DNA Repair And Cancer

Question 1

What is the difference between diploid and haploid?

Answer 1

Diploid - two sets of chromosomes, one from each parent

Haploid - one set of chromosomes

Question 2

What is aneuploidy?

Answer 2

An abnormal number of chromosomes in a cell

Question 3

What are is the difference between homologous chromosomes and sister chromatids?

Answer 3

Homologous chromosomes are two chromosomes (a set) of the same pair. One from each parent.
Sister chromatids are from the same chromosome. There are four sister chromatids in one pair of homologous chromosomes.

Question 4

What are amplified centromeres?

Answer 4

The presence of more than two centromeres, promotes cancer.

Question 5

Bipolar spindle?

Answer 5

Two centromeres

Question 6

Multipolar spindle?

Answer 6

More than two centromeres

Question 7

What are oncogenes?

Answer 7

Proto-oncogenes help with cell growth.

However when it mutates/makes too many copies, it can cause cells to growth out of control, causing cancer.

Question 8

What are tumour suppressor genes (TSG) and how can they cause cancer?

Answer 8

TSGs normally slow cell division/programme apoptosis. However, a mutation reducing TSG can lead to hyperproliferation of cells, therefore cancer.

Question 9

How can therapeutic treatments that inhibit the cluster of centromeres help to treat cancer?

Answer 9

Clustering of centromeres can lead to aneuploidy (abnormal number of chromosomes in a cell), which often leads to cancer.

Question 10

What is a base mismatch?

Answer 10

During replication, a wrong bases is put down e.g. C-T instead of C-G

Question 11

What is a mismatch repair?

Answer 11

A DNA repair mechanism fixing a base mismatch. It occurs very soon after DNA replication by an exonuclease.

Question 12

What is a base excision repair?

Answer 12

Happens after DNA replication.
An enzyme called DNA glycosylase ‘cuts’ of the base and the surrounding area and replaces it with the correct nucleotide.

Question 13

What effect does UV radiation have on DNA structure?

Answer 13

Cuts two thymine bases and sticks them together making a ‘thymine dimer’. In replication, the dimer (two bases) may be recognises as a single base, causing a frameshift mutation.

Question 14

What is nucleotide excision repair?

Answer 14

Important in correcting mutations made my UV light (thymine dimers). Proteins cut out a section of 24 nucleotides and replace it with new ones.

Question 15

What kind of break is the most damaging to DNA?

Answer 15

Double stranded breaks - can lead to cell death.

Question 16

What is homologous recombination?

Answer 16

A DNA repair mechanism used for double stranded breaks.
Uses an undamaged piece of DNA as a template and swap their genetic information so as to have two complete undamaged pieces of DNA.

Question 17

What is a Holliday junction?

Answer 17

A crossing over of products used in homologous recombination (DNA repair).

Question 18

What is non-homologous end joining?

Answer 18

In a double stranded DNA break, the damage section of DNA is cut off and proteins fix the strand by pushing them together.
This is not a very accurate from of DNA repair.

Question 19

What is slippage?

Answer 19

When a base pair ‘slips’ off the strand. Can lead to an extra nucleotide or a missing nucleotide depending which strand it is.

Question 20

What three components make a nucleotide?

Answer 20

A phosphate group, a sugar and a base pair.

Question 21

What bases go together?

Answer 21

Thymine - Adenine

Cysteine - Guanine

Question 22

How does a DNA mutation cause Huntington’s disease?

Answer 22

CAG repeats.
A normal DNA strand has 6-39 repeats however in a Huntingdon’s individual there are 35-121 repeats
The more repeats the earlier the onset of the disease

Question 23

What are some symptoms of Huntingdon’s disease and how likely is it to be passed onto a child?

Answer 23

Poor co-ordination
Problems swallowing
Depression
Speaking
NEURAL CONDITION
Autosomal dominant - 50% chance of passing it on

Question 24

What is the difference between a adenoma and a carcinoma?

Answer 24

Adenoma - benign tumour

Carcinoma - cancerous tumour

Question 25

What’s is Werner’s syndrome? How does it come about and what are some symptoms?

Answer 25

A mutation in the Werner protein, a type of helicase (‘unzipper’)
DNA damage lead to premature ageing and illness associated with ageing e.g. Cataracts, osteoporosis, skin ulcers.
Autosomal recessive

Question 26

What do the checkpoints on the mitosis cycle give time for?

Answer 26

DNA repair

Question 27

What is p53?

Answer 27

A tumour suppressor protein. A mutation in it is often the cause for many different types of cancer.
Known as the ‘guardian of the genome’.

Question 28

What is a heterogenous tumour?

Answer 28

A tumour which contains different types of tumour cells with different phenotypic profile.
These tumour can develop resistant clones to cancer treatments.
For example, a chemotherapy treatment will target and diminish one type of cell, but another type of cell in the tumour will develop resistance and could continue to grow.
This is called clinal expansion.

Question 29

What is camptothecin?

Answer 29

A type of chemotherapy that can lead to persistent single strand and double strand breaks in cells.