Molecular Genetics Lecture

Molecular Genetics Paul Rindler M.S.

Topics   

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Discovery of DNA DNA structure and replication Gene expression and protein synthesis Biotechnology toolkit Viruses

Discovery of DNA 

1800’s 

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Johann Miescher isolated a phosphorous containing acidic compound from the nucleus

1928 

Frederick Griffith demonstrates the existence of a chemical in bacteria that caries genetic information

Discovery of DNA 

1930’s 

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Various experiments identify chromosomes as the source of genetic information Chromosomes are composed of mainly proteins and deoxyribonucleic acid (DNA) The DNA molecule was considered too simple to be important so proteins were thought to carry the genetic information

Discovery of DNA 

1944 

Oswald Avery showed that degradation of DNA and not protein resulted in loss of genetic information

Discovery of DNA 

Rosalind Franklin (1951) 

Generated X-ray crystallography data suggesting a double helix with phosphates on the outside

Discovery of DNA 

Watson & Crick (1953)  

Used Franklin’s data to develop a model for DNA Received a Nobel Prize in 1962

Topics   

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Discovery of DNA DNA structure and replication Gene expression and protein synthesis Biotechnology toolkit Viruses

DNA Structure

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DNA composition   

Phosphate Sugar Nucleic acids (bases)

DNA Structure 

DNA Backbone 

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Alternating phosphates and sugars Bases are attached to sugars

DNA Structure 

DNA is composed of 4 different bases 

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Chargraff (1951) data suggested A-T and G-C base pairing Pairs are bonded by hydrogen bonds

DNA Replication 

Must be completed prior to cell division

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Helicase enzymes open the DNA

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Polymerase enzymes generate a new DNA strand on each old template

Topics   

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Discovery of DNA DNA structure and replication Gene expression and protein synthesis Biotechnology toolkit Viruses

Gene Expression    

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DNA codes for genes Genes are expressed as proteins Gene expression is regulated The genome of every cell in your body is identical Cell type is determined by the genes the cells express

Protein Synthesis 

DNA → RNA → Protein  

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DNA acts as a template for RNA synthesis 

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Transcription Translation

RNA has uracil (U) rather than thymine (T)

Protein synthesis requires 3 types of RNA 

Messenger (mRNA)

Protein Synthesis 

Transcription 

mRNA is transcribed from DNA

Protein Synthesis 

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mRNA is read by the synthesis machinery 3 nucleotides make up a codon which codes for 1 of 20 amino acids

Protein Synthesis 

Transfer (tRNA) 

Translates mRNA sequence into amino acids

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80 nucleotide RNA molecule

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The anticodon is specific to 1 of 20 amino acids

Protein Synthesis 

Ribosomal (rRNA)   

2/3 RNA & 1/3 protein 2 Subunits Coordinates protein synthesis

Protein Synthesis 

The Genetic Code 

64 possible codons

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1 start codon (AUG)

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3 stop codons (UAA, UAG, UGA)

Protein Synthesis

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Translation   

Initiation Elongation Terminatio n

Protein Synthesis

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Summary     

Transcription Translation Initiation Elongation Termination

Protein Synthesis 

Mutations 

Base substitution Conservative  Nonconservative 

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Insertion/deletio n 

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Frameshift

Jumping genes 

Mobile elements

Topics   

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Discovery of DNA DNA structure and replication Gene expression and protein synthesis Biotechnology toolkit Viruses

Biotechnology Toolkit 

Isolation of genes for study 

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Recombinant DNA

Gene Therapy  

Stem cell research Cloning

Recombinant DNA 

Isolation of genes for study    

Find a gene of interest Determine gene sequence Express the gene product Functional analysis

Recombinant DNA 

The Tools 

Plasmids Small circular DNA molecules  House sequences of interest 

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Bacteria Uptake and replicate plasmids  Express the gene of interest  Good bang for your buck 

Recombinant DNA 

The Method      

Insert gene of interest into a plasmid Bacterial transformation (often E.coli) Plasmid replication Gene expression Protein purification Protein analysis

Recombinant DNA 

Applications  

Determine gene function Synthesize useful proteins Insulin  Pest resistance 

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DNA mapping Gene Therapy

Gene Therapy 

Stem cell research 

Embryonic stem cells Readily available from fertility banks  Limited government resources  Ethical concerns  Compatibility problems 

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Adult stem cells Uses your own stem cells  Insufficient technology 

Gene Therapy 

Cloning 

Therapeutic Recreate specific body parts  Too technically challenging 

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Reproductive Exact replica of an entire organism  First achieved in 1997 with sheep  Human success in 2004 but data is questionable 

Gene Therapy 

Dolly (1997-2003)  

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Scotland 1997 Nucleus removed from unfertilized egg Nucleus from a sheep skin cell inserted New egg implanted into surrogate mother Died of premature old age

Topics   

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Discovery of DNA DNA structure and replication Gene expression and protein synthesis Biotechnology toolkit Viruses

Viruses   

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Very simple Nonliving organism Uses host to replicate 2 life cycles  

Lytic Lysogenic

Topics   

 

Discovery of DNA DNA structure and replication Gene expression and protein synthesis Biotechnology toolkit Viruses