BMS1030 - Fatty Acids

Question 1

What is Acetyl-CoA needed for? How is it made?

Answer 1

Needed to create fatty acids (and other compounds e.g. ketones)

Made from oxidising Pyruvate or B-oxidation of free FAs or deamination and oxidation of AAs.

Question 2

Why is FAs synthesis required?

Answer 2

For:
- energy storage
- hormones
- co-factors
- cell membrane parts
etc.

Question 3

What is the compound formed from Acetyl CoA which we actually need? How is it made?

Answer 3

Malonyl-CoA

Question 4

What are the 3 regions of acetyl CoA carboxylase?

Answer 4

Biotin carboxylase
Biotin carrier protein
Transcarboxylase

Question 5

How does Acetyl-CoA carboxylase form Malonyl-CoA? (steps using regions)

Answer 5

Biotin Carrier, carrying biotin binds to enzyme.

In biotin carboxylase region, bicarbonate (COO-) binds with use of ATP.

Conformation change - molecule transferred to transcarboxylase. Acetyl-CoA binds.

This transfers the COO- to the Acetyl-CoA, forming Malonyl-CoA.

Question 6

The synthesis of long chain FAs is catalysed by which enzyme?

Answer 6

Fatty acid synthase

Question 7

How many active sites does Fatty acid synthase have? Give some examples.

Answer 7

7 active sites

e.g. Acyl-carrier protein and Thio-esterase

Question 8

Name the 4 repeating steps of FA synthesis.

Answer 8

1. Condensation
2. Reduction
3. Dehydration
4. Reduction

Question 9

What is the first step of FA synthesis?

Answer 9

Condensation of activated Acyl group and Malonyl group. CO2 produced.

Question 10

What is the second step of FA synthesis?

Answer 10

Reduction of molecule using 1 x NADPH molecule.
(Ketone group converted to alcohol)

Question 11

What is the third step of FA synthesis?

Answer 11

Alcohol group dehydrated, eliminating 1x H2O and creating a trans double bond between the alpha and beta carbons.

Question 12

What is the fourth step of FA synthesis?

Answer 12

Reduction of C=C bond -> saturated C-chain, using 1 x NADPH

Question 13

For each rotation of the FA synthesis steps, the hydrocarbon chain increases by __C.

Using:
Eliminating:

Answer 13

2C

Using 2 x NADPH
Elimination 1 CO2 and 1 H2O

Question 14

How many rotations are needed to produce palmitate?

Answer 14

7

Question 15

How does the cycle start again?

Answer 15

Saturated carbon chain transferred onto thiolase (check).
Acyl carrier protein recharged with another malonyl group.

Question 16

Where does FA synthesis occur?

Answer 16

In the cytosol of animal/yeast cells. Chloroplasts of plant cells.

Question 17

How is FA synthesis regulated? i.e. what activates/inhibits it?

Answer 17

Activating:
- Citrate activates the acetyl-CoA carboxylase enzyme, increasing its Vmax.

Inhibiting:
- High levels of palmitoyl-CoA inhibits enzyme.
- Glucagon and adrenaline inhibit the enzyme via phosphorylation.

Question 18

What then happens to palmitate?

Answer 18

It is desaturated or elongated.

Question 19

What C=C positions on a 18C derived molecule only occurs in plants?

Answer 19

12 and 15

Question 20

What are 3 sources of FA fuels.

Answer 20

Diet
Stored in Adipose tissue (connective tissue throughout body)
Synthesised in organs and exported

Question 21

All cell catabolise fatty acids. Which organs use more than 50% of their energy from fats?

Answer 21

Liver, Heart and resting Skeletal muscle

Question 22

How is dietary fat taken up into the blood stream?

Answer 22

Bile salts -> form micelles
Intestinal Lipases (TGs–>FAs)
FAs taken up by intestinal mucosa –> TGs
TGs incorporated with cholesterol and proteins –> chylomicrons
Chylomicrons –> lymphatic system –> bloodstream tis

Question 23

What are Chylomicrons also known as?

Answer 23

Lipoproteins

Question 24

There are several classes of Lipoproteins. Which act as signals?

Answer 24

Apolipoproteins

Question 25

What is Lipoprotein lipase activated by? Where? What does it do?

Answer 25

apoC-II in capillaries converts TGs --> FAs, which enter cells

Question 26

When FAs enter cells, what happens to them? (2 options)

Answer 26

Either oxidised as fuel or re-esterified for storage (-->TGs)

Question 27

How does low blood sugar lead to the formation of cAMP?

Answer 27

Low blood sugar -> glucagon released. Binds to receptor on cell membrane. Adenylyl cyclase activated, ATP -> cAMP

Question 28

What does cAMP activate? What does this cause?

