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ESA1 Callum's cards > Metabolism S4 - Energy Storage > Flashcards

Metabolism S4 - Energy Storage Flashcards

1
Q

Describe the three major energy stores in the body of a 70kg man.

Include approximate weight and approximate energy content for each store.

A

Triacylglycerols (TAGs) - 15kg - 600,000kJ

Glycogen - 0.4kg - 4,000kJ

Muscle Protein - 6kg - 100,000kJ

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2
Q

How many reactions are involved in glycogen synthesis? (glycogenesis)

A

4

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3
Q

What’s the equation of the first reaction in glycogenesis?

Which enzyme catalyses the reaction?

A

Glucose + ATP —> G-6-P + ADP

Hexokinase

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4
Q

What’s the equation for the second reaction in glycogenesis?

What enzyme catalyses this reaction?

A

G-6-P —> Glucose-1-Phosphate

Phosphoglucomutase

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5
Q

What’s the equation for the third reaction in glycogenesis?

A

Glucose-1-Phosphate + UTP + H2O —> UDP-Glucose + 2Pi

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6
Q

What is the final reaction of glycogenesis?

What two enzymes are involved and what is the difference in their action?

A

Glycogen (n residues) + UDP-Glucose —> Glycogen (n+1 residues) + UDP

Glycogen synthase forms 1-4 glycosidic bonds

Branching enzyme forms 1-6 glycosidic bonds

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7
Q

how often is a branch produces during glycogen synthesis?

A

about every 10 subunits

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8
Q

Where is glycogen stored and what is it broken down in response to at each respective location?

A

Liver - In response to fasting

Skeletal muscle - In response to exercise

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9
Q

What is the equation for the complete degradation of glycogen?

A

Glycogen (n residues) + nPi —> 0.9n G-6-P + 0.1n Glucose

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10
Q

Is glycogen ever fully degraded?

A

No, small sections of primer always preserved

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11
Q

How many reactions are involved in the degradation of glycogen?

A

3

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12
Q

Give the equation for the first step of glycogen degradation

What enzymes catalyse this reaction and what varies between their action?

A

Glycogen (n residues) + Pi —> Glucose-1-Phosphate + Glycogen (n-1 residues)

Glycogen phosphorylase (1-4 glycosidic cleavage)

De-branching enzyme (1-6 glycosidic cleavage)

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13
Q

Give the equation for the second step of glycogen degradation

What enzyme catalyses this reaction?

A

Glucose-1-Phosphate —> G-6-P

Phosphoglucomutase

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14
Q

How is glucose liberated from glycogen used in the skeletal muscle as compared to the liver?

A

In skeletal muscle G-6-P produced by step 2 of glycogen breakdown is fed directly into glycolysis for utilisation.

The liver requires another reaction (step 3 of glycogen degradation) to use the liberated glucose

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15
Q

Give the equation for step 3 of glycogen degradation

What enzyme catalyses this reaction?

A

G-6-P + H2O —> Glucose + Pi

Glucose-6-phosphatase

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16
Q

Compare the functions of liver and skeletal muscle glycogen

A

Liver - Glucose store for all tissues

Muscle - G-6-P store, useful only to muscle cells

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17
Q

How do glycogen metabolic disorders arise?

A

Abnormality in one or more of the enzymes of glycogen metabolism

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18
Q

What are the three enzymes that may be defective in a patient with a glycogen metabolism disorder?

A

Glycogen phosphorylase

Phosphoglucomutase

Glucose-6-phosphatase

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19
Q

What 3 effects are seen in glycogen metabolic disorders?

A

Increased/Decreased amount of glycogen

Glycogen structure may be abnormal

Usually liver or muscle effects

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20
Q

What are the clinical consequences of increased or decreased levels of glycogen?

A

Decreased exercise tolerance

Fasting hypoglycaemia

Tissue damage if excessive storage

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21
Q

What is the process of producing glucose from non-carbohydrate sources called?

A

Gluconeogenesis

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22
Q

Why is gluconeogenesis necessary?

