Bio Gene Regulation in Bacteria 4.8

Types of Bacterial genetic material

chromosomal

plasmid dna

transpons

Bacterial chromosomes

4-5 kb in length, 3,000 genes, single origin of replication, replicate once every 20 minutes

transfer/recombination of bacterial DNA

conjugation, transduction, transformation

bacteria are a good model system for molecular genetics because:

1. small/simple genome

2. rapid multiplication

3. large amounts of genetic variation

chromosomal DNA

4-5 thousand length, 3,000 genes. single origin of replication, replicate once every 20 min.

only 1 circular copy

plasmid dna

extrachromosomal circular DNA, varying size, genes, and function. single origin of replication, replicate separately from chromosome (divided randomly throughout daughter cells during binary fission)

F-plasmid

fertility factor

93 kbin length

contains genes coding for “maleness”

transmitted through sexual mating

Episome

F’ plasmid, taken from the chromosome, can sometimes be longer (up to 100 kb)

R-plasmid

resistance factor,

genes for antibiotic resistance,

3-117 kb

larger than r-plasmid

C-factor

colicinogenic factor

4-141 kb

genes coding for toxins (colicin in e. coli)

some genes for sexual mating

transpons

transposable genetic elements, aka jumping genes

can move from one part of a chromosome to another

critical for mutations/ new gene combos aka genetic variation

Insertion sequence

simple, shorter transposon

contains inverted repeats at terminals

complex transposons

longer, more complex transposons

inverted repeats at terminals

code for antibiotic resistance

transposase

enzyme in transposons

cut into dna and self insert the jumping gene

conjugation

sexual mating of bacterium through f-pili

transduction

transfer of part of chromosome from one bacterium to another mediated through a phage

transformation

introduction of DNA from external medium

can be done through salt solution, heat shock, freezing/thawing, electroporation

gene expression

synthesis of RNA from DNA

more broadly, translation of mRNA into specific proteins resulting in specific phenotypes

operon

unit of bacterial DNA,

multiple genes under one promoter/operator

has a promoter, operator, and the coding sequence of genes

polycistronic

bacterial RNA is ___

many transcripts from one operon as a single mRNA in a single transcription

inducible operon

usually off, can be turned on when needed

catabolic pathways

active when there is a need to express the proteins for breakdown

inactive when there is no substrate to take in or break down

lac operon

inducible operon

no lactose: repressor active, no expression

lactose + glucose: inactive, low/moderate expression

only lactose: inactive and high cAMP levels, high level of expression

repressible operon

usually on, can be turned off as needed

used in anabolic pathways to synthesize compounds

active when proteins are needed for biosynthetic pathway

inactive when there is too much of the product

TRP operon

repressible operon

synthesize tryptophan

not enough tryptophan: inactive, high levels of expression

abundant tryptophan: active, no expression

signal factors

control gene regulation

bind to regulatory elements of bacteria to activate transcription

prokaryotes

unicellular

small cell size

short life span

small genome size

generate variations

recombination

ways bacteria have genetic variation

transformation

transduction

conjugation

recombination

mutation