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TOWSON / Biology / BIOL 309 / What do silent mutations mean?

What do silent mutations mean?

What do silent mutations mean?

Description

School: Towson University
Department: Biology
Course: Genetics
Professor: Masters
Term: Spring 2016
Tags: Genetics, bulmer, and towson
Cost: 50
Name: Genetics Exam II study guide
Description: This is a detailed version of the study guide he provide as well as an added bundle of all the notes since the last exam.
Uploaded: 10/14/2016
23 Pages 182 Views 5 Unlocks
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Genetics October 12, 2016; DISCLAIMER NOTES AND IMAGES MAY BE DIRECTLY FROM LECTURE  PRESENTATION


What do silent mutations mean?



∙ Mutations can be lethal in a restrictive condition but viable in a permissive condition.  ∙ Auxotrophs: Are unable to synthesize an essential metabolite, if the metabolite is present its  permissive if it is absent then it is lethal

∙ Transitions are a pyrimidine (one ring nucleotide) to another pyrimidine or a purine (two ring  nucleotide) to a purine. C???? T (Pyrimidine) and A????G Purine

∙ Transversions are a purine to a pyrimidine or vice versa  

∙ Transitions are more common than transversions  


What does germ line denote in the context of hereditability of mutation?



∙ Tautomeric shifts: Are reversible shifts in proton position in a molecule, causing them to shift  between keto and enol fomrs or between amino and imino forms  

o A G enol form pairs with T  

o A c imino form pairs with A

o Can cause mispairing  


What causes pyrimidine dimers?



Don't forget about the age old question of Why do people use twitter?

∙ Chemical mutagens  

o Mutagenic only to replicating DNA

o Mutagenic to both replicating and non-replicating DNA

o Mutagens that cause insertions/deletions (indels) during replication We also discuss several other topics like Is anxiety adaptive?

▪ Ex. Proflavin  

▪ Testing using the ames test We also discuss several other topics like What are the general rules for accento?

o UV Radiation also causes mutations

▪ Ionizing radiation causes changes in chromosome structure  

∙ This breaks chromosomes and can cause deletions, duplications,  

inversions, and translocations  

∙ These types of mutations usually display two-kit kinetics (both alleles  

need to be damaged to actually affect the phenotype)

∙ Can form thymine dimers which block DNA replication activating error

prone DNA repair mechanisms

∙ Dark skin protects against UV radiation

o Prevents the destruction of folic acid (needed for DNA  

synthesis)

∙ UV light is important  Don't forget about the age old question of What we perceive in the environment, and that our perceptions are meant to drive our actions?

o Needed to produce vitamin D  

∙ Albanism

o Albino individuals are sensitive to UV radiation

∙ Free radicals

o Reactive oxygen molecules that can damage DNA  

∙ Superoxides can damage DNA

o This is a byproduct of oxidative phosphorylation (the metabolic pathway that generates  ATP) We also discuss several other topics like Can gender dysphoria go away?

o Superoxide dismutase (SOD) catalyzes superoxide into oxygen and hydrogen peroxide

October 10, 2016

Genetics DISCLAIMER NOTES AND IMAGES MAY BE DIRECTLY FROM THE POWERPOINT  Point mutations

∙ A nucleotide change from one base to another  

∙ Usually happens with mistakes in replication

o Incorrected base complementation

o More likely to be transitions which changes bases to the same sizes (purine  switched with purine)  

∙ Most are deleterious (harmful)

∙ If they occur in the third codon position they are often silent  

Silent Mutations

∙ Nonsynonymous substitutions

o Random mutations that result in a harmful amino acid change  

∙ Synonymous substitutions

o Nucleotide changes that are harmless  

∙ Can be compared in two genes that have duplicated and diverged from an ancestral gene  o Expect many more differences that are generated by mutation at synonymous sites  than at nonsynonymous sites. We also discuss several other topics like What are the main characteristics of a perfectly competitive market?

