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MCBG > Energy Production: Lipids > Flashcards

Energy Production: Lipids Flashcards

1
Q

What are some features of lipids?

A

They are structurally diverse
Generally insoluble in water (hydrophobic)
Most only contain C,H,O.
They are more reduced than carbohydrates.

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2
Q

What lipids contain other elements than C,H, and O? What elements do they contain as well?

A

Phospholipids contain P and N as well.

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3
Q

What are the consequences of lipids being more reduced than carbohydrates?

A

It means that they release more energy when they are oxidised.
It also means that they require more oxygen.

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4
Q

What classes of lipids are there?

A

Fatty acids
Hydroxy-methyl-glutaric acids also called HMGs
Vitamins

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5
Q

What fatty acid derivatives are there? What are their functions?

A

Fatty acids - fuel molecules
Triacylglycerols also called triglycerides - fuel storage and insulation
Phospholipids
Eicosanoids - local mediators

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6
Q

What HMG acids derivatives are there?

A

Ketone bodies - water soluble fuel molecules
Cholesterol - membranes and steroid hormone synthesis
Cholesterol esters - cholesterol storage
Bile acids and salts - lipid digestion

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7
Q

What vitamins are there that are lipids?

A

Vitamin A, D, E and K.

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8
Q

How much energy does a healthy 70kg man need per day?

A

10-11000 kJ.

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9
Q

What is the structure of a triacylglycerol (TAG/triglyceride)?

A

3 fatty acid side chains and a glycerol back bone.

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10
Q

What is the process called that makes triacylglycerol from 3 fatty acids and 1 glycerol?

A

Esterification

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11
Q

What is the process called that breaks up the triacylglycerol into 3 fatty acids and 1 glycerol?

A

Lipolysis

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12
Q

What are some features of triacylglycerols?

A

They are hydrophobic so they are stored in an anhydrous form.
Utilised in prolonged exercise, in starvation and also in pregancy.

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13
Q

Where are triacylglycerols stored?

A

In adipose tissue

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14
Q

What makes triacylglycerols to be stored or released?

A

Hormones.

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15
Q

Very briefly explain triglyceride metabolism.

A

Broken down in the GI-tract by lipolysis into glycerol and fatty acids.
Glycerols are then taken up in the blood stream and then taken up in the liver.
Fatty acids are hydrophobic and needs to be repackaged into lipoproteins called chylomicrons. They are then taken up in adipose tissue and stored as triglycerides again and made into fatty acids again to reach muscle.

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16
Q

Where does stage 1 of triglyceride metabolism take place?

A

In the GI tract. Lipolysis turns triglyceride into glycerol and 3 fatty acids.

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17
Q

What is the enzyme that helps with the lipolysis?

A

Pancreatic lipases.

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18
Q

What are chylomicrons?

A

Fatty acids are repackaged into chylomicrons which are lipoproteins. This is because fatty acids are hydrophobic and can’t enter the blood stream.

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19
Q

What are fatty acids stored as?

A

Triglycerides

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20
Q

How do fatty acids from adipose tissue get to target tissue?

A

They are carried by a protein called FA-albumin.

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21
Q

Briefly explain the triglyceride/fatty acid cycle in adipose tissue.

A

When there is a high concentration of glucose, glucose is taken up from the blood stream in the adipose tissue.
By glycolysis glucose is converted into glycerol-1-P.
By esterification glycerol-1-P is converted into triglyceride.
Triglyceride can then undergo lipolysis in the adipose tissue to form fatty acids and glycerol. This is in case of starvation for example.
The fatty acids are then carried out to the blood stream with the help of FA-albumin.
Glycerol is transported out of the adipose tissue to the blood stream without any help.

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22
Q

What happens if there is a low concentration of glucose in the blood regarding the triglyceride/fatty acid cycle?

A

Glucose stop being taken up by the adipose tissue and it also promotes lipolysis to form fatty acids and glycerol.

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23
Q

Explain the structure of fatty acids and their features.

A

CH3(CH2)nCOOH which is has a large hydrophobic tail CH3(CH2)n and a smaller hydrophilic group COOH.
It can be either saturated or unsaturated, also polyunsaturated.

24
Q

How do saturated and unsaturated fatty acids differ?

A

Saturated fatty acids do not have carbon double bonds.

Unsaturated fatty acids have one ore more carbon double bonds.

25
Q

What is stage 2 in fatty acid metabolism? Where does it take place?

A

In the mitochondria.

It’s when fatty acids are converted into acetyl CoA.

26
Q

Briefly explain stage 2 of fatty acid metabolism.

A

Fatty acids are activated by linking to coenzyme A outside the mitochondrion.
They are transported across the inner mitochondrial membrane using a carnitine shuttle
Fatty acid cycles are then oxidative where C2 (2 carbons) removed each cycle.

27
Q

Why is activation of fatty acids by coenzyme A needed?

A

Because fatty acids do not readily cross the inner mitochondrial membrane.

28
Q

Where does activation of fatty acids by coenzyme A take place?

A

Outside of the mitochondrion in the cytoplasm.

29
Q

How does the carnitine shuttle work?

A

Acyl-CoA (fatty acid with CoA) reacts with carnitine to form Acyl Carnitine and only Coenzyme A.
Acyl Carnitine can now easily cross the inner mitochondrial membrane.
Acyl carnitine will now react with coenzyme A to then again form Carnitine and Acyl-CoA.
Acyl-CoA can now be found in the matrix.

30
Q

What happens to the Acyl-CoA in the matrix of the mitochondrion now?

