Prokaryotic Cell Structure & Function Flashcards
exterior morphology of prokaryotic cell
Plasma membrane: barrier, nutrient in, waste out, limit of interior and exterior
Cell wall: made of peptidoglycan, rigidity, withstands osmotic pressure, prevents burst open
Capsules/slime layer, s layer:
additional layer for protection and stick to surface
Fimbriae/pili: some pili involved in gene transfer
Flagella: motion
Interior morphology of the prokaryotic cell
cytoplasm: no division, no compartment, thick gel-like
DNA: highly condensed free-floating in cytoplasm
Plasmid: small circular DNA
RIbosomes: 1000s of many protein +RNA, big enough to see under microscope (grainy structure)
Vacuoles: carbon soures, gas vacuoles (inflate-float up or deflate, sink to bottom)
Inclusion bodies: nutrients, store energy
Bacterial envelopes
- Gram-negative (3 layers)
-Cytoplasmic membrane (inner or plasma membrane)
-Cell wall (peptidoglycan)
-Outer membrane: facing outside environment - Gram-positive (2 layers)
-Cytoplasmic membrane (inner or plasma membrane)
-Cell wall (peptidoglycan): very thick, don’t need another layer - Mycoplasma (1 layer) (usually parasite)
-Cytoplasmic membrane (inner or plasma membrane)
Gram positive envelop
cytoplasmic membrane:
periplasmic space
cell wall:
peptidoglycan
lipoteichoic acid
teichoic acid
Protect and keep shape
hard for bacteria phages to get in
Gram-negative envelop
Plasma membrane:
periplasmic space and peptidoglycan:
between plasma membrane and outer membrane
outer membrane:
porin
Braun’s lipoprotein
lipopolysaccharide
Have receptors that allow phages to attack (porins)
cytoplasmic (plasma) membran
functions+composition
Functions：
-Contain the cytoplasm
-Regulate what comes in and what goes out the cell
-Water and small neutral molecules can diffuse through
-Charged and larger molecules need specific transporters
Composition:
-a fluid phospholipid bilayer
· asymmetric phospholipids
· negatively charged polar heads
· hydrophobic long lipid tails or fatty acid （insoluble）
-proteins (50% dry weight):
· Transmembrane proteins (transporters)
· Peripheral membrane proteins, stuck on either side of the membrane not spanning it
*Fluid mosaic model-Proteins “float” in the phospholipid bilayer
Aggregation of phospholipids
1 layer: micelle, not membrane
2 layer: hydrophobic inside
The peptidoglycan cell wall
feature, function
Very thick around gram-positive cells, thin around gram-negative cells
Functions:
(coat of mail around the cell)
-Give the cell its shape and rigidity
-Withstand osmotic pressure
Composition
-peptidoglycan (murein)
-Peptido(peptides), glycan (polysaccharide)
-Glycan: long chains of alternating sugars, N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
NAG NAM交替，但是只有NAM上会有polypeptide
-Peptides: cross links between adjacent chains (NAM)
-gram-positive: teichoic acid, bind to different layers of peptidoglycan, solidifies its structure, cell wall is anchored to the cytoplasmic membrane by lipoteichoic acid(lipid anchor(embed) in plasma membrane
-gram-negative: the cell wall is anchored to the outer membrane by lipoprotein(lipid+tip of the protein: hydrophobic(interact with membrane)；protein bind to peptidoglycan)
hypotonic, hypertonic, isotonic
hypotonic
water diffuses in
Cells are always in the hypotonic situation because inside is always highly concentrated
hypertonic
water diffuses out
isotonic
no net change
penicillin
inhibit the peptide cross link between NAM, cause the cell wall unstable and when cell grow, the cell loses its cell wall, and then continue to swell, finally bursting open
Peptidoglycan cross-links
Gram-
direct link between D-Ala and DAP
Gram+
peptide interbridge(5 Gly) between D-Ala, and L-Lys
The outer membrane (gram-
Functions
-Protective barrier (toxic substances, antibiotics)
-Only water, small molecules and few gases can go through
-Other molecules needs to travel through pores (porins), porins is not specific tranporters
Composition
-a fluid phospholipid bilayer
-Inner layer is made of phospholipids
-Outer layer is made of lipopolysaccharides (LPS, endotoxin, release to blood, 小剂量可导致 high immune response) and some phospholipids (lipid A+polysaccharide)
Anchored to the cell wall by lipoproteins
-Protein part linked to the cell wall (peptidoglycan)
-Lipid part inserted in the inner layer of the outer membrane
stucture of LPS
lipid A, O side chain, core polysaccharide
only the fatty acid part in the lipid A is hydrophobic
O side chain: variable, recognition site of the immune system
Core polysaccharide: usually won’t change
Capsule, slime layer, S-layer(6)
Secreted outside the cell envelope
*Protection from phagocytes and protozoa; from desiccation, toxic compounds, ions, pH fluctuations, and destructive enzymes
*Reservoir of stored food (e.g., polysaccharides)
*Site for waste disposal
*Helps maintain shape and rigidity
