Metabolism S3 - Energy Production (Carbohydrates and Lipids) Flashcards Preview

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Flashcards in Metabolism S3 - Energy Production (Carbohydrates and Lipids) Deck (54):
1

The TCA cycle is a central pathway in the catabolism of what compounds?

Sugars, fatty acids, ketone bodies, alcohol and amino acids

2

The TCA cycle occurs where?

Mitochondria

3

Is the TCA cycle oxidative or reductive?

Oxidative

4

What does the TCA pathway require to function?

AcetylCoA, NAD+, FAD and oxaloacetate

5

What is the main function of the TCA cycle?

Break the C-C bond in acetate (as acetylCoA) and oxidise the C atoms to CO2

6

In the TCA cycle what is the involvement of H+ and e-?

Removed from acetate and transferred to NAD+ and FAD+

7

Can the TCA cycle function in anaerobic conditions?

Nope

8

Per molecule of glucose, what does the TCA cycle produce?

2 ATP

2 FAD2H

6NADH

4 CO2

9

Describe the chemical 'strategy' of the TCA cycle.

Produce intermediates (C5 tricarboxylic acids and keto acids) that readily lose CO2 producing C4 acids that are interconvertible.

10

What are the anabolic functions of the TCA cycle?

C5 and C4 intermediates used in non-essential amino acid synthesis

C4 intermediates used for the synthesis of haem and glucose

C6 intermediates used for synthesis of fatty acids

11

What is the main method of TCA cycle regulation?

One Irreversible step is catalysed by isocitrate dehydrogenase

This enzyme allosterically controlled by ADP/ATP and NAD+/NADH ratios

ADP activates (low energy signal)

NADH inhibits (high energy signal)

12

Give an equation for the complete oxidation of glucose and the overall release of energy

C6H12O6 + 6 O2 ---> 6 CO2 + 6 H2O

2870kJ/mol

13

by the end of the TCA cycle what has happened to glucose's bonds and bond energy?

All C-C bonds broken

All C atoms oxidised to CO2

All C-H bonds broken and H+/e- transferred to NAD+ and FAD

All energy has gone into ATP/GTP formation

Chemical bond energy of the e- is in NADH or FAD2H form.

14

How much energy is released from the oxidation of NADH and FAD2H?

NADH = 220kJ/mol

FAD2H = 152kJmol

15

What is the energy from the oxidation of NADH and FAD2H used for?

Oxidative phosphorylation

16

Give a brief description of electron transport

Electrons from NADH and FAD2H transferred through a series of carrier molecules in the inner mitochondrial membrane to molecular oxygen, releasing free energy

17

The free energy released from electron transport drives what process?

ATP synthesis

18

how many electron transfer complexes are their?

A series of 4

19

3 of the electron transport complexes have another function, what is this?

They act as proton translocation complexes (proton pumps)

20

how is an electrochemical gradient set up across the inner mitochondrial membrane?

Protons moved into the inter membrane space across the impermeable inner mitochondrial membrane of the mitochondrion using electrochemical energy generated from electron trnasport

21

how and why do NADH and FAD2H utilise the protons pump differently

NADH releases more energy, so uses all three proton pumps while FAD2H only uses 2

22

What is the role of oxygen in the electron transport chains?

final electron acceptor

23

How much energy is required to produce one ATP molecule via oxidative phosphorylation

31kJ/mol

24

How is the proton gradient across the inner mitochondrial membrane used in ATP synthesis?

Protons can only flow through ATP synthase complexes, this produces ATP from ADP and Pi.

25

How many moles of ATP produced per mole of NADH and FAD2H

NADH = 2.5

FAD2H = 1.5

26

electron transport and ATP synthesis are highly coupled, when ATP concentration is high, what happens to these processes?

ATP synthesis stops due to lack of substrate

This prevents H+ transport back into matrix

H+ concentration continues to increase in intermembrane space until reaching a level that prevents further buildup of H+

In the absence of proton pumping, electron transport stops.

27

What substances can increase permeability of the inner mitochondrial membrane to protons and what is this effect called?

dinitrocresol, dinitrophenol

uncoupling

28

what is proton leak?

protons crossing inner mitochondrial membrane into the matrix without passing through the ATP synthase complex

29

how is pmf dissipated when proton leak occurs?

 

What proportion of energy is leaked and under what curcumstances might this proportion increase?

As heat.

Normally 20-25% of Basal metabolic rate dissipated as heat, increases when uncoupling occurs

30

What is the purpose of uncoupling proteins?

Uncouple electron transport and ATP synthesis to produce heat

31

What are the three uncoupling proteins?