A

It undergoes something called beta-oxidation which removes C2 at every cycle.

31
Q

What are the products of beta-oxidation? Use stearic acid (C18) as an example.

A

From stearic acid (C18):
9 acetyl CoA are formed
8 FADH2, 8 NADH and 8H+ are formed.

32
Q

What happens to the products of beta-oxidation?

A

The 9 acetyl CoA undergo the TCA cycle (stage 3) to form even more reducing power.
The reducing power FADH2 and NADH + H+ move onto the electron transport chain and oxidative phosphorylation in stage 4.

33
Q

Where does beta-oxidation take place/Where does it not take place? Why does it not take place there?

A

In most tissues and white blood cells. (In the mitochondria)
It does not take place in the brain and red blood cells.
It doesn’t take place in the brain because fatty acids have a hard time to cross the blood-brain barrier.
It doesn’t take place in red blood cells because they don’t have mitochondria.

34
Q

Is there any ATP synthesis in beta-oxidation?

A

Not directly in beta-oxidation. But it lays a foundation for ATP synthesis because of the acetyl CoA formation and the formation of NADH and FADH2 as well.

35
Q

Where is glycerol metabolised?

A

In the liver.

36
Q

Briefly explain glycerol metabolism.

A

Glycerol uses ATP and glycerol kinase to form glycerol phosphate and ADP. Glycerol phosphate can then take two pathways. It can either go for triacylglycerol synthesis or go into DHAP and then be fed into glycolysis.

37
Q

What are the functions of acetyl CoA?

A

As it goes into the TCA cycle it can either undergo catabolic pathways or anabolic pathways. It can form fatty acids to then form triglycerides and phospholipids.
It can form HMG as well to then form ketone bodies and cholesterol.

38
Q

What three ketone bodies can be found in the body?

A

Acetoacetate (liver)
Acetone
beta-hydroxybutyrate (liver)

39
Q

What is the normal plasma ketone body concentration?

A

Less than 1 mM

40
Q

What is an indication of starvation?

A

A high plasma concentration of ketone bodies. (2-10 mM) This is called physiological ketosis.

41
Q

What is an indication of untreated type 1 diabetes?

A

A high plasma concentration of ketone bodies. Higher than 10 mM. This is called pathological ketosis.

42
Q

Where are ketone bodies synthesised?

A

In the liver by mitochondria.

43
Q

Briefly explain ketone body synthesis.

A

It is formed by acetyl CoA.
Acetyl-CoA is transported to the liver and then synthase converts Acetyl-CoA into HMG-CoA.
HMG-CoA can then be converted into cholesterol by HMG-CoA reductase or ketone bodies.
The ketone bodies are formed by lyase reacting with HMG-CoA. Acetoacetate is the first step here which can be converted into acetone or beta-hydroxybutyrate.

44
Q

What are regulators of ketone body synthesis?

A

If TCA is inhibited in some way this can cause acetyl-CoA to go into the ketone body synthesis pathway instead. This means that a high NADH concentration for example causes KB synthesis to increase.

45
Q

Where does the acetyl CoA in the liver for metabolism into ketone bodies come from?

A

Usually from beta-oxidation of fatty acids into acetyl CoA.

46
Q

Briefly explain metabolism of ketone bodies.

A

Fatty acids -> Acetyl CoA -> HMG-CoA -> acetoacetate.
Acetoacetate is then either converted into beta-hydroxybutyrate in the liver or released into the blood stream. Beta-hydroxybutyrate is then also released into the blood. Here in the blood acetoacetate can spontaneously be converted into acetone.
Acetoacetate and beta-hydroxybutyrate are then transported into a tissue like muscle.
beta-hydroxybutyrate is converted into acetoacetate.
Acetoacetate then react in the TCA cycle with Succinyl CoA to form Acetoacetyl CoA and then further converted into Acetyl CoA.

47
Q

In short outline metabolism of ketone bodies.

A

Ketone bodies such as acetoacetate and beta-hydroxybutyrate are converted into acetyl CoA in the muscle.

48
Q

What is ketone body synthesis more regulated by?

A

Insulin to glucagon ratio. Insulin promotes cholesterol synthesis. Insulin (fed state) means that there is a low production of ketone bodies.
Glucagon (starvation) promotes ketone body production to use ketone bodies for energy.

49
Q

What happens to HMG-CoA when insulin is high?

A

Cholesterol is formed.

50
Q

What happens to HMG-CoA when glucagon is high?

A

Ketone bodies are formed.

51
Q

Why are ketone bodies incredibly important in starvation?

A

Ketone bodies spare glucose in early starvation and in diabetes.

52
Q

Why is sparing glucose important in starvation?

A

Because RBCs and the brain only use glucose. So ketone bodies being used by muscle instead here makes spare glucose to be able to be used for the brain.

53
Q

What happens in late starvation?

A

Ketone bodies are used for energy in muscle. Amino acids in the muscle are then transported to the liver where they are converted into pyruvate which then undergo gluconeogenesis to form glucose.
Glycogen also undergo glycogenolysis in order to form glucose.

54
Q

What are some features of ketone bodies?

A

Water soluble molecules (hydrophilic)

55
Q

What is ketonuria?

A

When the ketone body concentration is above the renal threshold it is excreted in the urine. It means ketone bodies in the urine.

56
Q

What is ketoacidosis?

A

When there is a high concentration of acetoacetate and beta-hydroxybutyrate they are acidic and form an acidic environment.

57
Q

How can you detect high acetone concentrations?

A

By smelling the breath.

This is because volatile acetone may be excreted by the lungs.

MCBG (21 decks)

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