Lecture 2.1 - Energy production (carbohydrate 1-2)

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Questions and Answers

What is the primary function of the pentose phosphate pathway in the liver?

Storage of glucose as glycogen

Breakdown of glucose for energy

Production of NADPH for anabolic processes (correct)

Production of ATP

What is the primary consequence of hyperlactatemia above the renal threshold?

Increased blood pH

Decreased blood pH (correct)

No change in blood pH

Increased ATP production

What is the primary role of galactose in the body?

Storage of glucose as glycogen

Synthesis of glycolipids and glycoproteins (correct)

Energy production through glycolysis

Regulation of blood sugar levels

What is the primary site of galactose metabolism in the body?

Liver Signup and view all the answers

What is the consequence of galactose accumulation in galactosemia?

Decreased NADPH levels Signup and view all the answers

What is the primary enzyme deficiency in classical galactosemia?

Galactose 1-P uridyltransferase Signup and view all the answers

What is the primary function of lactase in the digestive system?

Hydrolysis of lactose into glucose and galactose Signup and view all the answers

What is the primary importance of detecting galactosemia in early life?

To initiate effective management and prevent complications Signup and view all the answers

What is the net ATP production per mole of glucose during glycolysis?

2 moles ATP Signup and view all the answers

What is the purpose of the lactate dehydrogenase reaction in anaerobic cells?

To regenerate NAD+ Signup and view all the answers

What is the function of glycolysis in terms of ATP production?

To produce ATP from ADP Signup and view all the answers

What is the byproduct of the lactate dehydrogenase reaction in the absence of oxygen?

Lactate Signup and view all the answers

What is the role of dihydroxyacetone phosphate in triglyceride synthesis?

It is converted to glycerol phosphate Signup and view all the answers

What is the purpose of the connecting stage 2-3 in carbohydrate catabolism?

To link glycolysis to the citric acid cycle Signup and view all the answers

What is the significance of 1,3-Bisphosphoglycerate in red blood cells?

It regulates oxygen affinity to haemoglobin Signup and view all the answers

What is the purpose of glycolysis in terms of NADH production?

To produce NADH Signup and view all the answers

What is the primary function of glycosidases in the GI tract during stage 1 of carbohydrate catabolism?

To hydrolyze glycosidic bonds to monosaccharides Signup and view all the answers

Which of the following is NOT a characteristic of stage 1 of carbohydrate catabolism?

Energy production Signup and view all the answers

What is the primary function of GLUT1-GLUT5 transporters in the small intestine?

To facilitate the uptake of glucose into intestinal epithelial cells Signup and view all the answers

Which tissue has an absolute requirement for glucose and cannot metabolize fatty acids?

Red blood cells Signup and view all the answers

What is the primary difference between the breakdown of starch and glycogen in the GI tract?

Starch is broken down into dextrins, while glycogen is broken down into glucose Signup and view all the answers

What is the function of isomaltase in the small intestine?

To break down alpha 1-6 bonds in polysaccharides Signup and view all the answers

Which of the following is a characteristic of glucose regulation in the body?

Glucose is regulated by hormonal regulation through insulin and glucagon Signup and view all the answers

What is the primary function of pancreatic amylase in the small intestine?

To break down alpha 1-4 bonds in polysaccharides Signup and view all the answers

Study Notes

Carbohydrate Metabolism

Hyperlactatemia: 2-5mM lactate, below renal threshold, no change in pH, kidneys can dispose of lactate
Lactic acidosis: >5mM lactate, above renal threshold, blood pH lowered

Pentose Phosphate Pathway (Hexose Monophosphate Shunt)

Not all glucose 6-phosphate enters glycolysis, some is metabolized via the pentose phosphate pathway (oxidative, no ATP produced)
Important pathway for liver, red blood cells, and adipose tissue
Functions:
- Produce NADPH (reducing power for anabolic processes such as lipid synthesis)
- Maintain free -SH (thiol) groups on cysteine residues in certain proteins (important in G6PDH deficiency)
- Produce C5-sugar ribose for nucleotide synthesis (DNA and RNA)

Galactose Metabolism

Galactose is required for the synthesis of glycolipids and glycoproteins (e.g., blood group antigens A, B, and O)
Dietary lactose is hydrolysed by lactase to release glucose and galactose, which are absorbed into the bloodstream
Galactose is metabolized largely in the liver (some in the kidney and GI tract)
Lactose = galactose + glucose

Galactosemia

Genetic condition with 2 variants: classical galactosemia (deficiency of galactose 1-P uridyltransferase) and non-classical galactosemia (deficiency of galactokinase)
Accumulation of galactose leads to accumulation of galactitol, which utilizes NADPH, depleting NADPH from tissues
Patient safety: galactosemia should be detected in early life for effective management

Catabolism of Carbohydrates - Stage 2

Intracellular (cytosol): glycolysis/pentose phosphate pathway
Intracellular (mitochondria): connecting stage 2-3
Phase 1 (reactions 1-3): energy investment (2 moles ATP per 1 mol glucose)
Phase 2 (reactions 4-10): energy production (4 moles ATP per 1 mol glucose)
Functions:
- Yields NADH (reducing power)
- ATP produced from ADP (net: 2 moles ATP per mol glucose)
- Produces C6 and C3 intermediates (links to other metabolic pathways)
Features:
- Exergonic (reactions 7 and 10 generate ATP)
- C6 (glucose) generates 2 C3 (pyruvate)
- Lactate from pyruvate can be generated in the absence of oxygen

Lactate Dehydrogenase Reaction

Occurs in cells with limiting oxygen availability (RBC, skeletal muscle, brain, skin, and GI)
Lactate released into blood and metabolized in the liver and heart, and is disposed of by the kidneys
Regenerates NAD+ needed for glycolysis when NADH is being used up
Blood levels < 1mM

Clinical Relevance - Stage 2

Glycolysis needs NAD+ to oxidize glucose
As total NAD+ and NADH is constant, when all NAD+ is converted to NADH, glycolysis stops
NAD+ needs to be regenerated by another route
Glycolysis intermediates are important for other metabolic routes:
- Triglyceride and phospholipid synthesis
- Regulator of oxygen affinity to hemoglobin

Catabolism of Carbohydrates - Stage 1

GI tract (extracellular): breakdown and absorption
Breakdown: hydrolysis of glycosidic bonds to glucose, galactose, and fructose
GI tract enzymes: glycosidases (amylases)
Saliva: amylase (starch, glycogen -> dextrins)
Pancreas: amylase (major enzyme)
Small intestine: disaccharides attached to brush border membrane of epithelial cells
No significant hydrolysis of cellulose, no enzymes to attack the beta 1-4 linkages

Clinical Relevance - Stage 1

Glucose requirements of tissues:
- Major sugar in blood
- All tissues can metabolize glucose
- Blood glucose regulated (~5 mM) by hormonal regulation (insulin, glucagon)
- Some tissues (RBC, lens of eye) have an absolute requirement on glucose
- Uptake by these tissues depends on blood glucose
- CNS (brain) prefers glucose and cannot metabolize fatty acids
- Some tissues need it for specialized functions (liver, adipose)

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Description

Learn about carbohydrate metabolism, including hyperlactatemia and lactic acidosis, and the pentose phosphate pathway, its functions and importance in various tissues.