THE GENETIC
MATERIAL
Chapter 6
Properties Of Genetic Material
1.
2.
3.
4.
5.
Repository of genetic information
Info must be accessible, allow cell to
respond
Info must be in form transmissible to
progeny
Physical and chemical stability
Potential for heritable change
Repository of Genetic Information

Types of information to be conveyed

Sequence of all RNAs
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Protein sequences
Signals
Start and stop for RNA pol
 RNA processing sites
 Translation start and stop signals
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Replication start and stop sites
Signals that affect topography of
chromosomes (centromeres, telomeres,
spacers, etc.)
Transmission of Information
Faithful replication necessary
 RNA short-lived, DNA persists
Pyrimidine:purine pairing maintains
consistent width, mismatches easily
detected
 Complementary copies allow quick
recognition of mistakes

Physical and Chemical Stability
Double–stranded
structure provides some
protection from chemical attack
Hydrophobic core
bases less subject to hydrolysis
Groups involved in base pairing are protected by a
hydrophobic barrier.
Physical and Chemical Stability



Bases generally stable
One major exception: Cytosine
EX Deamination of Cytosine
H-O-H
NH3
RULE: If you see uracil in DNA, cut it out
Limited Ability to Change-Mutations
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Mutation—the only source of new alleles
A change in the base sequence of DNA
Ability of a species to adapt lies in the
diversity of its alleles
though stability necessary, must have
some limited ability to generate new
alleles while preserving parent line
Mutagenesis

Chemical alteration of base that gives it
new H-bonding properties

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different base incorporated in
complementary strand
Replication errors

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Misincorporation
Extra base
Deletion
Mutations
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Transition----Purine replaced by purine,
pyrimidine by pyrimidine
Transversion---Pyr replaced with pur, pur
replaced with pyr.
Double stranded nature of DNA—a
safeguard in case the mutation doesn’t
work
RNA as Genetic Material
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DNA not only genetic material
RNA sometimes used by viruses
Considerations
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Viruses lack active cytoplasm
Produce huge # of progeny
Retrovirus Structure
Deamination of Cytosine and 5methylcytosine
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