THE GENETIC THE GENETIC MATERIALMATERIAL

Chapter 6Chapter 6

Properties Of Genetic Properties Of Genetic MaterialMaterial

1.1. Repository of genetic informationRepository of genetic information

2.2. Info must be accessible, allow cell Info must be accessible, allow cell to respondto respond

3.3. Info must be in form transmissible Info must be in form transmissible to progenyto progeny

4.4. Physical and chemical stabilityPhysical and chemical stability

5.5. Potential for heritable changePotential for heritable change

Repository of Genetic Repository of Genetic InformationInformation

Types of information to be conveyedTypes of information to be conveyed Sequence of all RNAsSequence of all RNAs

Protein sequencesProtein sequences Signals Signals

Start and stop for RNA polStart and stop for RNA pol RNA processing sitesRNA processing sites Translation start and stop signalsTranslation start and stop signals

Replication start and stop sitesReplication start and stop sites Signals that affect topography of Signals that affect topography of

chromosomes (centromeres, telomeres, chromosomes (centromeres, telomeres, spacers, etc.) spacers, etc.)

Transmission of Information Transmission of Information

Faithful replication necessaryFaithful replication necessary RNA short-lived, DNA persistsRNA short-lived, DNA persists

Pyrimidine:purine pairing maintains Pyrimidine:purine pairing maintains consistent width, mismatches easily consistent width, mismatches easily detecteddetected

Complementary copies allow quick Complementary copies allow quick recognition of mistakesrecognition of mistakes

Physical and Chemical Physical and Chemical StabilityStability

Double–stranded structure provides Double–stranded structure provides some protection from chemical attacksome protection from chemical attackHydrophobic core Hydrophobic core bases less subject to hydrolysisbases less subject to hydrolysis

Groups involved in base pairing are Groups involved in base pairing are protected by a hydrophobic barrier. protected by a hydrophobic barrier.

Physical and Chemical Physical and Chemical StabilityStability

Bases generally stableBases generally stable One major exception: CytosineOne major exception: Cytosine EX Deamination of Cytosine EX Deamination of Cytosine

RULE: If you see uracil in DNA, cut it out

H-O-H

NH3

Limited Ability to Change-Limited Ability to Change-MutationsMutations

Mutation—the only source of new Mutation—the only source of new allelesalleles

A change in the base sequence of DNAA change in the base sequence of DNA Ability of a species to adapt lies in the Ability of a species to adapt lies in the

diversity of its allelesdiversity of its alleles though stability necessary, must though stability necessary, must

have some limited ability to generate have some limited ability to generate new alleles while preserving parent new alleles while preserving parent lineline

MutagenesisMutagenesis

Chemical alteration of base that Chemical alteration of base that gives it new H-bonding propertiesgives it new H-bonding properties different base incorporated in different base incorporated in

complementary strandcomplementary strand Replication errorsReplication errors

MisincorporationMisincorporation Extra baseExtra base Deletion Deletion

Mutations Mutations

Transition----Purine replaced by Transition----Purine replaced by purine, pyrimidine by pyrimidinepurine, pyrimidine by pyrimidine

Transversion---Pyr replaced with pur, Transversion---Pyr replaced with pur, pur replaced with pyr. pur replaced with pyr.

Double stranded nature of DNA—a Double stranded nature of DNA—a safeguard in case the mutation safeguard in case the mutation doesn’t workdoesn’t work

RNA as Genetic Material RNA as Genetic Material

DNA not only genetic materialDNA not only genetic material RNA sometimes used by virusesRNA sometimes used by viruses ConsiderationsConsiderations

Viruses lack active cytoplasmViruses lack active cytoplasm Produce huge # of progeny Produce huge # of progeny

Retrovirus StructureRetrovirus Structure

Deamination of Cytosine and Deamination of Cytosine and 5-methylcytosine5-methylcytosine

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