BACTERIAAND

VIRUSES

DNA core

Protein coat(capsid)

Characteristics:•Parasitic•Replicate only inside host @ phenomenal rate

Size comparison

Often derived from hostcell membrane

Often useoverlappinggenes

Lytic cycle – immediate destruction (lysis) of host cellProphage – phage DNA integrated into bacterial chromosomeLysogenic cell – bacterial cell containing a prophage

Reproductive cycleof enveloped virus

HIV•Retrovirus•Nucleic acid is RNA•Reverse transcriptase•RNA→DNA

PROKARYOTIC REPLICATION

•One origin•2 directions

TRANSFORMATION – alteration of a bacterial cell’s genotype by the uptake of naked, foreign DNA

TRANSDUCTION:-Phages carry genesfrom one host cell to another

Generalized Transduction-Phage transfers bacterial genes at random

Specialized Transduction -Transfers only certain genes (those near prophage)

Both – transferred DNA may recombine with genome of new host

CONJUGATIONConjugation – direct transfer of genetic material

between 2 bacterial cells temporarily joined (pilus). One way donation

Plasmid – small, circular, self replicating DNAEpisome – genetic element, can exist as either a

plasmid or as part of the bacterial chromosome F – fertility, produce sex piliHfr – high frequency of recombinationR plasmids – genes w/ resistance to antibiotics

Conjugation & Recombination in E.coli

Transposons – piece of DNA that can move from one location to another in a cell’s genome. “jumping genes” Insertion sequences – simplest bacterial transposons

1) Transposase makes staggered cuts at target site, leaving short segments of unpaired DNA. Meanwhile, transposon cut out or copied at its initial site.

2) Transposon then joined to the single stranded ends at target site. Transposase holds things together during this process

3) Gaps in DNA filled by polymerase and sealed by ligase. Direct repeats on either side of transposon

INSERTION OF TRANSPOSON AND CREATION OF DIRECT REPEATS

ANATOMY OF A COMPOSITE TRANSPOSON

One or more genes located between twin insertion sequences.The transposon here has a gene for resistance to an antibiotic, which is carried along as part of the transposon when the transposon is inserted at a new site in the genome

REGULATION OF A METABOLIC PATHWAY

Tryptophan repressesgene expression

Tryptophan inhibits enzyme activity

Regulatory gene – codes for?Structural gene – codes for?Promoter – binding site for?Operator – binding site for?Operon components?

OPERONSREPRESSIBLE

• Usually___; can be turned ___.

• Regulatory gene makes __________ repressor.

• Repressed by ____________

INDUCIBLE• Usually ___; can be

turned ___.• Regulatory gene

makes a ________ repressor.

• Induced by ______________

The trp operon: regulation by repressible enzymes

Regulatory gene – codes for inactive repressor protein

RNA polymerase transcribes genes

trp operon

Tryptophan accumulates and inhibits its own production by activating the repressor protein

Trytophan binds to allosteric site causing its conformation to change to the active form

trp operon

Repressor switches operon off by binding to operator and blocking polymerase

The lac operon: regulation by inducible enzymes

lac repressor active and in absence of lactose, switches operon off by binding to the operator

lac operon

Allolactose (isomer) derepresses the operon by inactivating the repressor. The enzymes for lactose metabolism are induced.