Lipids, Fatty Acids, Triglycerids, Cholesterol : Wednesday

What are lipids?

Lipids are mostly nonpolar molecules that do not dissolve well in water. They dissolve better in organic solvents

Why are lipids poorly soluble in water?

Because they have long nonpolar hydrocarbon chains. Water is polar, so it does not mix well with nonpolar lipids

What does amphipathic mean?

A molecule has both a hydrophilic part and hydrophobic part.

What are the two major lipid categories from the slides?

Open-chain lipids and fused-ring lipids

What are examples of open-chain lipids?

• Fatty acids

• Triglycerides

• Sphingolipids

• phosphoaylglycerols

• Glycolipids

What are examples of fused-ring lipids?

• Cholesterol

• Steroid hormones

• Bile acids

What is a fatty acid?

A fatty acid is an unbranched carboxylic acid chain, usually 12-20 carbons long.

What is a saturated fatty acid?

A fatty acid with only single bonds between carbons

What is an unsaturated fatty acid?

A fatty acid with one or more carbon-carbon double bonds

What does a cis double bond do to a fatty acid?

It creates a bend or “kink” in the fatty acid chain

Why do unsaturated fatty acids have lower melting points?

Their kinks prevent tight packing, so they melt more easily

What happens to melting point as fatty acid chain length increases?

Melting point increases because longer chains have stronger van der Waals interactions.

What happens to melting point as the number of double bonds increases?

Melting point decreases because more kinks prevent tight packing

Why are oils usually liquid at room temperature?

They contain more unsaturated fatty acids, which have lower melting points

Why are fats usually solid at room temperature?

They contain more saturated fatty acids, which pack tightly and have higher melting points

What are triglycerides/ triacylglycerols?

Lipids made from glycerol attached to three fatty acids

What is the main function of triglycerides?

Long-term energy storage in adipose tissue/body fat

Why are fats good for long-term energy storage?

Fatty acids are highly reduced and store more energy per carbon than carbohydrates

Why do fats store more energy than glycogen?

Fats carry less water because they are nonpolar, so they are more concentrated energy storage

What are sphingolipids?

Membrane lipids built from sphingosine instead of glycerol. They are important in cell membranes and signaling

What are glycolipids?

Lipids with carbohydrate groups attached. They are important for cell recognition

How are glycolipids connected to blood type?

Blood groups antigens are based on different carbohydrate groups on cell-surface glycolipids/glycoproteins

What is cholesterol?

A fused-ring lipid found in membranes and used to make steroid hormones, bile acids, and vitamin D

How does cholesterol affect membranes?

It helps regulate membrane fluidity and stability

What are steroid hormones made from?

Cholesterol

What are examples of steroid hormones?

• Estrogen

• Testosterone

• Cortisol

• Aldosterone

What lipid-related disease is linked to high LDL and low HDL?

Atherosclerosis, which is plaque buildup in arteries

Why is high LDL a warning sign?

LDL can contribute to cholesterol buildup in blood vessels

Why is HDL considered “good cholesterol”?

HDL carries cholesterol from tissues back to the liver