A

To maintain constant glucose level in blood after glycogen been used

Some tissue are glucose dependent (eg. CNS)

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23
Q

Where is the main site of gluconeogenesis?

A

Liver

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24
Q

How long do glycogen stores last after eating?

A

8-10 hours

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25
What are the possible substrates for gluconeogenesis?
Pyruvate, Lactate, Glycerol Essential and non-essential amino acids whose metabolism involves pyruvate or intermediates of the TCA cycle
26
Is Acetyl-CoA a suitable substrate for gluconeogenesis? Explain.
No Pyruvate dehydrogenase reaction is irreversible
27
What is the overall equation for gluconeogenesis from pyruvate?
2 Pyruvate + 4 ATP + 2 GTP + 2 NADH ---\> Glucose + 4 ADP + 2 GDP + 2 NAD+ + 6 Pi + 2H+
28
How are the reversible steps of glycolysis bypassed in gluconeogenesis from pyruvate?
With irreversible reactions
29
How are the irreversible reactions of glycolysis bypassed in gluconeogenesis of pyruvate?
Steps 1 and 3 are bypassed by thermodynamically spontaneous reactions catalysed by phosphatases Step 10 is bypassed by two reactions driven by ATP/GTP hydrolysis
30
What are the equations for the bypass reactions of steps 1 and 3 in gluconeogenesis? What enzymes catalyse these reactions?
STEP 1 G-6-P + H20 ---\> Glucose + Pi Glucose-6-phosphatase STEP 2 Fructose-1,6-phosphate + H20 ---\> Fructose-6-Phosphate + Pi Fructose-1,6-biphosphatase
31
What are the two equations for the bypass of step 10 of glycolysis in gluconeogenesis? What enzymes catalyse these reactions?
1. Pyruvate + CO2 + ATP + H2O ---\> Oxaloacetate + ADP + Pi + 2H+ Pyruvate carboxylase 2. Oxaloacetate + GTP + 2H+ ---\> Phosphoenolpyruvate + GDP + CO2 Phosphoenolpyruvate carboxykinase (PEPCK)
32
How are products of amino acids that are also intermediates of the TCA cycle utilised by gluconeogenesis?
Oxaloacetate is featured in the TCA cycle and in gluconeogenesis, so the intermediates are converted to oxaloacetate so they can be utilised.
33
How is gluconeogenesis regulated and what are the major targets of control?
Hormonal control PEPCK and Fructose-1,6-biphosphatase
34
How is PEPCK activity controlled?
Increased - Glucagon, Cortisol Decreased - Insulin
35
How is Fructose-1,6-biphosphatase activity controlled?
Increased - Glucagon Decreased Insulin
36
In diabetics what is the significance of gluconeogenesis control?
Inadequate levels of insulin allow excess gluconeogenesis to occur which contributes heavily to hyperglycaemia
37
How are TAGs stored and what controls storage? Note: what promotes and depletes stores?
Anhydrous form in adipocytes Controlled hormonally Storage promoted by insulin Storage depletion activated by glucagon, cortisol, adrenaline, growth hormone and thyroxine
38
How are TAGs produced in the gut delivered to adipose tissue?
In the blood stream transported in chylomicrons
39
Describe the process of Beta-Oxidation of fatty acids. Hint: What happens to the fatty acids? What's required?
Cycled sequence of reactions oxidises and removes C2 units (acetate) from FAs continuously until only 2 remain Requires NAD+ and FAD Cannot occur without oxygen (needed to oxidise NADH and FAD2H formed) No direct ATP synthesis All C2 units linked to CoA to form AcetylCoA
40
Where does Lipogenesis occur?
The cytoplasm
41
Give the equation for the formation of a 16 carbon fatty acid
8 AcetylCoA + 7 ATP + 14 NADPH + 6 H+ ---\> Fatty acid (C16) + 14 NADP+ + 8CoA + 7 ADP + 7 Pi + 6 H2O
42
How are most steps of lipogenesis catalysed?
Multi enzyme complex known as fatty acid synthase complex
43
Describe how Fatty acids are built up during lipogenesis
Built up from C2 units donated from AcetylCoA
44
Is lipogenesis a reverse of fatty acid degradation? Explain
Nope, units added in the form of MalonylCoA (C3) with subsequent loss of CO2
45
How is malonylCoA produced? Give an equation and the enzyme that catalyses the reaction
Produced from AcetylCoA AcetylCoA + CO2 + ATP ---\> MalonylCoA + ADP + Pi AcetlyCoA carboxylase
46
