BACTERIA AND VIRUSES

DNA core Protein coat (capsid) Characteristics: Parasitic Replicate only inside phenomenal rate

Size comparison

Often derived from host cell membrane

Often use overlapping genes

Lytic cycle – immediate destruction (lysis) of host cell Prophage – phage DNA integrated into bacterial chromosome Lysogenic cell – bacterial cell containing a prophage

Reproductive cycle of 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 genes from 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

CONJUGATION Conjugation – direct transfer of genetic material between 2 bacterial cells temporarily joined (pilus). One way donation Plasmid – small, circular, self replicating DNA Episome – genetic element, can exist as either a plasmid or as part of the bacterial chromosome F – fertility, produce sex pili Hfr – high frequency of recombination R 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 represses gene expression Tryptophan inhibits enzyme activity

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

OPERONS REPRESSIBLE 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.