Heritability of Mutation  

∙ A mutation is a change in genetic information

∙ Germ line: Can be passed on

∙ Somatic Line: Cannot be passed on

∙ Can be reversed

o Back mutation: Second mutation at the same site  

o Suppressor mutation: Second mutation that compensates for the first mutation  ∙ Phenotypes associated with dominant deleterious mutations are less common than  recessive deleterious mutations  

∙ Mutations that block metabolic pathways are usually recessive  

o Ex. Tay-Sachs

October 5 2016 DISCLAIMER NOTES AND IMAGES MAY BE DIRECTLY FROM IN CLASS PRESENTATION  OR TEXTBOOK

∙ Intron: A DNA region within a gene that is not translated into protein  

∙ Exon: The region of the gene that is translated  

∙ Introns ???? pre-mRNA

∙ Introns are removed through splicing during processing  

∙ Spliceosomes cut out the intron regions  

and join the exon regions

∙ Video shown in class: http://www.youtube.com/watch?v=FVuAwBGw_pQ 

∙ Significance of Introns  

o Crossing over is ore likely to occur within a gene if it spans a greater genetic distance  o Alternate splicing of exons where one gene makes several different gene products  ▪ Ex. DSCAM (Down syndrome cell adhesion molecule)  

∙ This gene is found in individuals with down syndrome and it plays a role  

in forming neuron conncetions

o Relic of gene evolution  

o Introns may have old code or sections that were once translated  

o Introns may have functional significance  

o Introns may incode miRNAs(microRNAs) that regulate gene expression

∙ Self splicing  

o Intron acts as a ribozyme  

o No proteins are involved  

o Evolutionary relic of RNA world  

▪ RNA stored information like DNA and also acted as enzymes that supported  cellular or pre-cellular life  

▪ Theorized that this world evolved into our world  

∙ mRNA ???? Protein  

o Messengerr RNA provides the code for linking amino acids into a protein  

o Each of the 20 amino acids make up proteins through codons (3 set of nucleotides) o

Genetics October 14, 2016 DISCLAIMER NOTES AND IMAGES MAY BE DIRECTLY FROM LECTURE  PRESENTATION

Xerodermatic pigmentosum  

∙ Most common form due to mutation in the enzyme (endonuclease) that fixes DNA damage  o This fails to repair the damage

o Autosomal recessive pattern of inheritance  

o Mutated repair enzymes cannot fix or remove dimers  

UV Radiation causes pyrimidine dimers

∙ This distorts the double helix and blocks transcription and replication  

DNA repair

∙ Light  

dependant repair  

also known as  

photoreactivation  

through the use of  

photolyase  

∙ Excision Repair  

uses glucosylases to  

repair specific types of  

damage

∙ Video shown in class http://www.youtube.com/watch?v=HYS6EKnQcv0&feature=related ∙ Post replication Mismatch Repair in E. Coli  

o The A in a GATC sequence is methylated shortly after DNA replication o The newly replicated DNA, the Parental strand is methylated but the new strand is  not this allows the mismatch repair system to distinguish the new strand from the  old strand  

o The mismatched nucleotide is excised  

from the new strand and replaced with the  

correct nucleotide, using the methylated  

parental strand as a template.

o Video shown in class

https://www.youtube.com/watch?v=AgdMnMMbc8Q 

∙ One mutant gene = One metabolic Block  

o Garrod studied inherited disorders in human metabolic pathways, which are defects  in normal metabolism and are usually homozygous recessive  

∙ Steps in metabolic pathway  

o Determined with auxotrophic mutants  

o These mutants have a nonfunctional enzyme in the pathway  

o An example is the beadle/Tatum experiment on slide 16 - 20

▪ Used on bread mold (Neurospora Crassa)  

▪ Spores irradiated with X-rays to induce mutations in the enzymes that make  intermediate metabolites in the metabolic pathway

▪ They were grown on a minimal medium supplemented with different  metabolites – they grew when the missing metabolite was provided

DISCLAIMER: NOTES AND IMAGES MAY OR MAY NOT BE DIRECTLY FROM THE IN CLASS  PRESENTATION OR TEXTBOOK.

