tailieunhanh - Ebook High-Yield cell and molecular biology - Cell and molecular biology (3rd edition): Part 2

(BQ) Part 2 book "High-Yield cell and molecular biology - Cell and molecular biology" presents the following contents: Proto-Oncogenes, oncogenes and tumor-suppressor genes, the cell cycle, molecular biology of cancer, cell biology of the immune system, cell biology of the immune system, molecular biology techniques, identification of human disease genes, gene therapy. | Proto-Oncogenes Oncogenes and Tumor-Suppressor Genes Proto-Oncogenes and Oncogenes A. DEFINITIONS 1. A proto-oncogene is a normal gene that encodes a protein involved in stimulation of the cell cycle. Because the cell cycle can be regulated at many different points proto-oncogenes fall into many different classes . growth factors receptors signal transducers and transcription factors . 2. An oncogene is a mutated proto-oncogene that encodes for an oncoprotein involved in the hyperstimulation of the cell cycle leading to oncogenesis. This is because the mutations cause an increased activity of the oncoprotein either a hyperactive oncoprotein or increased amounts of normal protein not a loss of activity of the oncoprotein. B. ALTERATION OF A PROTO-ONCOGENE TO AN ONCOGENE. We know now that the vast majority of human cancers are not caused by viruses. Instead most human cancers are caused by the alteration of proto-oncogenes so that oncogenes are formed producing an oncoprotein. The mechanisms by which proto-oncogenes are altered include. 1. Point mutation. A point mutation . a gain-of-function mutation of a protooncogene leads to the formation of an oncogene. A single mutant allele is sufficient to change the phenotype of a cell from normal to cancerous . a dominant mutation . This results in a hyperactive oncoprotein that hyperstimulates the cell cycle leading to oncogenesis. Note proto-oncogenes only require a mutation in one allele for the cell to become oncogenic whereas tumor-suppressor genes require a mutation in both alleles for the cell to become oncogenic. 2. Translocation. A translocation results from breakage and exchange of segments between chromosomes. This may result in the formation of an oncogene also called a fusion gene or chimeric gene which encodes for an oncoprotein also called a fusion protein or chimeric protein . A good example is seen in chronic myeloid leukemia CML . CML t 9 22 q34 q11 is caused by a reciprocal translocation between