- by heart to turn back to pyruvate for energy - by liver and kidney for pyruvate for energy or gluconeogenesis

Carbs 2 Flashcards by Gabriela Vernon

Why does glycolysis need to be regulated

control flux in response to demand

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What is the most important regulatory enzyme in glycolysis

phosphofructokinase - 1

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What are the two ways phosphofructokinase-1 can be regulated

allosteric
hormonal

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What molecules allosterically inhibit phosphofructokinase-1

high ATP
high citrate

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What molecules allosterically stimulate phosphofructokinase-1

high AMP
high fructose-2,6-bisphosphate

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What are high energy signals

indicate cell has enough energy
ATP
NADH
FADH2
NADPH

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What are low energy signals

indicate the cell is using and requires energy
AMP/ADP
NAD
FAD
NADP

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What are two other regulatory enzymes in glycolysis

hexokinase (not glucokinase in liver)
pyruvate kinase

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how is hexokinase regulated in glycolysis

end product inhibition
G6P

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how is pyruvate kinase regulated

hormonal
high insulin : low glucagon

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Why is lactate produced

step 6 of glycolysis needs constant NAD source
done when insufficient oxygen
done in cells with no mitochondria e.g. RBC

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What enzyme produces lactate

lactate dehydrogenase

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What is the equation for pyruvate to lactate

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

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How is lactate used

by heart to turn back to pyruvate for energy
by liver and kidney for pyruvate for energy or gluconeogenesis

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What are normal plasma levels of lactate

less than 1 nm

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What lactate levels suggest hyperlactaemia

2-5 nm

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What plasma lactic levels suggest lactic acidosis

above 5nm

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what is the normal production of lactate in a day without exercise

40-50 g

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What can strenuous exercise increase plasma lactate levels by a min

10g

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what is galactose require for

synthesis of glycolipids and glycoproteins

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Where is galactose found in diet

lactose

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Where is galactose metabolised

liver

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What enzyme is used in the first reaction of glycolysis

galactokinase

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What is the reaction of galactokinase

galactose + ATP –> galactose-1-p + ADP + Pi

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What is the second enzyme in galactose metabolism

galactose-1-p uridyl transferase

What does the enzyme galactose-1-p uridyl transferase do

transfers a UDP group from UDP-glucose to galactose-1-p to make glucose-1-p (which enters glycolysis) and UDP galactose

How is UDP glucose regenerate and with what enzyme

UDP-galactose-4-epimerase converts UDP-galactose to UDP-glucose by changing orientation of OH group

Why is the UDP-galactose-4-epimerase enzyme important for pregnancy

allows production of lactose from glucose via UDP- glucose

Where does fructose come from in the diet

sucrose

where is fructose metabolised

liver

What is the first enzymes required in fructose metabolism

fructokinase

What is the reaction for fructokinase

fructose + ATP --> fructose-1-p + ADP + Pi

What is the second enzyme in fructose metabolism

adolase

What is the reaction for adolase

fructose-1-p cleaved into glyceraldehyde and DHAP

What enzyme converts glyceraldehyde into glyceraldehyde-3-p

triose kinase requires ATP

What enzyme converts DHAP into glyceraldehyde-3-p

TPI

What are the two conditions involving fructose

- essential fructosuria - fructose intolerance

What is essential fructosuria

fructokinase missing fructose in urine

What enzyme is missing in fructose intolerance

adolase

what is the result of fructose intolerance

fructose-1-p accumulates in liver cells depleted of Pi liver damage

how is fructose intolerance managed

remove all fructose and sucrose from diet

What is galactosemia

unable to digest galactose

What are the two causes of galactosemia

- galactokinase deficiency - transferase deficiency (most damage) - epimerase deficiency

What are the symptoms of galactosemia

- hepatomegaly and cirrhosis - renal failure - vomiting - seizure and brain damage - cataract - hypoglycemia

What happens when galactose accumulates

reduced to galacticol

What enzyme converts galactose to galacticol

aldose reductase

What does aldose reductase require to reduce galactose to galacticol

NADPH

Why does a lack of GALT enzyme cause a lot of damage

accumulation of galactose-1-p causes liver, kidney and brain damage and depletes cells of Pi

Explain how galactosemia can cause cataracts

- build up of galactose converted to galacticol by aldose reductase - this uses up excessive NADPH - compromises defences against oxidative damage - ox damage causes cross linkages of S-S disulphide bonds in lens causing crystallisation

How does galactosemia relate to glaucoma

accumulation of galactose and galacticol in lens increases intra-ocular pressure

What is the treatment for galactosemia

remove lactose from diet

What are the defences against oxidative damage

- glutathione ( uses NADPH for electron donor) - catalase (NADPH structural component) - thioredoxin system (NADPH electron donor) - thiltransferase system (uses glutathione as cofactor)

How can galactose still be produced on galactose free diet for lactation

using glucose and UDP galactose which can be made from UDP glucose to make lactose through lactose synthase

What is the importance of the pentose phosphate pathway

- major source of NADPH - generates pentose sugars for nucleotides

What is the starting point for pentose phosphate pathway

some of glucose-6-phosphate from glycolysis

What is the first enzyme in the pentose phosphate pathway

glucose-6-p dehydrogenase

What is the reaction for the enzyme glucose-6-p dehydrogenase

glucose-6-p + NADP --> 6-phosphogluconolacetone + NADPH

What happens to any unused 5C sugars from pentose phosphate pathway

converts any unused sugars 5C sugars to intermediates of glycolysis

What is the regulatory enzyme in the pentose phosphate pathway

glucose-6-p dehydrogenase

How is the enzyme glucose-6-p dehydrogenase regulated

NADP : NADPH ratio. NADPH inhibiting NADP activating

Where is the glucose-6-p dehydrogenase enzyme found

X chromosome

What does a deficiency in glucose-6-p dehydrogenase cause

low NADPH less glutathione this causes less protection from oxidative damage

Why is NADPH require for glutathione synthesis

NADPH require to reduce oxidised form of glutathione back to active reduced form

Why are RBC particularly affected by glucose-6-p dehydrogenase deficiency

pentose phosphate pathway is RBC only source of NADPH - Hb cross linked by disulphide bonds from ox damage - forms insoluble aggregates called Heinz bodies - haemolysis