Lecture 4: Lipid Metabolism

Question 1

Where is fatty acid metabolized?

Answer 1

Mitochondria

Question 2

Once taken up by the cell, what are fatty acids used for?

Answer 2

1) Precursor for synthesis of other compounds
2) Energy production
3) Substrate for ketone body synthesis

Question 3

What is the major form of energy storage?

Answer 3

Fat

Question 4

What is the structure of acetyl CoA?

Answer 4

Acetyl group and Coenzyme A

Question 5

What does Coenzyme A consist of?

Answer 5

• Beta-mercaptoethylamine
• Pantothenic acid (not synthesized in man = an essential nutrient)
• Phosphate
• 3’, 5’-adenosine diphosphate

Question 6

What is the structure of a fatty acid?

Answer 6

1) A long hydrocarbon chain
2) A carboxylic acid group

Question 7

What is the length of a hydrocarbon chain in a fatty acid? What is the most common length?

Answer 7

The chain length ranges from 4 to 30 carbons; 12-24 is the most common.

Question 8

What is the shape of a fatty acid?

Answer 8

linear

Question 9

Carbons in a fatty acid are always _____.

Answer 9

even

Question 10

How many double bonds does a saturated fatty acid have?

Answer 10

0 double bonds

Question 11

What are examples of a saturated fatty acid?

Answer 11

stearic acid and palmitic acid

Question 12

How many double bonds does a monosaturated fatty acid have?

Answer 12

1 double bond

Question 13

What is an example of a monosaturated fatty acid?

Answer 13

Oleic acid

Question 14

What configuration is a double bond in a fatty acid?

Answer 14

Cis configuration

Question 15

Fatty acids with how many double bonds are most prevalent in the human body?

Answer 15

Fatty acids with 1 double bond

Question 16

How do carbons appear in a polyunsaturated fatty acid?

Answer 16

3 carbon intervals
Ex: -C=C-C-C=C-

Question 17

How many double bonds are in a polyunsaturated fatty acid?

Answer 17

2 or more double bonds

Question 18

What is an example of a polyunsaturated fatty acid?

Answer 18

Linoleic acid

Question 19

Polyunsaturated fatty acids are NEVER _____.

Answer 19

conjugated

Question 20

What type of bridge does a polyunsaturated fatty acid create?

Answer 20

Methylene bridge

Question 21

What plays a significant role in the melting point of fatty acids?

Answer 21

Steric hindrance = causes backbone to bend

Question 22

The more double bonds in fatty acids = ______ melting point

Answer 22

lower

Question 23

Which type of fatty acid has a high melting point and is solid?

Answer 23

Saturated fatty acid

Question 24

Which carbon in a fatty acid is the 1st carbon?

Answer 24

Carboxyl/carbonyl carbon

Question 25

Which carbon in a fatty acid is the alpha carbon?

Answer 25

Carbon next to the carboxyl/carbonyl carbon

Question 26

Which carbon in a fatty acid is the beta carbon?

Answer 26

Carbon next to alpha carbon

Question 27

Which carbon in a fatty acid is the omega carbon?

Answer 27

The last carbon in the chain, farthest away from the carboxyl carbon

Question 28

Which fatty acids are essential to humans (must obtain from diet)?

Answer 28

Linoleic acid and Linolenic acid

Question 29

Where does fatty acid synthesis occur?

Answer 29

Cytoplasm of these tissues: Liver, adipose (fat), CNS, lactating mammary gland

Question 30

What are the products of acetyl CoA?

Answer 30

1) triglycerides 2) phospholipids 3) eicosanoids 4) energy (ATP) 5) ketone bodies 6) cholesterol (bile salts and steroid hormones)

Question 31

Where does acetyl CoA for fatty acid synthesis come from?

Answer 31

Mostly from glycolytic breakdown of glucose

Question 32

What is the major source of acetyl CoA for fatty acid synthesis?

Answer 32

Glucose

Question 33

What are the conditions that are conducive to fatty acid synthesis?

Answer 33

The ratio of insulin:glucagon is high

Question 34

What is the net equation of fatty acid de novo synthesis?

Answer 34

8 acetyl CoA + 7 ATP + 14 (NADPH + H+) (right arrow) palmitate (16:0) + 8 CoA + 7 (ADP + Pi) + 14 NADP+ + 6 H2O

Question 35

What is the rate-limiting step in fatty acid de novo synthesis?

Answer 35

Acetyl CoA carboxylase w/biotin

Question 36

Acetyl CoA carboxylase requires ______ as a cofactor.

Answer 36

biotin

Question 37

Which isoforms of acetyl CoA carboxylase (ACC) occur in the liver?

