Lipids

Key learning outcomes related to lipids

Importance of lipids; classification; saturated vs. unsaturated structure; membrane lipids; signalling and cofactor roles

What makes lipids insoluble in water?

Fewer polar OH groups and more non-polar CH bonds

Are lipids polymers like proteins and carbohydrates?

No, lipids are not polymers but they can aggregate

What are some simple lipids?

Oils, fats, waxes

What are examples of complex lipids?

Glycerophospholipids, steroids, prostaglandins

Major functions of lipids

Structure, energy storage, insulation, hormones, vitamins, signalling, protection, waterproofing

How many calories per gram do fats provide?

9 calories per gram

What are the two main classifications of fatty acids?

Saturated and Unsaturated

What structural difference exists between saturated and unsaturated fatty acids?

Saturated: straight chains; Unsaturated: kinked chains due to double bonds

What does the kink in unsaturated fatty acids do?

Prevents tight packing; lowers melting point; increases membrane fluidity

What is a triacylglycerol made of?

Three fatty acids esterified to one glycerol molecule

Why are triacylglycerols efficient for energy storage?

They are more reduced than carbohydrates and store more energy

What enzyme breaks down triacylglycerols?

Lipase

What is a glycerophospholipid?

Glycerol-3-phosphate with fatty acids at C1 and C2, phosphate group at C3

What property makes glycerophospholipids important for membranes?

They are amphiphilic (hydrophilic and hydrophobic ends)

What is phospholipase A2?

Enzyme that hydrolyzes the fatty acid at C2 in phospholipids

What are lysophospholipids and what do they do?

Breakdown products of phospholipids; act as detergents; cause membrane lysis and pain

What lipid-derived molecule is central to inflammation and pain?

Arachidonic acid (precursor to prostaglandins and other eicosanoids)

What class of lipids contains sphingosine?

Sphingolipids

How do sphingolipids differ from glycerophospholipids?

Use sphingosine instead of glycerol backbone

What is sphingomyelin and where is it found?

A sphingolipid found in the myelin sheath of nerve cells

What is the structure of cholesterol?

Steroid nucleus (4 rings), OH group (polar head), alkyl side chain

What are the roles of cholesterol in the membrane?

Provides rigidity and reduces fluidity

What are some steroid hormones derived from cholesterol?

Cortisol, aldosterone, testosterone, estradiol, progesterone

How is Vitamin D synthesized from cholesterol?

UV light opens the B ring in skin; liver and kidneys process into active Vitamin D

What vitamins are fat-soluble?

A, D, E, K

Which lipids act as enzyme cofactors?

Fat-soluble vitamins D, E, and K