Overview of Lipid Biochemistry

Question 1

Fatty acids are categorized as either ____________.

Answer 1

saturated or unsaturated

Question 2

What is triglycerol?

Answer 2

A three-carbon chain with hydroxyl groups on each carbon.

Question 3

Explain how fatty acids are a part of triglycerides –which can be put into gluconeogenesis –but cannot serve as substrates for gluconeogenesis.

Answer 3

The triglyceride carbons that go into gluconeogenesis come from the triacylglycerol backbone, not the fatty acid chains that get esterified to triacylglycerol to form triglycerides.

Question 4

Describe the overall structure of phospholipids.

Answer 4

Phospholipids are based on the structure of triglycerides: there are two hydrocarbon chains esterified to a glycerol backbone, but the third carbon is replaced by a phosphate group.

Question 5

Which kinds of lipids are the most polar? The least?

Answer 5

(Most polar)
Free fatty acids

(Least polar)
Triglycerides and cholesterol esters

Question 6

What phospholipid ratio is tested for evaluation of fetal lung disease?

Answer 6

Phosphatidylcholine (a type of lecithin) : sphingomyelin ratio greater than 2 indicates lung maturity

Question 7

Describe the synthesis of fatty acids and note the regulated step.

Answer 7

Acetyl co-a
(Acetyl co-a carboxylase) REGULATED STEP
Malonyl co-a
(Fatty acid synthase –two-carbon transfers of acetyl co-a on to malonyl co-a and the subsequent growing fatty acid)
Fatty acids

Question 8

Lipoprotein lipase does what ____________.

Answer 8

moves triglycerides from the blood to the adipose tissue

Question 9

VLDL serves what purpose?

Answer 9

It delivers fat from the liver to adipose tissue.

Question 10

Acetyl co-a carboxylase is stimulated by ___________.

Answer 10

glucose

Question 11

Triglycerides are moved out of adipocytes by ______________.

Answer 11

hormone-sensitive lipase

Question 12

When fatty acids move into liver or muscle cells, they bond with ____________.

Answer 12

acyl, for fatty acyl co-a

Question 13

What is the regulated step in lipolysis?

Answer 13

Carnitine palmitoyl transferase (which pumps acyl into mitochondria)

Question 14

True or false: free fatty acids are complexed to proteins in transport.

Answer 14

True.

Question 15

Ketones are made from ____________ by the enzyme _______________.

Answer 15

acetyl co-a; HMG co-a synthase

Question 16

Trace the cholesterol-synthesis pathway and list the regulated steps.

Answer 16

Acetyl co-a
(HMG co-a synthase)
HMG co-a (hydroxymethyl glutaryl co-a) 
(HMG co-a reductase) ***REGULATED STEP; USES NADPH***
Mevalonate
Cholesterol

Question 17

What are the five major groups of lipids?

Answer 17

Glycolipids
Phospholipids
Cholesterol
Triacylglycerides
Free fatty acids

Question 18

VLDL is ________________.

Answer 18

triglycerides packed with proteins circulating in the blood

Question 19

When glucagon is high and insulin low, triglycerides in adipose tissue are broken down by ______________.

Answer 19

hormone-sensitive lipase

Question 20

Lipase breaks down triglycerides to triacylglycerol and free fatty acids that ______________. After getting there, what happens?

Answer 20

circulate to the liver; they must be converted to acetyl carnitines that get pumped into the mitochondria of hepatocytes by carnitine palmitoyl transferase 1 (which is the rate-limiting step in fat oxidation)

Question 21

In the mitochondria of hepatocytes, fatty acids get _______________.

Answer 21

broken down in two-carbon fragments (beta oxidation) that enter the TCA cycle as acetyl co-a

Question 22

The rate-limiting step in ketogenesis is _____________.

Answer 22

synthesis of Hmg Co-a

Question 23

Sphingolipids have a ____________ backbone.

Answer 23

ceramide (nitrogen-containing because it is derived from serine)

Question 24

HDL is thought to ________________.

Answer 24

deliver peripheral cholesterol to the liver