Explain the importance of AcetylCoA carboxylase and explain how it is regulated
Plays important role in controlling rate of lipogenesis Allosterically controlled (AMP inhibits / citrate activates) Covalent modification (reversible phosphorylation) Insulin activates by promoting dephosphorylation Glucagon and adrenaline inhibit by promoting phosphorylation
47
In what stage of catabolism are amino acids first broken down?
Stage 2
48
Why is amino acid catabolism such a diverse process?
All amino acids have their own unique catabolic pathway
49
What factor is common to all amino acid catabolic pathways?
Initial deamination (-NH2 released and converted to urea)
50
What are some common products of amino acid deamination (C-skeleton products)
Pyruvate Oxaloacetate Succinate Fumarate Acetyl-CoA Alpha-ketoglutarate
51
What are ketogenic amino acids?
Amino acids (eg. leucine, lysine) that produce AcetlyCoA when catabolised that can be used in the synthesis of ketone bodies
52
What are glucogenic amino acids?
Amino acids that don't produce AcetylCoA when metabolised and the products are used in gluconeogenesis
53
What amino acids are ketogenic and glucogenic?
isoleucine, threonine, phenylalanine
54
What is transamination?
Transfer of an amino acids NH2 group to a keto acid
55
What is the most common keto acid and what is it converted to during transamination?
alpha-ketoglutarate converted to glutamate
56
What is the enzyme responsible for transamination of alanine? Give a reaction equation for this process Hint: The enzyme has two names
Alanine transaminase (ALT) aka glutamate-pyruvate transaminase Alanine + alpha-ketoglutarate ----\> pyruvate + glutarate
57
What is the enzyme responsible for transamination of Aspartate? Give a reaction equation for this process Hint: The enzyme has two names
Aspartate transaminase (AST) aka glutamate-oxaloacetate transaminase Aspartate + alpha-ketoglutarate ---\> glutamate + oxaloacetate
58
What apart from alpha-ketoglutarate can be used as a keto acid and what is it converted into?
oxaloacetate converted to aspartate
59
What stimulates transaminase synthesis and where are they synthesised?
Cortisol Liver
60
What is deamination?
Removal of NH2 group from amino acids to form ammonia (which is converted to ammonium)
61
What enzymes are responsible for deamination? What can be said about their specificity?
L and D amino acid oxidases Low specificity
62
Why are D amino acid oxidases important and where are they found in high concentration?
Important to convert D-amino acids to keto acids (not optically active) This is important as D-amino acids (found in plant and bacterial cells) must not be used in protein synthesis as the proteins would be structurally abnormal and non functional
63
What is the enzyme that deaminates glutamine and what is the product of the reaction?
Glutaminase Glutamate + NH3
64
Give the equation for the breakdown of glutamate into a keto acid. Give the enzyme that catalyses this reaction
Glutamate + H2O + NAD+ ----\> alpha-ketoglutarate + NH4+ + NADH + H+ Glutamate dehydrogenase
65
What is Phenylketonuria?
Inherited disorder resulting in large amounts of phenylketones in the urine
66
What is the metabolic basis for Phenylketonuria?
Phenylalanine is normally oxidised to tyrosine by phenylalanine hydroxylase, In PKU cases this enzyme is defective, causing buildup of phenylalanine. Phenylalanine is metabolised via other pathways to form phenylpyruvate which is excreted in urine
67
How is Phenylketonuria diagnosed?
Detection of phenylketones in urine or high phenylalanine blood concentration (\>0.1mM)
68
How is Phenylketonuria treated and what are the consequences of not treating it?
Treated with diet low in phenylalanine Left untreated it can inhibit brain development
69
What is the cause of homocystinuria?
Rare autosomal recessive defect in methionine metabolism
70
What is the metabolic basis of homocystinuria?
Cystathionine beta-synthase deficiency This enzyme normally metabolises homocysteine into cystathionine (which is further converted to cysteine). Deficiency causes elevated levels of homocyteine and methionine in plasma and homocysteine in the urine
