BSCI283 Lecture 3

4 components of the cell envelope

cytoplasmic membrane

cell wall

outer membrane

S layers

formula for fatty acids

CX:Y

X = number carbons

Y = number double bonds

saturated fatty acids

no double bonds

unsaturated fatty acids

1+ double bond

3 head groups of phospholipids

phosphatidylcholine

phosphatidylethanolamine

sugars

fatty acid structure

carboxylic acid group + hydrocarbon chain

phospholipid structure

glycerol + 2 fatty acids + phosphate + polar head group

how many tails does a … have

fatty acid

phospholipid

one

two

what do … assemble into

fatty acid

phospholipid

micelle

bilayer

what is the shape of a…

fatty acid

phospholipid

cone

cylinder

two key types of electron microscopy

SEM (Scanning Electron Microscopy)

TEM (Transmission Electron Microscopy)

SEM shows

surface

TEM shows

through (internal structures)

fluid mosaic model of membrane

fluid - rapid lateral diffusion

mosaic - mosaic of proteins spread throughout membrane

integral membrane proteins

embedded in membrane

peripheral membrane proteins

loosely attached to membrane

bacterial/euk vs. archael membranes

tail

linkage

fatty acid tail vs isoprene tail

ester bond vs ether bond

all bilayers vs some monolayers

3 key functions of cytoplasmic membrane

permeability barrier

protein anchor

energy conservation

cytoplasmic membrane function: energy conservation

site of generation and dissipation of proton motive force

5 types of transport

passive diffusion

facilitated diffusion

primary active transport

secondary active transport

PTS transport

1st law of thermo

matter neither created or destroyed

2nd law of thermo

systems tend to lose order

3rd law of thermodynamics

systems tend to lose free energy

does water diffuse through membranes easily or poorly

poorly (but everything else is worse!)

porin: type of transport

facilitated diffusion

aquaporin: type of transport

facilitated diffusion

aquaporin: structure (3)

tetramer embedded in membrane

inside lining has polar charged amino acids

only big enough for water

graph rate of solute entry vs. external concentration of solute

facilitated diffusion

passive diffusion

hits maximum

linear

what is a key limit to facilitated diffusion

saturation due to limited number of transporter enzymes

what limits facilitated diffusion transport rate at low concentration substrate

substrate

what limits facilitated diffusion transport rate at high concentration substrate

number of channels

ABC transporter: type of transport

primary active transport

ABC transporter: mechanism

biding protein binds specific substrate outside of cell

brings it to ABC transporter

ATP → ADP provides energy

ABC transporter changes shape and moves substrate into cell against gradient

ABC transporter: what does ABC stand for

ATP binding cassette (the portion that provides the energy)

two types of secondary active tranport

antiport → opposite direction

symport → same direction

PTS transport: PTS stands for

phosphoenolpyruvate-dependent transport system

PTS transport: occurs in what type of organism

bacteria

PTS transport: energy source

PEP (not ATP)

this is where the phosphate comes from

PTS transport: typical substrate

sugars

PTS transport: overview

transports sugar into the cell + phosphorylates it

PTS transport: key example

glucose → G6P once inside cell

PTS transport: path of phosphate

PEP → EI → HPR → EIIA → EIIB → sugar

PTS transport: EnzymeIIC function

help sugar cross membrane

PTS transport: flexibility

modular

EI and HPR shared

EIIA, EIIB, and EIIC substrate specific

PTS transport: efficiency

phosphorylated sugars are primed for glycolysis + phosphorylation traps substrate in cell

Candidatus meaning

has not been grown in pure culture

U. amorphum

requires other bacteria around it to grow

Candidatus Uab amorphum: shape

streptococcal

shape can change!

Candidatus Uab amorphum: size

unusually large, 4-10 um

Candidatus Uab amorphum: type of bacteria

planctomycete

planctomycete

unusual bacteria that lack proteins used in bacterial growth/division

common mode of planctomycete cell division

budding

Candidatus Uab amorphum

key feature found using TEM

significance

lots of internal membrane invaginations

it is engulfing other bacteria to eat them

Candidatus Uab amorphum: how do they obtain nutriends

engulf bacterium → enclose it in a membrane compartment → digest it → obtain nutrients

what is the name of the membrane compartment that Candidatus Uab amorphum use to engulf bacteria

phagocytic vacuole

why do Candidatus Uab amorphum have so many transport proteins

import nutrients from dissolved prey into cytosol

Candidatus Uab amorphum: what is a consequence of reliance on other bacteria for nutrients

lacks biosynthetic pathways

siderophore

organic molecule with high iron affinity and chelates iron

what compound is key for life but scarce in the environment

iron

siderophore mechanism

Siderophore binds Fe³⁺ outside → complex binds ABC transporter → ATP is used to import it → iron is released inside.

are siderophores universal

no - specific to each bacterium

Borrelia burgdorferi: what is so rare about it, what does it do instead

doesn’t use iron thus has no siderophores

use other metals (Mn) and enzymes