Answer 28

It actives Protein Kinase A (PKA), which phosphorylates Perilipin (along surface of lipid droplet) and hormone-sensitive lipase (activating it).

Question 29

What does phosphorylating perilipin cause?

Answer 29

CGI dissociates and binds to ATGL (Adipose TG lipase), activating it. TG-->DG.

Question 30

What does the phosphorylation of hormone-sensitive lipase cause?

Answer 30

Activated. DGs --> MGs

Question 31

What hydrolyses MGs into FAs in the cell? What then happens to the FAs when they leave the cell?

Answer 31

MGL (Monoglyceride lipase). The FAs leave the cell and bind to blood proteins (e.g. albumin) for transport.

Question 32

What do FAs enter into organs via? When happens then?

Answer 32

FA transporters. B-oxidation, TCA cycle, electron-transport chain.

Question 33

Fatty acids /= 14 carbons undergo ________ ________.

Answer 33

Mitochondria Enzymatic reactions (3)

Question 34

How do FAs enter mitochondria?

Answer 34

Carnitine Shuttle: 1. Acyl-CoA synthase FA + CoA + ATP --> FAcyl-CoA + AMP + PPi 2. Carnitine acyltransferase I Attached to carboxyl group of carnitine (-> fatty acyl-carnitine) in order to pass mitochondrial membrane 3. Carnitine acyltransferase II Transferred from carnitine back to CoA (--> FAcyl-CoA). Carnitine moves back outside mitochondria to be reused.

Question 35

What is the rate limiting step in transferring FAs into mitochondria? What inhibits it?

Answer 35

Carnitine Acyltransferase I enzyme. Inhibited by Malonyl Co-A (reducing movement of longer FAs into mitochondria for breakdown)

Question 36

What is Beta Oxidation?

Answer 36

The breakdown of FAs into their two carbon parts.

Question 37

What are the 3 stages of FA catabolism? (to form ATP)

Answer 37

1. Beta Oxidation (in mitochondria) 2. TCA / citric acid cycle (in mitochondria) 3. Electron-transfer chain (on inner mitochondria membrane)

Question 38

What is the first step of B-oxidation? (palmitic acid)

Answer 38

Acyl-CoA dehydrogenase oxidises Linolenic acid (C16) with FAD (-->FADH), producing a C=C bond between alpha and beta carbon in the trans conformation.

Question 39

What is the second step of B-oxidation?

Answer 39

Enoyl-CoA hydratase + H2O binds to C=C and forms an alcohol. (note: can only bind to TRANS conformation)

Question 40

What is the third step of B-oxidation?

Answer 40

B-hydroxy-acyl-CoA dehydrogenase dehydrates the alcohol, producing a ketone. Oxidation with NAD+ -> NADH

Question 41

What is the fourth and final step of B-oxidation?

Answer 41

Thiolase breaks molecule into two by substituting acetyl CoA for CoA-SH (->H goes onto CH3 etc). Steps repeat until only Acyl-CoA left.

Question 42

How many repeats of B-oxidation steps is needed to oxidise a C16 molecule (e.g. linolenic acid). Why?

Answer 42

7 repeats. Because FA decreases by 2C each round until only Acetyl-CoA left (2C).

Question 43

How much ATP does one FADH2 molecule produce?

Answer 43

1.5 ATP

Question 44

How much ATP does one NADH molecule produce?

Answer 44

2.5 ATP

Question 45

How much ATP does one Acetyl CoA molecule produce?

Answer 45

10 ATP

Question 46

Per B-oxidation round, how many FADH2, NADH and Acetyl CoA is produced? What is used up?

Answer 46

7 FADH2 7 NADH 8 Acetyl CoA 1 H2O 1 CoA-SH

Question 47

Overall, how much ATP produced in the Beta Oxidation of Palmitoyl CoA?

Answer 47

Cofactors: 1.5 x 7 -> 10.5 2.5 x 7 -> 17.5 = 28 ATP 8 Acetyl CoA produced 10 x 8 = 80 ATP 28 + 80 = 108 ATP

Question 48

Overall equation for B-oxidation?

Answer 48

Question 49

What is the difference between linoleic and palmitic acid>

Answer 49

Linoleic - unsaturated Palmitic - saturated

Question 50

For oxidising unsaturated FAs, which step is not needed? However what needs to be done instead?

Answer 50

The first step, as C=C bonds already there. So, only 6 FADH2 produced. Need to change cis to trans conformation using enzyme (enoyl-CoA isomerase).

Question 51

Does oxidising saturated or unsaturated FAs produce more ATP?

Answer 51

Oxidising saturated produced a little more ATP (1.5) than unsaturated -> one more step, so one more FADH2 produced).

Question 52

How is FA catabolism regulated?

Answer 52

Malonyl-CoA inhibits carnitine acyl-transferase I (so less FAs enter mitochondria for B-oxidation).