Biochemistry Exam 3

Kenny Kuo NCSU University BCH 351 Spring 2026

Biological functions of lipids

• storage of energy

• Insulation from environment

• water repellant'

• buoyancy control in marine animals (?) hypothesis

• membrane structure

• cofactors for enzymes

• signaling molecules

• pigments

• antioxidants

What do all FAs have?

Carboxylate group at their head (pka ~4.9) which is hydrophilic

Long hydrocarbon chain which is hydrophobic, 4-36 C (usually even)

Saturated vs unsaturated

Saturated → NO C=C

Unsaturated: Mono means 1 C=C, poly means more than 1 C=C. Can be cis or trans

How do you name a FA

1st number is how many carbons in the FA

2nd number is the number of =

c means cis, t means trans

3rd number is position of =

Lengthening the hydrophobic tail does what to Tm?

Increases

• forces = hydrophobic effects and van der waals

Increasing the number of double bonds does what to Tm?

Lowers

C=C in cis configuration introduce ____ to hydrocarbon tail, which does what?

Bends

• It prevents close packing → less hydrophobic effects and van der waals interactions → lower melting point

Triacylglycerol components

1 glycerol (3-carbon sugar alcohol)

Joined by Ester bonds

3 fatty acyl chains

Facts about triacylglycerols

• Very hydrophobic → water insoluble

• Dietary fats and oils

• Major form of energy storage

• Variation in FA chain length and saturation provides a great diversity of triacylglycerol structure (LONG = solid, SHORT = liquid)

Glycerophospholipids

Phosphate group at C3

1 Glycerol (backbone)

2 fatty acyl chains (1 at C1 and C2, vary in size/saturation)

R3 group (H or complex)

Amphipathic

Most abundant lipids in cell membranes

Name this glycerophospholipid

Phosphatidylserine

Name this glycerophospholipid

Phosphatidylethanolamine

Name this glycerophospholipid

Phosphatidylcholine

Name this glycerophospholipid

Phosphatidylinositol

Sphingolipid facts

• Backbone is sphingosine

• Second most abundant lipids in animal and plant membranes

• Sphingolipids are important in membranes of nerve cells and myelin sheaths

Sphingolipid structure

Backbone is sphingosine (18 C, trans double bond at carbon 4)

• Attached group is often a sugar on C1

• Attached group is often a FA on C2

Fatty acyl group linked to C2 amino groyp

precursors of all sphingolipids

Addition of a phosphocholine to ceramide at C1 makes a …

Sphingomyelin (sphingophospholipids)

Addition of a simple sugar to ceramide at C1 makes a…

Cerebroside (glycosphingolipid)

Addition of complex sugar to ceramide at C1 makes a…

Ganglioside (glycosphingolipid)

Steroids

The biosynthetic precursor of steroids is cholesterol, which consists of 4 rings structure (three 6-Carbon rings, A,B,&C, and a single 5-carbon ring, D).

• Very hydrophobic, with just one small polar group (OH at C3)

• Very bulky and rigid because its 4 rings

• Precursor for synthesis of hormones and component of cell membrane in animals