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Molecular Genetics
gene: specific region of DNA that
determines the type of proteins to be
made
* Therefore, DNA is a type of genetic
material, passed on parent to offspring
Nucleic Acids – serve as blueprints for the
construction of proteins
Two Types
1) DNA (DeoxyriboNucleic Acid)
2) RNA (RiboNucleic Acid)
nucleotides: monomers that combine to
form nucleic acids
Three Parts of a Nucleotide
1) Sugar
2) Phosphate Group
3) Nitrogen Base
• DNA has 4 nitrogen bases;
• Adenine
A
• Thymine
T
• Cytosine
C
• Guanine
G
• DNA has deoxyribose as its sugar
• RNA also has 4 nitrogen bases;
• Adenine
A
• Uracil
U
• Cytosine
C
• Guanine
G
• RNA has ribose as its sugar
• polynucleotide = nucleic acid polymer;
many nucleotides
What does DNA & RNA look like?
• Rosalind Franklin
- worked with X-ray photos of DNA
• James Watson & Francis Crick
- Nobel prize for deciphering structure
of DNA
RNA = single polynucleotide strand
DNA = double helix; 2 polynucleotides
wrap around each other (“spiral stairs”)
What does DNA & RNA look like?
In DNA, the 2 polynucleotides pair up &
bond (H-bond) at nitrogen bases:
Complementary Base Pairing in DNA
Adenine --- Thymine (A – T)
Cytosine --- Guanine (C – G)
• Long strands of DNA with A-T & C-G
base pairing is at the core of genetics,
• Therefore, in Interphase when
chromosomes are replicated, DNA is
also replicated
How is DNA replicated?
Template Hypothesis
• Two strands of parent molecule of DNA
separate
• Separated strands now serve as a
“template” for free nucleotides to attach;
remember nucleotides must match up
(A-T or C-G)
• Enzymes work to link nucleotides
together; new DNA is made
• New DNA molecule (daughter DNA)
identical to parent DNA
Template Hypothesis
DNA polymerase: primary enzyme
involved in assembling DNA molecules;
also checks for errors (wrong base
pairing)
DNA Replication
What is a ‘genotype’ or ‘phenotype’ in
molecular language?
• Genotype is gene (DNA) makeup of
organism
• DNA oversees protein synthesis
• DNA sends instructions in form of
RNA
• RNA programs cell to make certain
protein
Two Main Stages of Protein Synthesis
1) Transcription: DNA sending instructions
in the form of RNA; DNA transfers
genetic information to RNA
2) Translation: RNA transfers the
information into protein synthesis
• Phenotype is a physical trait of an
organism
• determined by specific proteins with
specific functions
e.g., some structural proteins comprise
hair, therefore, different ‘hair
proteins’ determine different hair
traits (color, curly, straight, coarse,
fine, etc…)
• codon: 3-base
code that are used
to produce amino
acids
• amino acids =
monomers =
building blocks for
proteins
Transcription: DNA to RNA
* Base pairing of RNA nucleotides using
DNA template (note pairings) – RNA
polymerase
Transcription:
• Nucleotide
sequence in
DNA starts
transcription
process
promoter -- RNA
polymerase
attaches here
Transcription:
• 2nd Phase =
RNA elongates
• RNA begins to
separate from
DNA template
• DNA strands
begin to reattach
Transcription:
• 3rd Phase – RNA
polymerase
reaches end of
gene
• = another unique
nucleotide
sequence in
DNA
(terminator)
Transcription:
• For eukaryotes,
newly formed
RNA molecule
is modified to
produce
messenger RNA
(mRNA)
• mRNA = extra
nucleotides on
ends (caps/tails)protection
mRNA
Transcription:
• Also remove
introns (noncoding
region)
• Resplice exons
(coding region =
genetic
information that is
ultimately
expressed as trait
• mRNA now leaves
nucleus
mRNA
Transfer RNA (tRNA)
• Serves as translator
between mRNA
and ribosomes
• In other words,
tRNA translates
nucleic acid
language (codons)
into protein
language (amino
acids)
• anticodon:
complement to
mRNA codon
tRNA
ribosomes
Translation
Summary of transcription & translation - 1
Summary of transcription & translation - 2
HIV AIDS
• HIV has 2 strands of RNA
• Reverses normal transcription process
(retrovirus)
• RNA used as template to make DNA
• New DNA made now has AIDS virus
genetic information & cells of infected
individual now make more AIDS virus
Evolution
• Charles Darwin
• Evolution:
1) Change in gene (allele) frequencies
in a population
Evolution
• Charles Darwin
• Evolution:
1) Change in gene (allele) frequencies
in a population
2) Modern organisms descended from
ancient organisms (shared traits)
Descent with Modification
•Look at the fossil record…
Macroevolution
* Major biological changes in species
(found in fossil record)
Speciation: origin of new species
Non-branching Evolution
vs.
Branching Evolution
Evolution
• Look at the fossil record…
• Compare common structures in
animals, e.g., forelimbs in human,
cat, whale and bat
• (homologous structures)
• * Common structures because of
common ancestor
Principles of Darwin’s Thinking
1) All organisms vary from one another &
some variations are heritable
2) All organisms have potential to produce
many young.
3) Limited resources influence number of
young that survive to reproduce
Natural Selection
• Primary theoretical mechanism of
evolution
• Deals with differential (unequal)
survival & reproduction
• “Survival of the Fittest”
• Those able to survive & reproduce,
will pass on their unique DNA to next
generation
Natural Selection
• Thus, evolution does not occur with an
individual, rather it does occur at
population level
Population Genetics
Microevoltion
gene pool: all of the genes in a
population at one time; includes all
alleles
• At population level, look for change in
allele frequencies over time.
• If allele frequencies change, gene pool is
changing & microevolution is occurring.
Population Genetics
Hardy-Weinberg Equilibrium
* Hypothetical, non-evolving population
* No change in allele frequencies
Assumptions:
1) No Natural Selection
2) No Mutation of genes
3) No Migration/No Gene Flow
4) LARGE Population
5) Random Mating
Population Genetics
How does Microevolution Occur in a
Population?
Five Possible Mechanisms
1) Natural Selection
2) Mutation of genes = DNA changes =
new alleles formed
3) Gene Flow
4) Population is small
5) Nonrandom Mating
Small Populations
genetic drift: certain alleles lost due to
chance events
Genetic Drift
Small Populations
bottleneck effect: some event
unselectively removes large part of
population; remaining individuals may
be genetically similar & subject to
genetic drift
Bottleneck Effect
Small Populations
founder effect: few individuals colonize a
new area; small, new population subject
to genetic drift