Triglyceride (fat or oil) esters formed between alcohol (glycerol) and 3 fatty acids

+-

Phosphoglycerides Contain a phosphate ester. The phosphate also forms an ester with an amino alcohol. (e.g. ethanolamine R = H, choline R = CH3, or serine)

CH2-O

CH-O

CH2-O

O-C-R=

O-C-R'=

O-P-O-CH2-CH2-NR3

+==

O-

O-C-R= O-C-R'=

O-C-R''=

CH2-O

CH-O

CH2-O

Triglyceride - Fatty acid storage – Primary energy reserve source for metabolism

Lecithin (a phospholipid/phosphoglyceride) Primary membrane lipid component

Cholesterol – a steroid - Moderates fluidity of animal cell membranes with DT.

Tranport of lipids through blood.

Since lipids are generally nonpolar they do not dissolve readily in the aqueous medium of the blood.

Therefore – Proteins in the blood assist in the solubility and transport of lipids between organs. e.g. ….. intestines to liver – intestines to cells – liver to cells – cells to liver etc.

Serum Albumin - Dominant protein in serum Carries fatty acids through blood Also carries many drugs/antioxidants/etc. Osmotic Pressure due primarily to Serum Albumin

Lipo proteins - Carries triglycerides and cholesterol esters through blood.Apo lipoproteins A, B, C, & E.Includes HDL (good cholesterol) and LDL (bad cholesterol).

Table 2Lipoproteins in the blood

lipoprotein apoproteins

major lipid carried

role

HDL A cholesterol esters ‘cells’ liver into bile or IDL/LDL

IDL B100, E cholesterol esters liver (processed or LDL)

LDL B100 cholesterol esters Liver ‘cells’ for incorporation

VLDL B100, C, E

TG & cholesterol esters

Intestines & liver ‘cells’

Chylomicron remnants

B48, E Dietary cholesterol esters

Intestines liver

chylomicron B48, C, E

dietary TG Intestines & liver ‘cells’

Lipoproteins

good

bad

Lipoproteins

Apolipoprotein modules

Phospholipids cholesterol

Triglycerides & cholesterol esters

Lipid bilayers & Cell Membranes

Why membranes?

Membrane Rafts– contain ordered clusters of glycosphingolipids with longer-than-usual tails– allow segregation of proteins in the membrane

Membrane surfaces are not all uniform

e.g. Prion Protein (PrP)

Functions of Membrane Proteins

Transport material - active or passive transporters or channels

Typically form channel surrounded by TM a-helices

Signal Transduction – receptors (transport ‘message’)

Catalysis in Nonpolar solvent

combinations of the above

Many Integral Membrane protein belong to a family with 7 TM helices

Aquaporins allow rapid water passage through membranes

Although the tranmembrane helices typically have nonpolar side chains, polar or charged groups often line the pores through a ring of helices.

Protein content of Membranes

Inner Mitochondria Red Blood Cell Myelin Sheath

80% Protein & 20% Lipid50% Protein & 50% Lipid20% Protein & 80% Lipid

Cells have many different receptors, transporters, etc.

GLUCOSE TRANSPORTER

• Muscle• passive• deployed - insulin• direction - one way “in” only because [glucose] in blood is high

• Liver• passive• always present• direction: 2-way [Glucose] high → low

Glucose Transporter in the Membrane

There are multiple glucose transporters• A Na+-glucose symporter and a glucose uniporter

operate on opposite sides of epithelial cells• Cells can also have asymmetry, with distinct proteins

confined to one side

Liver/Brain Muscle

I

I

I

Insulin secretion in response ↑ [glucose] in blood, leads to deployment of Glucose transporter in Muscle cells.

This leads to a drop in [glucose] in the blood with a corresponding rise in The [glucose] in muscle cells.

Represents the glucose transporter

Model for Glucose Transport

Chapter 11: Summary

• membranes are composed of various lipids and proteins• phospholipids form a selectively permeable bilayer • properties of the bilayer depend on the lipid composition, which

varies strongly from – organism to organism – tissue to tissue– organelle to organelle

• membrane proteins play a variety of structural and functional roles, especially in the transport of solutes across the membrane

• Active transport of solutes across membranes requires ATP but can be accomplished in many different ways

In this chapter, we learned: