Chapter 15 ( Lipid Synthesis And Storage )

Question 1

What is the primary product of fatty acid synthesis ?

Answer 1

Palmitic acid

Question 2

The 2 essential fatty acids ?

Answer 2

Linolenic FA

Linoleic FA

Question 3

What FA does Arachidonic acid formed from ? Its precursor for what ?

Answer 3

Linoleic acid 
Precursor for :
Prostaglandins 
Thromboxanes
Leukotrienes

Question 4

How Omega-3 FAs in diet decrease cardiovascular disease risk ?

Answer 4

By replacing some of the arachidonic acid in platelet membranes which may lower the production of thromboxane and tendency of the platelets to aggregate

Question 5

In which configuration are the double bonds of FAs?

Answer 5

Cis-configuration

Question 6

How does fatty acids activation occur ?

Answer 6

By attaching Coenzyme A to them by fatty acyl-CoA synthetase

Question 7

Role of insulin in fatty acids biosynthesis ?

Answer 7

Promotes many steps in the conversion of glucose into acetyl-CoA in liver :
1- glucokinase
2- PFK2/PFK1
3- pyruvate dehydrogenase
Both of the major enzymes of fatty acid synthesis are affected also by insulin :
1- acetyl-CoA carboxylase
2- fatty acid synthase

Question 8

2 sources for NADPH in FA synthesis ?

Answer 8

HMP shunt

Malic enzyme

Question 9

Acetyl-CoA carboxylase requirements and activators ?

Answer 9

Requires : 
ATP
Biotin
CO2
Activators : 
Insulin
Citrate

Question 10

Sources for glycerol-3-phosphate for triglyceride synthesis ?

Answer 10

1-Reduction of DHAP from glycolysis by glycerol-3-p dehydrogenase which present in both liver and adipose tissue
2-phosphorylation of free glycerol by glycerol kinase which found in liver only

Question 11

Functions of Glycerophospholipids ?

Answer 11

Membrane synthesis
Producing hydrophilic layer on lipoproteins
Serve as reservoir of second messengers in cell membranes such as : DAG , IP3 and arachidonic acid

Question 12

Chylomicrons : functions , attached apoproteins ?

Answer 12

Transport dietary triglyceride and cholesterol from intestine to tissues
ApoB-148
ApoC-ll
ApoE

Question 13

Apo proteins ? Their functions ?

Answer 13

Apo A : activator of LCAT
Apo B , Apo E : involved in receptor lipoprotein interactions
Apo C : activator of LPL

Question 14

VLDL function and its apoproteins ?

Answer 14

Transport triglyceride from liver to tissues
ApoB-100
ApoC-ll
ApoE

Question 15

IDL function and its apoprotein ?

Answer 15

Picks up cholesterol from HDL to become LDL , picked up by liver
ApoB-100
ApoE

Question 16

LDL function and its apoprotein ?

Answer 16

Deliver cholesterol into cells

ApoB-100

Question 17

HDL function and its apoprotein ?

Answer 17

Picks up cholesterol accumulating in blood vessels
Deliver cholesterol to liver and steroidogenic tissues via Scavenger receptor (SR-B1)
Shuttles apoC-ll and apoE in blood
ApoA-1

Question 18

Abetalipoproteinemia defect and hallmark ?

Answer 18

Defect in apoB-48 leading to accumulation of fat in enterocytes and hepatocytes
Hallmark : decreased triglycerides
Effects : malabsorption of fat soluble vitamins and the 2 essential fatty acids
Symptoms :
Steatorrhea
Cerebellar ataxia
Pigmentary degeneration the retina
Acanthocytes ( decreased vit E )
Possible loss of night vision ( decreased vit A )

Question 19

Liver pathways for acquiring cholesterol ?

Answer 19

1- de novo synthesis
2- endocytosis of LDL
3- transfer of cholesterol from HDL vis SR-B1 receptor
4- endocytosis of chylomicron remnants with residual dietary cholesterol

Question 20

Increased cholesterol in hepatocytes repress the expression of genes for what ?

Answer 20

1- HMG-CoA reductase
1- LDL receptor
2- SR-B1 receptor

Question 21

Difference between ACAT and LCAT ?

Answer 21

ACAT : intracellular enzyme which makes cholesterol esters for storage
LCAT : blood enzyme which makes cholesterol esters for trapping in lipoproteins

Question 22

Factors contributing to blood vessel endothelium damage ?

Answer 22

1- normal turbulence of blood
2- elevated LDL ( especially oxidized LDL )
3- free radicals from cigarette smocking
4- homocystinemia
5- diabetes
6- hypertension

Question 23

Type 1 hypertriglyceridemia ? Defect ? Lipid elevated ? Lipoprotein elevated ? Symptoms ?

Answer 23

Defect : deficiency of familial lipoprotein lipase or apoC-ll
Lipid elevated : triglyceride 
Lipoprotein elevated : chylomicrons
Symptoms :
Red orange eruptive xanthomas
Fatty liver 
Acute pancreatitis 
Abdominal pain after fatty meal

Question 24

Type lla(familial) hypercholesterolemia ? Deficiency of what ? Lipid elevated ? Lipoprotein elevated ? Symptoms ?

Answer 24

Autosomal dominant 
Deficiency of LDL receptor 
Lipid elevated : cholesterol 
Lipoprotein elevated : LDL
Symptoms : 
Risk of atherosclerosis and its complications 
Homozygous die < 20 years 
Xanthomas of Achilles tendon 
Corneal arcus 
Tuberous xanthomas on elbows 
Xanthelasmas

Question 25

Factors contributes to hyperlipidemia in Type 1 hypertriglyceridemia ?

Answer 25

Decreased glucose and triglyceride uptake in adipose tissue
Over active hormone-sensitive lipase
Underactive lipoprotein lipase

Question 26

What’s the most common type of hyperlipidemia ?

Answer 26

Type V : patients have elevated triglycerides in VLDL and chylomicrons in response to a meal containing carbohydrates and fat

Question 27

Functions of cholesterol in human ?

Answer 27

1- membrane synthesis
2- steroid and vitamin D synthesis
3- bile acids synthesis

Question 28

Rate limiting enzyme of cholesterol synthesis ? Its direct product ? Activator ? Inhibitor ?

Answer 28

HMG-CoA reductase on the SER
Direct product : Mevalonate 
Activator : insulin 
Inhibitor : glucagon , statin drugs 
Cholesterol repress its gene expression and increase its degradation

Question 29

Uses of Farnesyl pyrophosphate in the body ?

Answer 29

1- synthesis of Coenzyme Q for ETC
2- synthesis of dolichol pyrophosphate , required cofactor in N-glycosylation of proteins in ER
3- prenylation of proteins ( posttranslational modification ) that need to be held in the cell membrane by a lipid tail , Example : p21ras G protein

Question 30

Cholestyramine mechanism ?

Answer 30

Increase elimination of bile salts which force the liver to increase their synthesis from cholesterol which in turn increase LDL receptor expression allowing hepatocytes to remove more LDL cholesterol from the blood

Question 31

Most common side effect of statin ?

Answer 31

Muscle pain due to decreased Farnesyl PPi which lead to decreased CoQ synthesis which is important for ETC in mitochondria , myoglobinuria may be associated

Question 32

Function of glycerol kinase in liver other than triglyceride synthesis ?

Answer 32

During fasting it allows the liver to trap glycerol released into the blood from lipolysis in adipose tissue for subsequent conversion to glucose ( gluconeogenesis )