Eukaryotes (higher organisms) have muliple chromosomes in a genome which is separated from the rest of the cell by a nuclear membranes.

Prokaryotes lack a membrane bound nucleus, their DNA occurs in a circular form.

Oncogenes

Proto-oncogenes and oncogenes encode growth factors. A single aa mutation is enough to change the proto-oncogene into an oncogene.

Mutated proto-oncogenes that cause cancer are called oncogenes.

Examples of oncogenes are:

Ras oncogene is involved in sporadic tumours (colon and lung) and rhabdomyosarcomas.

c-myc translocation occurs in Burkitt's lymphoma.

N-myc proto-oncogene is seen in neuroblastoma.

SRC oncogene is associated with sarcoma.

*Ras is the commonest oncogene (others include myc, fos and jun)

Fas ligands and caspases trigger apoptosis. Bax, Bad and Bak are members of the oncogenes which promote cell death.

Bcl-2 inhibits apoptosis.

Bcl-2 prevents cell death by blocking apoptosis, preventing p53 mediated cell destruction and prevent cell death.