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Towson - MBBB 309 - Exam III Study Guide - Study Guide

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Towson - MBBB 309 - Exam III Study Guide - Study Guide

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background image Genetics Exam III Study Guide 
Chapter 13—Mutation, DNA Repair, and Recombination 
  Point mutations vs. Frameshift mutations  o  Point Mutation: Only affects one or very few nucleotides, typically changes  one nucleotide for another   o  Frameshift Mutation: Changes the “frame” in which the template strand is  read. Is caused by Indels (Insertions or deletions) of a pair of nucleotides  o  Therefore, the differences between the two are that point mutations only  affect one nucleotide and frameshift mutations affect more than one 
nucleotide and how the entire code is read.  
  Somatic vs. Germline mutations  o  Somatic Mutations: Mutation in a non-germline cell that can be passed to  the progeny through cell division  o  Germline Mutations: Inherited genetic mutations in the sex cells 
o  Therefore, the primary difference between the two is the cells in which they 
occur      Spontaneous vs. Induced mutations  o  Spontaneous: Occurs without a known cause  
o  Induced: Mutation that occurs due to exposure to a chemical or physical 
agent that causes changes in the structure of DNA     Transition vs. Transversion  o  Transition: Changes a Purine to a Purine (A  G) or a pyrimidine to a  pyrimidine (CT)  o  Transversion: Changes a Purine to a Pyrimidine or vice versa  
o  Purine: Two ring nucleotide  
o  Pyrimidine: One ring nucleotide 
  Mutation via Base Analogs (e.g. 5-bromouracil)  o  Inducible mutation 
o  Base analog: Unnatural purine or pyrimidine bases that differ slightly from 
the normal bases and that can be incorporated into nucleic acids   o  5-Bromouracil    A pyrimidine     Thymine analog     Bromine at the 5 th  position is similar to the methyl (-CH ) group in  thymine    Changes the charge distribution and increases the frequency of  tautomeric shifts     In stable Keto form in bonds with adenine    After a tautomeric shift to its enol form it bonds with guanine 
  In keto form, it causes a G:C  A: T transition 
  In enol form it causes an A: T  G:C transition    Mutations induced by radiation (e.g. thymine dimmers) and superoxides  o  Ionizing Radiation: X-Rays, gamma rays, and cosmic rays     High energy  
background image   Used for medical diagnoses and penetrate living tissue through  substantial distances    Cause ionization measured in roentgen units     Can cause mutation  o  Non-ionizing radiation: Ultraviolet light     Low energy 
  Penetrate only surface cell 
  Do not cause ionization but excitation or the movement of electrons in  outer orbitals to higher energy levels     More likely to cause mutation in single cellular organisms   o  Cells either ionized or excited are more chemically reactive than their normal  forms  o  These mutations can cause cancer    Ames Test  o  Pages 346 – 348  
o  Carcinogens: Mutagenic substances that induce cancer in living cells  
o  It essentially provides a simple and inexpensive method for detecting the 
mutagenicity of chemicals   o  Step 1: Grow Salmonella his -  auxotroph’s carrying a frameshift mutation   o  Step 2: Prepare a solution of the potential mutagen  
o  Step 3: Spread bacteria on agar medium containing a trace of histidine (plates 
skips steps 4 and 5 acting as the control)  o  Step 4: Place a solution containing potential mutagen on filter paper disk  
o  Step 5: Place disk with potential mutagen in experimental plate 
o  Step 6: Incubate at 37degrees Celsius 
  Repair Mechanisms (Pages 348-351)  o  Light Dependent Repair    Carried out by a light activated enzyme called DNA photolyase   o  Excision Repair    Step 1: DNA repair endonuclease or endonuclease-containing enzyme  complex recognizes, binds to, and excises the damaged base or bases 
in DNA 
  Step 2: DNA polymerase fills in the gap by using the undamaged  complementary strand of DNA as template     Step 3: DNA ligase seals the break left by DNA polymerase to  complete the repair process     Base excision repair: Remove abnormal or chemically modified bases  from DNA    Can be initiated by a group of enzymes call DNA glycosylases  that recognize abnormal bases in DNA       They then cleave the glyosidic bond between the abnormal  base and 2-Deoxyribose creating AP sites (apurinic or 
background image   AP sites are recognized by endonucleases which act with  phosphodiesterase to excise the sugar-phosphate groups at 
these sites 
  DNA polymerase replaces the missing nucleotide per the  specifications of the complementary strand     DNA ligase seals it     Nucleotide excision repair: Pathways remove larger defects like  thymine dimers     Excinuclease activity begins on either side of the damaged  nucleotide and excises an oligonucleotide containing the 
damaged bases 
  In E. coli  o  Figure shown on page 349 
o  Requires the product of uvrA, uvrB, and uvrC 
o  A trimeric protein (2 uvrA and 1 uvrB polypeptide) 
recognizes the defect damaged site and binds to it 
using ATP to bend the DNA at the site of damage. 
o  UvrA dimer is then released and the UvrC protein bind  to the UvrB/DNA complex  o  UvrC protein cleaves the 4 th /5 th  phosphodiester linkage  from the damaged 5’ side   o  DNA helicase II releases the excised dodecamer  
o  DNA polymerase I fills the gap  
o  DNA ligase seals the remaining nick in the DNA 
o  Mismatch Repair    Repairs mismatched pairs after replication.    Typically, with normal bases     Detected by identifying the template strand and the new strand     Based on Methylation process because there is a portion of time  where the template strand is methylated and the newly synthesized 
strand is not. 
  In E. Coli     Requires the products of mutH, mutS, and mutU (Also uvrD)    MutS protein recognizes mismatches and binds to them to  initiate the repair process    MutH and MutL proteins join the complex     MutH contains GATC-Specific endonuclease activity and  cleaves the unmethylated strand at the hemi methylated (half 
methylated) GATC sites in either the 5’ or 3’ 
  If the incision occurs at the 5’ then a 5’ 3’ exonuclease  activity (Exonuclease Vii) is needed     If the incision occurs at the 3’ the 3’5’ Exonuclease activity  (Exonuclease I) 

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School: Towson University
Department: Biology
Course: Genetics
Professor: Masters
Term: Spring 2016
Tags: bulmer, Genetics, biol309, towson, and University
Name: Exam III Study Guide
Description: This study guide is in depth and based on the study guide provided by Professor Bulmer as well as information from his Power Points.
Uploaded: 11/05/2016
10 Pages 52 Views 41 Unlocks
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