bio 207: lecture 2, cell structure, transport, and function

a gram negative cell envelope includes

• outer membrane

• cell wall

• periplasm

• inner cell membrane

biochemical composition of bacteria

• mostly water

• proteins

• nucleic acids and lipids'

• essential ions

cell composition can vary with

species, growth phase, and environmental conditions

half the cell membrane is composed of proteins, which allows a diverse array of functions including

structural support, cell-cell signaling, detecting signals from the environment, selectively permeable barrier & transport

a bacterial cell membrane must be [?] enough to stay structured but [?] enough to allow proteins to work

rigid; fluid

unsaturated fatty acids are more [?], while saturated fatty acids are more [?]

fluid; rigid

archaeal cell membrane is made up of glycerol and fatty acids that are linked by

ether links, not ester links, which are more stable and rigid

what kind of materials can pass through the membrane with passive diffusion?

small, uncharged molecules; often gases

what kind of materials can pass through the membrane only with active transport?

polar and charged molecules; some large molecules

bacteria have a special kind of cell wall that consists of

a single interlinked molecule of peptidoglycan, which forms a cage-like structure

• highly porous to ions and organic molecules

• cell wall helps with shape and rigidity

• cell wall helps cell withstand pressure of fluid uptake

differences in gram-positive and gram-negative cells

• gram-positive: no outer membrane, thicker cell wall containing many layers of peptidoglycan, teichoic acids (thicker cell wall retains crystal violet stain)

• gram-negative: single-layer peptidoglycan + outer membrane

periplasm

the space between the outer membrane and inner membrane of gram-negative bacteria

• contains peptidoglycan, proteins, ions, enzymes

myobacterial cell envolope

complex cell envelopes uncommon in bacteria, containing unusual membrane lipids (myocolic acids) and unusual sugars

capsules/slime layers

• additional protection from antibiotics and phagocytosis

• made of polysaccharide/glycoprotein

• can be found in both gram-positive and negative bacteria

s-layers

• additional protective layer commonly found in bacteria and archaea

• crystalline layer of thick protein/glycoprotein subunits

• contributes to cell shape

• protects cell from predation, osmotic stress

peptidoglycan is made up of

A single interlinked molecule

Inward facing leaflets of the lipid bilayer have phospholipids with

lipoproteins connecting the outer membrane to the peptidoglycan cell wall

Outer leaflets of the lipid bilayer have

lipopolysaccharides that contains an endotoxin

Selective permeability is achieved in three ways

1. Substrate-specific carrier proteins

2. Credited nutrient - binding proteins in the periplasmic space

3. Membrane-spanning protein channels/pores

Facilitated diffusion

No energy used; facilitates movement along concentration gradients

Coupled transport is

Using the energy released by transferring another molecule down the concentration gradient to transport one against its concentration gradient.

ABC transporters

• family of energy driven transport systems

• protein complexes w hydrophobic membrane units, atp binding units, substrate binding protein

• uptake type: transport nutrients like sugar, amino acids

• efflux type: multidrug efflux pumps (antibiotics)

siderophores

channel protein that transports iron; only in prokaryotes

group translocation

active transport but the molecule is modified as it is transported which creates a gradient that the molecule always moves down

specialized structures of archaea and bacteria

• carboxysomes: full of rubisco for carbon fixation

• gas vesicles: gas filled protein bound structures increasing buoyancy

• pili, flagella: movement