DNA Polymerization

DNA synthesis has an absolute requirement for  

∙ A. 3’ OH  

∙ A template  

In Vitro DNA synthesis  

∙ Kornberg (1957)

o DNA polymerase I from E. coli

o dNTPs, (dATP), dTTP, dGTP, dCTP

o Mg2+

o DNA (template and primer)

∙ DNA polymerase I

o 5’ ???? 3’ polymerase activity  

o 5’ ???? 3’ Exonuclease activity  

o 3’ ???? 5’ exonuclease activity  

∙ Exonuclease activity is important for repair

∙ Slide 4 goes with this image  

∙ RNA Primase: Initiates new strand synthesis  

∙ DNA Polymerase: Adds nucleotides too free 3’ OH group in the 5’???? 3’ Direction ∙ DNA ligase: Covalently closes nick in DNA between free OH and phosphate groups  ∙ Helicase: Unwinds DNA at the replication fork

∙ Single stranded binding proteins: Stabilizes single stranded DNA at the replication fork ∙ Topoisomerases: Releases mechanical stress of unwinding

∙ DNA polymerase III: Adds deoxyribonucleotides to RNA primer at initiation of replication  fork  

o Elongation of DNA chain 5’ ???? 3’  

o 3’ ???? 5’ exonuclease activity proofreading  

∙ Limitations as DNA polymerase I

o Only adds nucleotides to the 3’ – OH end, and is unable to initiate new chain o Leading and lagging synthesis (Okazaki fragments)

Video shown in lecture https://www.youtube.com/watch?v=dKubyIRiN84 ∙ DNA polymerase III – Holoenzyme is the primary complex involved I prokaryotic DNA  replication  

∙ DNA polymerase II (IV and V) repair enzyme primarily synthesized during stationary phase of  bacterial growth

∙ DNA polymerase I removes RNA primers with 5’ ???? 3’ exonuclease and replaces DNA with 5’  ???? 3’ polymerase activity  

Polymerases in mammals  

∙ Polymeraseα --starts up polymerization. It has RNA primase activity.

∙ Polymeraseβ--Implicated in repairing DNA, in base excision repair and gap-filling synthesis. ∙ Polymerase δ--Thought to be the main polymerase involved in lagging strand synthesis. ∙ Polymerase ε--Thought to be the main polymerase involved in leading strand synthesis. ∙ Polymerase γ --mitochondrial DNA replication

Telomerase -Replication of Chromosome Termini

∙ Telomerase makes telomeres: Which are nucleotide repeats at the end of chromosomes  ∙ DNA replication results in shortening of chromosomes  

∙ With each round replication chromosomes get shorter and may cause apoptosis (Cell death)

∙ Video shown in class http://www.youtube.com/watch?v=AJNoTmWsE0s ∙ Telomerase adds tandem repeats at chromosome termini in germline cells  ∙ Telomerase activity often lacking in somatic cells and the cells get shorter after each round  of replication

∙ Progeria disease (Werner Syndrome): The aging disease where telomeres degrade rapidly  ∙ Hayflick Limit

o Normal human fetal cells in cell culture divide between 40 or 60 times  o Each mitosis shortens the telomeres on DNA of the Cell. Telomere shorting in  humans eventually blocks cell division and correlates with aging  

o Cancers cells produce telomerase and do not shorten, Book: The immortal life of  Henrietta Lacks by Rebecca Skloot  

o Hayflick limit may prevent normal cells from becoming cancerous

∙ ^ PCR or Polymerase chain reaction  

∙ Taq polymerase: One of the most important enzymes in molecular biology  ∙ Thermostable DNA polymerase named after the thermophilic bacterium Thermus aquaticus  ∙ Video shown in Lecture  

http://www.youtube.com/watch?v=n0mDBQcquGA&feature=related 

∙ What do you need to complete a PCR reaction

o DNA polymerase

o Mg2+ 

o NTP (ATP, CTP, GTP, TTP)

o Primer

o Template  

∙ Why can inhibiting telomerase combat cancer

o The production of telomerase prevents cell death, most cells have a hayflick limit  and it prevents them from being eternal

