Chapter 27- Lipid Catabolism

Question 1

What is the structure of fatty acids?

How are they named?

Answer 1

Carbonyl group and a hydrocarbon chain (always an even number of carbons)
Unsaturated have a kink where a cis double bond occurs (can have as many as 6 double bonds)
Slide 4
Slide 5 naming

Question 2

How are fatty acids stored and where?

How much energy does this store?

Answer 2

Stored as triacylglycerols in adipose tissue
Slide 6- connect to glycerol backbone do cells can tolerate

Fatty acids are toxic at high concentrations in cells so we convert them to another form that cells are tolerant to

Triacylglycerols are stored energy- 37kJ/g (~100 ATP from 1 fatty acid)
Carbs are 16 kJ and proteins are 17kJ

Question 3

What does excessive triacylglycerols storage do?

Answer 3

Causes obesity and diabetes
Too much fat or adipose tissue causes this

High levels of triacylglycerols in blood cause heart attack/stroke

Question 4

How are triacylglycerols transported across membranes into small intestine and enterocyte?

Answer 4

They are broken down by lipases into monoacylglycerol and then reassembled to triacylglycerol once across the membrane
Fatty acids can cross the membrane too (converted to these by pancreatic lipase)

Slide 10-11

Question 5

How are triacylglycerols transported in the circulatory system to tissues? (Liver muscle adipose)
What are the 4 different lipoproteins?

Answer 5

Chylomicrons transport it (fat shuttle)
It is a lipoprotein synthesized only in intestine
On the surface is phospholipids and cholesterol
The core is triacylglycerols
Slide 12, 14

1. Chylomicron - very large but not a lot of substance to them
2. Very low density lipoprotein (VLDL)
3. Low density lipoprotein (LDL)
4. High density lipoprotein (HDL) - tiniest but very dense

Question 6

What does lipoprotein lipase do?

Answer 6

It binds to cell surface and releases fatty acids from triacylglycerol
To adipose tissue or muscle tissue

Question 7

What are lipid droplets?

Answer 7

Fatty acids are stored as Triacylglycerols in lipid droplets in adipose tissue
Adipose tissue has very high capacity for TG storage
Slide 17
Lipid droplets have a phospholipid monolayer and the core is a hydrophobic environment ideal to store non polar molecules (TG)
Has perilipin which is a protein coat on the outside
Slide 18

Question 8

What is lipolysis?

What are the 3 enzymes?

Answer 8

Triacylglycerols broken down to glycerol and fatty acids in adipose tissue
Adipose tissue TG lipase (ATGL)
Hormone sensitive lipase (HSL)
Monoacylglycerol lipase (MAG lipase)
Phosphorylation of perilipin allows access to triacylglycerols and activates ATGL
Phosphorylation of hormone sensitive lipase activates HSL
Slide 19-20

Question 9

If fatty acids are moved on to be oxidized, what happens to glycerol?
What are two steps to fatty acids being oxidized?

Answer 9

Glycerol kinase (liver) converts glycerol to glycerol 3-phosphate then dihydroxyacetone phosphate then to gluconeogenesis
Slide 21
To be oxidized, fatty acids need to be activated by being bound to CoA and transported by a carnitine shuttle
Slide 22

Question 10

What is step 1 of the oxidation of fatty acids (activation by CoA)?
What reaction occurs with what enzyme?

Answer 10

Slide 23
Activation of fatty acid to fatty acyl CoA (any fatty acid bound to CoA)
Acyl CoA synthetase (cytosol) takes CoA-SH and converts it to Acyl CoA by using ATP
At the same time pyrophosphatase converts pyrophosphate to 2 phosphate

Fatty acid must be activated in the cytosol before it enters the mitochondria
Slide 23-24

Question 11

What happens in step 2 of oxidation of fatty acids (transport by carnitine shuttle)?

Answer 11

Acyl CoA can cross in mitochondrial membrane so it is used in the reaction by carnitine Acyltransferase I to convert carnitine to acyl carnitine releasing CoA and acyl carnitine crosses the membrane then the reverse reaction occurs by the same enzyme but II and released Acyl CoA
This works by anti porter
Slide 25

Question 12

What is the rate limiting step of fatty acid oxidation?

Answer 12

Fatty acid transport into the mitochondria

Slide 26

Question 13

What are the 3 steps of production of ATP from fatty acids?

Answer 13

1. β-oxidation- degradation of fatty acids (Acyl CoA), 2 carbons at a time producing acetyl CoA
2. Acetyl CoA from β-oxidation are oxidized to CO2 (TCA cycle)
3. Production of ATP (oxidative phosphorylation)

Question 14

What are the 4 steps of β-oxidation of saturated fatty acids?
What is palmitate?

Answer 14

Palmitate- simple fatty acid to oxidize (saturated no double bonds, 16 carbons even number)
1. Oxidation- slide 29 acyl CoA to transΔ-enoyl CoA (introduces double bond)
2. Hydration- slide 30 enoyl CoA hydratase converts transΔ to 3-hydroxyacyl CoA(removes double bond)
3. Oxidation- slide 31 hydroxyacyl is converted to 3-ketoacyl CoA
4. Cleavage- slide 32 thiolysis converts 3-ketoacyl CoA to acetyl CoA and acyl coa (shortened by 2 carbons)
Step 1 releases FADH2
Step 3 releases NADH
Overview slide 33-34

Question 15

What is the overall equation for the oxidation of palmitate?

Answer 15

Palmitoyl CoA + 7CoA+7FAD+7NAD+7H2O -> 8 Acetyl CoA+7FADH2+7NADH+7H

Net production of ATP= 106 ATP
SLIDE 35

Fatty acid oxidation occurs (removing 2 carbons per cycle) until the entire fatty acid is converted to acetyl CoA

Question 16

How are odd fatty acid chains oxidized in plants?

Answer 16

Slide 38
Propionyl CoA is converted to methylmalonyl CoA by propionyl CoA carboxylase
D-Methylmalonyl CoA is converted to L-methylmalonyl CoA by methylmalonyl CoA epimerase
L-methylmalonyl CoA is converted to succinyl CoA by methylmalonyl CoA mutase
Slide 38

Question 17

How does you fasting or being fed depend change:
The amount of acetyl CoA/malonyl CoA
Fatty Acid synthesis
Carnitine shuttle
β-oxidation

Answer 17

Fasting:
⬇️acetyl CoA/malonyl coa
⬇️fatty acid synthesis
⬆️carnitine shuttle
⬆️β-oxidation

Fed:
⬆️acetyl CoA/malonyl coa
⬆️fatty acid synthesis
⬇️carnitine shuttle
⬇️β-oxidation

Question 18

What are ketone bodies?

Answer 18

Alternative to glucose as a fuel or energy source (important for brain)
Formed by Ketogenesis in liver
Produced at low rate
Used by extrahepatic tissues (brain) when glucose is low
Slide 41

Question 19

How are Ketone bodies formed?

Answer 19

Occurs in liver
Condensation of 3 acetyl CoA to form acetoacetate
Acetoacetate is converted to 3-hydroxybutyrate and acetone
3 Ketone bodies= acetoacetate, this gives life to other two, 3 hydroxybutyrate and acetone

Acetone isn’t used for energy so we forget about it
Slide 42-43

Question 20

How can acidosis occur from ketone bodies?

Answer 20

They are extremely acidic and when over produced lead to acidosis
In diabetes in the absence of insulin the body over produces ketone bodies for energy which leads to acidosis

Slide 45