Bacteria Flashcards
What are bacterial cell walls made of?
Peptidoglycan
What are the 3 common shapes of bacteria?
Bacillus, coccus, spiral
What are bacterial chromosomes like?
Single, circular chromosome
What is a nucleoid?
Region of condensed DNA that is anchored to the membrane, but not membrane enclosed
What 3 structures are only found in some bacteria?
Flagella, pili, capsules
What’s the difference between gram-positive and gram-negative bacteria?
Gram positive have a thick PG layer on the outside of the cell membrane, gram-negative have a thin PG layer sandwiched between two membranes
Are the outer and inner membranes in gram-negative bacteria composed of the same things?
No, the outer membrane has lipopolysaccharides in the outer leaflet
What is the structure of LPS?
Hydrophilic polysaccharide heads, hydrophobic fatty acid tails
What does LPS do?
Acts as a chemical barrier against proteins, antibiotics, toxins
Why are gram positive bacteria easier to kill?
They only have the physical protection from the PG, they don’t have the chemical protection of the LPS
How do gram-negative bacteria get nutrients across the LPS?
Selective porins in the outer membrane
How is peptidoglycan structured?
Repeating sugar units of NAG and NAM, with a tetrapeptide chain attached to the NAM sugar. The peptide chain is cross-linked to form a super strong 3D network
How is the genetic information in a bacterial cell organized?
Most species have a single circular chromosome, a few have multiple chromosomes, a few more have linear chromosomes
Why is the prokaryotic genome streamlined?
Very little DNA is non-coding compared to eukaryotes
How is the prokaryotic genome streamlined?
- No telomeres because the chromosome is circular
- No centromeres because replication happens by binary fission instead of mitosis
- Intergenic regions and regulatory elements are small
How is the bacterial chromosome condensed?
Looping and supercoiling
Do histones aid with DNA condensation in prokaryotes?
No. There are looping proteins but they aren’t histones
Why are transcription and translation able to be coupled in prokaryotes?
No membrane is separating transcription and translation, so ribosomes can attach to a binding as soon as its transcribed
Why is coupled transcription and translation advantageous?
Allows really fast gene expression
What are the 8 reasons why bacteria are good model organisms?
- Haploid
- Easy to grow
- Fast generation time
- Asexual reproduction
- Easy to count
- Easy to isolate
- Easy to store
- Easy to genetically manipulate
Why does being haploid make bacteria and phages good model organisms?
You only need one copy of a mutation to see an effect since they’re expressed immediately
Why can being haploid be disadvantageous for genetic studies?
Difficult to maintain lethal mutations, and mapping can be difficult
Why does being easy to grow make bacteria good model organisms?
Can grow really well different mediums that are easy to make, in both solid and liquid medium
When would you grow bacteria on a solid plate vs in liquid medium?
If wanting single colony isolates, use solid medium. For lots of colonies, use liquid medium
What is generation time?
The time for an organism to reach maturity and reproduce
Why does having a short generation time make bacteria good model organisms?
Makes it really easy to get lots of cells in a short period of time
Why does having asexual reproduction make bacteria good model organisms?
They divide by binary fission and produce 2 genetically identical daughter cells (clones)
Why are bacteria so easy to count?
Every colony that grows originated from a single cell, and easy to plate a serial dilution and do some math to get the original concentration
What are we assuming when we do plate counts?
Every colony is genetically identical and the cells are all viable and able to divide
Why are the units of a plate count Cfu/ml instead of cells/ml?
Plate counts only count viable cells (aka cfu)
Why are bacteria easy to isolate?
Can looks at thousands of colonies at a time to look for a mutant. Much more organisms in a smaller space
What is colony purification?
Isolating individuals from a mixture of colonies on a plate, streaking it, taking a single colony, streaking it, and repeating until all colonies are genetically identical
Why are bacteria easy to store?
They can be frozen with a cryoprotectant and liquid N2 and stay viable for 20 years. Some also form endospores that can be freeze-dried and stored indefinitely
Why are bacteria easy to genetically manipulate?
Can undergo 3 types of genetic exchange (conjugation, transformation, transduction)
What is transformation?
The uptake of new DNA from the cell’s surroundings
What is conjugation?
The transfer of DNA directly from cell to cell
What is transduction?
The introduction of new DNA sequences through a viral vector
