Chapter 2: Microvial Cell Structure and Function

Sections I and II

cell envelope

consists of several layered structures that surround the cytoplasm and govern cellular interactions with the external environment

way for us to classofy microbes

protoplasm

cytoplasm of prokaryotes

estimated number of prokaryotic cells

4-6 × 10³⁰

bacterial species harbored by humans

1000+

cell envelope function

1. governs cell transport of nutrients, in and waste out of the cell

2. site of energy conservation

3. governs cell shape

4. protects from mechanical stress

5. can help cell attach to surfaces

6. protect from attack

cellular evelope comports

1. cytoplasmic membrane

2. cel wall

3. outer membrane

4. S-layers

phospholipid bilayer

comprised of a hydrophobic region (fatty acid) and a hydrophilic region (phosphate, glycerol(glycerolphosphate), and a side chain (sugar, ethanol amine, choline, or another funtional group)) in the hydrophilic group, groups are both conected to the phosphate.

types of membrane bound proteins

integral (significantly embedded in the. membrane)

transmembrane (extend completely across the membrane)

peripheral (outward facing and lossely attached.)

peripheral proteins

they can attach by containg a small hydrophobic reagion that gets imbeaded in the membrane, secreat somthing that associates with the hydrophylic region of the cell membrane, or can binding with other anchored proteins

they are typically ues for transport of energy mtabolism

isoprene

makes up the hydrophobic reagion of archaea and is a 5 carbon hydrocarbon that is repeated to form this region (see notes 1 p 7)

these isoprenoid chains link at their termini to form a lipid monolayer

phytanyl

C₂₀ side chain that cen be present in phosphoglyceral diethers to make up the cell membrane of archaea

biphytanyl

C₄₀ side chain that cen be present in diphospoglycerol tetraethers to make up the cell membrane of archaea

archea polar head

can be sugars, wthanolamin or other molecules

cell membrane function

1. stops passive leaks in and out of the cell

2. anchors several proteins that catalyze several key cell functions

3. big role in energy conservation and consumption in Archaea and Bacteria

transporter proteins

fucntion to accumulate solutes against the concentration gradient (req energy)p. most substances travelling in and out of the cell must be accompanied by theses

proton motive force

activated state of prokaryotic and archeic membranes ause by the deprotenation that results in H+ and OH-, across the membrane. when energy is released and the membrane is restored, the energy can power transport, locomotion, and biosythesis of atp.

in eukaryotes, this process is done in the membrane of the mitochondria or chloroplast.

active transport systems

any system that transports solutes agains the concentration grain. there are 3 types

1. single transport system

2. group translocation

3. ABC transport systems

simple transport system

consists of only a transmembrane transport protein

group translocation

uses a series of proteins in a single transport event

ABD transport systems

ATP binding cascade. has three components: a binding protein, a transmembrnae transporter, a ATP-hydrolyzing protein

symport

one of two major transport events that are catalyzed by the energy inherent in the proton motive force. this is when the solute and a proton are cotransported in the same direction

anitport

send major trans event that is catalized by a proton. It is when the proton and the solute are transported in opposite directions

common supporters

phosphate, sulfate, etc.

group translocation (differences)

1, the transported substance is chemically alterd while it is being transported

2. energy rich organic moleucles frive the trans event as opposed to the proton motive force

E. coli Transport system

transports the sugras glucose, mannose, and fructose. during uptake, the sugras are phosporylated by the phosphotransferase system

phosphotransferase system

system of five protiens (family) the work together to transport suguar. they are phosporylated and transfer this to eachother before Enzyme II_c phophorylates the sugar as it enters the cytoplasm. These proteins are a mix of transmembrane, peripheral, cytoplasm proteins.

turgor pressure

osmotic pessure that results from the highger concentration of dissolved solutes in the cell

can cause cell lysis

grahm positive cells

purple in color and tend to have a cytoplasmic membrane and thicker cell walls

contains a thick peptidoglycan wall, 20-35nm thick (as much as 90% of the cell envolope can be peptidoglycan) can be 15 or more layers thick. sideline links can occur horizontally and vertically to stabilize the wall in 3D.