71
What are the physiological effects of Homocystinuria?
Chronic elevated levels of homocyteine cause disorders of connective tissue, muscle, CNS and cardiovasular system
72
Why is homocystinuria easily misdiagnosed in childhood?
Symptoms are similar to Marfan's syndrome's symptoms
73
What is the clinical relevance of measuring creatinine concentration in the blood and urine?
Amount of creatinine excretion in 24hr in the urine is proportional to muscle mass
74
How and when is creatinine produced?
Spontaneous reaction in muscles all the time at constant rate, increases during muscle wasting and high protein diet
75
In what form is ammonia normally present in the body and where does the ammonia come from?
98.5% of ammonia in ammonium ion form Produced by many tissues and absorbed from the gut
76
What is hyperammonaemia associated with and what tissues are particularly sensitive to it? Explain
Hyperammonaemia seen in liver disease Associated with blurred vision, tremors, slurred speech coma and eventually death. Also affects pH in cells of CNS and interferes with neurotransmitter synthesis/release CNS sensitive to hyperammonaemia due to disruption of TCA cycle which CNS relies on more heavily than other cells
77
Why is ammonia toxic to the body?
Reacts with alpha-ketoglutarate to form glutamate in mitochondria which removes alpha-ketoglutarate from the TCA cycle and disrupts energy supply
78
How is ammonia detoxified?
Conversion to N-compounds such as glutamine or conversion to urea
79
Can ammonia be excreted in urine?
Yup
80
Give an equation for glutamine synthesis from ammonium and the enzyme required
NH4+ + glutamate + ATP ------\> Glutamine + ADP + Pi Glutamine synthetase
81
What happens to glutamine in the liver an kidneys? Why? Give an equation and any enzymes required
Glutamine ---\> Glutamate + NH4+ Glutaminase Ammonium then excreted in kidneys Converted to urea in liver
82
Why is urea a good way of disposing of nitrogen?
Non-toxic metabolically inert water soluble high nitrogen content (47%)
83
Where does urea synthesis occur and what is the name of the enzyme pathway responsible? After urea synthesis, what happens to it?
Synthesis in liver via the urea cycle Transported to kidneys for excretion
84
Give the full equation for conversion of NH4+ into urea
NH4+ + HCO3- + Aspartate + 3 ATP ---\> Urea + Fumarate + 2ADP + AMP + 4Pi
85
How is the Urea cycle regulated?
Enzymes are inducible Induced by high protein diet Suppressed by low protein/starvation
86
When treating starvation/low protein diet why is it important to reintroduce food gradually?
Starvation has suppressed enzymes of the urea cycle and so lots of protein in the diet all of a sudden will result in hyperammonaemia as ammonia is not metabolised fast enough
87
With inherited disorders of the urea cycle what are the two effects all disorders have?
Hyperammonaemia Accumulation or excretion of urea cycle intermediates
88
What are the symptoms of defects in the urea cycle and what does their severity depend on?
Depends on severity of defect and how much protein eaten Vomiting, lethargy, irritability and generally includes mental retardation Severe cases may include seizures, coma and eventual death.
89
How are defects in the urea cycle managed?
Low protein diet Replacing essential amino acids in diet with keto acids that use up NH4+ when converted to amino acids
90
How does hyperammonaemia arise as a consequence of liver disease such as cirrhosis?
Livers ability to remove ammonia from portal blood is impaired
91
During excretion of urea from the kidneys how is urea lost from the blood stream if not from filtration in the kidney? How is this reabsorbed?
Diffuses across the intestinal wall and is broken down by gut bacteria into ammonia to be reabsorbed
92
How does kidney failure affect ammonia concentration in the blood?
Gut bacteria produce ammonia which is absorbed into the blood stream and cannot be metabolised, contributing to hyperammonaemia
93

ESA1 Callum's cards (34 decks)

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