase to initiate transcription.

Question 17

How does the Oetrogen steroid hormone work

Answer 17

1. Is lipid soluble and therefore easily diffuses through the phospholipid bilayer into the cytoplasm of the cell.
2. It binds to a complimentary receptor molecule on the transcription factor.
3. this causes a tertiary structure change that means the DNA binding site on this transcription molecule changes shape, and is now complimentary to DNA.
4. The transcription factor enters through the nuclear pore and binds to a specific base sequence on the DNA.
5. This stimulates transcription of the gene

Question 18

what is the name of the main drug used to treat breast cancers which are oestrogen dependent tumours

Answer 18

tamoxifen. This drug is effective because ti has a similar shape to oestrogen. Therefore it can permanently bind to oestrogen receptors in the tumour cells, and blocks oestrogen itself from binding to them, and therefore prevents transcription and cell division.

Question 19

name a drug that could be used for a non-oestrogen dependent tumour

Answer 19

Herceptin (the monoclonal antibody)

Question 20

active genes

Answer 20

these are more accessible to transcription factors because the DNA is not so tightly coiled around the histone proteins

Question 21

inactive genes

Answer 21

these genes are less accessible to transcription factor because the DNA is tightly coiled around the histones

Question 22

imprinted genes

Answer 22

genes that do not have epigenetic markers removed after fertilisation.

Question 23

methylation

Answer 23

when a methyl group is added to DNA. This methyl group prevents transcription. Opposite is DNA de-methylation which removes the methyl groups so allowing more transcription to occur.

Question 24

what is methylation controlled by

Answer 24

a group of enzymes called DNA methyltransferases (DNMT’s).

Question 25

acetylation

Answer 25

histone molecules contain the amino acid lysin. Acetyl groups (COCH3) may be added to these lysine residues, replacing one of their hydrogen ions. By removing the positively charged hydrogen ion, this causes the proteins to become lass wrapped around the DNA as theres less attraction.
AcetylCoA (same as in Krebs) adds the Acetyl group.

Question 26

heterochromatin

Answer 26

tightly packed chromatin (= gene switched off)

Question 27

euchromatin

Answer 27

loosely coiled chromatin (= gene switched on)

Question 28

effect of DNA hypomethylation

Answer 28

to little methylation can activate oncogenes

Question 29

effect of DNA hypermethylation

Answer 29

can silence / inactivate tumour suppressor genes

Question 30

what is siRNA

Answer 30

short interfering RNA

Question 31

RNA interface and how it prevents translation

Answer 31

1. DS RNA is produced in the nucleus when the concentration of mRNA becomes too high
2. the dsRNA is cut into very short lengths of siRNA by an enzyme.
3. a protein in the cytoplasm then separates out the two strands. one of the strands is then removed by degradation by enzymes.
4. the other strains then binds to an enzyme and guides the enzyme to an mRNA molecule.
5. once in position, the enzyme cuts the mRNA into smaller sections meaning that the mRNA is no longer capable of being translated into a polypeptide and so the gene is not expressed.

Question 32

repairing mutations

Answer 32

nucleotide excision repair:

1. damage is cut out (excised) by an endonuclease enzyme
2. the missing sequence is then repaired by DNA polymerase
3. This is then sealed by Ligase enzyme

Question 33

tumour suppressor genes

Answer 33

produce proteins that…

• slow down cell division
• repair mistakes in the DNA
• destroys cells by apoptosis if the mistakes in the DNA are beyond compare

they are generally recessive.

Question 34

3 examples of tumour suppressor genes

Answer 34

TP53
BRACA1
BRACA2

Question 35

what does the TP53 gene do

Answer 35

codes for the p53 proteins. This protein is involved in the process where if DNA is damaged beyond repair it triggers apoptosis.

Question 36

proto oncogenes

Answer 36

normal proto-oncogenes code for G proteins. These enable cells to respond to growth factors which cause cells to divide. They are inactivated by their own enzyme GTPase

Question 37

what happens when a mutation turns a protoctist-oncogene into an oncogene

Answer 37

it produces G proteins that are deficient in GTPase. This means that the G proteins are active for longer and therefore there is uncontrolled cell growth. This is dominant.

Question 38

effects of the chemical mutagen nitrogen dioxide

Answer 38

e.g.. Nitrogen dioxide can directly alter the structure of DNA or interfere with transcription.

Question 39

effects of the chemical mutagen tobacco

Answer 39

Benzopyrene is a constituent of tobacco sample that inactivates the tumour suppressor gene TP53 leading to cancer.

Question 40

effects of the chemical mutagen mustard gas

Answer 40

mustard gas adds an alkyl group to guanine, which triggers the guanine to be released and therefore a space is left to be replaced by another base.

Question 41

chemical mutagens and examples

Answer 41

• nitrogen dioxide
• tobacco
• caffeine
• some pesticides

some chemical mutagens have a structure to the bases and therefore can be placed in the DNA molecule in place of a real base.