peptide “interbridges”

cross-links in grahm positive bacteria cell walls can contain these. amino acids vary by species

grahm negative

pink in color and tend to have a cytoplasmic membrane, thinner cell walls, and a periplasm

the peptideoglycan has bonds betwen the DAP on on glycan strand and the terminal D-amin on the adjacent one. the wall is 2-7nm think and single layered (can be up to three layers). it is flexible and porous but still resists turgor pressure

periplasm

compatment between the cytoplasmic and outer membranes

peptidoglycan

major component of bacterial cell walls and a target for many antibiotics

it is a ridgid polysaccharide that confer the structural strength of the cell wall. It is present in ALL bacterial cell walls but not found in Archea or Euks.

peptidoglcin units line up parrallel around the circumfrince of the cell and they sidechains link together covalently to form one gian molecule

teichoic acids

present in many grahm positve cell bacteria cell walls. composed of glycerol phophate or ribitol phosphate with attached molecuels of glucose or D-alanin (or both). molecules are covalently bonded together the linked to the peptidoglycan.

can be bound to membrane lipids, and are called lipoteichoic acid

penicilin

anitbiotic that blocks the formation of peptiddoglycan, peptide cross-links (strangth of the peptidoglycan) causing cell lysis for bacterial cells

Archea cell wall

non peptidoglycan or ourter membrane (grahm staining not effective). Most do not have a polysaccharide containing cell and instead have an S-layer

S-layer

ridgid protein shell that prevents osmotic lysis. the archaeal version of the cell wall.

cell wall (archea)

when present, is structurally different but fucntionally similar

pseudomurein

structurally and functionally similar to peptidoglycan but is immune to destruction by lysozyme and penicillin.

outer membrane

sencod lipid bilayer, external to the cell wall

LSP

lipopolysaccharide

containing polysaccharide molecules covalently bound to lipids (in the outer membrane)

porins

transmembrane proteins that allow for nonspecific transport of solutes

comprized of 3 identical polypeptides

LPS structure

2 components; core polysaccharide and the O-specific polysaccharide

the presence of ionic bonds in these components give strength to outermembrane that rivals the grahm negative cell wall,.

LPS replaces much phospholipid in the outerhalf of the membrane

L in LPS

not tradittional lipids,fatty acids are bound to amino acids groups and form a disaccharide of glucosaminphosphate.

braun lipoprotein

likes the outer membrane to the peptidoglycan layer (cell wall)

endotoxin

refers to the toxic component of LPS (in particular lips A). it is toxic to animals

ex. salmonella, shigella, escherichia

periplasm function

area where proteins that must react out of cell that does not allow dor them to diffuse away (outer membrane is impenitrable to proteins and large moleculs; thought to be its function)

15 nm

outie (cytoplasmic membrane) to innie

proteins in the periplasm

1. hydrolytic enzymes (inital degradation of polymeric substances)

2. binding proteins (transport substrates)

3. chemoreceptors (chemotaxis response)

4. ones that construct extracellular structures (i.e. construct peptidoglycan and the outer membrane)

aquaporins

located in the ceytoplasmic membrane and facilitate wwater transport across the membrane

nonspecific porins

water filled channels where very spall hydroplilic substances can pass

specific porins

contain a binding site for one or a group of structurally related substances

s-layer

made of paracrystalline monplayer of interlocking moleculs of proteins or glycoproteins

outermost layer when present

s-layer thickness (bacteria)

5-20nm

s-layer thickness (archaea)

up to 70 nm thick

s-layer function (archea)

thick ones can replace the cell wall and take on its roles (strength, no lysis, shape). can also create a periplasmic like space

molecular sieves

pores in archaea s-layers that rank 2-10 nm in diameter that let low MW compounds througth be trap proteins and other large molecules betwen s-layer and cell membrane

rxns can occur in the gap

s-layer interactions

can facilitate attachment, promoting adheison, or protect the cell from host defenses