∙ Central dogma of Molecular Biology

o DNA ????1 RNA ????2 Protein = Gene Expression

▪1Transcription

▪2Translation  

o Collinearity: DNA Base sequence determines protein amino acid sequence  o DNA ????1 mRNA ????2 Protein  

▪ Information flow goes in one direction, DNA to protein  

▪ Evolutionary implication

∙ Phenotype cannot influence genotype  

∙ Acquired phenotypic characteristics cannot be inherited  

(Lamarckian)

o Transcription and Translation occurs in all cellular organisms  

▪ Prokaryotes: Transcription and translation occur simultaneously  

▪ Eukaryote cells: Transcription in the nucleus (Includes RNA Processing)  Translation occurs in the cytoplasm  

o Uracil  

▪ Base pairs with adenine and replaces thymine during DNA transcription into  RNA  

▪ Methylation of uracil produces thymine  

▪ Uracil believed to be the original base when life first evolved. Thymine  replaced uracil as one of the bases in the heritable code because it is more  stable and allows for more efficient DNA replication  

∙ RNA stability  

▪ RNA polymerase 5” ???? 3’ chain elongation does not need a primer for  initiation  

▪ Only one strand of DNA required for template of RNA synthesis could be  either strand  

▪ RNA polymerase starts at a specific sequence that promotes polymerization Promoter  

▪ Nontemplate strand = Sense strand = Coding strand  

o Four stages of Transcription  

▪ Promoter recognition  

∙ Specific DNA sequences for RNA polymerase binding which are

conserved (Consensus sequence)  

▪ Chain initiation  

∙ RNA polymerase unzips double helix  

∙ Bind/Unwind then first few phosphodiester bonds made

∙ E. coli RNA Polymerase has a complex of proteins, α2β β’ form  complex and then σ factor added for initiation- sigma factor  

released after 8-9 bases transcribed.

∙ Eukaryotic RNA polymerase must have the TATA binding protein  and several other transcription factors attached at the promoter  region to initiate transcription

▪ Chain elongation

∙ RNA Polymerase moves down DNA with transient transcription  bubble  

∙ d

▪ Chain termination

∙ Prokaryotes  

o Rho independent: G + C rich to form a hairpin structure  

followed by A+ U rich region  

▪ Self terminating  

o Rho dependednt: 50- 90 bases long (Rich in C bases and low  in G bases) Rho releases the RNA transcript when  

polymerase encounters sequence  

∙ Eukaryotes  

o 1000 -2000 bases downstream from the last nucleotide that  will be part of the protein coding message

o Actual signals for termination unknown  

o mRNA cleaved 11-30 bases down from conserved sequence  AAUAAA

∙ Video shown in class  

http://www.youtube.com/watch?v=WsofH466lqk 

▪ mRNA processing

∙ Early in the Transciption process 7-methyl guanosine cap is added to  the 5’ End of pre-mRNA

∙ Important in translation initiation

∙ Potects mRNA from 5’ degradation

∙ After transcription termination a poly-A tail (200 adenine  nucleotides long) is added to the 3’ end of the mRNA protects  against 3’ Degradation of the mRNA

