Fatty Acid Metabolism

Question 1

where does synthesis of fatty acids occur?

Answer 1

liver, adipose tissues and mammary glands are the main sites

Question 2

Can all fatty acids be synthesized?

Answer 2

All except C18:2 and C18:3

Question 3

what is the substrate for synthesis of fatty acids?

Answer 3

acetyl CoA

Question 4

What is acetyl CoA carboxylated to? what is this catalyzed by?

Answer 4

Malonyl CoA, catalyzed by acetyl CoA carboxylase

Question 5

the step wise addition of 2- carbon molecules to a growing chain is catalyzed by what?

Answer 5

multifunctional enzyme “fatty acid synthase”

Question 6

what are the steps in synthesis of fatty acids?

Answer 6

1. glucose enters liver cells and is converted to pyruvate (glycolysis)
2. pyruvate enters the mitochondria and is converted to acetyl- CoA by pyruvate dehydrogenase and to oxaloacetate by pyruvate carboxylase
3. acetyl-CoA and oxaloacetate condense to form citrate which leaves the mitochondria
4. in cytosol, citrate is cleaved to oxaloacetate and acetyl-CoA by citrate lyase (requires ATP + induced by insulin)
5. acetyl CoA is converted by acetyl CoA carboxylase to malonyl CoA
6. growing fatty acyl chain on the fatty acid synthase complex is elongated, 2-carbons at a time by the addition of the 3-carbon compound malonyl CoA which is decarboxylated
7. palmitate is converted to other fatty acyl CoAs by elongation and desaturation
8. the fatty acyl-CoA combines with glycerol-3-p to form triacylglycerols by a pathway in which phosphatidic acid serves as an intermediate
9. triacylglycerols packaged in VLDL are secreted into blood

Question 7

which enzyme cleaves citrate to oxaloacetate and acetyl CoA? what does it require?

Answer 7

Citrate lyase it uses ATP

Question 8

which enzyme converts pyruvate to acetyl-CoA?

Answer 8

Pyruvate Dehydrogenase

Question 9

which enzyme converts pyruvate to oxaloacetate?

Answer 9

Pyruvate Carboxylase

Question 10

which enzyme converts Acetyl-CoA to malonyl CoA?

Answer 10

Acetyl CoA carboxylase

Question 11

fatty acid synthase requires _______ to reduce the growing chain

Answer 11

NADPH

Question 12

where does the NADPH come from?

Answer 12

from the pentose phosphate pathway

Question 13

what is the product released by fatty acid synthase complex?

Answer 13

Palmitate

Question 14

fatty acyl CoA combines with what to form triacylglycerols?

Answer 14

Glycerol-3-Phosphate

Question 15

how do triacylglycerols get into the blood?

Answer 15

they are packaged in VLDL

Question 16

what inhibits Fatty acid synthase?

Answer 16

Epinephrine, glucagon inhibit PP2A (protein phosphatase 2A)

Question 17

what reactivates acetyl-CoA carboxylase?

Answer 17

Insulin through stimulation of PP2A which reactivates acetyl-CoA carboxylase and citrate stimulates acetyl-CoA carboxylase

Question 18

What inhibits Acetyl CoA carboxylase?

Answer 18

Palmitoyl-CoA

Question 19

what are the sources of fatty acids?

Answer 19

• de novo synthesis
• hydrolysis of cellular triglycerides
• fatty acids from circulation

Question 20

What pathways synthesizes triglycerides: Fatty acid + ATP –> Fatty acyl CoA + AMP

Answer 20

mainly Glycerol-3-phosphate pathway

Question 21

what mediates fat mobilization?

Answer 21

hormone sensitive lipase (HSL)

Question 22

what process regulates HSL ?

Answer 22

phosphorylation-dephosphorylation process

Question 23

In what state is HSL dephosphorylated by insulin (inactivation)?

Answer 23

the fed state

Question 24

What happens to HSL in the fasting state?

Answer 24

HSL is phosphorylated by epinephrine and norepinephrine

Question 25

HSL changes **triacylglycerol** to what?

Answer 25

triacylglycerol--\> **glycerol + 3 fatty acids**

Question 26

What is another word for catabolism of fatty acids?

Answer 26

**ß-oxidation**

Question 27

**where** does B-oxidation occur?

Answer 27

in the **mitochondria** to generate **energy**

Question 28

why do fats generate more energy?

Answer 28

because they exist in **more reduced form of CHO**

Question 29

when is **oxidation** of fatty acids **high**? why?

