biochem 3 last merge

General lipid properties

Hydrophobic or amphipathic biomolecules made mostly of C and H

Lipid solubility

Insoluble in water, soluble in organic solvents

Why lipids store energy well

Highly reduced (many C–H bonds)

Main lipid functions

Energy storage, insulation, cushioning, membrane structure

Lipids in membranes

Form barriers to water and polar molecules

Major membrane lipid classes

Glycerophospholipids, sphingolipids, sterols

Fatty acid definition

Long hydrocarbon chain with carboxylic acid (R–COOH)

Fatty acid structure

Unbranched, even number of carbons (12–20 typical)

Fatty acid charge at pH 7

Ionized (–COO⁻)

Fatty acid classification

Saturated, monounsaturated, polyunsaturated

Saturated fatty acids

No double bonds

Unsaturated fatty acids

One or more double bonds

Cis double bonds

Introduce kinks in fatty acid chains

Effect of kinks

Prevent tight packing → increase fluidity

Fatty acid notation example

18:3Δ9,12,15 (linolenate)

Omega (ω) carbon

Carbon farthest from carboxyl group

Effect of chain length on melting point

Longer chain → higher melting point

Effect of double bonds on melting point

More double bonds → lower melting point

Trans fats

Artificial fats with trans double bonds

Why trans fats are harmful

Pack like saturated fats, disrupt membranes

Essential fatty acids

Must be obtained from diet

Example essential fatty acid

α-linolenic acid (omega-3)

Arachidonic acid

Precursor for signaling molecules (eicosanoids)

Triacylglycerols (TAGs)

Storage form of fatty acids

TAG structure

Glycerol + 3 fatty acids (ester bonds)

TAG properties

Neutral, highly hydrophobic

Why TAGs store more energy than carbs

No water and more reduced carbon

Energy comparison

~2–3× more than carbs/proteins

Why glycogen stores less energy

Requires water solvation

Glycerophospholipids

Amphipathic membrane lipids

Structure of glycerophospholipid

Glycerol + 2 fatty acids + phosphate + head group

Amphipathic molecule

Has both hydrophilic and hydrophobic regions

Typical fatty acid positions

C1 saturated, C2 unsaturated

Phosphatidate

Precursor to glycerophospholipids

Head group function

Determines lipid interactions and properties

Lipases

Enzymes that hydrolyze ester bonds in lipids

Why phospholipids form bilayers

Shape + amphipathic nature

Why fatty acids form micelles

Wedge shape, less amphipathic

Plasmalogens

Glycerophospholipids with vinyl ether linkage

Where plasmalogens are found

Muscle and nerve tissue

Sphingolipids

Lipids with sphingosine backbone

Sphingosine structure

Long-chain amino alcohol

Ceramide

Basic sphingolipid (sphingosine + fatty acid)

Sphingomyelin

Ceramide + phosphocholine

Cerebrosides

Ceramide + single sugar

Gangliosides

Ceramide + complex oligosaccharide

Where sphingolipids are found

Cell membranes, especially neurons

Ganglioside function

Cell recognition and signaling

Disease linked to gangliosides

Tay-Sachs disease

Blood group antigens

Determined by glycosphingolipid oligosaccharides

Lipid degradation location

Lysosomes

Phospholipase function

Remove fatty acids from phospholipids

Isoprenoid lipids

Derived from 5-carbon isoprene units

Steroid structure

Four fused rings (3 six-membered + 1 five-membered)

Cholesterol structure

Rigid, mostly hydrophobic sterol with small polar OH

Cholesterol function

Modulates membrane fluidity

Cholesterol location

Between phospholipid tails

Cholesterol as precursor

Steroid hormones and bile salts

Cholesterol esters

Storage/transport form of cholesterol

Waxes

Long-chain fatty acid + long-chain alcohol

Wax function

Waterproofing and protection

Eicosanoids

Signaling lipids derived from arachidonic acid

Examples of eicosanoids

Prostaglandins