BROCK BIOLOGY - CHAPTER 2

cell envelope

it consists of a series of layered structures that surround the cytoplasm and govern cellular interactions with the external environment

phospholipid bilayer

A thin, double-layered structure (lipid bilayer) that forms the core matrix of the cytoplasmic membrane in Bacteria and Eukarya (and parts of Archaea), measuring roughly 8–10 nm wide

hydrophilic

water-loving

hydrophobic

water-hating

bacteria and eukarya

has fatty acid tails bound to glycerol

archaea

has isoprenoid tails bound to glycerol

ester linkages

linkages in bacteria and eukarya

ether linkages

linkages in archaea

glycerophosphate

bacteria and eukarya is consist of glycerol molecule bound to a phosphate

transmembrane proteins

firmly embedded in the membrane and act as channels and carriers for nutrient transport and energy conservation system

peripheral membrane proteins

loosely attached to a membrane surface and do not span the bilayers, and assist in cell signaling, energy processing, metabolic reaction steps

permeabilty barrier
protein anchor
energy conservation

major functions of cytoplasmic membrane

active transport

the process by which cells accumulate solutes against the concentration gradient

simple transport
abc transporter systems
group translocation

three basic mechanism of active transport

simple transport

driven by the energy of the proton motive force

abc transporter system

consists of tbinding proteins where energy comes directly from ATP

group translocation

the transported substance is chemically modified during transport, driven by an energy-rich compound like phosphoenolpyruvate (PEP)

cell lysis

process in which cell bursts and dies due to the rupture of its cytoplasmic membrane

cell wall

can withstand high internal osmotic turgor pressure to prevent cell lysis and maintain cell shape

peptidoglycan

• unique to bacteria

• composed of glycan backbone of alternating repeats of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)

• joined by beta-1.4 linkages

gram-positive

has thick peptidoglycan layer contaning acidic molecules called teichoic acids

gram-negative-

has thin peptidoglycan layer

lysozyme

• enzyme that can destroyed the peptidoglycan

• in humans it can be found in tears and saliva

• causing cell lysis when cleaves with beta-1,4 glycosidic bond b/w G and M

penicillin

• can destroyed peptidoglycan

• prevents the formation of peptide cross-links

outer membrane

a second lipid bilayer found external to the cell wall, but structure and function differs from cytoplasm

outer membrane

found exclusively in gram-negative bacteria, positioned outside the thin peptidoglycan layer

lipopolysaccharide

instead od phospholipids, the outer leaflet of the outer membrane is composed of

lipid a
core polysaccharide
0-specific polysaccharide

LPS structure

lipid a

• innermost anchor

• functions as an endotoxin, causing toxic symptoms like fever, diarrhea, and vomiting in infections by salmonella, shigella, and e.coli

core polysaccharide

short sugar chain connecting lipid a to the outer chain

o-specific polysaccharide

long, variable outer sugar chain used for species recognition and immune evasion

porins

trimeric transmembrane proteins forming water-filled channels in the outer membrane that allow the non-specific or specific diffusion of small hydrophilic solutes, making th eouter membrane more permeable thatn cytoplasmic membrane

periplasm

• 15 nm aqueous compartment between the cytoplasmic and outer membrane

• contains hydrolytic enzymes, substrate-binding proteins for trasnport, chemoreceptors, and structural assembly proteins