Chapter 15: Lipid Structure and Function

Question 1

What are many lipids made from?

Answer 1

fatty acids

Question 2

What are some of the roles that lipids serve in the body?

Answer 2

• energy storage
• cell membranes
• endocrine signaling

Question 3

Describe fatty acids

Answer 3

• consist of a carboxylic acid and a hydrocarbon tail 4-36 C long
• the most abundant fatty acids are unbranched chains of 12-20 carbons and are even numbered
• can covalently bond to proteins to tether proteins to biological membranes

Question 4

Compare saturated to unsaturated fats

Answer 4

Saturated fats contain fully reduced methylene groups (maxed out on H) and are typically solid at room temp

Unsaturated fatty acids contain at least one double bond (makes a kinked shape). Monounsaturated have one double bond while polyunsaturated FA contain multiple double bonds. They are typically liquid at room temp

Question 5

Why are saturated FAs solid and unsaturated FAs liquid at room temp?

Answer 5

Saturated FAs have regular packing and more extensive intermolecular interactions.

Unsaturated FAs have looser packing and fewer intermolecular interactions due to the branching in their tails

Question 6

What is hydrogenation?

Answer 6

The commercial process of using H2 gas to reduce C to C double bonds.

This process raises the melting point of lipid mixtures and converts unsaturated fatty acids to saturated fatty acids.

It produces a semisolid mixture.

Question 7

What are trans fats?

Answer 7

Fatty acids created by partial hydrogenation. They are associated with high rates of cardiovascular disease. They were ruled unsafe by the FDA in 2013, and have been found to increase levels of LDL while decreasing levels of HDL

Question 8

What are waxes?

Answer 8

Molecules classified as lipids that contain long chain alcohols linked to long-chain fatty acids.

They have high melting points.

Question 9

How much energy is released from the full oxidation of a triglyceride?

Answer 9

~ 38 kJ/g

Question 10

How are dietary TGs packaged?

Answer 10

as chylomicrons

Question 11

How are TGs synthesized in the liver packaged?

Answer 11

as VLDL particles (lipoprotein)

Question 12

How are TGs released from adipose packaged?

Answer 12

as albumin

Question 13

Describe the process of TG packaging to VLDLs in the liver.

Answer 13

• Triacylglycerol biosynthesis uses acetyl-CoA and proteins to generate palmitic acid in the cytosol
• palmitic acid is converted to triacylglycerols and exported as VLDL particles
• liver VLDL assembled in endoplasmic reticulum and Golgi body, then repackaged and exported to circulatory system
• liver cells synthesize cholesterol from acetyl-CoA, which is packaged into VLDL particles as cholesterol esters
• VLDL particles deliver triacylglycerols and cholesterol esters to tissues throughout the body

Question 14

What are lipid droplets?

Answer 14

storage vehicles for newly formed triacylglycerols from adipocytes

they are surrounded by a phospholipid monolayer containing perilpin

Question 15

How are triacylglycerols metabolized?

Answer 15

They are cleaved by lipases to generate free fatty acids and glycerol

Fatty acids can pass through the membrane on the luminal side of intestinal epithelial cells

Question 16

How is the glucagon signaling pathway involved with fatty acid metabolism?

Answer 16

Glucagon signaling initiates a cascade resulting in fatty acid release to the bloodstream

Question 17

What are the three major membrane lipids?

Answer 17

1. glycerophospholipids
2. sphingolipids
3. cholesterol

Question 18

Describe glycerophospholipds

Answer 18

• they are the most abundant membrane lipids
• they are an important source of FA derived signaling molecules, which are released by phospholipase enzyme catalysis
• contain two FAs and a phosphate group attached to a glycerol

Question 19

Describe sphingolipids

Answer 19

they are derived from sphingosine and one FA

Question 20

What is Tay-Sachs Disease?

Answer 20

A lipid based genetic disorder. Normally, the enzyme hexosaminidase A acts on ganglioside GM2 (a sphingolipid) to remove its terminal moiety and form ganglioside GM3.

In patients with Tay-Sachs, hexosaminidase A is defective causing a building up GM2 ganglioside in the spleen and brain.

Symptoms include developmental delays, cognitive dysfunction, and death.

Question 21

What proportion of lipids in the plasma membrane is composed by cholesterol?

Answer 21

25-40%

Question 22

What is the structure of cholesterol?

Answer 22

contains 27 carbons and a rigid four-ring steroid core

Question 23

What function does cholesterol serve in the membrane?

Answer 23

affects membrane fluidity

Question 24

What are lipid rafts?

Answer 24

Protein aggregated into discrete patches as densely packed protein complexes.

These areas contain large transmembrane proteins and act as receptors for extracellular signaling.

Question 25

How do lipids function in cell signaling?

Answer 25

The hydrophobic property of lipids contributes to their function as high-affinity stereospecific ligands that bind to hydrophobic pockets in receptor proteins

Question 26

What is cholesterol a precursor to?

Answer 26

steroid hormones and bile acids derived from mevalonate

Question 27

Excess levels of cholesterol contribute to what condition?

Answer 27

cardiovascular disease

Question 28

What do steroid hormones do?

Answer 28

They can act as ligands for nuclear receptor proteins which mediate hormone signals by altering the expression for specific genes They are potent signaling molecules that have a critical role in: - cell development - reproductive biology - organismal physiology

Question 29

progesterone

Answer 29

synthesized by corpus luteum functions in menstration, development of mammary tissue

Question 30

cortisol

Answer 30

synthesized by adrenal cortex functions in liver metabolism, immune functions, adaptation to stress

Question 31

aldosterone

Answer 31

synthesized by adrenal cortex functions in ion transport in the kidneys, blood pressure regulation

Question 32

testosterone

Answer 32

synthesized by testicles, adrenal cortex functions in development of male reproductive organs

Question 33

estradiol

Answer 33

synthesized by ovaries development of female reproductive organs

Question 34

What are synthetic hormones?

Answer 34

Agonists that mimic the biological response of the hormone

Question 35

dihydrotestosterone

Answer 35

natural androgen agonist that promotes male reproductive development

Question 36

nandrolone

Answer 36

potent synthetic androgen agonist that has been used by bodybuilders

Question 37

bicalutamide

Answer 37

nonsteroidal androgen antagonist used to treat prostate cancer

Question 38

Vitamin D

Answer 38

the "sunshine" vitamin converted to the active form 1,25-dihydroxyvitamin D3 from 7-dehydrocholesterol

Question 39

What are eicosanoids?

Answer 39

A group of signaling molecules derived from 20C polyunsaturated fatty acids. They have important roles in inflammation. Eicosanoids are released from the membrane by phospholipids and modified by mitochondrial enzymes. They're produced by cells at their sites of action (paracrine) and have half-lives on only a few minutes.

Question 40

What are the four major classes of eicosanoids?

Answer 40

prostaglandins prostacyclins thromboxanes leukotrienes

Question 41

What are NSAIDs?

Answer 41

non-steroidal anti-inflammatory drugs

Question 42

Why are selective COX inhibitors preferred to non-selective versions?

Answer 42

Selectively inhibiting COX-2 it can prevent unwanted side effects. Non-selectively inhibiting COX-1 along with COX-2 can lead to GI issues since COX-1 is more broadly expressed and has more functions.