UNT BIOL 3451 - Cancer and Regulation of the Cycle (6 pages)

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Cancer and Regulation of the Cycle



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Cancer and Regulation of the Cycle

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Finishing up cancer and the different ways in which it can be produced.


Lecture number:
24
Pages:
6
Type:
Lecture Note
School:
University of North Texas
Course:
Biol 3451 - Genetics
Edition:
1
Documents in this Packet
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BIOL 3451 1st Edition Lecture 24 Outline of Last Lecture I 17 7 Gene Regulation in a Model Organism Transcription of the GAL genes of Yeast II 17 8 Posttranscriptional Gene Regulation Occurs at All the Steps from RNA Processing to Protein Modification III 17 9 RNA Silencing Controls Gene Expression in Several Ways IV 19 1 Cancer is a Genetic Disease That Arises at the Level of Somatic Cells V 19 2 Cancer Cells Contain Genetic Defects Affecting Genomic Stability DNA Repair and Chromatin Modifications Outline of Current Lecture I 19 2 Cancer Cells Contain Genetic Defects Affecting Genomic Stability DNA Repair and Chromatin Modifications II 19 3 Cancer Cells Contain Genetic Defects Affecting Cell Cycle Regulation III 19 4 Proto oncogenes and Tumor Suppressor Genes Are Altered in Cancer Cells IV 19 5 Cancer Cells Metastasize and Invade Other Tissues V 19 6 Predisposition to Some Cancers Can Be Inherited VI 19 7 Viruses Contribute to Cancer in Both Humans and Animals VII 19 8 Environmental Agents Contribute to Human Cancers Current Lecture I 19 2 Cancer Cells Contain Genetic Defects Affecting Genomic Stability DNA Repair and Chromatin Modifications o Cancers show chromosomal defects that we use to diagnose the type and stage of cancer Chronic myelogenous leukemia CML involving translocation of the C ABL gene on chromosome 9 into the BCR gene on chromosome 22 1 Figure 19 4 2 this structure known as the Philadelphia chromosome Xeroderma pigmentosum o Number of cancers caused by defects in genes that control DNA repair Xeroderma pigmentosum XP 1 Defective nucleotide excision repair leading to skin cancer Hereditary nonpolyposis colorectal cancer 1 Autosomal dominant syndrome These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II 2 Increased risk check a box off of colon ovary uterine and kidney cancers 3 8 genes implicated with four involved in DNA mismatch repair a Could be just one of these or several b Alleles oncogenes can be dominant or recessive to the wild type i Increases risk o Epigenetics study of factors that affect gene expression but do not alter the nucleotide sequence of the DNA DNA methylation Barr bodies 1 Responsible for gene silencing associated with parental imprinting heterochromatin gene expression X chromosome inactivation Histone acetylation and acetylation histone modification of histone code 1 Genes that encode histone acetylases deacetylases methyltransferases and demethylases are often mutated or aberrantly expressed in cancer cells Genomic patterns and locations of these modifications can affect gene expression and be passed on from generation to generation 19 3 Cancer Cells Contain Genetic Defects Affecting Cell Cycle Regulation o Growth and differentiation of cells are strictly regulated Involves multiple processes with multiple steps This allows for lots of opportunity for regulation In cancer cells these are mutated or aberrantly expressed leading to uncontrolled cell proliferation 1 Lock one part of the step into the mutation o Interphase of cell cycle is when cell grows and replicates its DNA most cells are in G1 stage Cells that stop proliferating enter G0 where they do not grow or divide but are metabolically active 1 Neurons Cancer cells are unable to enter G0 and cycle continuously o Signal transduction initiates a program of gene expression that propels the cells out of G0 and back into the cell cycle Cancer cells often have defects in signal transduction pathways o Checkpoints G1S do I replicate DNA G2 M did I replicate correctly M monitors spindle formation and attachment to kinetochores These all decided whether to move on to next cell cycle Fig 19 5 o Regulation of checkpoints mediated by Cyclins III Cyclin dependent kinases CDKs Regulate synthesis and destruction of cyclin proteins Fig 19 6 and 19 7 o Cells halt progress through cell cycle if DNA replication repair or chromosome assembly is aberrant o If DNA damage is so severe that repair is impossible the cell may initiate apoptosis or programmed cell death Prevents cancer by having defective cells that could kill you kill themselves 1 BAX homodimer promotes apoptosis Also eliminated cell not contributing the final adult organism Most cancer patients have P53 problems controls apoptosis and DNA repair o Steps in apoptosis are Fragmentation of nuclear envelope Disruption of internal cellular structures Dissolution of cell into small spherical apoptotic bodies called vesicles Engulfing of the apoptotic bodies by phagocytic cells A series of proteases cascade called caspases 1 Responsible for initiating apoptosis and digesting intracellular components 19 4 Proto oncogenes and Tumor Suppressor Genes are Altered in Cancer Cells o Proto oncogenes normal genes whose products promote cell growth and division Encode 1 Transcription factors stimulate expression of other genes 2 Signal transduction molecules that stimulate cell division 3 Cell cycle regulators that move through the cell cycle o In cancer cells one or more proto oncogenes are altered in such a way turned on in improper way that their activities cannot be controlled normally Table 19 1 show some proto oncogenes and tumor suppressors that have been discovered o Oncogene is proto oncogene that is mutated or aberrantly expressed and contributes to the development of cancer only one allele o tumor suppressor genes products of these that normally regulate cell cycle checkpoints and initiate the process of apoptosis says don t divide when mutated cells unable to respond normally t cell cycle checkpoints or are unable to undergo apoptosis if DNA damage is extensive leads to more mutations and development of cancer o Ras genes encode for signal transduction molecules that are associated with the cell membrane and regulate cell growth and division Fig 19 9 IV Mutations to convert the ras proto oncogene to an oncogene freeze the ras protein into its active conformation constantly stimulating the cell to divide o p53 tumor suppressor gene encodes a nuclear protein that acts as a transcription factor that represses or stimulates transcription of more than 50 different genes It is continuously synthesized but rapidly degraded thus present low levels Increased levels result from increases in protein phosphorylation acetylation and other posttranscriptional modifications Fig 19 10 P53 can arrest cell cycle at several phases Cells lacking p53 are


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