Metabolic pathways: lipid catabolism

Question 1

What does increased fat intake without appropriate energy expenditure lead to?

Answer 1

Increased numbers of adipocytes
More fat in adipocytes
i.e. obesity

Question 2

Why is fat required?

Answer 2

Energy - energy content of 1g of fat is much greater than 1g of protein of carbohydrate
For fat soluble vitamins - A, D, E, K require fat for absorption

Question 3

What are essential fatty acids?

Answer 3

Fats required by the body but are not synthesised by the body, e.g. some polyunsaturated fats

Question 4

Which configuration are double bonds in fatty acids usually in?

Answer 4

Cis

Question 5

What is the most common fatty acid in humans and how many carbons does it contain?

Answer 5

Palmitic acid, 16C

Question 6

Which carbon is the alpha carbon in fatty acid nomenclature?

Answer 6

The carbon adjacent to the carboxyl group

Question 7

What carbon is the omega carbon in fatty acid nomenclature?

Answer 7

The carbon furthest away from the carboxyl group

Question 8

What is an omega three fatty acid?

Answer 8

A fatty acid with a double bond three carbons away from its omega group

Question 9

Which factors affect the melting point of a fatty acid?

Answer 9

The length of the carbon chain

The presence of double bonds (double bonds lower the melting point)

Question 10

Why do animal fats tend to be solid at room temperature?

Answer 10

Mainly consist of saturated fatty acids

Question 11

What are the main products of fat digestion?

Answer 11

Glycerol
Fatty acids
Monoglycerides

Question 12

Where are the products of fat digestion absorbed in the gut?

Answer 12

Absorbed in the mucosal cells of intestine

Question 13

Short and medium length fatty acids enter the portal blood. What happens to longer chain fatty acids once absorbed into intestinal mucosa?

Answer 13

Re-synthesised to triglycerides and coated with protein, phospholipids and cholesterol to form chylomicrons

Question 14

Where do newly formed chylomicrons exit into from the intestinal mucosa?

Answer 14

Lymph system

Question 15

What happens to chylomicrons when they meet muscle and adipose tissue?

Answer 15

Chylomicrons are attacked by lipoprotein lipases and the trigylcerides in them are cleaved

Question 16

When does lipolysis occur?

Answer 16

When energy is needed

Question 17

How is lipolysis initiated?

Answer 17

By hormone sensitive lipases

Question 18

Before fatty acids can be oxidised, what must happen to them?

Answer 18

They have to be converted to CoA derivatives

Question 19

Where does conversion of fatty acids to CoA derivatives occur?

Answer 19

Cytoplasm

Question 20

How much energy is required to convert fatty acids to CoA derivatives?

Answer 20

2ATP

Question 21

What is acyl-CoA?

Answer 21

Any fatty acid with a CoA attached

Question 22

How is acyl-CoA transported into the mitochondrial matrix from the cytoplasm?

Answer 22

The carnitine shuttle

Question 23

How does the carnitine shuttle work?

Answer 23

The acyl-CoA has its CoA removed and replaced with carnitine to be transported across the membrane
When it reaches the other side, the carnitine dissociates and another CoA group attaches back onto the acyl
The free carnitine moves out of the mitochondria again

Question 24

How many reactions occur in beta oxidation in each cycle?

Answer 24

It is a cycle of four reactions

Question 25

How many carbons is the fatty acid chain shortened by in beta oxidation?

Answer 25

2 - produces one acetyl-CoA per cycle, with each acyl-CoA shortened by two carbons

Question 26

What are the products of each cycle of beta oxidation?

Answer 26

1 acetyl CoA
1 acyl-CoA, shortened by 2 carbons
1 FADH2
1 NADH + H+

Question 27

What happens to the glycerol from fat breakdown?

Answer 27

Can be converted to glycerol-3-phosphate by glycerol kinase - this is present in liver and kidney

Question 28

Where are ketone bodies formed?

Answer 28

Liver mitochondria from acetyl Co-A from beta oxidation

Question 29

Why does ketone body formation mainly occur in liver mitochondria?

Answer 29

Liver mitochondria contain most of dietary fat

Question 30

When are ketone bodies formed?

Answer 30

When there is lots of acetyl-CoA

Question 31

What do peripheral tissues use ketone bodies for?

Answer 31

Conversion back to acetyl-CoA to be used in TCA cycle

Question 32

When does ketone body production problematic and why?

Answer 32

During starvation - oxaloacetate is used for gluconeogenesis
Fatty acid oxidation used to provide energy, producing lots of acetyl CoA which builds up because there is no oxaloacetate
Acetyl CoA is converted to ketone bodies, causing high levels in blood and blood becomes acidotic