UNT BIOL 3451 - Final Exam Study Guide (20 pages)

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Final Exam Study Guide



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Final Exam Study Guide

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A Study of Gene Expression in Prokaryotes and Eukaryotes, Cancer, Recombinant DNA technology, and Genomics.


Pages:
20
Type:
Study Guide
School:
University of North Texas
Course:
Biol 3451 - Genetics
Edition:
1
Documents in this Packet
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BIOL 3451 1nd Edition Exam 3 Study Guide Lectures 19 27 Lecture 19 November 4 15 2 Spontaneous Mutations o Not natural due to an outside source o Three types of DNA base damage Depurination base falls out usually purine guanine or adenine Deamination oxidize amino group to double bond carbon keto group A T converted to G C Oxidative Damage Reactive oxidants cause chemical modifications in DNA o Superoxides o Hydroxyl radicals o Hydrogen peroxide o Transposons move within or between genomes Good because important for evolution lateral transfer of genes in same generation and can happen between different species Bad because bacteria have become resistant to antibiotics and can transfer that resistance 15 3 Induced Mutations o Increase rate of mutation via mutagens o Occurs in many forms Base analogs trick enzymes into making them into nucleotides thus becoming substitutes for purines or pyrimidines Increases tautomeric shifts and sensitivity to UV light Alkylating agents donate alkyl group to an amino or keto group in nucleotides which alters base pairing affinity transition mutations Intercalating agents chemicals with a shape that allows them to be wedged between DNA base pairs and unwinding DNA Some are used as stains ethidium bromide Adduct forming agents substance that covalently binds to DNA which alters its conformation and interferes with replication and repair UV light creates pyrimidine dimers that distort DNA conformation by pulling them together too much to where the bases can t line up correctly during replication errors tend to be introduced Ionizing radiation stable molecules obliterated into free radicals that can directly and indirectly affect DNA by ionizing molecules encountered X rays gamma rays cosmic rays More active than UV radiation Produces many chromosomal aberrations Less than 20 from human made sources 15 4 Single Gene allele mutations o Most gene mutations are polygenic caused by several genes that can cause monogenic diseases o 30 of time these mutations create nonsense mutations Triggers rapid decay of mRNA o Usually they are missense mutations that alters amino acid sequence of a protein and makes more frameshift mutations which creates internal nonsense codons o Beta Thalassemia is example of genetic disease caused by large number of mutations Over 250 mutations in Beta globin gene reduction or absence of hemoglobin Several mild symptoms Affects people in certain areas o Trinucleotide repeat sequences causes mutant genes when specific short DNA sequences are repeated many times Over 20 disorders can show more than 200 repeats 30 repeats is normal Fragile X Huntington Disease Myotonic Dystrophy 15 5 Counteracting Mutations Using DNA Repair Systems o Helps to maintain integrity of genetic material o If fix then okay by replacing incorrect nucleotides using DNA polymerase III called proofreading o Next mismatch repair is activated cutting and removing incorrect nucleotides Strong match between this and cancer o Then Postreplication Repair occurs AFTER damaged DNA has not been repaired and failed to finish replication also called homologous recombination repair Copy it leave a hole skip it then bring matching sequence form other side to patch it then fix other one o SOS repair system last resort to fix DNA damage just fix it the best you can which may still be wrong nucleotide but it may be better than alternative o Photoreactivation repair photoreactivation enzyme cleaves bonds between thymine dimers Done in E coli humans don t use it Enzyme absorbs photon of light to do this o Excision Repair cut and paste mechanisms found in all prokaryotes and eukaryotes done in three steps Recognizes and cuts distortion DNA polymerase fills in gap by inserting complementary nucleotides DNA ligase seals final nick Two types Base excision corrects DNA containing damaged DNA base Nucleotide excision repairs bulky lesions that alter distort the double helix o Nucleotide Excision Repair and Human Diseases Xeroderma pigmentosum XP affects NER pathway and doesn t fix mutations from radiation NER pathway defects gives rise to Cockayne Syndrome Trichothiodystrophy o Double strand break repair DSB repair reattaches two broken DNA strands repair system involving two strands of DNA Homologous recombination repair one pathway involved in DSB repair occurs in late S or early G2 phase Nonhomologous end joining doesn t recruit homologous region of DNA during repair done in G1 phase Lecture 20 November 6 15 6 Ames Test and Mutagenicity o Uses strains of Salmonella typhimurium for its ability to reveal presence of specific types of mutations Mutate a mutant reversion Known carcinogens discovered through Ames test in cigarettes 15 7 Mutations Used to Study Gene Function o Mutations induced to identify genes and processes o Ionizing Radiation Ethyl methanesulfonate EMS and nitrosoguanidine Have to sequence whole genome to fine where alkyl group added o Do a genetic screen to detect mutants 15 8 Transposable Elements o Transposons insert themselves into various locations within genome o Bacteria has two types Insertion sequence IS elements if inserted into gene gene regulatory region can cause mutations Bacterial transposons TN elements introduce drug resistance onto bacterial plasmids R factors which are very mobile o Transposable mutations in corn Dissociation Ds Activator Ac Movement of Ds gene is dependent on Ac gene o Transposable mutations in Drosophila Copia and P More than 30 families of transposable elements found in Drosophila o Transposable elements in humans Appear to be inactive Can disrupt normal gene function in various ways resulting in phenotypic changes or disease May contribute to variability underlying evolution 16 1 Gene Expression in Prokaryotes Responds to Environmental Conditions o Studied in E coli o Highly efficient genetic mechanisms evolved because life cycle so short Turn transcription of specific genes on and off use one that is most efficient Due to changes in environment as well as regular cellular activity o Bacteria adapt to environment by producing inducible enzymes adaptive inducible enzymes Enzymes produced based on chemicals in environment Constitutive enzymes Enzyme produced continuously regardless of environment Doesn t mean you make a lot of it Need all the time no matter what Repressible system abundance of end product in environment represses gene expression of it Positive transcription occurs only if a regulator molecule directly stimulates


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