Week 7 - Lipid metabolism

Question 1

What parts of lipids are hydrophilic and what parts are hydrophobic?

Answer 1

Fatty acid tails are hydrophobic. The longer the fatty acid chain and fewer double bonds = lower solubility of water.

Polar heads and cholesterol and hydrophilic.

Question 2

What is the difference between a saturated and unsaturated fat?

Answer 2

Unsaturated fat has a double bond between Carbon where saturated fats have no double bonds.

Question 3

What does a phospholipid consist of?

Answer 3

A glycerol unit connected by 2 fatty acids and phosphoric group attached to an alcohol via ester bonds.

Question 4

What type of lipid is the majority consumed from dietary fat?

Answer 4

Triacyglycerol

Question 5

What does a triacylglycerol molecule consist of?

Answer 5

One glycerol unit and 3 fatty acids connected by ester bonds

Question 6

How can hydrophobic molecules be processed when 65% of body is water? (3 ways)

Answer 6

o Ingestion: Large lipid droplets are reduced in size to fine lipid droplets by bile acids, made in liver & released by gallbladder.
o Intestinal lumen: Pancreatic lipase hydrolyses the ester bonds to yield 2 fatty acids and 2-monoacylglycerol.
o Enterocytes: These products freely enter the intestinal cells where TAG is reformed.

Question 7

Where are lipids mainly stores in the body?

Answer 7

Mainly stored in specialised tissue called adipose tissue, as well as muscle.

Question 8

Where is adipose tissue mainly found in the human body?

Answer 8

Under the skin (subcutaneous fat) and around our internal organs (visceral fat).

Question 9

What is the cytoplasm of an adipose tissue dominated by?

Answer 9

A large lipid droplet filled with triacylglycerol (around 80%).

Question 10

Why are triacylglycerol stores (contained in lipid droplets) next to mitochondria?

Answer 10

Close proximity to mitochondria minimises distance fatty acids move for degradation & ATP production.

Question 11

When is lipolysis optimal?

Answer 11

During aerobic exercise.

Question 12

By what process does exercise speed up FFA degradation in adipose tissue and muscle?

Answer 12

Beta-oxidation.

Question 13

What is the product of b-oxidation and where doe it go?

Answer 13

acetyl coA - enters TCA cycle.

Question 14

Where does triacylglycerol breakdown AND synthesis occur?

Answer 14

Cytosol

Question 15

What 3 enzymes are involved in triacylglycerol breakdown?

Answer 15

o Adipose TAG Lipase (AGTL)
o Hormone sensitive lipase (HSL)
o Monoacylglycerol acyltransferase (MGL)

Question 16

How is triacylglycerol synthesised?

Answer 16

o Glycerol generated from dietary glucose forms the TAG glycerol backbone.
o 3 fatty acids are then added in 2 steps via the enzyme glycerol phosphate acyltransferase.

Question 17

What is the relationship between triacylglycerol synthesis and breakdown in a fed state?

Answer 17

Synthesis > breakdown

Question 18

What is the relationship between triacylglycerol synthesis and breakdown during exercise?

Answer 18

Breakdown > synthesis

Question 19

What are FFA’s used for in the muscle?

Answer 19

B-oxidation and ATP provision

Question 20

How and where are fatty acids degraded in the muscle?

Answer 20

Fatty acids are degraded through the pathways of B-oxidation in the mitochondria

Question 21

Name and describe the 3 steps of fatty acids degradation

Answer 21

1) Activation: FFA’s are activated by a reaction with CoA forming Acyl-CoA. This can then pass to the inter membrane space.
2) Carnitine binding: Carnitine takes the Acyl group (Acylcarnitine), allowing transport into the mitochondrial matrix.
3) CoA restoration: The acyl chain is then taken from carnitine to reform Acyl-CoA inside the mitochondrial matrix.

Question 22

What happens to acyl-xoA in the mitochondrial matrix?

Answer 22

Acyl-coA enters the B-oxidation pathway

Question 23

What is the energy yield of B-oxidation?

Answer 23

8 acetyl coA, 7FADH2 and 7NADH - these enter TCA cycle and ETC.

B-oxidation is not energetically favoured and produced NO ATP.

Question 24

How many carbons does B-oxidation remove at a time?

Answer 24

2

Question 25

What happens if a fatty acid contains an odd number of carbons?

Answer 25

Once acylCoA is reached (5C), it is broken down into Acetyl Coa (normal) and Propionyl CoA (3C).

This undergoes 3 reactions to form Succinyl CoA which enters reaction 5 of TCA cycle.

Question 26

Name 4 ways in which exercise speeds up fatty acid oxidation in muscle.

Answer 26

1) Stimulates lipolysis in adipose tissue and muscle
2) Increases blood flow to the working muscle, thus increasing FFA delivery
3) Enhancing translocation of fatty acid binding protein at the plasma membrane for FFA uptake into muscle.
4) Increasing activity of AMP-activated protein kinase (AMPK), which deactivates acetyl coA carboxylase, thus reducing fatty acid synthesis (preventing acetyl CoA from becoming Malonyl CoA)

Question 27

What is the blood plasma fatty acid profile during low intensity exercise.

Answer 27

Slight initial increase, maintained throughout, small post exercise increase, return to baseline.

Question 28

What is the blood plasma fatty acid profile during moderate intensity exercise.

Answer 28

Slight initial decrease, gradual increase throughout, large post exercise increase, return to baseline.

Question 29

What is the blood plasma fatty acid profile during high intensity exercise.

Answer 29

Large initial decrease, sustained low throughout, large post exercise increase, post exercise suppression.

Question 30

How are lipids packaged for transport?

Answer 30

FFA is carried by Albumin.

Question 31

What is the ratio of LDL:HDL a key indicator of?

Answer 31

Cardiovascular health