Fatty Acid Synthesis

Question 1

Chylomicrons

Answer 1

fat molecules surrounded by amphiphilic proteins that shield fat from the aqueous environment and move fat into the blood via the lymphatic system.

Question 2

Sources of fat into blood stream

Answer 2

diet
adipose
liver

Question 3

When do adipose cells release fatty acids?

Answer 3

During fasting, when insulin drops and glucagon rises.

Question 4

How do fatty acids exist in the bloodstream & why?

Answer 4

Bound to albumin molecules - allows them to be in aqueous environment.

Question 5

How do we get fatty acids into the bloodstream from the liver?

Answer 5

The liver turns excess glucose into fatty acids -> packages them into triacylglycerides -> then packages them with cholesterol into very low density lipoproteins to be released into the bloodstream.

Question 6

What is the precursor for fatty acid synthesis? What does it become?

Answer 6

Acetyl CoA (C-C) (monomer) linked together to form fatty acid chain (polymer)

Question 7

Because Acetyl CoA is not able to cross the mitochondrial membrane, how does it get to the enzymes in the cytoplasm that turn it into fatty acids?

Answer 7

Transported as Citrate via shuttle, which is then broken down into oxaloacetate and Acetyl CoA.

Question 8

What happens to oxaloacetate when citrate is broken down?

Answer 8

It is converted into pyruvate and goes back into the mitochondria.

Question 9

Where does to NADPH needed for reducing AcetylCoA in fatty acid synthesis come from?

Answer 9

The oxidation of oxaloacetate into pyruvate, or from the pentose phosphate pathway.

Question 10

What molecules break down chylomicrons in the bloodstream? What hormone stimulates them?

Answer 10

lipoprotein lipase - stimulated by insulin b/c dietary glucose usually comes with fat

Question 11

How are chylomicron remnants processed?

Answer 11

They are recognized by receptors on the liver, and packaged into VLDL with the fatty acids made from excess glucose in the liver

Question 12

How are fatty acids utilized in the liver during times of fasting?

Answer 12

fatty acids are broken down to generate ATP to fuel gluconeogenesis, which is needed for making glucose to fuel the brain, etc.

Question 13

What happens in the liver regarding fatty acids when insulin drops/during fasting?

Answer 13

fatty acids are broken down to fuel gluconeogenesis, and glucose conversion into fatty acids is halted, as this process is stimulated by insulin.

Question 14

What is NADPH used for in the reaction of Acetyl CoA into palmitic acid?

Answer 14

reduces the carbonyl bond C=O so instead of C-C=O-C-C=O-C its just C-C-C-C-C-C x16

Question 15

What molecules are required for FA synthesis?

Answer 15

Acetyl CoA, ATP, and NADPH

Question 16

What are the products of FA synthesis?

Answer 16

palmitic acid, NADP+, H2O, ADP, CoA

Question 17

What is the rate-limiting/regulated step of FA synthesis?

Answer 17

carboxylation of Acetyl CoA by Acetyl CoA carboxylase (adds CO2)

Question 18

What stimulates Acetyl CoA carboxylase and why?

Answer 18

Citrate stimulates it because it is the precursor and as it is shuttled into the cytoplasm, the cell wants to turn it into FAs.

Insulin stimulates it because after a meal we have excess glucose in the blood that is being converted into AcetylCoA and can be converted into fatty acids.

Question 19

What inhibits Acetyl CoA carboxylase and why?

Answer 19

long chain fatty acids (product inhibition)

glucagon:
- during fasting there is not an excess of glucose, and therefore not an excess of AcetylCoA that can be stored at FAs

• Glucagon is also breaking down FAs in adipose to extract the energy - don’t want to be making more while breaking it down.

Question 20

Where is CoA lost in FA synthesis?

Answer 20

removed when malonylCoA and acetyl CoA form sulfide bonds with FA synthase

Question 21

How does the double bond form between malonyl CoA molecules?

Answer 21

the carboxyl group dissociates, giving the adjacent carbon its electrons, then this carbon attacks the next malonyl carbon that is brought close via FA synthase. This then dissociates from FA synthase via the attacked carbon giving its electrons to the sulfur of the FA synthase