∙ Video shown in class  

http://www.youtube.com/watch?v=YjWuVrzvZYA&feature=related

October 7, 2016 DISCLAIMER NOTES AND IMAGES MAY BE DIRECTLY FROM LECTURE PRESENTATION  OR TEXTBOOK

∙ Polypeptides  

o tRNA’s and mRNA bring amino acids in close proximity  

o Enzyme activity in ribosomes links amino acids with a peptide bond forming a  

polypeptide

o Video shown in class  

http://www.youtube.com/watch?v=D3fOXt4MrOM&feature=related 

o Molecular interactions determine protein structure

o Levels of protein structure, review from Biol 202  

∙ Macromolecules of translation  

o Polypeptides and RNA molecules of the ribosme  

o Amino acid activating Enzymes  

o tRNA Molecules  

o Soluble proteins involved in polypeptide chain initiation(Small ribosome subunit and  first tRNA come together, then large ribosome subunit joins), elongation (Polypeptide  chain is synthesized), and  

termination (Completed polypeptide  

released)

o rRNA synthesis occurs in the  

nucleolus of eukaryotes

o Further information slides 12-

15 but this video from class  

summarizes the entire process  

http://www.youtube.com/watch?v=D3fOXt4MrOM&feature=related 

∙ Codons or groups of 3 nucleotides = an amino acid

Beta sheet

∙ In a test tube you can have 3 reading frames in life it depends on the location of the start codon

Genetics Exam II Study Guide: DISCLAIMER SOME NOTES AND IMAGES MAY BE  DIRECTLY FROM LECTURE PRESENTATION OR TEXTBOOK.  

Chapter 7:  

∙ Linkage: When two traits are located on the same structure or portion of the chromosome ∙ Genetic Map: This is the map that shows the location of the various alleles ∙ Be able to do a linkage map from recombination frequencies: To do this you would be  

given a table with the offspring of a cross. In this table you would identify the parent  genotype by located the allele combination that has the highest number of individuals. Anything without this parent type is a recombinant. To find the position of the genetic  map you add up all the recombinants for those two alleles, then divide by the total  number

∙ Ex. Question 7.23 In the textbook found on page 161

Chapter 9: DNA Structure

∙ Evidence of DNA vs. Protein

o It was believed that protein stored the genetic material in the early 1900 because it  has a greater variability  

o DNA’s composition was and is uniform in cells and more stable than RNA and  proteins  

o Griffith/Avery: This experiment used a form of bacteria called Streptococcus  pneumoniae, these bacteria have two forms either IIIS virulent which has a  polysaccharide capsule or IIR nonvirulent which does not.  

McCarty and MacLeod

∙ The first experiment shows that type IIR can pick up the “transforming agent” for a  polysaccharide coat from the heat killed IIIS bacteria. This indicates that the

“transforming agent” is not protein since it would likely be denatured at that high heat.  The second experiment proves what the first experiment indicated.  

∙ Hershey & Chase: The DNA of bacteriophage was radiolabeled with 32P and the protein  was radiolabeled with 35S. 32P radioactivity was found inside the cells but not 35S  radioactivity. https://www.youtube.com/watch?v=5RRa-1Ywyjw 

∙ Gel electrophoresis: In gel electrophoresis DNA is fragmented and is put in a medium  and a charge is applied. This charge pushes the DNA fragments from the wells in the top  to the bottom of the solution. Smaller fragments move further down the solution and  larger ones stay closer to the top. This can be used to determine heredity, size of DNA,  and more

Chapter 10: DNA Replication

∙ Semiconservative replication—experiments of Meselsohn and Stahl

∙ Origins of Replication

∙ Eukaryotic vs. Prokaryotic (Know different polymerase) properties

∙ Polymerase characteristics

o Eukaryotic

▪ DNA polymerase I

∙ 5’→3’ polymerase activity

∙ 5’→3’ exonuclease activity

∙ 3’→5’ exonuclease activity

∙ removes RNA primers with 5’→3’ exonuclease and replaces with  

DNA with 5’→3’ polymerase activity.

▪ DNA polymerase II (IV and V): Repair enzyme primarily synthesized  during stationary phase of bacterial growth. Lacks 5’→3’ exonuclease  

activity.

