Lipids and Membranes

1 Lipids and Membranes

Outline - Chapter 9 in Text

Classes of lipids
- Fatty Acids
- Triglycerides
- Phospholipids
- Steriods
Lipoproteins
Membranes - Structure and Transport

2 Fatty Acids

Carboxylic acids

Mostly Non-polar
- Long, unbranched, hydrocarbon chain
- » 14-26 carbons per chain (usually even #)

Polar Head group
- Carboxylate (-COO ^-1 ) at physiological pH

Normally found in low concentrations

3 Saturated Fatty Acids

CH ₃ -[CH ₂ ] _n -COOH

(n » 12-24)

Saturated: No C=C

Lowest energy structure is » linear

4 Unsaturated Fatty Acids

18:1 ^D9

Unsaturated: Contains C=C
- Geometry around C=C is cis.
- Monounsaturated - only 1 C=C
- Polyunsaturated - more than 1 C=C

Lower melting points

5 Nomenclature: Linoleic acid

Following system used:

18:2 ^D9,12

18: number of C in chain

2: # of C=C double bonds

9, 12: Position of C=C (starting with COOH)

Example:

CH ₃ -(CH ₂ ) ₄ -CH=CH-CH ₂ -CH=CH-(CH ₂ ) ₇ -COOH

6 Triacylglycerols

Commonly called triglycerides

Purpose:

Energy: High density (9 Cal/g, non-polar)

Insulation

7 Fats in Our Diet

Essential Fatty Acids
- Humans are unable to synthesize certain fat acids
- Ex. linoleic (18:2 ^D9,12 ) and linolenic (18:3 ^D9,12,15 )

Partial Hydrogenation & Trans Fats
- Saturated: solid, more stable
- Unsaturated: liquid
- Partial hydrogenation
  - Designed to give optimal shelf life and texture
  - Trans fat implicated in cancer, ...

8 Phospholipids

Major component of membranes

9 Cholesterol

Cholesterol is composed of four fused rings.

All steroids have this same 4-ring core.

10 Good vs. Bad Cholesterol

Cholesterol is a single molecule. It does NOT have a ``good'' and a ``bad'' form. ``Good'' and ``Bad'' refer to the cholesterol carrier.

VLDL: Very Low-Density Lipoprotein
Transports cholesterol from liver to tissue.

LDL: Low-Density Lipoprotein
Further transport cholesterol to tissue.

HDL: High-Density Lipoprotein
Transports cholesterol from tissue to liver for ``disposal''.

11 Membranes

This ``cartoon'' represents some of the important aspects of cellular membranes. The surface interacts well with water, but the interior is NOT water-soluble.

12 Lipid Bilayer

File translated from T_EX by T_TH, version 3.02.
On 14 Mar 2002, 13:46.