W2 The Cell Flashcards
size of E.coli, bacillus megatherium and red blood cell
e.coli: 1.5 micrometers
BCM: 4 micrometers
rbc: 8 micrometers
why do prokaryotes grow faster than eukaryotes
due to large surface area to volume ratio > allow greater uptake of systems
definition of monomorphic and pleomorphic
monomorphic: one shape
pleopmorphic: multiple shapes
- changes during growth
- cells become smaller as they age
- response to environmental cues
- sporulation (nutrient limitation)
properties of the bacterial membrane
permeability barrier: prevents leakage and functions as gateway for transport of nutrients in and out of cell
protein anchor: site of many proteins involved in transport, bioenergetics and chemotaxis
energy conservation: site of generation and use of proton motive force
properties of the bilayer in bacteria
selective permeability barrier
macromolecules can transverse
no exo or endocytosis
head groups: phospatidyl ehtanolamine/serine/glycerol and cardiolipin
functions of membrane proteins
nutrient transport
cell wall synthesis
signal transduction
protein secretion
chemotaxis
electron transport
lipid synthesis
how does gram stain work
cells stained with crystal violet > iodine > complex formed > gram negative cells decolourised with alcohol while gram positive cell’s peptidoglycan too which for CV-I complex to be washed out > gram positive cells stained purple while gram negative colourless but becomes pink when counter stained with safranin
difference between gram positive and negative cells
positive: single membrane with thick peptidoglycan
negative: double membrane with thin peptidoglycan
what are the monomeric units of peptidoglycan in gram negative bacteria
amino acids
glycan = NAM + NAG disaccharide; beta(1,4) glycosidic bond
4 amino acids linked together by peptide bonds
function of teichoic acid on gram positive cell walls
extends from surface of cell wall
gives cell wall a negative charge
provides flexibility to an otherwise rigid structure
what is lipopolysaccharide (LPS) in gram negative bacteria cell wall
important barrier against host defenses
lipid A is an endotoxin to animals
o-specific polysaccharide varies from species to species
order of LPS is uniform: lipid A - ketodeoxyoctonate - core - o specific
what is the periplasmic space
contains enzymes that participate in nutrient acquisition and metabolism
only in gram negative cells
contains chemolithotrophs: extensive arrays of electron transport proteins extending to the outer membrane for uptake and metabolism of inorganic ions
oxidation of toxic chemicals
what are polyhydroxyaloanates
biodegradable polyesters produced by certain bacteria as a form of energy storage
4 types of cellular inclusions
- carbon storage beta hydroxybutyrate in both bacteria and archaea
- sulfur storage in chromatium buderi (purple sulfur bacterium)
- magnetosomes allow bacteria to orient and migrate along geomagnetic fields; usually associated with oxygen concentration
- gas vesicles: important for aquatic microorganisms > allows them to float in large mats on water surface and sink to nutrient rich water at night
types of flagella in bacteria
attached at one end
attached at both ends
tuft at one end
all around cell surface
structure of flagella in gram negative bacteria
filament: flagellin
hook: hook protein
basal body: 3 rings
motor driven by proton motive force, not atp
development process of flagellum
MS ring assembled in cytoplasmic membrane
P ring forms in periplasm
L ring forms in LPS
hook and cap form
flagellin protein flows through hook to form filament
structure of gram positive flagellum
has filament-hook-basal body structure
proton motive force
homologous
only has two rings since there is no LPS
how does chemotaxis work
bacteria sense attractants > flagella rotate counter clockwise > flagella bundle together and propel bacterium forward in a straight line
bacteria sense repellants > flagella rotate clockwise > flagella spread apart > bacterium randomly change direction away from repellant
function of pili
cover surface and form conjugation bridges between bacterial cells for transferring DNA
function of T4P and how it works
responsible for twitching mobility: pili extend and attach to surface > retract and pull bacterium forwards
how do some bacteria move by slime extrusion from nozzles
bacteria secrete a slimy polysaccharide substance through nozzle > slime pushes against surface > allow bacteria to move
what is sporulation
process where certain bacteria form spores when conditions are unfavourable to protect cell contents > spores are highly resistant, dormant structures designed to withstand environmental conditions
process of sporulation
dna replication and asymmetric cell division > pre spore forms > mother cell engulfs pre spore > cortex formation (thick layer to protect spore) > spore adds additional layers and becomes metabolically inactive > mother cell breaks down and release mature spore > germination and growth into vegetative cell again once environmental conditions become favourable again
properties of gram positive endospores
occurs as bacteria age due to nutrient deprivation
NOT triggered in response to environmental stress
extremely resistant to environmental stress
controlled by complex cascade of sigma factor gene expression events
how do spores return to their vegetative state
activation: heat endospore to sublethal temperature
place in nutrient broth
germination: very rapid; synthesises RNA, protein, dna, breaks and discards spore coat
what is dipicolinic acid
makes up 10% dry weight of endospores
high in calcium ion concentration > crosslinks DPA molecules
helps lower water content in spores so that they will become highly resistant to heat and other harsh conditions
function of exoenzymes in gram positive cells
gram positive have no periplasmic space and which peptidoglycan layer > prevent molecules from directly entering cell
secrete exoenzymes to aid in transporting nutrients into cell
