Glycolysis in Muscle Cells and Red Blood Cells

Anaerobic Metabolism: Glycolysis

Structure and Function of Glucose and Glycogen

• Glucose: a monosaccharide, approximately 10g in plasma, osmotically active, immediate energy source through glycolysis
• Glycogen: a polysaccharide, approximately 400g in tissue stores, low osmolarity, medium-term fuel source, synthesized and broken down in the liver

Glycolysis: Key Points

• Definition: conversion of glucose to pyruvate
• Location: cytosol, involving 10 soluble enzymes
• Tissues: all tissues
• Functions: energy trapping (ATP synthesis), intermediates for fat synthesis, intermediates for amino acid synthesis

Sources of Glucose for Glycolysis

• Sugars and starch from diet
• Breakdown of stored glycogen from the liver
• Recycled glucose (from lactic acid, amino acids, or glycerol)

The Glycolysis Pathway

• A 10-reaction pathway converting glucose to pyruvate
• Divided into 4 stages: activation, splitting, oxidation, and ATP synthesis

Activation Stage of Glycolysis

• Reaction 1: hexokinase or glucokinase converts glucose to glucose 6-phosphate, using ATP
• Reaction 2: phosphohexose isomerase converts glucose 6-phosphate to fructose 6-phosphate
• Reaction 3: phosphofructokinase converts fructose 6-phosphate to fructose 1,6-bisphosphate, using ATP

Splitting of 6C Sugar to 3C Units

• Reaction 4 and 5: aldolase and triose phosphate isomerase convert fructose 1,6-bisphosphate to glyceraldehyde 3-phosphate and dihydroxyacetone phosphate

Oxidation Step

• Reaction 6: glyceraldehyde 3-phosphate dehydrogenase converts glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate, reducing NAD+ to NADH

ATP Synthesis Stages

• Reaction 7: phosphoglycerate kinase converts 1,3-bisphosphoglycerate to 3-phosphoglycerate, producing ATP
• Reaction 8: phosphoglycerate mutase converts 3-phosphoglycerate to 2-phosphoglycerate
• Reaction 9: enolase converts 2-phosphoglycerate to phosphoenolpyruvate
• Reaction 10: pyruvate kinase converts phosphoenolpyruvate to pyruvate, producing ATP

Yields of ATP from Glycolysis

• Early stages use 2 ATP
• Later stages produce 4 ATP
• Net yield: 2 ATP (plus further ATP from mitochondrial metabolism)

Anaerobic Glycolysis

• Occurs when oxygen supplies are limited, converting pyruvate to lactate to regenerate NAD+
• Important in red blood cells, skeletal muscle, and cancer cells

Regulation of Glycolysis

• Under allosteric control and hormonal control
• One example of allosteric control is the inhibition of phosphofructokinase by ATP and citrate

Specialized Functions in Tissues

• Skeletal muscle: ATP production during intense exercise
• Red blood cells: only pathway for ATP production, no mitochondria
• Brain: major source of ATP, cannot use fats as fuels

The Warburg Effect

• Tumor cells preferentially generate energy through anaerobic glycolysis, producing lactate at a high rate even when mitochondria are intact

Quiz about glycolysis in muscle cells and red blood cells, covering topics such as lactate dehydrogenase, ATP gain, substrate-level phosphorylation, and NAD+ role.