3- Biosynthesis of lipids

Question 1

What are the 2 fates of the fatty acids synthesized or ingested by an organism ?

Answer 1

1- incorporation into triacylglycerols for the storage of metabolic energy
2- incorperation into phospholipid components of membranes

Question 2

Why dose animal cells make large amounts of triacylglycerol (TAG) ?

Answer 2

For further use

Question 3

How long glycogen stores in liver and skeletal muscle last ?

Answer 3

Approximately 12 hours

Question 4

How much TAG dose a 70kg adult human store and how much dos it last a human?

Answer 4

Approximately 15 kg and it last 12 weeks

Question 5

What happens to excess amounts of carbohydrates ?

Answer 5

They are converted to TAG and stored in adipose tissue

Question 6

When TAG does not enter the cell directly what happens ?

Answer 6

TAG is cleaved into fatty and glycerol by lipoprotein lipase (LPL)

Question 7

What synthesizes lipoprotein lipase ?

Answer 7

By adipocytes and is released to neighboring endothelial cells

Question 8

What are endothelial cells ?

Answer 8

Inner lining of the blood vessels

Question 9

What are the two precursor molecules for triacylglycerol and glycerophospholipids ?

Answer 9

Fatty acyl-CoA and l-glycerol 3-phosphate

Question 10

What is the precursor for triacylglycerol synthesis in adipose tissue ?

Answer 10

Dihydroxyacetone phosphate (DHAP)

Question 11

What dose insulin stimulate ?

Answer 11

The conversion of carbohydrates and proteins present in a diet to fats.

Question 12

What happens to the excess amounts of glucose and amino acids administrated to the body ?

Answer 12

It is directed to the fatty acid synthesis via the activation of pyruvate dehydrogenase, citrate lyase and acetyl-CoA carboxylase by insulin .

Question 13

What is glyceroneogenesis ?

Answer 13

It is conversion from pyruvate to DHAP then to glycerol 3-phosphate by using cytosolic NAD linked glycerol 3-phosphate dehydrogenase.

Question 14

What are the three roles of glyceroneogenesis ?

Answer 14

1- In adipose tissue glyceroneogenesis
is coupled with reesterification of the free fatty acids that controls the rate of free fatty acid release to the blood.
2- In brown adipose tissue, the same pathway may control the rate at which free fatty acids are delivered to mitochondria for use in thermogenesis.
3- In fasting humans glyceroneogenesis in the liver alone supports the synthesis of enough glycerol 3-phosphate to account for up to 65% of fatty acids reesterified to TAG.

Question 15

How is the flux through triacylglycerol cycle between liver and adipose tissue is controlled ?

Answer 15

PEP carboxykinase which limetes the rate of both gluconeogenesis and glyceroneogensis

Question 16

What dose of stimulation of glyceroneogenesis leads to ?

Answer 16

An increase in the synthesis of triacylglycerol molecules in the liver and their release in to the blood .

Question 17

Where dose glucocorticoid hormones stimulate ?

Answer 17

It stimulate glyceroneogenesis and gluconeogensis in the liver

Question 18

What are the 6 uses biosynthesis of membrane phospholipids ?

Answer 18

1. Glycerophospholipids
2. Sphingolipids
   In general assembly of phospholipids from simple precursors
   requires:
3. Synthesis of the backbone molecule
4. Attachment of the fatty acid(s) to the backbone through an ester or amide linkage
5. Addition of hydrophilic head group through a phosphodiester linkage
6. Alteration or exchange of the head group to yield final phospholipid product.

Question 19

In the eukaryotic cells where dose phospholipid synthesis occur ?

Answer 19

primarily on the surfaces of the smooth endoplasmic reticulum and mitochondrial inner membrane.

Question 20

What is the most prevalent steroid in animal cells ?

Answer 20

Cholesterol

Question 21

Where is vitamin D3 is derived from ?

Answer 21

7-dehydrocholesterol

Question 22

Where is the primary site of cholesterol biosynthesis ?

Answer 22

Liver (cytosol)

Question 23

Who is the regulation of cholesterol synthesis in mammals ?

Answer 23

By intracellular cholesterol concentration and by insulin and glucagon

Question 24

What is the rate-limiting in the regulation of cholesterol synthesis pathway ?

Answer 24

Conversion of HMG-CoA to mevalonate ( HMG-CoA reductase )

Question 25

How is the small fractions of the cholesterol made by the liver is incorporated into the membranes of hepatocytes ?

Answer 25

1. Biliary cholesterol
2. Bile acids
3. Cholesteryl esters