Cell Metabolism II - Lipids

Question 1

what are the three primary sources of fats?

Answer 1

1. the diet
2. the liver (cholesterol metabolism)
3. storage depots in adipose tissues

Question 2

where are bile salts generated and stored?

Answer 2

generated: liver
stored: gall bladder

Question 3

what can bile salts do to fats?

Answer 3

they can emulsify the fats (to incr. their surface area for lipase to break down) and fat soluble vitamines = aids their digestion and absorption in intestine

Question 4

what can a lack of bile salts lead to?

Answer 4

fats pass through gut unabsorbed = steatorrhea (fatty stool)

Question 5

what does the term “ampiphatic” molecules?

Answer 5

can interact with both hydrophobic molecules and hydrophobic molecules

Question 6

how does the structure of bile salts relate to their function?

Answer 6

• they are flat
• hydrophilic groups face outdoes and hydrophobic groups face inside so they can transport the otherwise non-water solute/hydrophobic fats

Question 7

how can medications aid with obesity?

Answer 7

Orlistat → can be used as a potent inhibitor of gastric and pancreatic lipase = fats passed out unabsorbed.

Question 8

how are lipids transported around the body?

Answer 8

lipoproteins in the plasma

Question 9

where are chylomicrons produced?

Answer 9

(lipoprotein)

enterocytes cells that - line the small intestine

Question 10

how do chylomicrons transport the dietary fats around the body?

Answer 10

1. dietary products enter the enterocytes e.g. triglycerides
2. the triglycerides are resynthesized using enzymes and incorporated into the chylomicrons
3. transported in the lymphatic system → blood
4. they take up apoproteins (from HDL) into their membrane once they have reached the blood stream

The hydrophilic phospholipid monolayer, and apoproteins allow for the transportation of the core hydrophobic fats

Question 11

By what and where do chylomicrons get broken down?

Answer 11

They are broken down by lipoprotein lipases, found in the on the capillary endothelial cells lining e.g. adipose, heart and skeletal muscle

Question 12

What happens once the chylomicrons are broken down?

Answer 12

Fatty acids undergo β-oxidation. Glycerol is returned to the liver for use in gluconeogenesis

Question 13

why do chylomicrons have apoproteins?

Answer 13

so that they can be recognised by tissues

Question 14

where are lipoproteins synthesised?

Answer 14

liver

Question 15

what is the main role of lipoproteins?

Answer 15

they transport hydrophobic molecules in a aqueous environment

Question 16

what is the structure of lipoproteins?

Answer 16

• phospholipid monolayer
• cholesterol (esterified them to make them more hydrophobic so that they pack more tightly)
• apoproteins

Question 17

What are the lipoproteins that transport fat to and from the liver? (Chylomicrons are from the intestine)

Answer 17

VLDL (very low density lipoproteins) - found in the liver and are responsible for endogenous fat transport
IDL (intermediate density lipoproteins) - comes from VLDL and is an LDL precursor (substance from which LDL can be made)
LDL (low density lipoproteins) - comes from IDL and is responsible for cholestrol transport from liver to peripheral tissues
HDL (high density lipoproteins) - comes from LDL and is responsible for reverse cholestrol transport from peripheral tissues to liver

Question 18

What are cholestrol esters and where are they found?

Answer 18

Synthesized in the plasma from cholesterol

Question 19

What are the 3 main steps for making Acetyl CoA from Fatty Acids?

Answer 19

1. fatty acid → acyl CoA
2. Transfer Acyl CoA into mitochondria via carnitine shuttle
3. Beta Oxidation - finally produces Acetyl CoA

Question 20

what is step 1 to make acetyl CoA?

Answer 20

fatty acid → acyl CoA

Question 21

describe the carnithine shuttle

Answer 21

cytoplasm → matrix of mitochondria

1) carnitine + acyl CoA→ acyl carnitine + CoA
2) acyl carnitine moved across outer membrane through translocase
3) acyl carnitine + CoA→ carnitine Acyl CoA

only carnitine and all carnitine can move across membrane through translocase

Question 22

What is Primary carnitine deficiency and what are the symptoms?

Answer 22

• reduces cells ability to take up canitine which is needed for beta-oxidation of fatty acids
• muscle weakness, cardiomyopathies hypoglycaemia

Question 23

describe the beta oxidation cycle

Answer 23

(OHOT) oxidation → hydration → oxidation → thiolysis

from acyl CoA to acetyl CoA which is two carbons shorter

Question 24

When can acetyl coA from beta oxidation enter TCA??

Answer 24

if β-oxidation = carbohydrate metabolism as oxaloacetate is needed for entry

Question 25

When is acetyl CoA from fatty acids used to make ketone bodies?

Answer 25

When fat breakdown predominates e.g. during fasting

-if not sufficient oxaloacetate is produced from carb metabolism

Question 26

Which ketone bodies does Acetyl CoA make?

Answer 26

• acetoacetate
• D-3-hydroxybutyrate
• acetone

Question 27

How does fatty acid metabolism compare to glucose metabolism in terms of no. of ATP produced?

Answer 27

significantly more ATP/mole of substrate is produced in fatty acid metabolism

Question 28

Which family of enzymes catalyse the initial step in each cycle of fatty acid β -oxidation?

Answer 28

acyl-CoA-dehydrogenases (oxidation)

Question 29

What is a disease to do with lipid metabolism?

Answer 29

cancer → FA biosynthesis only happens in liver, adipose tissue and lactating breast

Question 30

What are the 4 reactions of lipogenesis? (and enzymes involved)

Answer 30

1) condensation
2) reduction
3) dehydration
4) reduction

CRDR (lengthening carbonchain by 2)

Question 31

why are HDLs referred as “good cholesterol” and LDLs bad?

Answer 31

• HDL take the cholesterol bad k to the liver for disposal = lower cholesterol levels
• LDL can lead to atherosclerosis (hardening of the arteries) as

Question 32

What are the 4 reactions of lipogenesis? (and enzymes involved)

Answer 32

1) condensation
2) reduction
3) dehydration
4) reduction

CRDR
(lengthening carbon chain by 2)

Question 33

What does the desaturation of fatty acids require?

Answer 33

fatty acyl-CoA-desaturases

Question 34

In adults, where is de novo FA biosynthesis restricted to?

Answer 34

• liver
• adipose tissue
• lactating breast

Question 35

What occurs in certain cancer cells?

Answer 35

reactivation of FA synthesis