prokaryotic cell structure Flashcards
common features in prokaryotes and eukaryotes
- plasma membrane
- DNA
- cell wall (plant, fungal, almost all bacteria)
most common bacterial cell shapes
- coccus (circle)
- coccobacillus (rod)
- vibrio (comma)
- bacillus (long)
- spirillium (helical)
- spirochete (long and helical)
dividing bacteria
- can stay together for a period of time
- in pairs (diplococcus, break off after next division)
- in a chain (streptococci, associated for a longer time, more divisions occur)
tetrad
- alternate orientation of plane of division so 4 bacteria stay together
- break up after 4
e.g. micrococcus
cyanobacteria
- divide alternately to create single layer mats
- can float in water and photosynthesise
e.g. Merismopedia spp.
sarcinae
- alternate planes of division to form clumps of 8
ununiform division
- divide in random directions and stay together until clump gets too big, so break off and start dividing
e.g. S. aureus
structure of a prokaryote
- cell membrane (+cell wall)
- cytoplasm with inclusions
- external structures
(capsules, flagella, pili)
cell wall
- outside cell membrane in most
- some lack cell wall e.g. mycoplasmus
- peptidoglycan
- maintains shape of cell (no cytoskeleton)
- prevents cell from osmosis by stopping too much water diffusing in
peptidoglycan
- alternating sugars to create strands
- N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
- crosslinked with tetrapeptide chains to create strong layers
teichoic acid
- in cell wall of gram-positive bacteria
- glycerol, phosphates, ribitol (sugar alcohol)
- projects on/through peptidoglycan layer
- involved in movement of ions in/out cell
- bacteriophages can attach on
outer membrane
- gram-negative bacteria only
- outside peptidoglycan layer
- porin proteins form channels through outer membrane for transport
- surface antigens and receptors for cell recongition
periplasmic space
- gap between peptidoglycan layer and outer membrane in gram-negative bacteria
- contains digestive enzymes
ribosomes
- all free in cytoplasm
- polyribosomes = chains of ribosomes
- 70s (80s in eukaryotes)
- antibiotics including streptomyocin and erythromyocin bind specifically to 70s ribosome, disrupting bacterial protein synthesis but not eukaryotic
pili
- short hollow projections
- conjugation- gene transfer
- attachment to surfaces (host invasion)
inclusions
- glycogen or polyphosphate storage granules (energy store)
- gas or lipid vesicles (storing energy or regulating buoyancy)
flagellum
- for movement
- helically coiled
- thinner than eukaryotic flagella, ~20nm diameter
capsule/slime layer
- covers antigens on cell surface so can help evade host immune system
cell membrane
- separates cytoplasm from exterior
- phospholipid bilayer, proteins including transporters
nucleoid
- nuclear region
- DNA, usually one circular chromosome
e.g. vibrio cholerae has one large one small chromosome - smaller circular plasmids holding extrachromosomal non-essential DNA
storage granules in biotechnology
e.g. PHB granules, biodegradable plastic
parasporal BT crystal, insecticide (very selective)
suflur globules, carboxysomes
endospores
- resistant resting structure
e.g. in Bacillus and Clostridium spp. - allows bacteria to survive inhospitable conditions
- protected against heat, UV, desiccation by spore coat
- one spore per bacterium triggered when nutrients start to die out
- mother cell deteriorates
- when conditions improve, spore germinates
monotrichous (flagella)
single polar flagellum
lophotrichous (flagella)
multiple polar flagella
amphitrichous (flagella)
one flagella at each end
peritrichous (flagella)
flagella all over surface
atrichous (flagella)
no flagella