gene fight

Question 1

types of mutations

Answer 1

insertion=addition of nucleotide
deletion=removal
substitution=swapping

Question 2

DNA sequence determines

Answer 2

activity and amount of protein

Question 3

what does wild type mean, what do wild type coding sequences and promoters do

Answer 3

wild type coding sequence encodes a functional protein

wild type promoter ensures the correct amount of protein is produced

wild type=naturall occuring, unmutated

Question 4

what does a mutation in the coding sequence of a gene cause

Answer 4

function change in protein, changes substrate specificity

Question 5

mutations of proteins involved in proliferative signalling leads to…

Answer 5

constitutive expression, cells receiving signal to proliferate when it shouldnt

Question 6

mutations in regulatory regions like promoters lead to…

Answer 6

more/less expreession

Question 7

proto oncogenes code for products that are…

Answer 7

pro-proliferative and anti-apoptotic

Question 8

tumour suppressor genes encode for proteins that…

Answer 8

protect against over proliferation

Question 9

waht are tumour suppressor genes (TSG)

Answer 9

makes tumour suppressor proteins that help control cell growth

Question 10

what are DNA repair/stability genes

Answer 10

encodes for proteins that maintain DNA stability by repairing DNA and protecting against accumulation of mutations

Question 11

example of 2 oncogenes

Answer 11

MYC, RAS

Question 12

example of TSGs

Answer 12

TP53, Rb1

Question 13

what are the most frequently mutated genes in cancer

Answer 13

TP53, RB1, MYC, RAS

Question 14

describe what TP53 does

Answer 14

(tumour protein 53 kDa)
blocks cell cycle in response to cellular damage. allows damage to be repaired or apoptosis, leads to changes in gene expression

Question 15

what is RB1 and what does it do

Answer 15

retinoblastoma 1

-inhibits E2F transcription factors, RB1 inhibited by phosphorylation by CDK4
-E2F transcription factors required for cell cycle progression
-when RB1 phosphorylated, its inactive, transcription factors can now bind to DNA to regulate genes in proliferation (mutated)
-when RB1 is unphosphorylated, its active, binds to E2F, transcription factors prevented from binding, cell cycle cant progress beyond G1

Question 16

what does MYC do

Answer 16

transcription factor, promotes proliferation, upregulated in response to oncogenic stimuli

-binds to DNA as heterodimer to positively and negatively regulate expression of many genes

-MYC gene mutations lead to too many MYC protein produced or over active MYC protein, either way proliferation is promoted/too much proliferation, risk of cancer increased

Question 17

what is RAS

Answer 17

single subunit small GTPase, upregulated by growth signals, activates downstream signalling pathways

GTP bound=on

GDP bound=off

Question 18

name the 6 DNA repair types

Answer 18

one step, nucleotide excision, base excision, mismatch, homologous recombinational, non homologous end joining

Question 19

what is each repair type used for: one step, nucleotide excision, base excision, mismatch, homologous recombinational, non homologous end joining

Answer 19

one step repair=reversal of alkylation

nucleotide excision repair (NER)=for helix distorting damage

base excision repair (BER)=for chemically modified bases

mismatch repair=for errors in replication

homologous recombinational repair and non homologous end joining=for double strand breaks

Question 20

explain one step repair

Answer 20

-alkylating agents (methylnitrosurea/procarbazine/dacarbazine) damage DNA by addition of an alkyl group, especially oxygen 6 of guanines

-DNA repair protein O6-alkylguanine DNA alkyltransferase (MGMT,AGT,AGAT) reverses DNA alkylation, MGMT overexpression can confer resistance to alkylating chemotherapy drugs

Question 21

explain nucleotide excision repair

Answer 21

-cyclopyrimidine dimers caused by UV, bulky DNA adducts

steps:

1. transcription coupled damage detection
2. global damage detection
3. mechanism once detected ?

-mutations in NER genes associated with xeroderma pigmentosum, increased risk of skin cancer

Question 22

explain base excision repair

Answer 22

glycosylases identifies damaged bases and removes them leaving an abasic sit (no nucleotide present), damage strand is cut, damaged nucleotide replaced by DNA polymerase beta, then sealed by DNA ligase

Question 23

explain mismatch repair

Answer 23

-MSH2/6 and MSH2/3 identifies mismatch
-MLH1/PMS2 joins the complex.
-nuclease removes mismatch and neighbouring nucleotides on the newly synthesised strand
-DNA polymerase δ resynthesizes new strand
-mutations in MLH1 or MSH2 associated with HNPCC (hereditary non-polyposis colorectal cancer)

Question 24

explain homologous recombinational repair

Answer 24

-repairs double strand breaks using sister chromatids as templates (active in S and G2 phase of cell cycle) (diagram in notes)

Question 25

explain non homologous end joining

Answer 25

-repairs double strand breaks by directly ligating broken ends -active in all stages of the cell cycle but error prone -Ku70/80 heterodimer bind to break -NHEJ machinery recruited (DNA-PKcs, XRCC4, XLD, DNA ligase IV, APLF) -break is protected and stabilised -DNA end processing can occur to prepare the DNA for religation -DNA ligase IV joins the ends together