▪ DNA polymerase III

∙ Adds deoxyribonucleotides to RNA primer at initiation of  

replication fork.

∙ Elongation of DNA chain 5’ ???? 3’

∙ 3’ ???? 5’ exonuclease activity proofreading- double checks dNTP  

that has been put in place.

∙ Only adds nucleotides to a 3’-OH end so unable to initiate new  

chain (requires RNA primer).

∙ Leading and lagging strand synthesis—Okazaki fragments on the  

lagging strand.

∙ All enzymes/proteins involved in process

o Topoisomerase: releases mechanical stress of unwinding.

o Helicase: unwinds DNA at the replication fork.

o Single-stranded binding proteins: Stabilizes single stranded DNA at the  replication fork.

o DNA polymerase: Adds nucleotides too free 3’OH group (5’???? 3’ direction  ONLY)

o RNA primase (primosome): Initiates new strand synthesis with 10 bp RNA  primer.

o Ligase: covalently closes nick in DNA between free OH and phosphate group. o

∙ Leading vs. Lagging Strand—Okazaki fragments

∙ Proofreading function of DNA polymerase

∙ Telomerase/telomeres: Makes telomeres( nucleotide repeats at chromosome ends). Each  round of replication results in a shortening of the chromosome. This would occur until  gene interruption causes cell death however, the presence of telomers prevents this  shortening. http://www.youtube.com/watch?v=AJNoTmWsE0s 

∙ https://www.youtube.com/watch?v=dKubyIRiN84 

∙ PCR

o http://www.youtube.com/watch?v=n0mDBQcquGA&feature=related o http://www.youtube.com/watch?v=eEcy9k_KsDI 

Chapter 11: Transcription and RNA processing

∙ Central Dogma of Molecular Biology

∙ Information flow and the inheritance of acquired characteristics (Lamarck) ∙ Initiation, elongation and termination stages of transcription

∙ Identifying the promoter (prokaryotes)

∙ Identifying the template strand

∙ Eukaryotic vs. Prokaryotic properties

∙ Post-transcriptional RNA processing: 5’cap, 3’ tail, remove introns and splice exons ∙ Possible role of introns (exon shuffling, increased recombination, alternate splicing) ∙ RNA self splicing/RNA world

∙ Reverse transcriptase/cDNA/recombinant DNA

Chapter 12: Translation

∙ Translation: In prokaryotic cells transcription and translation occur simultaneously. In  eukaryotic cells transcription occurs in the nucleus and translation in the cytoplasm ∙ Initiation: RNA polymerase unzips double helix, bind/unwind then first few  phosphodiester bonds made. For Eukaryotic transcription to occur there must first be the  TATA region.  

∙ Elongation: RNA polymerase moves down DNA with transient transcription bubble  ∙ Termination:

o In prokaryotes.  

▪ Rho independent: G + C rich to form a hairpin structure followed by A +  U rich region—self terminating.

▪ Rho dependent: 50-90 bases long (rich in C bases and low in G bases).  Rho releases the RNA transcript when polymerase encounters sequence.

o In eukaryotes  

▪ 1000-2000 bases downstream from the last nucleotide that will be part of  the protein coding message

▪ -actual signals for termination not fully known (GU rich).

▪ mRNA cleaved 11-30 bases down from a conserved sequence AAUAAA.

∙ Stages of translation: mRNA provides the code for linking together amino acids in a  protein. For the codons to pair with an amino acid tRNA is required.  

o tRNA: Attaches the amino acids and aligns them for polymerization o http://www.youtube.com/watch?v=D3fOXt4MrOM&feature=related o Stage 1: Initiation: mRNA and tRNA come together and create the ribosome o Stage 2: Elongation: The polypeptide chain is synthesized

o Stage 3: Termination: Completed polypeptide is released.  

