Energy Production In Carbohydrates 2

Question 1

What are the 2 important intermediates in glycolysis?

Answer 1

Glycerol phosphate

2,3-bisphosphoglycerate

Question 2

Glycerol phosphate intermediate

Answer 2

Dihydroxyacetone phosphate -> glycerol phosphate
Uses glycerol 3-phosphate dehydrogenase and NADH is oxidised to NAD+
Comes from step 4 and 5 in glycolysis
Important to triglyceride and phospholipid biosynthesis

Question 3

2,3-bisphosphoglycerate intermediate

Answer 3

1,3-bisphosphoglycerate -> 2,3-bisphosphoglycerate
Phosphate group swaps from carbon 1 to 2
In RBC
Regulator of O2 affinity of haemoglobin, helps to release O2

Question 4

Oxidation/reduction in step 6

Answer 4

Glyceraldehyde-3-P to 1,3-bisphosphoglycerate
2 moles of NADH produced per mole of glucose
Requires NAD+
Total NAD+ and NADH in cell is constant, glycolysis would stop when all NAD+ converted to NADH

Question 5

How is NAD+ regenerated in step 6 of glycolysis?

Answer 5

Lactate dehydrogenase
NADH + H+ + pyruvate lactate + NAD+
Produced by RBC and skeletal muscle
Released into blood, metabolised by liver and heart, remove lactate from blood

Question 6

How is lactate produced?

Answer 6

From glucose via pyruvate

Rises with strenuous exercise and pathological situations

Question 7

Elevations of plasma lactate concentration

Answer 7

Conc determined by relative rates of production, utilisation and disposal
Normal conc < 1mM
Hyperlactaemia 2-5mM, below renal threshold no change in blood pH due to buffering capacity
Lactic acidosis > 5mM, blood pH lowered

Question 8

Metabolism of fructose

Answer 8

Metabolised in liver
Essential fructosuria - fructokinase missing, fructose in urine, no problems
Fructose intolerance - aldolase B missing, fructose-1-P accumulates in liver

Question 9

Metabolism of galactose

Answer 9

Deficiency in galactokinase, uridyl transferase or UDP-galactose epimerise can cause galactosaemia
UDP-glucose acts catalytically as it is regenerated

Question 10

What is galactosaemia?

Answer 10

Unable to utilise galactose
Galactokinase deficiency (rare) - galactose accumulates
Transferase deficiency (common) - galactose and galactose-1-P accumulate

Question 11

What is the problem with galactosaemia?

Answer 11

Galactose enters other pathways
Galactose -> galactitol using aldose reductase, converts NADPH to NADP+
Depletes lens of NADPH
Accumulation can affect liver, kidney and brain, causes inappropriate disulphides bond formation

Question 12

What is the pentose phosphate pathway?

Answer 12

Series of non-oxidative reactions

Convert 5C sugars to 6C and 3C sugars which can be used in glycolysis

Question 13

Where does the 2 stage pathway of pentose phosphate pathway take place?

Answer 13

Cytoplasm

Question 14

What is the first stage in pentose phosphate pathway?

Answer 14

Oxidative decarboxylation

Glucose-6-P -> C5 sugar + CO2 using glucose-6-P dehydrogenase, converts NADP+ to NADPH

Question 15

What is the second stage in pentose phosphate pathway?

Answer 15

Rearrangement to glycolysis intermediates
3 C5 sugars —> 2 fructose-6-P + 1 glyceraldehyde-3-P
No ATP production
Loss of CO2 therefore irreversible
Controlled by NADP+/NADPH ratio

Question 16

Functions of pentose phosphate pathway

Answer 16

Produce NADPH in cytoplasm

Produce C5 sugar for nucleotides needed for nucleic acid synthesis, high activity in dividing tissues

Question 17

Where does pentose phosphate pathway start?

Answer 17

Glucose-6-phosphate

Question 18

Pentose phosphate pathway is an important source of NADPH required for:

Answer 18

Reducing power for biosynthesis
Maintenance of GSH levels
Detoxification reactions

Question 19

Is ATP synthesised in pentose phosphate pathway?

Answer 19

No but CO2 is produced

Question 20

What is the rate limiting enzyme of pentose phosphate pathway?

Answer 20

Glucose-6-phosphate dehydrogenase