oncogenes, tumour supressors quick flashcards

what are oncogenes

arise from mutation or overexpression of proto oncogenes,

also can be introduced by a virus

cause cancer

what gene changes cause cancer

oncogenes

mutations in tumour suppressor genes

mutations in DNA repair genes

what are proto oncogenes

promote cell growth and cell cycle, prevent normal cell death

eg growth factors, regulatory GTPases, transcription factors

can become oncogenes when mutated

what is Ras GTPase

the gene Ras encodes this protein. Ras is a proto oncogene

Ras is commonly mutated to yield an oncogene

this oncogene is found in 20% of human cancers

explain Ras signalling

the normal protein relays a signal from growth factor receptors

mutations can result in a hyperactive ras that signals without growth factors

what are tumour suppressor geens

prevent DNA damage / persistence of mutations

slow down cell division so DNA repair can take place

what is p53

tumour suppressor gene

encodes a protein that can detect DNA damage, stop cell cycle and promote DNA repair

if too much DNA damage, p53 can trigger apoptosis

more than half of all cancers have mutations in p53

what is Rous sarcoma virus

virus isolated from chicken fibroblast sarcoma

if injected into normal chicken embryos - causes sarcomas

RSV carries an oncogene (SRC) a non receptor tyrosine kinase that promotes cell proliferation

examples of virus induced cancers

Epstein-Barr virus - LMP1 induces growth factor & suppresses cell death genes

Hepatitis B - can integrate into human genome → hepatocellular carcinoma

HPV - linked to cervical cancer, virus protein (E6) binds p53

what are BRCA1 and BRCA2

encode for proteins breast cancer type 1 & 2 that help repair damaged DNA ie. tumour suppressor genes

mutations in BRCA genes have been found in inherited forms of breast cancer

example of DNA repair gene mutations and germline cancer mutations

how is the philadelphia chromosome linked to leukemia

abnormality of chromosome 22 where part of chromosome 9 is transferred to it → makes abnormal oncoprotein

bone marrow cells containing philadelphia chromosome often found in leukemia

how can hormones contribute to cancer

hormones naturally promote cell growth in target tissues but can contribute to proliferation in some cancers

eg elevated levels of oestrogen in breast cancer, elevated levels oh hormone receptors, thyroid hormones in thyroid cancers

what is apoptosis

cell suicide eg following DNA damage or cell damage

controlled, important in development to remove unwanted/damaged cells

how does apoptosis work

enzymes (mainlyl capases) break down cell component and organelles

cell fragments removed by immune cells

how can cancer cells avoid apoptosis

many cancers overexpress proteins that can block apoptosis

eg bcl-2 (pro-survival_ found in some lymphomas and leukaemias

what are telomeres

extra DNA at ends of chromosomes that protect chromosomes

each cell division, telomeres become shorter → limits the number of cell divisions possible for normal cells

what is telomerase

adds DNA repeat units to telomeres

in stem cells and many cancer cells