∙ Shine Dalgarno sequence: The AGGAGG sequence in mRNA that base complements  with the matching sequence in rRNA

∙ Cap binding protein: (Eukaryotic) this binds to the 7-methyl guanosine cap and aligns the  mRNA with the subunit of the ribosome. Waits for the first AUG before beginning. ∙ http://www.youtube.com/watch?v=D3fOXt4MrOM&feature=related ∙ Genetic code:  

o Degenerate: Is repetitive

o Universal: Is the same in all organisms, prokaryotic and eukaryotic o Codon: A nucleotide triplet that codes for an amino acid

o Start codon: Met or AUG

o Stop codons: UAA, UAG, and UGA

o Anticodons/wobble hypothesis:

o Experimental evidence for the codon composition of three nucleotides ▪ Deletions and insertions alter the reading frame and change the amino acid  sequence  

o Experiments used to determine the genetic code (in vitro translation) ▪ They used only one nucleotide in a repetitive sequence to determine what  amino acid was created. UUUUUU created a string of Phenylalanine

meaning UUU is phenylalanine

∙ Reading frameshifts: Causing the way the sequence is read to be changed for example  UCU UAU CAG could be shifted to read CUU AUC  

∙ Mutation:  

o point mutations: A nucleotide change from one base to another

o missense mutations: Changes a codon so it specifies for a different amino acid.  o nonsense mutations: A Condon has been altered to a stop codon

o silent mutations (synonymous): Random mutations that do not change the amino  acid

o amino acid changing mutations (nonsynonymous): Random mutations that  changes the amino acid

o deleterious mutation: Mutations that are harmful  

o adaptive mutation: Advantageous mutations

o transitions: The substitution of one pyrimidine or purine base with another of the  same type

o Transversion: The substitution of a pyrimidine with a purine or vice versa.

Genetics October 12, 2016; DISCLAIMER NOTES AND IMAGES MAY BE DIRECTLY FROM LECTURE  PRESENTATION

∙ Mutations can be lethal in a restrictive condition but viable in a permissive condition.  ∙ Auxotrophs: Are unable to synthesize an essential metabolite, if the metabolite is present its  permissive if it is absent then it is lethal

∙ Transitions are a pyrimidine (one ring nucleotide) to another pyrimidine or a purine (two ring  nucleotide) to a purine. C???? T (Pyrimidine) and A????G Purine

∙ Transversions are a purine to a pyrimidine or vice versa  

∙ Transitions are more common than transversions  

∙ Tautomeric shifts: Are reversible shifts in proton position in a molecule, causing them to shift  between keto and enol fomrs or between amino and imino forms  

o A G enol form pairs with T  

o A c imino form pairs with A

o Can cause mispairing  

∙ Chemical mutagens  

o Mutagenic only to replicating DNA

o Mutagenic to both replicating and non-replicating DNA

o Mutagens that cause insertions/deletions (indels) during replication

▪ Ex. Proflavin  

▪ Testing using the ames test

o UV Radiation also causes mutations

▪ Ionizing radiation causes changes in chromosome structure  

∙ This breaks chromosomes and can cause deletions, duplications,  

inversions, and translocations  

∙ These types of mutations usually display two-kit kinetics (both alleles  

need to be damaged to actually affect the phenotype)

∙ Can form thymine dimers which block DNA replication activating error

prone DNA repair mechanisms

∙ Dark skin protects against UV radiation

o Prevents the destruction of folic acid (needed for DNA  

synthesis)

∙ UV light is important  

o Needed to produce vitamin D  

∙ Albanism

o Albino individuals are sensitive to UV radiation

∙ Free radicals

o Reactive oxygen molecules that can damage DNA  

∙ Superoxides can damage DNA

o This is a byproduct of oxidative phosphorylation (the metabolic pathway that generates  ATP)

o Superoxide dismutase (SOD) catalyzes superoxide into oxygen and hydrogen peroxide

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