Prokaryotes Flashcards
What makes bacteria different from archea?
- Bacteria have a peptidoglycan cell wall
- Different membrane lipids
- Bacteria have one kind of RNA polymerase; archea have several kinds (like eukarya)
- Initiator AA for protein synthesis = formyl-methionone
- Introns are rare in bacteria
- No histones associated with DNA
What are the 3 types of shape in bacteria?
Rods, spherical/cocci and spirillum
Compare the size of a prokaryotic cell vs a eukaryotic cell
Prokaryotic cells are generally smaller than eukaryotic cells
What type of SA:vol ratio do prokaryotes need?
They need a high SA:vol ratio so that they can meet metabolic needs by diffusion of substances across their membranes
It hugely limits the size that prokaryotic cells can become
What is the chromosomal DNA in a prokaryote called?
Nucleoid
How does the fluidity of the cell membrane vary? Why?
- Can be very fluid to very viscous
- Fluid: unsaturated FA tails are present in the phospholipids - this causes the tails to kink, meaning they cant fit together as tightly, and lose rigidity
- Viscous: FA tails in the phospholipids are saturated, meaning they can fit together as tight as possible, and the membrane becomes rigid
Ideally, a balance is struck between these two extremes in cell membranes
How is the phospholipid bilayer dynamic?
- Lateral movement: swap with direct neighbour phospholipid to left/right
- Flip-flop: swap with the opposite phospholipid up/down
Lateral mopvement happens REALLY often, but a flip-flop is quite rare
What prokaryotes have double cell membranes?
Gram negative bacteria
This double cell membrane has implications for recognition and function
What are the different types of proteins that can be associated with the cell membrane?
- Transmembrane proteins
- Peripheral membrane proteins (surround other membrane proteins)
- Integral membrane proteins (embedded partially in the membrane)
Their location/orientation is linked with their function
What are the 4 major differences between bacteria and archea membranes
Archeal membranes have:
1. Isoprene units instead of FA chains
2. Hydrocarbon links are branched, affecting the way that the tails fit together
3. Ether linkages attach them to the glycerol unit
4. The glycerol is chiral
This allows them to live in more extreme environments
What is the role of the cell membrane?
- Permeability barrier
- Protein anchor
- Energy production and conservation
Why is it important for the cell membrane to act as a permeability barrier?
- To prevent proteins/DNA/ions from leaving the cell
- Allow the influx/efflux of water
What allows the movement of water in and out of the cell via the cell membrane?
Aquaporins
They are difficult to close completely so there is normally some slight osmosis out of the cell - cell membrane is therefore very permeable to water
Why is the role of the cell membrane as a protein anchor important?
Ensuring the following are all correct for the membrane-associated proteins:
- Orientation
- Concentration
- Association
- Recycling
- Recognition
e.g. enables channel proteins to carry ions across the membrane
Why is the role of the cell membrane in energy production important?
ATP synthase protein complexes (enzymes) are embedded in cell membranes, enabling entry of protons, and the generation of ATP
structure of this molecule is highly conserved across nearly all organisms
Why is a cell wall necessary for bacteria?
The bacteria are often more concentrated than the media they are in, and therefore they need the turgor of the cell wall to create enough pressure, and retain the contents of the cell - prevents osmotic lysis
What is the function of the flagella? How does its movement vary between species?
- Locomotion
- Wavelength is characteristic for any given species
Wavelength referrs to the movements it makes to move itself
What are the different positionings of flagella called?
- Peritrichous: all around the organism
- Polar: on one end of the organism
- Lophotrichous: multiple embedded at one end of the cell
What protein allows for the movement of the flagellum? How?
Mot protein:
- H+ move up/down the Mot protein
- Electrostatic changes to drive rotation of the charged ring structure (MS ring and C ring) at the base of the flagellum
What is the function of the fimbriae?
- Used for movement and attachment
Keep it in one place
What is the fucntion of the pili?
- Used to transfer genetic material (plasmid) between two bacterial cells
- Essentially, this is bacterial sex
Steve calls them little straws that run from one bacterium to another
how to tell if bacteria is gram positive or negative? How do you do this?
Gram staining:
- Add crystal violet to the smear for 1 min (this can’t penetrate the outer cell membrane of the gram negative bacteria and stain the paptidoglycan layer of the cell wall)
- Add iodine for 1 min (helps intensify the colour)
- Decolorise with alcohol for approx 20s (colour washes off the Gram negative bacteria bacteria)
- Counterstain with safranin for 1min (stains the Gram negative bacteria but not the gram positive)
What is the difference between Gram positive and Gram negative bacteria?
- Gram positive have thick peptidoglycan cell walls and then an inner membrane
- Gram negative bacteria have an outer membrane, then a thinner peptidoglycan cell membrane, and then an inner cell membrane
This therefore chnages the way that infection by these bacteria are treated
what are gram positive bacteria?
- Thick outer peptidoglycan cell wall
- Inner cell membrane
The cell wall is a good target for antibiotics
