Lipids & Lipid Catabolism

Question 1

Most fatty acids are __ to __ carbons in length.

Answer 1

16; 18

Question 2

Most fatty acids have an [even/odd] number of carbons.

Answer 2

even

Question 3

The majority of fatty acids in plants and animals are ______.

Answer 3

unsaturated (Often polyunsaturated/PUFAs)

Question 4

The first double bond is usually between carbon __ and carbon __.

Answer 4

9; 10

Question 5

In PUFAs, are double bonds conjugated or not?

Answer 5

Not conjugated

Question 6

Fatty acid double bonds are almost always [cis/trans], giving them a rigid __º bend.

Answer 6

cis; 30

Question 7

Melting point [increases/decreases] with chain length and [increases/decreases] with unsaturation/double bonds.

Answer 7

increases; decreases

Question 8

The oxidation of fatty acids to ___ and ___ is highly [endergonic/exergonic].

Answer 8

CO2; H2O; exergonic

Question 9

What is the chemical formula for fatty acids?

Answer 9

CH3(CH2)nCOOH

Question 10

What’s the difference between saturated and unsaturated fatty acids?

Answer 10

Saturated: No double bonds
Unsaturated: Contains at least one double bond

Question 11

Where is the alpha carbon in a fatty acid?

Answer 11

Next to C1, the carboxylate carbon

Question 12

For PUFAs, C1 is assigned to the _____ _____ _____, and it’s also designated __.

Answer 12

terminal methyl carbon, omega (ω)

Question 13

Cis double bonds restricts _____ and causes a _____ in the hydrocarbon tail.

Answer 13

rotation; bend

Question 14

Saturated fatty acids pack into ______ ______.

Answer 14

crystalline arrays

Question 15

Glycerol and fatty acids are esterified to generate a _______.

Answer 15

triacylglycerol/triglycerides

Question 16

What are the two advantages that triglycerides (as storage forms of energy) have over polysaccharides?

Answer 16

1. More reduced than carbohydrates, so contain 2x as much energy per gram
2. Since hydrophobic, don’t need to carry the weight of water necessary for hydration

Question 17

Trans fats make oils ____ at room temperature.

Answer 17

solid

Question 18

Why are trans fats bad for you?

Answer 18

1. Increased risk of heart disease
2. Increases LDL (bad) cholesterol
3. Lowers HDL (good) cholesterol

Question 19

Trans fatty acids are _____, making their melting points [higher/lower] than those with cis bonds.

Answer 19

linear; higher

Question 20

Lipid bilayers are amphipathic. What does this mean?

Answer 20

They have both polar/hydrophilic and non-polar/hydrophobic regions.

Question 21

What model is used to illustrate membrane structure? What does it look like?

Answer 21

Fluid mosaic model

Integral proteins float in this sea of lipid.
Proteins and lipids are free to move laterally in the plane of the bilayer.
(Movement from one leaflet of the bilayer to the other is restricted)

Question 22

Why do lipid bilayers form?

Answer 22

Each lipid molecule has a very hydrophobic tail, which forces surrounding H2O molecules to become highly ordered.

This goes against the second law of thermodynamics, which says that the entropy of an isolated system not in equilibrium will tend to increase over time (become more random).

Question 23

Clusters of lipid molecules and micelles increase entropy. Why?

Answer 23

Only lipid portions at the edge of the cluster force the ordering of water. Fewer H2O molecules are ordered.

All hydrophobic groups are concealed from water in micelles.

Question 24

Steroid hormones are [slow/fast]-acting, and they effect gene expression by doing what?

Answer 24

slow; activating nuclear receptors

Question 25

Some lipids are fast acting and bind to what?

Answer 25

Membrane receptors

Question 26

Cyclooxygenase (COX) converts arachidonic acid to what?

Answer 26

C20 eicosanoids (Ex. Prostaglandins, thromboxanes, and leukotrienes)

Question 27

What do nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen do?

Answer 27

They block the formation of prostagladins and thromboxanes from arachidonate by inhibiting the enzyme cyclooxygenase (COX)

Question 28

Aspirin is a [covalent/noncovalent], _____ inhibitor. Ibuprofen is a [covalent/noncovalent], _____ inhibitor.

Answer 28

covalent; suicide noncovalent; competitive

Question 29

Why are omega-3 fatty acids healthy?

Answer 29

They're converted to arachidonic acids more slowly than omega-6 fatty acids, increasing the omega-3/omega-6 ratio and reducing inflammation

Question 30

Fats provide __ times the metabolic energy of an equal weight of hydrated glycogen.

Answer 30

6

Question 31

The rate of lipid digestion depends on what?

Answer 31

The surface area of the interface

Question 32

Triacylglycerols are degraded into free fatty acids and glycerol by what?

Answer 32

Lipases

Question 33

What do pancreatic lipases do?

Answer 33

Catalyze the sequential hydrolysis of triacylglycerols at their 1 and 3 positions, generating two free fatty acids and a 2-monoglyceride

Question 34

Phospholipids are also degraded by what? How?

Answer 34

Pancreatic phospholipase A2 cleaves C2 fatty acid to yield lysophospholipids, which are detergents that emulsify fats

Question 35

What are the three steps of free fatty acid catabolism?

Answer 35

Activation: Conversion of a fatty acid to a fatty acyl-CoA by fatty acyl-CoA synthetase Transportation: The transport of fatty acyl-CoA across the mitochondria inner membranes through carnitine acyltransferases Fatty acid beta oxidation: Sequential removal of 2-carbon units by oxidation at beta-position of the fatty acyl-CoA molecule

Question 36

What are the three stages of fatty acid oxidation?

Answer 36

Stage 1: Fatty acid is oxidized to acetyl-CoA (beta-oxidation) Stage 2: Acetyl groups oxidized to CO2 via the citric acid cycle Stage 3: Electrons derived from the oxidations of stages 1 and 2 pass to O2 via the respiratory chain, providing the energy for ATP synthesis by oxidative phosphorylation

Question 37

Most fatty acids consumed are unsaturated. How are they metabolized?

Answer 37

Oxidation requires an additional isomerase to reposition the double bond, converting the cis isomer to a trans isomer, an intermediate in beta oxidation.

Question 38

What happens to acetyl-CoA in ketogenesis?

Answer 38

It's converted to acetoacetate or beta-hydroxybutyrate

Question 39

Name the three ketone bodies

Answer 39

Acetoacetate, beta-hydroxybutyrate, and acetone

Question 40

Normally, ketone body formation is [high/low].

Answer 40

low

Question 41

When does acetyl-CoA accumulate?

Answer 41

During starvation or untreated diabetes

Question 42

Ketone body formation occurs where?

Answer 42

The matrix of the liver mitochondria

Question 43

Why is acetyl-CoA converted to ketone bodies in the liver and not metabolized through the TCA cycle during starvation?

Answer 43

1. Oxaloacetate is limiting 2. Mito NADH levels are high from beta-oxidation, which shuts down some enzymes