Cell envelope alt. configs

many alt configs, see p 86

bacteria and archaea w/out cell wall

have unusually tough cytoplaasmic membranes with sterols

sterols

promot regidity and strenth in aytoplasmic membanes of eukaryotes and bacteria and arche without cell walls

mycoplasmas

pathogenic bacteria that grow within a host cell (has sterols and thought to not get recognized bacuse of the lack of cell wall components

capsule and slime layer

secreted substances on cell surface (outside of envelope) of bacterial and archaea cells (ffenerally polysacchrides or proteins

can protect form pathogen recognition

capsule

polysaccharides that are tightly held together with no small particles and atttached tightly to the cell

slime layer

Easy to distort, loosely attached, and easily penetrable by particles. It is more difficutlt to se under the microscope.

pili

2-10 nm dia filamentouss structures made of protiens that extend form the suraface of the cell

produced by ALL gram (-) bactera as well as many gram +

fimbriae

short pili that mediate attachment

pellicles

this sheets of cells on a liquid surface

conjugative pili

used for congugation (horizontal gene transfer)

type IV pili

facilitate adhesion and twitching mobility (cell movement in certain bacteria)

Atp req and kinda like sticky grapping hand (multi)

also in archea

hams

presnet in SM1 archea, similar to type IV pili but with hooked ends (grappling hook) that allow them to afix to a surface and to eachother to make a biofilm

inclusions

seperate part s of the cytoplasm that store energy or nutrients or some specialized fumction

often visible indo microscope and enclosed by a single-layer membrane of proteins

carbon stoorage polymers

when excess carbon, carbons is turned int o PHB and PHA so that it can be broken down as carbon or energy source when conditions warrant it.

glycogen

similar to PHA, resovior for carbons and energy (made when carbon excess). similar to starch but different linkage of glucose units

phospahatte granules

accumulate phosphates that can be used for nucleic acid and phospholipid biosythesis when phosphat is low.

some orgs can sythesize eneryg-rich compund ATP from ADP

sulfer bacteria

organism that can oxidise reduced sulfer compounds

biomineralization

microbial process for producing minerals

gas vesicles

allow some bacteria and archaea to float

blooms of cynobacteria (oxygenic photosynthesis) are able to form because of these

gas vesical description

conical shape, hollow and risgid with variable length, can be few or hundrends to a cell, are impermable to water and solutes but permeable to gas

gas vesical dimensions

l: 300-1000nm

w:45-120 nm

magnetosomes

biomineralized paricals of magnetic oxides mafnetite that allow some bacteria to orient themselves in a magnetic field

magnetotaxis

process of migrating along the earths magnetic field lines

magnetosomes mophologies

many are present (species specific)

most common are square, rectangular, or spice-shaped

endospore

highly differentiated dormant cells that functions as survival structures and can tolerate harsh conditions.

NOT reproductive, just dormant stage of bacterial life cycle

bacterial life cycle

vegetative cell → endospore → vegitative cell

endospores

only spores that cann tolorate high heat and can live formant for 100-1000(perhaps) years

becuase they only contain ¼ of og water

Bacillales and clostridiales

only two bacteria that can make endospores, gram + and phylum Firmicutes

sporulation

happens through cellular differentiation, generally trigered by limited avalibility of some nutrient

germination

conversion from en endospore to a vegitative cell (rapid)

triggered by nurtient avalibility (generally)

germination steps

activiation

germination

outgrowth

(detailed descript. on p. 92)

endospore under the microscope

stongley refractive, nonreceptive to mosst dies (shows up as light are), except malachite green applied with steam

endospore structure

many layer abscent

core - dna, ribosomes → cytoplasm

inner membrane → cytoplasmic membrane

cortex → peptidoglycan

outer membrane → is specially form during sporulation

endospore coat → layers of spot-specific protiens

some have outer proteinaceous layer → exosporium

dipicolinic acid

accumulatio of this allows for the dehydration of endospores

works with high precens of calcium which binfs water → dehydration

SASPS

small acid-soluble spore proteins. These bind tightly to DNA, preventing heat andradiation damage then in outgrowth, serves as a carbon and energy source.