Answer 29

During the **starvation state** due to increased concentrations of fatty acids in blood

Question 30

what is the **first step** in B-oxidation?

Answer 30

synthesis of **fatty acyl CoA** in the cytosol by ***fatty acyl CoA synthetase***

Question 31

what mediates the transport of fatty acyl CoA into the mitochondria?

Answer 31

**Carnitine**

Question 32

which fatty acids produces **more energy?** unsaturated fatty acids or saturated fatty acids?

Answer 32

**Saturated fatty acids** produce more energy

Question 33

during what **state** is acetyl-CoA from B-oxidation, oxidized to CO2 and water in TCA cycle?

Answer 33

the well **fed **state

Question 34

what does the **liver** convert during the **starvation state**?

Answer 34

the liver converts **acetyl CoA to ketones** (acetoacetate & B-hydroxybutyrate)

Question 35

what are **ketone bodies** used for?

Answer 35

used for fuel source (**energy**) by extrahepatic tissues (not the liver)

Question 36

which produces **more energy**: fatty acids or ketone bodies?

Answer 36

ketone bodies produce less energy than **fatty acids**

Question 37

when might a person have **high blood concentrations of ketone bodies**?

Answer 37

**diabetes**, **starvation** or very **low CHO diet**

Question 38

what **inhibites** carnitine acyl transferase?

Answer 38

**Malonyl CoA**

Question 39

**Hypoglycemia** (low blood sugar= glucose) _________ **lipolysis** in some cases ketone body formation

Answer 39

**STIMULATES**

Question 40

HSL is **inactivated** by what hormone?

Answer 40

**INSULIN**

Question 41

\_\_\_\_\_ glucose level and ______ insulin level **favors lipolysis.**

Answer 41

**LOW, ** **LOW**

Question 42

HSL is **activated** by which hormones?

Answer 42

**epinephrine and norepinephrine**

Question 43

what **stimulates** synthesis of **acetyl CoA**?

Answer 43

**Citrate**

Question 44

What is **atherosclerosis**?

Answer 44

it is a degenerative disease of **vascular endothelium**

Question 45

what happens in **atherosclerosis**?

Answer 45

* accumulation of **cholesterol** and cholesterol esters **blocks capillaries** causing them to tear up, * recruitment of **immune cells**: cytokines, macrophages, monocytes and T lymphocytes accumulate. * **LDL is uptaken by phagocytic cells** and an increased deposition of lipids in blood vessels (**fatty plaque**)

Question 46

what is associated with a **high** amount of LDL ?

Answer 46

**high fat diet** + **high cholesterol**+ cholesterol esters

Question 47

what are the main lipid risk factors for **Cardiovascular disease?**

Answer 47

* Cholesterol * Saturated and Unsaturated fatty acids * Trans fatty acids

Question 48

how can risk of CVD be **reduced**?

Answer 48

by maintaining a **low LDL : HDL** ratio

Question 49

**Apo A: Apo B** can be a measure of what?

Answer 49

**Cardiovascular disease risk** ApoB= LDL ApoA=HDL

Question 50

What type of fatty acids are **HYPO**cholesterolemic (**low** lvls)?

Answer 50

**Unsaturated fatty acids** (double bonds)

Question 51

what type of fatty acids are **HYPER**cholesterolemic (**high** lvls)?

Answer 51

**Saturated fatty acids**

Question 52

which fatty acid is **neutral**?

Answer 52

C18:0

Question 53

**Plant** PUFA are ____ effective than **marine** PUFA

Answer 53

**LESS**

Question 54

why can **saturated fatty acids** be associated with a **high** risk of cardiovascular disease?

Answer 54

* they suppress bile acid excretion * increase synthesis of choleserol + LDL * reduce uptake of LDL

Question 55

**trans fatty acids** come from partial hydrolysis of what?

Answer 55

**Polyunsaturated fatty acids** (PUFA)

Question 56

what is the most abundant **trans fatty acid**?

Answer 56

**Elaidic acid** (C18:1 FA) and isomers

Question 57

**trans** fatty acids are ______ **cholesterolemic**

Answer 57

**HYPER** = high levels of cholesterol

Question 58

which one is more **detrimental**, saturated fatty acids or trans fatty acids?

Answer 58

**Trans fatty acids**

Question 59

Trans is _______ than Cis

Answer 59

**WORSE**

Question 60

as LDL + total cholesterol **increases**, HDL \_\_\_\_\_\_\_\_.

Answer 60

**decreases**