prokaryote cell Flashcards
Why is studying prokaryotic cell structure important?
Food preservation/fermented food
Agriculture: nitrogen fixation, nutrient cycling, animal husbandry
Gut microbiota-new links with other parts of body
Disease-fighting disease eg. Plague/TB
Energy/environment-methanogenic bacteria
Biotechnology: genetic modification, pharmaceutical production, gene therapy
What is the difference between Bacteria and Archaea? (prokaryote=bacteria+archaea)
nuclear envelope: B=no, A=no
membrane-enclosed organelles: B=no, A=no
peptidoglycan in cell wall: B=yes, A=no
membrane lipids: B=unbrached hydrocarbons, A= some branched hydrocarbons
RNA polymerase: B=one kind, A=several kinds
initiator amino acid for protein synthesis: B=formyl-methionine, A=methionine
introns: B=rare, A=present in some genomes
response to antibiotics streptomycin and chloramphenicol: B=growth inhibited, A=growth not inhibited
histone associated w DNA: B=no, A=yes
circular chromosome: B=yes, A=yes
ability to grow at temperatures >100C: B=no, A=some species
How do the size and shape of prokaryotic and eukaryotic cells compare?
prokaryotic cells can come in a range of shapes:
coccus: 1mm(spherical)
rod: 2mm(cylindrical)
spirillum: 5mm(coil-shaped)
eukaryotes:2mm-200mm(spherical)
prokaryotes:2mm-20mm(1um in diameter)
SA:V in bacteria(prokaryotes) is a major limiting factor on single celled organisms
What is the structure of the prokaryotic cell membrane?
8nm thick
Made up of phophatidyl choline
Consists of saturated and monounsaturated fatty acids
Do not normally contain sterols (eg. Cholesterol)
Fluid and dynamic-lipids flip/modify(laterally and flip flop)
Some have double membrane-different recognition/functioning
Proteins: transmembrane, peripheral, integral
What are the major purposes of the cell membrane?
Protein anchor
Energy production and conservation
Permeability barrier
-> selective control of substances across membrane
barrier to influx/efflux of water
contains aquaporins-can close itself to certain extent but always open to water molecules
Ion channels(potassium, sodium)
What are the key structural features of the prokaryotic cell membrane and Cell wall?
permeability barrier
protein anchor
energy production and conservation
Compare and contrast the structure of gram negative and gram positive cell walls.
gram-positive: peptidoglycan thick outer cell wall
- very robust
- good target for antibiotics, targeting cell wall integrity so bacteria explodes
gram-negative: thin cell wall on the inside between 2 membranes
- ‘periplasm’ in the middle between the membranes
- cell wall still capable of supporting the cell
- outer membrane has complex structure
peptidoglycan
Composed of repeating units of two sugar derivatives, N-acety|glucosamine and N-acetylmuramic acid and a small number of special amino acids
Peptidoglycan is only found in the cell walls of species of bacteria
peptidoglycan - in e.coli
sheets of peptidoglycan surround the cell
formed of individual strand of peptidoglycan lying adjacent to one another
glycosidic bonds connecting sugars cannon provide rigidity in all directions
chains are cross-linked by amino acids
peptidoglycan cross-linkage
cross linkage occurs by way of a peptide interbridge
linkage occurs by peptide linkage of the amino acid group of (DAP) to the carboxyl group of the terminal D-alanine
kinds and number of amino acids vary between species
gram negative >10% of cell wall is peptidoglycan
gram positive >90% of cell wall is peptidoglycan but also teichoic acid is present in small amounts
another feature is the presence of 2 amino acids that have the D configuration
D-alanine and D-glutamic acid
gram positive cel wall structure
wall-associated protein
teichoic acid-embedded in cell wall
lipoteichoic acid
peptidoglycan
cytoplasmic membrane
teichoic acids -ve charged
partially responsible for the ive charge of cell surface
they also bind Ca2+ and Mg2+
gram negative cell wall structure
in outer membrane:
O-polysaccharide
core polysaccharide
lipid A
protein
porin
lipopolysaccharide(LPS)
phospholipid
lipoprotein
periplasm-made out of peptidoglycan
cytoplasmic membrane
lipid and polysaccharide linked in outer membrane to form a lipopolysaccharide complex,
Because of this the outer membrane is often called the lipopolysaccharude layer(LPS)
lipopolysaccharide structure in gram-bacteria:
2 components:
core polysaccharide and O-polysaccharide
lipid protion of the lipo. is called lipid A
Archaea cell walls
highly variable - wide range of different wall types, depending on habitat and environmental stresses
structure of the wall depends on the environmental stresses being addressed
polysaccharide similar to peptidoglycan called pseudopeptidoglycan
beta1-3 Glycosidic linkage(not beta1-4)
alternating repeats of NAG and NAT
prokaryotic cell structure: secretory(secretion) systems
Fimbriae and pili
complicated multi-protein structures that are embedded in the membrane, and act as either movement, recognition or secretory structures
eg.: type II secretion system, type IV pilus, Archaeal flagella, bacterial transformation system
Fimbriae:
used for movement and attachment
pilus:
used to transfer genetic information(in the form of plasmid) between 2 bacterial cells
prokaryotic cell structure: flagella
types:
peritrichous
polar
lophotrichous
the positioning of the flagellum/flagella will determine how the bacterium moves, how fast, and how much energy is required
-helical shaped
-when flattened, show a constant distance between adjacent curves called the wavelength
-wavelength is a characteristic for any given species
structure:
-series of rings embed base in the membrane
-Fli proteins cause rotation of the flagellum
-rotation of the base causes the body to spin and produce ‘whip-like’ movement
-Mot protein uses electrostatic charge changes to drive rotation of the ring structures
