Fatty Acid Synthesis

Question 1

How is glucose converted to fatty acid

Answer 1

The pyruvate generated in glycolysis loses a carbon, and become acetyl coA
The enzyme to catalyze this is PDH.
to derive FA, we need to link C bonds together. The acetyle CoA is a 2 C molecule that we can use to do this.

So to transport ACETYL CoA we link oxaloacetate (OAA) and ACETYL CoA together to form CITRATE which can be transported through the MM

n the cytoplasm, CITRATE can be broken down into ACETYL CoA and oxaloacetate (OAA)

OAA is converted to malate and then PYRUVATE to re-enter mitochondria and continue the previous cycle

The ACETYL CoA now in the cytoplasm (thanks to the transport by citrate from the mitochondria) is converted to MALONYL CoA

MALONYL CoA reacts with another ACETYL CoA molecule to produce ACETOACETYL-ACP

Question 2

What enzyme catalyses the transport of citrate into the cytoplasm/ citrate shuffle

Answer 2

Tricarboxylate

Question 3

What is the citrate shuttle and why is needed

Answer 3

to transport ACETYL CoA out of the mitochondria we link oxaloacetate (OAA) and ACETYL CoA together to form CITRATE which can be transported through the Mitochondrial membrane

The ‘citrate shuttle’ – required because enzymes to transfer Acetyl CoA to cytosol not available

Question 4

What activates fatty acid synthesis from glucose

Answer 4

Insulin

Question 5

What inhibits fatty acid synthesis from glucose

Answer 5

Glucagon

Question 6

What are fatty acids synthesised from

Answer 6

Lipids and carbohydrates we consume or new FA can be synthesised in the liver from glucose

Question 7

Where are new fatty acids synthesised

Answer 7

Cytosol of the liver and adipose tissue

Question 8

What are fatty acids stored as

Answer 8

Triglycerides

Question 9

Why can FA be synthesised from glucose but not glucose from FA

Answer 9

Link reaction (pyruvate to acetyl CoA) is irreversible

Question 11

What enzyme converts citrate back to acetyl CoA once outside the mitochondria (post citrate shuttle)

Answer 11

ATP citrate lease (ATP-CL)

Question 12

What happens to the Oxaloacetate

Answer 12

Converted back to pyruvate to enable the cycle to continue

Question 13

Which enzymes are involved in the conversion of OAA back to pyruvate

Answer 13

Malic enzyme and malate dehydrogenase

Question 14

What happens to the acetyl CoA once in the Cytosol

Answer 14

Converted to malonyl CoA by Acetyl CoA carboxylase (ACC)

Question 15

What does malonyl CoA regulate

Answer 15

How many Fa can enter the mitochondria for beta oxidation

Question 17

What is the primary enzyme that regulates FA synthesis

Answer 17

Acetyl CoA carboxylase (ACC)

Question 18

What happens when ATP and citrate concentrations are high

Answer 18

Lipogenesis occurs

Question 19

How are FA synthesised from malonyl CoA

Answer 19

MALONYL CoA reacts with another ACETYL
CoA molecule to produce ACETOACETYL-ACP

Question 20

What enzyme complex catalyses the production of FA chains from acetoacetyl-ACP

Answer 20

Fatty acid synthase complex

Question 21

What does ACP stand for

Answer 21

Acyl carrier protein

Question 22

What is an ACP

Answer 22

Acyl carrier protein that sits on the end of the molecule to ensure clockwise rotation of the chain so that the acetyl CoA molecule is accepted to extend the chain

Question 23

What happens when there is an excess of glucose

Answer 23

Activates the synthesis of FA in the Cytosol of the cell from acetyl CoA (link reaction product)via malonyl CoA

Question 24

Where is glucose converted to glycerol

Answer 24

In adipose tissue

Question 25

What promotes the uptake of FA into adipose for storage

Answer 25

Insulin

Question 26

Describe hormonal control of triglyceride synthesis after eating

Answer 26

TAG synthesis is promoted by insulin and inhibited by glucagon

Question 27

Describe TAG synthesis during exercise

Answer 27

FA are oxidised to produce ATP before TAG synthesis during exercise

Question 28

What enzyme is an important regulator of FA synthesis and degradation

Answer 28

ACC acetyl CoA carboxylase

Question 29

What are ketone bodies

Answer 29

Fuel source for the brain when glucose availability low, spare glucose to preserve lean mass, only produced in small quantities

Question 30

What 3 molecules are classified are ketone bodies

Answer 30

Acetoacetic acid, 3-hydroxybutyric acid and acetone

Question 31

In what situations are ketone bodies produced in larger quantities

Answer 31

During reduced carbohydrate availability, prolonged fasting/starvation and during prolonged exercise, when a large amount of FA are being used as primary fuel source

Question 32

Why are more ketone bodies produced in these situations

Answer 32

This is because when large amounts of FA are used, the liver cannot oxidize them quick enough, so the increased acetyl CoA avalaible is converted to ketone bodies. These are then released in the blood for energy.

Question 33

How are ketone bodies produced

Answer 33

Acetyl CoA is produced from beta oxidation of FA, a series of reactions is then used to convert Acetyl CoA into ketone bodies

Question 34

What are the function of ketone bodies once in circulation

Answer 34

Ketone bodies can be transported in the blood and are used by the brain, heart, kidney and skeletal muscle to produce ATP via the TCA cycle in these cells

Question 35

What must happen to ketone bodies before they can be used in the TCA cycle for energy production

Answer 35

Must be converted back to acetyl CoA