Transcript Molecular Genetics & Evolution

Molecular Genetics
gene: specific region of DNA that
determines the type of proteins to be
made
Nucleic Acids – serve as blueprints for the
construction of proteins
Two Types
1) DNA
(DeoxyriboNucleic
Acid)
2) RNA (RiboNucleic
Acid)
Nucleic Acids
nucleotides: monomers that combine to
form nucleic acids
Three Parts of a
Nucleotide
1)
• 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
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)
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
Two Main Stages of Protein Synthesis
1) Transcription:
2) Translation:
• 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 =
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 --
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
Transcription:
• For eukaryotes,
newly formed
RNA molecule
is modified to
produce
messenger RNA
(mRNA)
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)
Evolution
• Charles Darwin
• Evolution:
Evolution
• Charles Darwin
• Evolution:
Descent with Modification
•Look at the fossil record…
Macroevolution
* Major biological changes in species
(found in fossil record)
Speciation: origin of new species
Evolution
• Look at the fossil record…
• Compare common structures in
animals, e.g., forelimbs in human,
cat, whale and bat
• (homologous structures)
• *
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”
Natural Selection
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
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: