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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.