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ESA1 Callum's cards > Metabolism S2 - Energy Production (Carbohydrates) > Flashcards

Metabolism S2 - Energy Production (Carbohydrates) Flashcards

1
Q

Describe some features of monosaccharides

A

3-9 carbons, commonly 3/5/6

Either aldose (C1 chiral) or ketose (C2 chiral)

Chiral carbon known as anomeric carbon and has two forms, alpha or beta

Enzymes can distinguish between the two

All but dihydroxyacetone have stereoisomers (D naturally occurring)

Exist largely as hemiactal ring structures (aldehyde/ketone group reacts with oxygen group of same sugar)

Hydrophilic

Partially oxidised (require less oxidation than fatty acids for complete oxidation)

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2
Q

How are disaccharides formed?

What bond is formed?

A

Condensation reaction

Glycosidic bond

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3
Q

What are the 3 major dietary disaccharides?

A

Sucrose (glucose - fructose

)Lactose (glucose - glactose)

Maltose (glucose - glucose)

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4
Q

Name 4 common polysaccharides of glucose and include what type of linkages are found in each.

A

Glycogen (1-4, 1-6)

Amylose (1-4)

Amylopectin (1-4, 1-6)

Cellulose (beta 1-4)

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5
Q

Why is cellulose indigestible?

A

Humans do not have the required enzymes to break beta 1-4 glycosidic bonds

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6
Q

What two polysaccharides are found in starch?

A

Amylose

Amylopectin

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7
Q

How and where are polysaccharides broken down?

What are they broken down into at first?

A

Glycosidase enzymes

Salivary amylase in mouth, pancreatic amylase in duodenum

Broken down to glucose, maltose and other small polysaccharides (dextrins)

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8
Q

How are broken down polysaccharides further digested?

Hint: Where? What is released? What enzymes involved?

A

Maltose, dextrins and disaccharides broken down in duodenum and jejunum

Large glycoproteins complexes on microvilli brush borders

Key enzymes are:

sucrase/isomaltase

Lactase

Glycoamylase

Releases glucose, galactose and fructose

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9
Q

Where is major site of galactose and fructose metabolism?

A

Liver

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10
Q

What can be said about glucose concentration in the blood?

A

Must be kept constant due to an absolute requirement for it by certain tissues

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11
Q

What are the tissues that have an absolute requirement for glucose and what is their overall glucose requirement per day?

A

RBCs, WBCs, kidney medulla, lens of the eye

40g.day-1

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12
Q

What is the overall glucose requirement per day?

A

180g per day

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13
Q

What is the daily requirement of the CNS for glucose?

A

140g per day

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14
Q

How many enzymes are involved in glycolysis?

A

10

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15
Q

Where does glycolysis occur?

A

Cytoplasm

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16
Q

What is generated by glycolysis?

A

ATP

NADHH

Useful intermediate compounds (C3)

Pyruvate

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17
Q

What are the key features of glycolysis?

A

No loss of CO2

Overall exergonic

All intermediates phosphorylated and can in turn phosphorylate ADP

2 moles of ATP required per mole of glucose, 4 produced, 2 net produced

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18
Q

What 3 steps of glycolysis are irreversible and what enzymes are they catalysed by?

A

1 - hexokinase (in liver glucokinase)

3 - phosphofructokinase-1

10 - pyruvate kinase

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19
Q

When there is not enough oxygen supply to a cell or a cell has no mitochondria how is ATP produced?

A

Anaerobic glycolysis

Reduction of pyruvate to lactate

20
Q

What enzyme is involved in the pyruvate to lactate reaction?

A

Lactate dehydrogenase

21
Q

What is the equation for the reduction of pyruvate to lactate?

A

2 pyruvate + 2 NADH + 2 H+ —> 2 lactate + 2 NAD+

22
Q

What is the overall equation of anaerobic glycolysis?

A

Glucose + 2 Pi + 2 ADP —> 2 Lactate + 2 ATP + 2 H2O

23
Q

What happens to lactate after it’s production in tissues?

A

Released into blood stream

Converted back to pyruvate in cardiac muscle

Then oxidised to CO2

OR

Converted back to glucose in liver

24
Q

What effect does Lactate dehydrogenase have on NAD+ conc?

A

Increases NAD+ conc in anaerobic conditions

25
Q

What is the normal level of lactate in the bloodstream?

A

<1mM

26
Q

What can increase the level of lactate production and hence it’s conc in the blood plasma?

