Energy production (Carbs 2) Flashcards
What enzyme hydrolyses lactose?
lactase into glucose and galactose
Where is galactose metabolised?
liver - and kidney and GI tract
What is the overall reaction for galactose + ATP?
galactose + AMP –> glucose-6-phosphate + ADP
How can galactose be converted into glucose?
-epimerase reversible reaction
-galactose can be made from glucose via UDP-glucose
When is the epimerase reaction important?
during lactation when breast tissue is synthesising large amounts of lactose for milk production
Name two conditions that affect galactose metabolism
lactose intolerance and galactosaemia
Why can’t those with galactosaemia utilise galactose?
they lack the kinase or transferase enzyme
How can you tell the difference between lacking a kinase or transferase enzyme in galactosaemia?
-kinase - rarer, accumlation of galactose in tissues
-transferase - more common, more serious as both galactose and galactose-1-phosphate accumulate in tissues
What does the accumulation of galactose in tissues lead to?
-galactose gets reduced to galactitol due to aldose reductase
-this depletes some tissues of NADPH
How can cataracts be formed due to accumulation of galactose?
-loss of NADPH, structure of lens is damaged
-high conc of galactose can cause non-enzymatic glycolysation of lens protein
How does glaucoma form?
accumulation of galactose and galactitol in the eye may lead to raised intraocular pressure (glaucoma)
Describe the metabolism of fructose
-liver
-soluble enzymes that catalyse the conversion to glyceraldehyde-3-phosphate
What happens to some of the glucose-6-phosphate if not entered into glycolysis?
metabolised by the pentose phosphate pathway
What are the major functions of the pentose phosphate pathway?
-produce NADPH in cytoplasm
-produce ribose for synthesis of nucleotides
What happens in phase 1 of the pentose phosphate pathway?
glucose-6-phosphate is oxidised and decarboxylated by the enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in reactions that require NADP+
What happens in phase 2 of the pentose phosphate pathway?
a complex series of reactions converts any unused 5C sugar phosphates into intermediates of glycolysis
-fructose-6-phosphate
-glyceraldehyde-3-phosphate
What is the overall equation for the pentose phosphate pathway?
3 glucose-6-phosphate + 6NADP+ –> 3CO2 + 6NADPH + 6H+ + 2 fructose-6-phosphate + glyceraldehyde-3-phosphate
How do you regulate the pentose phosphate pathway?
by controlling the activity of glucose-6-phosphate dehydrogenase - by the NADP+/NADPH ratio in the cell
How does the NADP+/NADPH ratio control glucose-6-phosphate dehydrogenase?
NADPH inhibits, NADP+ activates
Describe the G6PD deficiency defect
- x-linked gene defect found in those originating from the mediterranean region and black USA males
-point mutations in the gene coding for glucose-6-phosphate, reduced activity of enzyme, low levels of NADPH
Why is NADPH required for the structural integrity and function of key proteins?
-this is dependent on glutathione which is made by the body
-GSH protects the cell against oxidative damage
-in order to do this NADPH is required to recycle GSH back to its active reduced form
Which cells are most impacted by G6PD deficiency and why?
RBC because the pentose phosphate pathway is their only source of NADPH and they are at increased risk of oxidative damage
How is haemolysis caused?
haemoglobin and other proteins become cross-linked by disulphide bonds due to oxidative damage and form insoluble aggregates (Heinz bodies) - leading to premature destruction of RBC and haemolysis
What chemicals can cause acute haemolysis?
chemicals that reduce the levels of NADPH like antimalarials, sulphonamides, glycosides
