oncogenesis and tumor suppressor genes

Question 1

characteristics of cancers

Answer 1

• increased growth
• failure for apoptosis/senescence
• loss of differentiation
• unstable genome (failure to repair DNA damage)

Question 2

briefly, why do cancers have an increased growth

Answer 2

loss of growth regulation and stimulation of environmental factors that promote growth

Question 3

what is the result of the loss of differentiation in cancer cells

Answer 3

behave as immature cells .’. cells can migrate from site to site

Question 4

what is a proto-oncogene

Answer 4

a normal gene, involved in promoting growth pathways. express proteins in tightly regulated manner that allows cell to grow.

Question 5

what happens if the proto-onogene becomes mutated

Answer 5

starts expressing its proteins in an unregulated manner .’. is called an oncogene and these are then abnormal.

Question 6

proto-oncogene mutant effects are recessive. what does this ean

Answer 6

only one allele has to be mutated in order for entire protein to become dysregulated and make that progression step towards cancer.

Question 7

are protooncogene mutations usually inherited or sporadic mutations

Answer 7

rarely inherited. usually somatic mutations that have occurred sporadically.

Question 8

are TSG mutations usually inherited or sporadic

Answer 8

tend to be inherited

Question 9

what is an oncogenic retrovirus

Answer 9

retrovirus that can directly cause cancer

Question 10

how many retroviruses are there

Answer 10

only one that we know of so far

Question 11

a retrovirus contains 3 genes in its DNA what are these

Answer 11

Gag = capsid proteins
Pol = reverse transcriptase gene
Env = envelope proteins allow infection of new cells

Question 12

what is a nondefective retrovirus

Answer 12

RNA genome = Gag, Pol, Env. aka fully intact genome, only tend to cause cancers by insertational mutagenesis.

Question 13

what is an acute transforming retrovirus

Answer 13

retroviruses that have lost part of their genome.

Question 14

how do acute transforming viruses cause cancer

Answer 14

unable to reproduce effectively by itself, depend on co-infection of a host cell with a non-defective retrovirus that can express its envelope proteins.

Question 15

what are acutely transforming nondefective viruses

Answer 15

rare. have all the genes required for viral replication but has also acquired the viral oncogene.

Question 16

how does retrovirus infect

Answer 16

retrovirus surface envelope binds to cell surface protein. fuses cell &uncoats .’. its DNA enters the cell. Reverse transcriptase = rna transcribed into ssDNA. replicates .’. dsDNA. viral genome inserted into host genome.’. production of viral proteins. If inserted genome contains viral oncogene, can cause cell to undergo continuous growth

Question 17

how do retroviruses that DO NOT contain viral oncogenes cause tumours

Answer 17

proto-oncogenes may become dysregulated due to promoter insertion when the viral genome integrates.
LTR (long terminal repeats) that contain viral promoters &enhancers can actually stimulate the expression of proto-oncogenes

Question 18

what chromosomal abnormality is associated with burkitt’s lymphoma

Answer 18

translocation between MYC gene on chromosome 8 and Ig heavy chain on chromosome 14(less commonly with Ig light chain on chromosome 2/22)

Question 19

what happens n Burkitt’s lymphoma

Answer 19

in a lymphocyte there is high expression of Ig genes. These initially require rearrangement of Ig genes in order to give specificity. here, brings together proto-oncogene and Ig gene .’. aberrant expresion of that gene