UCP1 (Thermogenin)

UCP2

UCP3

32

What is the function of Thermogenin and where is it found?

Non-shivering thermogensis enabling mammals to survive the cold

Expressed in brown adipose tissue

33

Where is UCP2 found and what diseases is it linked to?

Widely distributed

Heart failure, diabetes, obesity, metabolic syndrome

34

Where is UCP3 found and what are its functions?

Found in skeletal muscle, brown adipose tissue and the heart.

Uncoupling of electron transport

Appears to be involved in fatty acid metabolism and protecting against reactive oxygen species damage.

35

what are noradrenaline's effects on metabolism?

Stimulates lipolysis and hence more NADH and FAD2H are produced

Activates UCP1

Hence higher levels of pmf dissipated as heat

36

What are the differences between substrate level and oxidative phosphorylation

Oxidative requires membrane associated proteins, substrate level requires soluble enzymes

In oxidative couple occurs indirectly through creation and utilisation of pmf, in substrate level energy coupling occurs directly through phosphoryl group transfer

Oxidative cannot occur without oxygen, substrate level can occur to limited extent anaerobically

Oxidative is a major process in high energy cells, substrate level is a minor process in high energy cells

37

What are the general features of a lipid?

Hydrophobic

Most contain CHO (phospholipids contain P and N)

More reduced than carbohydrates

38

What are the three major classes of lipid?

Fatty acid derivatives

Hydroxy-methyl-glutaric acid derivatives

Fat soluble vitamins

39

What types of fatty acid derivatives are found in the body and what are their functions?

Fatty acids - Fuel molecules

Triacylglycerols - Fuel storage and insulation

Phospholipids - Components of plasma membranes and plasma lipoproteins

Eicosanoids - Local mediators/signalling molecules

40

What types of Hydroxy-methyl-glutaric acid derivatives are found in the body and what are their functions?

Ketone bodies - Water soluble fuel molecules

Cholesterol - Membranes and steroid hormone synthesis

Cholesterol esters - Cholesterol storage

Bile acids and salts - Lipid digestion

41

How are triacylglycerols broken down in the small intestine and what are the products of breakdown?

Pancreatic lipase in a complex process requiring colipase and bile salts

Releases glycerol and fatty acids

42

Where is glycerol metabolised?

Liver

43

Why are some polyunsaturated fatty acids required in the diet? Give an example of a required polyunsaturate and it's use

Cannot be synthesised by the body

Arachidonic acid - Starting point of eicosanoid synthesis

44

What are the three ketone bodies produced by the body?

Acetoacetate

Acetone - formed from spontaneous decarboxylation of above, not intentionally formed

B-hydroxybutyrate

45

Where are ketone bodies synthesised and what from?

Liver

AcetylCoA

46

What is the normal level of ketone bodies in the blood and what could be responsible for this rising?

<1mM is normal

This can increase during starvation to 2-10mM = Physiological ketosis

10mM = Pathological Ketosis, caused by type 1 diabetes

47

What are the basic properties of ketone bodies and what are clinical consequences of these properties?

Water soluble - allows excretion in urine (ketonuria) and high plasma concentration

Strong organic acids - In high concentration can cause ketoacidosis

48

How is acetone useful in diagnosis of type 1 diabetes

Acetone is volatile so can be excreted through the lungs. There is a strong smell of acetone on the breath of untreated type 1 diabetes patients

49

During ketone body synthesis what ratio controls what key enzyme?

Insulin/glucagon ratio

Controls Hydroxy-methyl-glutaryl CoA (HMG-CoA) Lyase/reductase enzymes

50

How do changes in the Insulin/glucagon ratio affect ketone synthesis?

Reduction in insulin and increase in glucagon stimulates HMG-CoA lyase and hence increased levels of ketone bodies produced

Vice versa.

51

What does the synthesis of ketone bodies require? (substrate and conditions)

Fatty acids available for oxidation (excess lipolysis)

Plasma insulin/glucagon ration to be low, normally due to fall in plasma insulin

52

How and where are ketone bodies used and how does plasma concentration affect their use?

As fuel molecules in all mitochondria containing cells including the nervous system

Converted to AcetylCoA and used in TCA cycle

Rate of use proportional to plasma concentration

53

What is Acetyl CoA produced by?

Metabolism of:

Fatty acids

Sugars

Alcohol

Certain Amino acids

54

How and where is AcetylCoA utilised?

Oxidised in TCA cycle (mitochondria)

Important intermediate in lipid biosynthesis (the major site of which is the liver, some in adipose tissue)