Lecture 9. Other Sugars, Gluconeogenesis and Pentose Phosphate Pathway Flashcards
How does lactose intolerance occur?
When the enzyme that breaks down lactose is not present
What is the name of the rare condition where galactose cannot be broken down?
Galactosemia
What other dietary sugars fit into glycolysis?
Galactose and fructose
What stage of glycolysis does fructose enter?
Stage 2
How long can naked mole-rats survive in a totally oxygen deprived environment (anoxia)?
18 minutes
What is gluconeogenesis?
The sequence of reactions that converts pyruvate to glucose
Where does gluconeogenesis mostly take place?
The liver and kidneys
What is the main purpose of gluconeogenesis?
To maintain adequate glucose levels in the blood
What does gluconeogenesis use?
ATP and GTP
What occurs in the futile cycles?
Net loss of ATP by hydrolysis
How are futile cycles avoided?
Tight regulation of metabolic pathways
PFK and Fructose-1,6-bisphosphatase both tightly and oppositely regulated
What enzyme converts pyruvate to oxaloacetate?
Pyruvate carboxylase
What enzyme converts oxaloacetate to PEP?
PEP carboxykinase
What is the starting material for gluconeogenesis in lactate and some amino acids?
Pyruvate
What is the starting material for gluconeogenesis in some amino acids?
Oxaloacetate
What is the starting material for gluconeogenesis in glycerol?
Dihydroxyacetone
Where does gluconeogenesis take place?
Cytosol
How is gluconeogenesis regulated?
Oppositely to glycolysis
What is the pentose phosphate pathway?
The sequence of reactions that converts glucose to pentoses (then to hexoses and trioses) with the production of NADPH
Why are pentoses needed?
Ribose-5-P needed for DNA and RNA (and ATP, NAD⁺, FAD, CoA) synthesis
What happens in the oxidative stage of the pentose phosphate pathway?
G-6-P to ribulose-5-P giving 2 NAPDH
What happens in the non-oxidative stage of the pentose phosphate pathway?
Ribulose-5-P to ribose-5-P and glycolytic intermediates
Oxidative step 1 in PPP
Glucose 6-P Dehydrogenase oxidises to an intramolecular ester forms NADPH (control step)
What controls glucose-6-P entry into the PPP?
Glucose-6-P-DH
What controls glucose-6-P-DH activity?
The level of NADP⁺
Oxidative step 2 in PPP
Gluconolactonase hydrolyses intramolecular ester
Oxidative step 3 in PPP
6-P gluconate DH oxidatively decarboxylates - forms NADPH, releases CO₂
Non-oxidative stage in PPP
Ribulose 5-P → Ribose 5-P through aldose isomerisation
What is transketolase?
C₂ transfer
What is transaldolase?
C₃ transfer
How many modes does the PPP have?
4
What is mode 1 of PPP?
No NADPH production, G-6-P completely converted to ribose-5-P
What is mode 2 of PPP?
Production of both NADPH and ribose-5-P
What is mode 3 of PPP?
NADPH needed but not ribose-5-P
What is mode 4 of PPP?
Cells need NADPH and ATP
What is favism?
Recessive X-linked disorder
Hemolytic anemia when eating fava beans and sometimes other legumes
Glucose-6-P dehydrogenase deficiency
