Cancer and Aids Study GuideExam 2 DNA Mutations and Cancer-errors are rare, but do happen and result in substitution What happens if substitution is not corrected? -a substitution that happens during DNA synthesis is called a point mutation The effect varies:-silent mutation: mutation that does not alter protein function-missense mutation: different amino acid; resulting protein may have partial function-nonsense mutation: specified stop codon; truncated, non-functional protein-there are other mutations that can happen during DNA replication-a base can be added or deleted by mistake-this causes a frameshift mutationFrameshift mutation-Frame simply refers to the reading frame of the gene. An addition or deletion changes the reading frame. For example: Thesunwashotbuttheoldmandidnotgethishat-If a mutation occurs where another letter is added to the sentence, say “g”, then all the letters to the right of the insertion will shift one position to the right :Thesunwashotbutgtheoldmandidnotgethishat-which would read: The sun was hot but gth eol dma ndi dno tge thi sha t-A deletion of a letter would cause a shift to the left and the sentence would not make sense eitherHow else can mutations happen?-mutations result from mutagen exposure-agent that includes change is a mutagen-two general types: chemical, radiationChemical Mutagens-can cause substitutions or frameshift mutations -classes-Alkylating agents: act by adding molecular components to DNA bases thus altering the protein product-Cross-linking agents: create covalent bonds with DNA bases-Polycyclic aromatic hydrocarbons: (PAHs) are metabolized by the human body into other potentially mutagenic moleculesRadiation-ultraviolet irradiations forms thymine dimers-covalent bonds between adjacent thymines-cannot fit into double helix; distorts molecule-replication and transcription stall all distortion-cell will die if damage not repaired-x-rays cause single and double strand breaks in DNA-double strand breaks often produce lethal deletionsCommon mutations – red hair, blue eyes, frecklesMutations and CancerAlteration in genes involved in controlling cell proliferation and survival fall into three main categories(gene families):1Oncogenes: presence contribute to uncontrolled cell proliferation and leading to cancer. Arise from normal proto-oncogenes or viral oncogenes23Tumor Suppressor Genes – absence (inactivation) contribute to uncontrolled cell proliferation and cancer4DNA Repair Genes – mutations in DNA repair genes lead to lack of DNA repair and can progress to cancer depending on the importance of the protein that is coded for by the mutated gene-Growth Factor : a protein that stimulates cell division-Receptor: a protein on cell surface that binds the growth factor and initiates the growth signal by activating DNA transcription factors-Transcription factor: a protein that binds to DNA and initiates transcription-tumor suppressor genes are a family of normal genes whose loss of inactivation (via mutation) can lead to cancer-most tumor suppressor proteins will survey the cell including daily activities, DNA health, and cell division progression (cell cycle). -tumor suppressor proteins can stop cell division if DNA damage is detected. They recruit DNA repair proteins to the site of damage and help with repair. They can also induce apoptosis if repair is not effective.-loss of a tumor suppressor gene function allows the cell to grow and divide continually. Proto-Oncogenes/Oncogenes-proto-oncogene is the name of a healthy properly functioning gene. It is only called an oncogene when a mutation occurs and the protein product can no longer properly function-proto-oncogenes code for proteins that help to regulate cell growth and differentiation-when a proto-oncogene is mutated into an oncogene, this oncogene will accelerate cell growth and divisionDNA Repair Genes-DNA repair genes code for proteins whose normal function is to correct errors that are not repaired bythe proof reading function of DNA polymerase; i.e. during DNA replication prior to cell division-DNA polymerase has a proof reading function, but errors still occur-mutations in DNA repair genes can lead to a failure in repair, because the DNA repair protein is not made or is not functional-DNA repair proteins detect and repair DNA damage at other times so their loss can affect daily cell functionGenes implicated in cancer: oncogenes, tumor suppressor genes, DNA repair genesCancer Screenings, Diagnosis, and TreatmentWhy Screen?-screening tests can help find cancer at an early stage, before symptoms appear-when abnormal tissue of cancer is found early, it may be easer to treat or cure -by the time symptoms appear, the cancer may have grown and spread. This can make the cancer harder to treat or cure-it is important to remember that when your doctor suggests a screening test, it does not always mean he or she thinks you have cancer-screening tests are done when you have no cancer symptomsWarning Signs: fatigue, weight loss, night sweats, blood in urine, chronic cough, loss of appetite, recurrent fever, sudden depression, new and persistent pain, enlarged lymph nodes, recurrent nausea or vomiting, blood in stool, changes in size or color of a mole or changes in a skin ulcer that does not healTypes of TestsPhysical Exam and history: an exam of the body to check general signs of health, including checkingfor signs of disease, such as lumps or anything else that seems unusual. A history of the patient's health habits and past illnesses and treatments will also be taken. Laboratory Tests: Medical procedures that test samples of tissue, blood, urine, or other substances inthe bodyImaging Procedures: Procedures that make pictures of areas inside of the body.Genetic Tests: Tests that look for certain gene mutations (changes) that are linked to some types of cancerImaging TechniquesMRI – uses magnets to energize electrons. Release of energy = imageCT or CAT scan – uses multiple high-resolution x-rays to generate a composite imageUltrasound – uses sound wavesPositron emission tomography (PET)-a nuclear medical imaging technique that produces a three-dimensional image or picture of functional processes in the body.-Detects pairs of gamma rays emitted indirectly by a positron- emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Three-dimensional images of tracer concentration within the body are then constructed by computer
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