Answer 37

ACCʆ and ACCβ

Question 38

Which isoform of acetyl CoA carboxylase (ACC) occurs in skeletal muscle?

Answer 38

ACCβ

Question 39

Which isoform of acetyl CoA carboxylase (ACC) occurs in adipose tissue?

Answer 39

ACCʆ

Question 40

Which isoform of acetyl CoA carboxylase (ACC) occurs in the heart?

Answer 40

ACCβ

Question 41

What are the mechanisms used for the short-term regulation of ACC?

Answer 41

Phosphorylation (inactive) and phosphorylation (inactive)

Question 42

When ACC is phosphorylated it is _____.

Answer 42

inactive

Question 43

When ACC is dephosphorylated it is ______.

Answer 43

active

Question 44

Phosphorylation _____ ACC activity.

Answer 44

inhibits

Question 45

Which enzymes phosphorylate ACC?

Answer 45

AMP-dependent protein kinase & Protein Kinase A

Question 46

What activates AMP-dependent protein kinase & Protein Kinase A which phosphorylates ACC?

Answer 46

Activated by high glucagon

Question 47

Which enzyme dephosphorylates ACC?

Answer 47

phosphoprotein phosphatase

Question 48

What activates phosphoprotein phosphatase which dephosphorylates ACC?

Answer 48

Activated by high insulin

Question 49

What is a positive effector of ACC in allosteric regulation (long-term)?

Answer 49

Citrate = activation

Question 50

What is a negative effector of ACC in allosteric regulation (long-term)?

Answer 50

Long-chain fatty acids = inhibition

Question 51

What does ChREBP stand for?

Answer 51

Carbohydrate-Responsive Element Binding Protein

Question 52

What is ChREBP?

Answer 52

a major glucose-responsive transcription factor

Question 53

Where is the expression of ChREMP induced and why is it induced?

Answer 53

Induced in liver in response to increased glucose uptake

Question 54

ChREBP acts synergistically with which protein?

Answer 54

Sterol Response Element Binding Protein (SREBP)

Question 55

What happens when ChREBP acts synergistically with SREBP?

Answer 55

Induces lipogenic genes such as ACC and fatty acid synthase

Question 56

What happens to ChREBP when glucose (basal) concentrations are low?

Answer 56

ChREBP is phosphorylated and resides in the cytosol

Question 57

What happens to ChREBP when glucose levels are high?

Answer 57

ChREBP is dephosphorylated and translocates to the nucleus where it binds to Carbohydrate Response Elements (ChoREs) to stimulate transcription of lipogenic genes

Question 58

What happens to ChREBP when glucose levels are normal?

Answer 58

ChREBP is phosphorylated but will not activate lipogenic genes in the cytosol which will not produce fatty acids

Question 59

What enzyme elongates/lengthens fatty acids?

Answer 59

Fatty acid elongase

Question 60

Fatty acid elongase uses _____ ____to add 2 carbons at a time in the ______.

Answer 60

Acetyl CoA, mitochondria

Question 61

Fatty acid elongase uses _____ ____to add 2 carbons at a time in the ______.

Answer 61

malonyl CoA, microsomal (ER)

Question 62

Fatty acid elongase elongates the chain from the ____.

Answer 62

front

Question 63

Do acetyl CoA carbons increase or decrease the carbon #?

Answer 63

increase

Question 64

Where does fatty acid desaturase occur and what does it do?

Answer 64

Occurs in ER and is required to introduce double bonds

Question 65

What reduces fatty acid desaturase?

Answer 65

NADH

Question 66

What are the 4 distinct desaturases?

Answer 66

∆9, ∆6, ∆5, ∆4 (act on the 9th, 6th, 5th, or 4th carbons)

Question 67

What is the minimum chain length required for desaturation?

Answer 67

16-18 carbons

Question 68

Which desaturase is the main desaturase?

Answer 68

∆9

Question 69

Elevated levels of which fatty acid is an indication of essential fatty acid deficiency?

Answer 69

Mead acid = 20:3 ∆ 5,8,11

Question 70

What deficiency causes scaly dermatitis?

Answer 70

Essential fatty acid synthesis

Question 71

What is the major storage form of fat?

Answer 71

Triaclyglycerides

Question 72

What are the primary organs of triacylglyceride synthesis?

Answer 72

liver and adipose cells

Question 73

What is the major fatty acid synthesized de novo?

Answer 73

Palmitate

Question 74

List the lipogenic genes

Answer 74

1) Acetyl-CoA carboxylase 2) Fatty acid synthase 3) ATP citrate lyase 4) Glucose-6-phosphate dehydrogenase 5) 6-phosphoglucoronate dehydrogenase 6) Malic enzyme 7) Fatty acid desaturase