Carbohydrates 4 Flashcards
What tissues rely completely on glucose as their main source of energy?
- Brain
- Nervous system
- RBCs
- Testes
- Embryonic tissues
What happens if we do a lot of exercise or fast and we need more energy?
Glucose can be generated from other non-carbohydrate molecules which usually occurs in the liver in response to hormonal controls.
What is gluconeogenesis not
A reverse of glycolysis
How many glycolysis reactions are reversible?
7 out of 10
What prevents reactions in glycolysis from being reversible?
Large –ve ΔG
How does the cell bypass the irreversible reactions?
With enzymes that catalyse a separate set of irreversible reactions
How many reactions sidestep the 3 irreversible reactions?
4 bypasses
What do the bypass reactions in glycolysis allow?
Independent control of the glycolysis and gluconeogenesis pathways and ensures they do not cancel each other out
Where do the bypass reactions occur?
- A+B =mitochondria
- B+D= cytosol
What is usually the end point of gluconeogenesis?
F-6-P being converted to G-6-P
Where does the final step to make free Glc take place?
Lumen of ER
What does the process of making free Glc require?
Requires G-6-P to be shuttles into the lumen and the Glc to be shuttled back out to the cytoplasm
What metabolises most fructose?
Liver
Where can fructose and galactose enter glycolysis?
At various points
What are the enzymes in the fructose -1- phosphate pathway?
- Fructose-1-phosphat aldolase
- Triose kinase
What is the end product of the fructose-1-phosphate pathway?
Glyceraldehyde-3-phosphate
How does galactose enter glycolysis?
- Galactose is converted to G-1-P through a sugar-nucleotide derivative UDP-galactose
- UDP-glucose and UDP-galactose amounts remain unchanged as they are recycled, therefore the net product is G-1-P
What are the products of the pentose phosphate pathway?
- NADPH
- Pentoses
What are pentoses?
5C sugars that are precursors of ATP, RNA and DNA
What are the 2 parts of the pentose phosphate pathway?
- Oxidative, irreversible part
- Reversible, non-oxidative part
What takes place in the oxidative part off the PPP?
- Generation of NADPH
- Converts G-6-P to a pentose phosphate
What takes place during the non-oxidative part of the PPP?
-Interconverts G-6-P and pentose phosphate to form lots of different 3,4,5,6 and 7C sugars
When does the reversible part take place?
When lots of NADPH is needed
When does the irreversible part take place?
When lots of nucleotides are required
What links catabolic and anabolic reactions in the PPP?
nadph
When is NAD used?
In metabolism of dietary sugars in the redox reactions of glycolysis and the CAC
When is NADP used?
- In anabolism to convert simple precursors into things like fatty acids
- Also acts as an antioxidant
What stops NAD and NADP being used interchangeably?
Enzymes involved in pathways having differing specificities for the two electron carriers
What happens when people get drunk?
Reduced gluconeogenesis
What happens in the liver when excess alcohol is consumed?
- Ethanol is converted to acetyl CoA through intermediates producing NADH.
- Acetyl CoA can then be stored as fat or proceed through the CAC and terminal respiration.
What does the inhibition of gluconeogenesis lead to?
- Lactiacidaemic (increased [blood lactate])
- Hypoglycaemia (decreased[blood Glc])
What is black water fever?
G-6-P dehydrogenase deficiency
What does black water fever cause?
Low RBC NADPH levels which allows damaging free radicals and H2O2 to build up which damages the membranes of the RBC
What is the result of damages RBC in black water fever?
They are unable to suffer the extra trauma of infection
What is the result of overexpression of PEPCK?
Lots of PEP in muscle from lactate
