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
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–
–
–
–
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
• a
membranes
• Strengthen and stabilize
membranes
– Hopanoids
• Structurally similar to
sterols
• Present in membranes
of many Bacteria
a = sterol (cholesterol)
b = hopanoids
Phospholipids
• H2C-OH
• HC-OH
• H2C-OH
Glycerol
• 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 • Archaea contain ether(bacteria and eukarya)
linked lipids
– Polar headglycerol
– Nonpolar tailfatty acid
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