*Prevent infection by bacteriophages or attack by predacious bacteria like Bdellovibrio (small gram-, live inside bacteria cytoplasm) (these structure occlude the receptor on membrane)
*Aid in cell adhesion and motility (gliding bacteria, help gliding on surface)
Capsule
virulence factor
*Polysaccharides
*Thick and well-organized / Not easy to remove
*See well by microscopy
ex. Streptococcus pneumoniae (cause pneumoniae in human)
Slime layer
*Polysaccharides, glycoproteins, glycolipids
*Thin and less organized / Easy to remove
*Not easy to see by microscopy
ex. Bacteroides (useful in human gut)
Surface layer (S-layer)
*Proteins, glycoproteins
*Highly organized / Not easy to remove
*See well by microscopy
*not attached other structure, so even the cell burst, can still see S layer
ex. deinococcus radiodurans
Surface appendages of bacteria
Flagella (singular, flagellum)
-Movement of bacterial cells (rotate, helical)
-Vary in numbers and arrangements
-Made of a protein polymer (flagellin)
Pili (singular, pilus) or fimbriae (singular, fimbria)
-Hairlike, thinner than flagella (»1,000/cell)
-Adherence to solid surfaces
-Sex pili for mating (DNA transfer, just transfer, not sexual reproduction)
·Larger than fimbriae (1-10/cell)
·Genetically determined by sex factors or conjugative（1 to 1） plasmids
Typical arrangements of bacterial flagella
*Monotrichous: single flagellum at one pole
ex.Pseudomonas
*Amphitrichous: single flagellum at each pole
*Lophotrichous: two or more flagella at one or both poles
ex. Spirillum
*Peritrichous: flagella all over the surface
ex. P.vulgaris
Bacterial movement (taxis)
Monotrichous
-Counterclockwise, cell goes forward
-Clockwise, cell tumbles
Peritrichous
-Counterclockwise, flagella form a single rope-like structureand the cell goes forward
-Clockwise, cell tumbles
- Chemotaxis: towards or away specific chemical agents
- Aerotaxis: towards or away regions rich in oxygen
- Phototaxis: towards light
- Magnetotaxis: follow magnetic lines of force (magnetosomes)
cytoplasm
Site of numerous chemical reactions (metabolism)
*Composition
-90% water (very thick / gel-like composition)
-Can see by microscopy
· Nucleoid
Irregular mass of DNA (circular) (no nucleus)）
· Ribosomes
Produce proteins (20,000/cell)）
Large and small subunits made of rRNAs and proteins
· Inclusion bodies (none or single layer membranes)
Storage granules (reserve of nutrients)：Carbon, sulfur, nitrogen, phosphate
Gaz vacuoles (help bacteria to float)
Magnetosomes for magnetotaxis(iron-containing)
*Organized by a cytoskeleton (less complex than eukaryotic cell）divide fast, don’t want to waste energy on this
Bacterial endospopres (spores）
*Most resistant biological structures known (some Gram + bacteria)
-Survive millions of years (heat, dehydration, radiation)
*Nongrowing, resting structures, no metabolism, survival state
*Formation is induced when growth conditions are unfavorable (no more nutrients, harsh environment)
*In favorable conditions they start growing again (germinate) (sense their environment)
-growing cells are called vegetative cells
*The formation of endospores is called sporulation
-Reduce water content from 90% to 15% （DNA and protein are stable, since enzyme need water)
-Increase concentrations of calcium and dipicolinic acid
Sporulation
· Cell divides into two unequal parts
· The larger part engulf the smaller part (forespore)
· Forespore matures to become an endospore
1.Synthesis of a protective thick wall
-Inner cortex (peptidoglycan)
-Exosporium (proteins, polysaccharides, lipids)
-Spore coat (keratin-like protein)
2.Dehydration of the endospore (90% to 15%)
-dipicolinic acid: help dehydrate
3.Lysis of the vegetative cell to release the endospore
Germination
-Permeability of the wall changes, water entry
-Endospore swelling and rupture of the coat
-Germ tube grows out of the protective coat
The position of endospore
terminally
sub-terminally
centrally
Cell division type (3)
1.Binary fission: divide near the midpoint to form two daughter cells
-Bacteria, unicellular algae, most protozoa, and fission yeast
2.Budding: forming a bubble-like structure that comes out and eventually separates from the parent cell
-Some bacteria, budding yeast
3.Others: Fragmentation (filamentous growth), exospore formation
Cell division process
chromosome attach to the cytoplasmic membrane at attachement site
Partially replicated chronmosome
daughter chromasomes separate
new membrane and wall material growing through the cell midsection
Membrane ad wall material deposited at the cell midsection divide the cytoplasm in two
Budding yeast
bud scar
won’t affect the permeability of the cell
mother cell don’t grow in size, pass cytoplasm and geno to bud
grow to enough size detaches from mother cell
filamentous growth of fungi
isotropic growth
establishment of polarity
maintainance of polarity
regulation of polarity
ex.Actinomyces