A

Strenuous exercise

27
Q

What is the renal threshold for lactate and if exceeded what is the effect?

A

>5mM and exceeds renal threshold, causing lactic acidosis as the buffering capacity of blood plasma is exceeded

28
Q

How does lactose intolerance come about?

A

Low activity of lactase enzymes meaning lactose cannot be digested.

29
Q

What is the overall equation for galactose metabolism to glucose-6-phosphate and where does this reaction chain occur?

A

Galactose + ATP —-> G-6-P + ADP

Liver

30
Q

In the case of Galactosemia what is the effect on metabolism and how does this come about?

A

Cannot metabolise galactose

Missing galactokinase or galactose-1-phosphate uridyltransferase enzymes

31
Q

Which of the 2 enzymes is it rarer to have missing in Galactosemia and what is the difference between the effects of missing either enzyme?

A

Galactokinase rarer to have absent

Causes build up of galactose in tissues

G-1-P Uridyltransferase more common to have missing however G-1-P builds up in tissues too (is more hepatotoxic)

32
Q

When galactose builds up in galactosaemic patients what is it metabolised into and by what enzyme?

What is the knock on metabolic effect of this?

A

Galactitol

Aldose reductase

Depletes NADPH in some tissues

33
Q

What are the clinical consequences of NADPH depletion in some tissues of a galactosemic patient and how do they come about?

A

Lens of eye damaged by -S-S- bonds formed in absence of NADPH cross linking of proteins causes cataracts

Random glycosylation of lens proteins may also contribute to cataracts

Intraocular pressure rises (glaucoma) due to accumulation of galactose and Galactitol.

G-1-P accumulation leads to damage of liver, kidney and brain, this could be caused by sequestration of Pi by G-1-P

34
Q

In what tissues is the pentose phosphate pathway important?

A

Liver, RBCs, adipose tissue

35
Q

What are the major functions of the pentose phosphate pathway?

A

Produce NADPH in the cytoplasm

Provides reducing power for lipid synthesis

Maintains free -SH groups in haemoglobin in RBCs

Used in various detox mechanisms

Produces C5 ribose for the synthesis of nucleotides

36
Q

Why does the pentose phosphate pathway have a high activity in dividing tissue?

A

Produces ribose sugars for use in nucleotides

37
Q

Is the pentose phosphate pathway oxidative or reductive overall?

A

Oxidative, no ATP and some CO2 formed

38
Q

Describe phase 1 of the pentose phosphate pathway, give an equation.

A

G-6-P is oxidised and decarboxylated by G-6-P dehydrogenase and 6-phosphogluconate dehydrogenase in a reaction requiring NADP

G-6-P + 2 NADP –> ribose phosphate + 2 NADPH + 2 CO2 + 2 H+

39
Q

Describe phase 2 of the pentose phosphate pathway, give an equation.

A

Complex series of reactions converting any unused C5 sugars to glycolysis intermediates

3 C5 sugar phosphate –> 2 fructose-6-phosphate + glyceraldehyde-3-phosphate

40
Q

When NADPH is depleted in an rbc what can happen to haemoglobin?

A

Can form insoluble polymers (Heinz bodies) due to cysteine cross linkage (disulphide bridges)

41
Q

What is the rate limiting enzyme for the pentose phosphate pathway?

A

G-6-P dehydrogenase

42
Q

Deficiency in G-6-P dehydrogenase is caused by what type of genetic mutation?

A

X linked point mutation

43
Q

Mutation of G-6-P dehydrogenase has what effect on its function and leads to low levels of?

A

Reduces function

Low levels of NADPH

44
Q

Formation of Heinz bodies in RBCs leads to what?

A

Premature Haemolysis

45
Q

Pyruvate is converted to acetylCoA by what enzyme?

A

Pyruvate dehydrogenase

46
Q

What is significant about the action of pyruvate dehydrogenase in terms of reversibility and acetylCoA’s use in gluconeogenesis?

A

Irreversible reaction meaning loss of CO2 from pyruvate is irreversible and hence acetylCoA cannot be converted back to pyruvate for use in gluconeogenesis.

47
Q

Explain the 3 methods of pyruvate dehydrogenase control.

A

AcetylCoA allosterically inhibits Pyruvate Dehydrogenase

ATP/NADH inhibit and ADP promotes allosterically

Activated when there’s plenty of glucose to be catabolised (activated by insulin)

ESA1 Callum's cards (34 decks)

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