ch 3 prokaryote cell structure and function

bacterial cell envelope

contain outer membrane; possess cell wall; may consist of only cell/plasma membrane

inner cell membrane

phospholipids; proteins; maintains gradient

Cytoplasm

proteins, rna, macromolecules; water; inorganic ions; small organic molecules; nucleoid (DNA); ribosomes

cell wall

peptidoglycan - sugar peptide polymer; gram positive and negative bacteria

gram positive bacteria

thick cell wall

gram negative bacteria

thin cell wall; outer cell membrane; lipopolysaccharide layer (LPS)

external structure

pili/fimbriae; flagellum (motile); capsule - surrounds cell wall (virulence factor)

molecule abundancy

water is most abundant

rna, proteins, and dna make up 25%

transport across membranes

simple: o2, co2

facilitated: amino acids, sugars, transport proteins

osmosis: h2o

group translocation

modification of substrate during transport; source substrate moving down gradient

abc transporters

amino acid, carb transport; expends ATPs to transport

membrane permanent weal acids/bases

small neutral weak acid/weak basic diffuses into cell and causes pH to rise(basic) or fall(acidic); cell must counteract

prokaryote cell envelope

bacterial archaeal inner cell membrane protected by structural support layers: cell wall, s layer, outer membrane, complex mycobacteria species

cell envelopes of 2 major taxonomic groups distinguished by gram stain

bacterial cell wall

structural support, protection, and porous

composed of peptidoglycan (polymer of disaccharides, glycan, peptide tetramers)

peptidoglycan synthesis

synthesis complex extends chains of amino sugars

helical direction of synthesis by complect via MreB (cytoskeletal element)

MreB

polymerizes along arc beneath plasma membrane (inner)

gram positive

thick cell wall; peptidoglycan layers w teichoic acids

gram negative

porous to most ions and small organic compounds

outer membrane proteins contain nonspecific porins transporting sugars and peptides

LPS layer has endotoxin released when cell dies: lipid A - short chain fatty acids linked to glucosamine dimers, core polysaccharide- 5 sugars, O polysaccharide - linked to core polysaccharide

s layer

surface layer of crystalline array of protein or glycoprotein; porous

periplasm

between inner and outer membranes; contains enzymes and nutrient transporters

atypical cell envelops

mycoplasma: smallest, lack cell wall

archaea: comprised pf pseudomurien

mycobacteria: tuberculosis, leprosy; contain mycolic acids (waxy lipids)

external structures

capsule: polysaccharide layer outside envelope, protein in nature, can be virulence factor; organized and tightly associated to cell than slime layer; biofilms surrounded by exopolysaccharide matrix

bacterial cytoskeleton

provides shape and form; provide protection; FtsZ protein; MreB protein; CreS protein

Ftsz protein

determines cell diameter; forms z ring for cell division and septation

MreB protein

travels in helical arc under cell membrane; guides cell wall synthesis

CreS protein

crescentin; curves inner side of bacteria

division and septation

septum is partition splitting envelope; septum grows inward and constricts; rapid synthesis of envelope; managed by divisome; facilitated by FtsZ

polysome

can result in protein product from expressed gene

polar aging

related to cell division in rod shaped bacteria; asymmetrical

old poles age: cell wall degrades and susceptible to lysis; accumulation of non functional protein aggregates in stressed cells

differ in antibiotic resistance

bacillus: endospore forms at one pole

c bacteria: pole gens flagellum or stalk during division

replisome

one at each replication fork in DNA

bacterial transcription and translation

occurs in nucleoid simultaneously

nucleoid

chromosome; singular, circular, double stranded DNA, loops/domains; ori is origin of replication; supercoiling compacts DNA (gyrase); DNA condensation via binding proteins

transcription/translation

tightly coupled; polysome/polyribosome formation

translated proteins

functions in cytosol; synthesized at membrane directed by signal recognition particles

cell division

fission; segregation and partitioning; clones; 20 min - 2 hrs

dna replication

begins at ori site, strands separate

dna polymerase complexes (repliosomes) synthesize dna: 2 dna polym per repliosome → leading and lagging strand synthesis

end of replication → z rinng formation via ftsz → septation and division

specialized structure

adapt to metabolic strategies and environments

phototrophs - thylakoids, gas vacuoles, carboxysomes

thylakoids

inner cell membrane foldings with photosynthetic components

carboxysomes

protein covered bodies with rubisco ( co2 fixation enzyme)gas

gas vacuole

maintain depthso

storage granules

metachromatic: inorganic phosphate

polysaccharide: glycogen, starch → glucose polymers

sulfur: insoluble, oxidation of h2s; h2s → s0

lipid inclusion: polyhydroxybutyrate

magnetosomes

magnetite crystals

orient along magnetic field

anaerobic or microaerophilic bacteria

move to lower oxygen depth

pili, fimbriae

adherence. protein monomer pilin

attach to mucous membrane

attach to surfaces → biofilm formation

twitching motility

sex pilus connects donor cell to recipient cell

stalk

extension of cytoplasm

attaches bacteria via secretion of adherence (holdfasts)

nanotubules

cell envelope extensions connecting cytoplasm between cells

share proteins and mrnaf

flagella

motility via rotary motion

filament of monomers of protein arranged in chains

h antigen: protein

filament attached to protein attached to hook attached to basal body anchored to wall and membrane

required ATP

clockwise → tumbles; counterclockwise → runs