Sean - B-Oxidation Continued

Question 1

How many additional steps are needed for the B-oxidation of a monounsaturated fatty acid?

Answer 1

One additional chemical reaction

Question 2

How many additional steps are needed for the B-oxidation of a polyunsaturated fatty acid?

Answer 2

Three additional chemical reactions

Question 3

How many additional steps are needed for the B-oxidation of a fatty acid with an uneven numbered carbon chain?

Answer 3

Three additional chemical reactions

Question 4

How is a monounsaturated fatty acid broken down?
(6)

Answer 4

The fatty acyl-CoA is transported via the carnitine shuttle into the mitochondrial matrix

B-oxidation occurs as normally up until the double bond

In the next cycle the first step is skipped

Enoyl-CoA hydratase only adds H2O across a trans double bond

An enoyl-coA isomerase catalyses the conversion of the cis bond into a trans bond -> H2O then added

B-Oxidation then continues as normal

Question 5

How does all B-oxidation reactions begin?

Answer 5

The fatty acyl-CoA is transported via the carnitine shuttle into the mitochondrial matrix

Question 6

What must be done to monounsaturated cis fatty acids?

Answer 6

The cis bond must be converted to a trans bond by the Enoyl CoA hydratase isozyme

Question 7

How is a polyunsaturated fatty acid B-oxidised?
(7)

Answer 7

The fatty acyl-CoA is transported via the carnitine shuttle into the mitochondrial matrix

Cycle occurs as normally up until the first double bond

If the first bond is cis it is converted to a trans bond by enoyl-CoA isomerase

First step of B-oxidation is carried out

A dienoyl CoA reductase adds two H to the molecule to break remaining double bonds - and by creating another cis double bond

An enoyl-coA isomerase catalyses the conversion of the cis double bond to a trans double bond

B-oxidation then occurs as normal from step 3

Question 8

List the three additional steps in B-oxidation of polyunsaturated fatty acids

Answer 8

Enoyl-coA isomerase converts the cis bond to a trans bond

Dienoyl-CoA reductase adds two H to the molecule, breaking two double bonds and forming a double cis bond

Enoyl-CoA again converts the cis bond to a trans bond

Question 9

Explain how B-oxidation of odd-number fatty acids occurs
(5)

Answer 9

Oxidised as normal but we are left with a three carbon propionyl-CoA

Propionyl-CoA is carboxylated to D-methylmalonyl-CoA

D-methylmalonyl-CoA is converted to L-methylmalonyl-CoA

L-methylamonyl-CoA is convverted into succinyl-CoA

Succinyl-CoA enters the Krebs Cycle

Question 10

What is the 3 C fatty acid we are left over with called in the B-oxidation of odd number fatty acids

Answer 10

Propionyl-CoA

Question 11

What is propionyl-CoA converted into?

Answer 11

Propionyl-CoA is carboxylated to D-methylmalonyl-CoA

Question 12

What is D-methylmalonyl-CoA converted into

Answer 12

D-methylmalonyl-CoA is converted to L-methylmalonyl-CoA

Question 13

What is L-methylmalonyl-CoA converted into?

Answer 13

L-methylamonyl-CoA is converted into succinyl-CoA

Question 14

What happens to succinyl-CoA?

Answer 14

Succinyl-CoA enters the Krebs Cycle

Question 15

Give one point that limits fatty acid oxidation

Answer 15

The carnitine shuttle

Question 16

How is the carnitine shuttle an important point in B-oxidation regulation?

Answer 16

Because once the fatty acid has entered the mitochondrion it is committed to oxidation

Question 17

What inhibits the carnitine shuttle?

Answer 17

Malonyl-CoA

Question 18

What does malonyl-CoA inhibit?

Answer 18

Inhibits the carnitine acyltransferase I thus inhibiting the transfer of fatty acids into the mitochondria

Question 19

What points of B-oxidation are inhibited?
(2)

Answer 19

Hydroxyacyl-CoA dehydrogenase

Thiolase

Question 20

What inhibits hydroxyacyl-CoA dehydrogenase?
(2)

Answer 20

High NADH ratio

(this enzyme gives two hydrogens to NAD+ to make NADH therefore if there is already enough NADH there is no point for B-oxidation)

Question 21

What inhibits thiolase?
(2)

Answer 21

High acetyl-CoA concentrations

(thiolase forms acetyl-CoA molecules therefore it is inhibited if there is already enough CoA)