4.21 Prokaryotic Genetics

By Lance Goodridge and Devin Callanan

Defining Prokaryotes

•Unicellular organisms

•Lacks cell nucleus

•Lacks mitochondria + chloroplasts

Defining Prokaryotes 2

•Very small

•Live near water

•Extremophiles

Evolution of Prokaryotes

•Organized into two kingdoms

•Very Old

•Controversy

Escherichia Coli•The ‘guinea pig’ bacteria

•Good for studying

Genomes•Prokaryotes have a genome

•DNA = tight loop (shown right)

Plasmids•Also have Plasmids

•Additional genes

•Can be integrated into bacteria’s DNA (shown right)

OriC•Starts replication process

•“Unzips” the DNA

•Many AT bases

Helicase

•2 enzymes for DNA replication

•Breaks H-bonds

•“Supercoils” DNA

•Note: The helix of the DNA was omitted for clarity =>

Gyrase•Releases tension

•Rejoins strands

•Rejoins bonds

DNA Polymerase I•Arthur Kornberg – 1957

•Key to DNA polymerization

•Two types

Polymerase and Exonuclease

•5’ to 3’ polymerase

•5’ to 3’ exonuclease

•3’ to 5’ exonuclease

Other DNA Polymerases

•Two other polymerases

•Pol II

•Pol III

Klenow Fragment

•5’ to 3’ exonuclease removed

•Labels DNA

•Nick translation

3 Ways Bacteria Acquire New Genes

•Mainly reproduce asexually (binary fission shown => NOT an example of gaining new genes)

•Three ways to acquire new genes

The F factor (Detailed)

• F+: Bacteria w/ F plasmid + pili

• F-: Does not have F factor or pili

• Hfr: F factor integrated into host's chromosome + pili

• F': Hfr w/o F factor + pili

Bacteria Conjugation

•F-factor – bacteria grows pili

•Forms conjugation tube

•If plasmid integrates – Hfr

Transformation•Transfer of exogenous DNA into bacteria

•Does not use bacteria or other viruses

Transduction

•Infects bacteria with phages

•Phage head + assembly shown =>

•Generalized Trans.

•Specialized Trans.

Phage Reproduction

•Phages have a lytic cycle =>

•Breakdown

•Relatively quick cycle

Restriction system

•Restriction enzymes

•Restriction endonuclease

•Restriction methylase

•Two together = restriction system

Sites Referenced• “Principles of Genetics” Online Textbook

• http://www.sciencegateway.org/resources/biologytext/pge/tools.html

• http://en.wikipedia.org/wiki/Prokaryote

• http://www.biology.ewu.edu/aHerr/Genetics/Bio310/Pages/ch15page/LN13final.pdf