I can describe how genetic variation occurs in bacteria.
Prokaryotic cells Lack nuclei Lack membrane- bound organelles (have ribosomes for protein synthesis) May have flagella for movement May have capsule around cell wall Various shapes, arrangements
Single, circular bacterial chromosome in nucleoid region Often contain one or multiple plasmids “Bonus” genes independent of bacterial chromosome Code for traits such as antibiotic resistance, fertility factors
Even though bacteria are asexual, they are not clones! Variation introduced by: Mutations Chromosome and/or plasmid replication Transformation Transduction Conjugation Transposable elements/transposons
Changes in DNA during replication Grow and divide FAST, so errors happen and get passed on quickly Ex: drug resistant bacteria
Alteration of a bacterial cell’s genotype and phenotype by the uptake of naked, foreign DNA from the surrounding environment Ex: harmless Streptococcus pneumoniae bacteria can be transformed to pneumonia-causing cells
Phages carry bacterial genes from one host cell to another Generalized transduction – random genes are transferred Specialized transduction – genes adjacent to prophage site in temperate phages
The direct transfer of genetic material between cells Bacterial ‘sex’
Transposable genetic elements “jumping genes” Pieces of DNA that move around within the genome
I can describe how bacterial cells use the operon system to regulate gene expression.
Prokaryotes must use substances and synthesize macromolecules fast enough to meet their needs If enzymes aren’t needed, genes for their production must be “off” Conservation of resources
Genes grouped together operating together in prokaryotic cells Can be inducible Normally “off” but able to turn “on” when needed Can be repressible Normally “on” but able to turn “off” when not needed Coordinated control of genes required for metabolism
I can identify and explain the functions of the following structures with regard to the operon system.
Promoter Region of DNA that signals for RNA polymerase to bind Operator Region of chromosome to which the repressor binds when the operon is turned “off” Repressor A protein that suppresses the transcription of a gene Regulatory gene Codes for production of the repressor protein Structural gene Codes for enzyme product Inducer Molecule that binds to and changes repressor’s shape
I can use the trp operon as an example to describe a repressible operon and explain how this system works.
Repressible Genes are normally “on” and produce tryptophan for the cell If tryptophan is present, genes are turned “off” and tryptophan in the environment is utilized
Cell requires tryptophan for metabolism Typically has to make it for itself To do this: Repressor is inactive and not bound to the operator Promoter is available to RNA polymerase Structural gene is transcribed mRNA is translated into enzymes Enzymes produce tryptophan
No tryptophan present in environment Cell makes its own tryptophan-producing enzymes
If the cell has adequate supply of tryptophan, it turns the operon “OFF” and uses what is available Save resources – don’t make it if it’s already there! To do this: Tryptophan binds to the repressor, activating it Activated repressor binds to the operator This blocks RNA polymerase from transcribing mRNA No genes are transcribed no proteins produced
Tryptophan is present in environment No need to produce tryptophan producing enzymes
Inducible Genes are normally “off” in absence of lactose If lactose is present, genes are turned “on” and enzymes to digest it are produced
If no lactose if present in the cell, no lactose-digesting enzymes are produced Save resources – don’t make it if it’s not needed! To do this: Active repressor binds to operator This blocks RNA polymerase from transcribing mRNA No genes are transcribed no proteins produced
No lactose in environment No need to produce lactose-digesting enzymes
Lactose is not normally present If it is, bacteria will digest and use it To do this: Allolactose inducer binds to repressor, inactivating it Inactivated repressor cannot bind to operator RNA polymerase can bind to promoter Genes coding for lactose-digesting enzymes transcribed mRNA is translated into enzymes that digest lactose When lactose supply is depleted, inducer separates from repressor, allowing it to bind to operator again and block transcription
Lactose is present in environment Enzymes to digest it are produced