Prokaryotic genetics Flashcards
What are the 4 reasons for studying prokaryotic genetics?
- Provides a basic understanding of molecular biology + genomics and where research came from etc
- Bacteria fundamental to human health + disease so understanding of genetics = important
- Bacterial ecology; what bacteria are in environment, how do they interact etc.
- Applications to biotechnology; manipulating bacteria for human uses.
History of genetics - who was involved and when?
- Lamarck, 1800 -> species aren’t fixed.
- Darwin, late 1800s -> “Origin of species”
- Beadle and Tatum 1941 -> “One gene, One enzyme”
- etc
2003 = human genome project -> current = post genome era.
What is the definition of bacterial genetics?
Bacterial genetics = study of mechanisms of heritable information in bacteria.
What are the 4 mechanisms studied in bacterial genetics?
Studying:
- Chromosomes
- Plasmids
- Transposons
- Phages
What techniques can be used to study bacterial inheritance mechanisms?
Techniques:
- Culture in defined media
- Replica plating, mutagenesis, transformation, conjugation and transduction
ALL = methods of moving genes around.
What is the abundance of bacteria in the world?
30% of DNA on earth = bacterial
Vast majority of organisms = archaea or bacteria etc (single celled organisms)
Spread of cells in the body eukaryotic vs bacterial?
Aprx bacterial cells = eukaryotic cells in body.
What are the 6 factors that make bacteria model organisms ?
- Haploid = one gene for everything means easy study
- Asexual reproduction = cell division creates identical daughter cells meaning easy to workout reproduction
- Short generation time = useful in research
- Growth in defined media for some = full control of nutrients means defining metabolic pathways
- Easy to store
- Easy to genetically mutate
What does bacterial genome look like?
- Single, circular double stranded DNA chromosome
What bacterium’s chromosome is the exception?
Borrelia burgdorfei (limes disease causer) -> Single linear chromosome.
What is a bacterial genome size?
Varies hugely - 0.58 mega base pairs => >10 mbp
What is special about the bacterial genome?
- Little space in-between genes (more % overall are gene coding versus eukaryotic genomes)
- Lack of introns (unlike eukaryotes)
- Genes grouped into operons
- Often carry plasmids
What are operons?
Genes with related functions grouped together under one promoter
What are plasmids?
Plasmids =
small circular DNA that replicates independently.
often w extra genes important for e.g. antibiotic resistance etc.
E. coli genome in detail - How big?
EC => DNA = 1mi long
Same thickness as spiderweb
How do bacteria reproduce?
Via asexual reproduction
Cell elongates and content volume is increased
The cell divides into two => creates identical daughter cells w copy of plasmids and DNA in each cell.
3 essential steps in bacterial reproduction
- Cell grows to 2x length
- Septum then forms in middle
- Cell grows from either end then pinches to break cell into 2.
Why is generation time important?
- Many bacteria are fast to replenish and divide. (EC = 20mins)
- Some are 1000s of years or unable to be cultured but vast majority are useful.
What affects generation time?
Optimum conditions = fastest growth time.
Conditions:
Nutrients
pH
Temperature
etc
What is needed to grow EC?
1940s = modern model organism
Synthesises all own cellular components using inorganic nutrient + carbon.
- Able to grow on really defined media. => useful for metabolism and growth studies
EC minimal media with glucose - composition?
Phosphates -> pH control + phosphate source.
Nitrates -> source of nitrogen
Magnesium -> useful for nucleotides + proteins.
Calcium chloride -> useful for sensing + membrane transport
Trace metals -> important for protein function
Glucose -> a carbon source + used for energy
What is the point of growing EC on minimal media?
Looking for mutants that won’t grow without certain nutrients.
What is a prototroph?
Wild type EC = doesn’t need any nutrients. => can grow on minimal media
What is an auxotroph?
Mutants of a wild type that now require certain nutrients to be able to grow => can no longer grow on minimal media.
What is a biosynthetic auxotroph?
Need additional nutrients to be able to grow e.g. amino acids, nucleotides, vitamins etc.
What is a catabolic auxotroph?
Mutants that can no longer catabolise certain carbon sources.
If using glucose as carbon = unaffected. (cannot break down glucose = death)
What are housekeeping genes?
Genes essential for survival. (DNA replication, glycolysis etc)
Mutations = fatal
What are conditional lethal mutants?
Mutant that is fatal under repressive conditions but not in permissive conditions.
(change environment = life or death)
What are temperature sensitive mutants?
Mutants that only grow at a permissive temperature not at a restrictive temperature.
represented by “ts”
How can we explain the reason for there being temperature sensitive mutants ?
Mutant protein will fold differently at different temperatures, e.g. in EC permissive = 30C , restrictive = 37C; proteins will fold better at 30 due to less energy in system.
Protein stability - depends on temp.
What is the opposite to temperature sensitive mutants?
Cold sensitive mutants (may grow at higher temps but not at lower temps)
Why are conditional lethal, temp and cold sensitive mutants important ?
These help to work out which genes are housekeeping genes.
How to properly write gene annotation?
All in italics:
1. Three lowercase letters = biochem pathway gene product involved in.
2. Capital letter = denotes gene.
3. Maybe a number for which allele
How to properly write protein nomenclature?
Proteins will be encoded by genes (NO ITALICS)
1. Capital letter start
Protein will always have a capital letter starting.
How to properly write phenotypes?
- 3 letters total, first = capital
- 3 letters not italicised.
- If mutant -> phenotype shown by superscript +/-
