Chapter 3

Part 2

This chapter contains a lot of chemistry

• Read your textbook!!!• Find your biology 1107 textbook or cell

biology textbook and read about membranes

• Look at your organic chemistry/chemistry textbooks

• Read about esters, ethers, glycerol and phospholipids

Look at chapter 3 chemistry worksheet

Outline• Membrane structure

• Basic backbone• Differences between eukaryotes and

prokaryotes• What is different about archae?

• Membrane function• Transport mechanisms

Membranes• Get together with a partner(s)• Draw a membrane

– Include 3 of the 4 class of molecules in nature– What is on the outside?– What is one the inside?– Or, inbetween?– How is a eukaryotic membrane diff. from

prokaroytic?– What is the function(s) of a membrane?

Membrane lipids– Sterols

• Rigid, planar lipids

found in eukaryotic

membranes

• Strengthen and stabilize

membranes

– Hopanoids

• Structurally similar to

sterols

• Present in membranes

of many Bacteria

• a

a = sterol (cholesterol)b = hopanoids

Phospholipids• H2C-OH• HC-OH Glycerol• H2C-OH

• In phospholipids, two of the OH groups are linked to fatty acids and one of the OH groups is linked to a phosphorylated alcohol

• Fatty acids have a carboxyl group with long hydrocarbon tails

Phospholipid Backbone• Ester linked

phospholipid (bacteria and eukarya) – Polar headglycerol– Nonpolar tailfatty

acid

• Archaea contain ether-linked lipids

Bacterial /Eukaryotic membranes

• glycerol ester link• R=fatty acid (saturated or unsaturated)

Archae are different from eukarya and bacteria

• Ether linkage between glycerol and hydrophobic side chains

• Instead of fatty acids, they have side chains composed of the 5C hydrocarbon isoprene– extra CH3 group

Archaeal Membranes– Ether linkages in phospholipids

– Different from Bacteria and Eukarya that have

ester linkages in phospholipids

– Archaeal lipids lack fatty acids, have

isoprenes instead

– Major lipids are glycerol diethers

Two types of lipids in archaeal membranes

• Glycerol diether– Contains phytanyl– 4 linked isoprene

units (5 carbons)

Two types of lipids in archaeal membranes

• Diglycerol tetraether– Contains 2 phytanyl

groups linked together

Archaea membrane lipids

Archaea Lipid Structure

• Glycerol diether (phytanyl) forms a bilayer

• Diglycerol tetraether

(biphytanyl) forms a

monolayer

Questions on Membrane lipids

Membrane transport systems

• Simple transporters • Phosphotransferase-type transporters (group

translocation)• ABC (ATP-binding cassette) transporters

• All require energy in some form, usually proton motive force or ATP

Membrane transport systems

Simple transport

• Transport proteins = carrier proteins

• Enery or no energy• 1 or 2 molecules

Proton motor force (PMF) drives transport in symport or antiport

• protons concentrated on outside of cell generates potential energy

• Protons (H+) move from high to low energy• Energy released used to drive the movement of

another molecule from low to high energy

H+ goes from high to low concentration while another molecule goes from low to

high concentration

Next group of transporters = group translocation

• Phosphotransferase-type transporters • the transported substance

is chemically altered during transport

• Examples: glucose, mannose and fructose• Enzymes are first

phosphorylated• Then sugars are

phosphorylated during transport

• Energy derived from PEP

Last transporters = Periplasmic binding proteins and ABC

transporters

• Periplasm found in

gram – bacteria• Contains numerous

proteins involved in

transport

ATP binding cassette

• 3 parts

• Periplasmic binding protein• Membrane spanning transporter• ATP hydrolyzing protein

ABC: ATP Binding Cassette

• Binding protein• Extremely high affinity for substrate• Uptake of nutrients in really low concentration (EX. Maltose)• Gram – cells: periplasmic protein and is mobile• Gram + cells: membrane spanning protein and is attached

• Transporter• Membrane spanning

• ATP hydrolyzing protein• Spans membrane and extends into cytoplasm

• ATP provides energy for transport