lipid metabolism

Question 1

name a short term energy store

Answer 1

carbohydrates

Question 2

name long term energy stores

Answer 2

lipids and ketone bodies

Question 3

where is fat stored in the body?

Answer 3

white adipose tissue

Question 4

what does lipid breakdown release and how are they used?

Answer 4

fatty acids - oxidised for energy in tissues or converted to ketone bodies in the liver
glycerol - used in glucose synthesis in the liver

Question 5

what does hormone sensitive lipase (HSL) do?

Answer 5

breaks down triglycerides into fatty acids and glycerol

Question 6

what hormones control HSL and what control do they have?

Answer 6

glucagon - increase activity
insulin - decreased activity
Adrenaline
Adipose triglyceride lipase

Question 7

how are fatty acids carried around the blood and why?

Answer 7

bound to albumin bc they’re not soluble

Question 8

what are the stages of fatty acid oxidation?

Answer 8

1. Activation of fatty acid by acetyl-CoA
2. Transport into the mitochondria from the cytoplasm via the carnitine shuttle
3. Beta oxidation in the mitochondria

Question 9

what is the carnitine shuffle?

Answer 9

various steps to move fatty acid from cytosol to mitochondrial matrix to get access to the enzymes that do beta-oxidation

Question 10

what are the stages of the carnitine shuffle?

Answer 10

1. Fatty acid converted to fatty acyl-CoA by acyl-CoA synthase using ATP.
2. Fatty acyl-CoA moved through outer mitochondrial membrane to form fatty acyl-carnitine by CPT-I (Carnitine palmitoyltransferase I).
3. Fatty acyl-carnitine is moved through inner mitochondrial membrane by translocase.
4. Converted back to fatty acyl-CoA in mitochondrial matrix by CPT-II

Question 11

what is beta oxidation?

Answer 11

when fatty acids are oxidized by acetyl-CoA dehydrogenases in the mitochondrial matrix

Question 12

in what tissues does beta oxidation occur?

Answer 12

all tissues apart from the brain and RBCs

Question 13

what are the products of beta oxidation?

Answer 13

NAD and acetyl CoA

Question 14

how is catabolism of fatty acids controlled?

Answer 14

Malonyl-CoA inhibits transports
Glucagon stimulates transport via cAMP
Regulated transcriptionally

Question 15

what is lipogenesis?

Answer 15

the process by which acetyl-CoA is converted to triglycerides (how fat is made)

Question 16

where does lipogenesis occur?

Answer 16

the liver, white adipose tissue and lactating mammary glands - stimulated in response to high blood sugar

Question 17

what are the stages of lipogenesis?

Answer 17

Glucose goes through glycolysis to make pyruvate –> TCA cycle –> citrate –> cytosol –> acetyl CoA –> malonyl CoA –> fatty acid chains

Formation of malonyl CoA
Fatty acid synthetase – elongates the chain by 2 carbon units

Question 18

what is the main enzyme in lipid synthesis?

Answer 18

acetyl-CoA carboxylase

Question 19

how is acetyl-CoA carboxylase controlled?

Answer 19

Polymerization: promoted by citrate
Phosphorylation: by AMP dependent kinase and PKA.
Genetic Control (longer term).

Question 20

where are ketone bodies produced?

Answer 20

in the liver by mitochondria

Question 21

explain the stages of ketogenesis

Answer 21

Starts with 2X acetyl-CoA
Combine to form acetoacetyl-CoA (CoA group removed)

Converted to 3-hydroxy-3methylglutaryl-CoA by HMG-CoA synthase

Converted to ACETOACETATE (ketone) by HMG-CoA lyase.

Acetoacetate can be split into further ketone bodies (D-beta-hydroxybutyrate and acetone).

Question 22

in starvation, what energy stores does the brain use?

Answer 22

brain switches from 100% glucose to 50% ketone bodies

Question 23

what tissues/organs use ketone bodies?

Answer 23

heart
skeletal muscle
the brain

Question 24

what are the liver phases of glucose homeostasis?

Answer 24

Stage 1 - glucose from food
Stage 2 - liver glycogen to maintain blood glucose
Stage 3 - liver gluconeogenesis
Stage 4 - drop in the rate of gluconeogenesis bc the brain is replacing glucose with ketone bodies so less gluconeogenesis is needed.

Question 25

which hormone inhibits ketone body production?

Answer 25

insulin

Question 26

why do diabetics struggle with ketoacidosis?

Answer 26

without insulin, more fatty acid is transported into the mitochondria of the liver –> more acetyl CoA builds up –> more acidic ketone bodies –> ketoacidosis

Question 27

what is metabolic flexibility?

Answer 27

ability to switch between using glucose and lipids

Question 28

what effect does a sedentary lifestyle have on metabolic flexibility?

Answer 28

less metabolic flexibility