oncogenesis and tumor suppressor genes Flashcards
characteristics of cancers
- increased growth
- failure for apoptosis/senescence
- loss of differentiation
- unstable genome (failure to repair DNA damage)
briefly, why do cancers have an increased growth
loss of growth regulation and stimulation of environmental factors that promote growth
what is the result of the loss of differentiation in cancer cells
behave as immature cells .’. cells can migrate from site to site
what is a proto-oncogene
a normal gene, involved in promoting growth pathways. express proteins in tightly regulated manner that allows cell to grow.
what happens if the proto-onogene becomes mutated
starts expressing its proteins in an unregulated manner .’. is called an oncogene and these are then abnormal.
proto-oncogene mutant effects are recessive. what does this ean
only one allele has to be mutated in order for entire protein to become dysregulated and make that progression step towards cancer.
are protooncogene mutations usually inherited or sporadic mutations
rarely inherited. usually somatic mutations that have occurred sporadically.
are TSG mutations usually inherited or sporadic
tend to be inherited
what is an oncogenic retrovirus
retrovirus that can directly cause cancer
how many retroviruses are there
only one that we know of so far
a retrovirus contains 3 genes in its DNA what are these
Gag = capsid proteins Pol = reverse transcriptase gene Env = envelope proteins allow infection of new cells
what is a nondefective retrovirus
RNA genome = Gag, Pol, Env. aka fully intact genome, only tend to cause cancers by insertational mutagenesis.
what is an acute transforming retrovirus
retroviruses that have lost part of their genome.
how do acute transforming viruses cause cancer
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.
what are acutely transforming nondefective viruses
rare. have all the genes required for viral replication but has also acquired the viral oncogene.
how does retrovirus infect
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
how do retroviruses that DO NOT contain viral oncogenes cause tumours
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
what chromosomal abnormality is associated with burkitt’s lymphoma
translocation between MYC gene on chromosome 8 and Ig heavy chain on chromosome 14(less commonly with Ig light chain on chromosome 2/22)
what happens n Burkitt’s lymphoma
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
