molecular genetics gene: specific region of dna that determines the type of proteins to be made *...
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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 Populationsgenetic drift: certain alleles lost due to
chance events
Genetic Drift
Small Populationsbottleneck effect: some event
unselectively removes large part of population; remaining individuals may be genetically similar & subject to genetic drift
Bottleneck Effect
Small Populationsfounder effect: few individuals colonize a
new area; small, new population subject to genetic drift