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