mechanisms of oncogenesis

Question 1

examples of chemical agents associated with cancer

Answer 1

coal tar
cigarette smoke
aflatoxin

Question 2

examples of physical agents associated with cancer

Answer 2

asbestos (dibre structure damages DNA)

UV light

Question 3

examples of viral agents associated with cancer

Answer 3

hepatitis B

ebstein Barr

Question 4

how can we observe if an agent is potentially carcinogenic using bacteria on plates

Answer 4

if you take a bacteria that is mutated in AA synthesis pathways and plate it without AA, it shouldn’t grow,
BUT if you plate it with direct carcinogens, it causes a back-mutation to convert mutated nonfunctioning gene into one that works so overnight colonies form +grow

Question 5

what are procarcinogens

Answer 5

indirect carcinogens eg benzopyrene.
on their own they are not carcinogenic but after metabolised by microsomal enzymes in the liver the product is carcinogenic as it contains an epoxide group

Question 6

how to test procarcinogen using bacteria plates

Answer 6

So if we plate the procarcinogen and add mutated bacteria = no growth
If we plate the procarcinogen and liver microsome enzymes, then add mutated bacteria = growth

Question 7

how to test carcinogen using a live mouse (skin)

Answer 7

paint a series of repetitive doses of a direct carcinogen onto a mouse after a while a cancerous tumour of the skin appear
if you paint on the direct carcinogen and then apply doses of tumour promoter you see the development of cancer

Question 8

what happens if you paint tumour promoter and then the direct carcinogen

Answer 8

no cancer. direct carcinogen acts as the tumour initiator, by introducing mutations in the cell. The tumour promoter on the other hand promotes cell growth.

Question 9

what happens if you paint the direct carcinogen and then tumour promoter

Answer 9

introducing a few mutation into a small number of cells.
tumour promoter expands the number of these mutated cells .’.greater pool of cells w/ few mutations .’.likely that one of these cells will eventually, acquire enough multiple hits to become cancerous.

Question 10

what are tumour promoters

Answer 10

substance thar stimulate cell growth that increases likelihood of cancer

Question 11

types of radiation that can cause DNA damage

Answer 11

ionising radiation (X-rays, nuclear radiation) and UV radiation.

Question 12

what happens when exposed to damaging radiation (eg ionising radiation)

Answer 12

=damage to DNA inside cells generally causing DNA to break

Question 13

what happens when exposed to damaging radiation (eg UV)

Answer 13

UV radiation is absorbed by pyrimidine and causes the production of pyrimidine dimers (thymine and cytosine) can form cross-links in the DNA.

Question 14

mutations in genome/DNA damage is common, how does the body respond to this

Answer 14

DNA repair processes removing the incorrect bases and inserting the correct ones or rejoining the correct DNA back together

Question 15

heritable conditions that = defects in DNA repair proteins .’. allowing accumulation of mutations that cause cancer

Answer 15

Ataxia telangiectasia, Bloom’s syndrome, Fanconi’s anaemia, Li-Fraumeni syndrome, Lynch type II, Xeroderma pigmentosum

Question 16

chromosomal abnormalities that predispose individuals to cancer

Answer 16

Down’s syndrome

Klinefelter’s syndrome (47XXY)

Question 17

which cancer is associated with Epstein -Barr Virus

Answer 17

Burkitt’s lymphoma and nasopharyngeal carcinoma

Question 18

which cancer is associated with papilloma Virus

Answer 18

cervical carcinoma and warts

Question 19

which cancer is associated with hepatitis B

Answer 19

hepatoma

Question 20

the only RNA virus associated with cancer

Answer 20

HTLV-1 associated with cervical carcinoma and warts

Question 21

Properties a virus must possess in order to cause cancer

Answer 21

• stable association with cells
• must not kill the cell
• must evade immune surveillance

Question 22

what is Knudson’s hypothesis for hereditary cancer

Answer 22

two- hit hypothesis. An individual must develop mutations in both allele.
In hereditary cancers, the first genetic event occur in germline .’. only need one hit to result in nonfunctional protein .’. develop cancer earlier

Question 23

knudson’s hypothesis in familial adenomatous polyposis

Answer 23

inherited = massive increase in risk of colon cancer
by the time they are an adolescent, have hundreds of polyps in their colon -benign tumours. But there are so many that it is likely that one of these polyps will undergo a change that causes it to become cancerous

Question 24

what is meant by loss of heterozygosity

Answer 24

where an individual who has one normal allele and one mutated allele loses the normal allele they may get cancer

Question 25

cytogenic mechanisms for loss of heterozygosity

Answer 25

non-disjunction
mitotic recombination
deletion of normal chromosome
gene conversion
point mutation