Lecture 16 - Glycolysis & Glycogenolysis Flashcards
Glucose Metabolism
Major fuel of most organisms
Also supplies large array of metabolic intermediates
Glucose Transport into Cells
GLUT Proteins Family of membrane bound proteins Expression depends on tissue - GLUT 1 in RBC - GLUT 2 in liver and kidney - GLUT 4 in adipose and muscle cells
Characteristics of Glycolysis
First metabolic pathway to be elucidated
Pathway has largest flux of C in most cells
Anaerobic
Importance of Glycolysis
Principal pathway for metabolism of glucose and other carbs
Generates energy in absence of O
- important in skeletal muscle and RBC
Supplies metabolic intermediates for other pathways
Glycolysis Process
Occurs in cytoplasm Conversion of one glucose to 2 pyruvate molecules Releases small amount of ATP NAD+ is reduced to NADH Aerobic glycolysis - pyruvate Anaerobic glycolysis - lactate
Role of Phosphate in Glycolysis
P groups ionised at pH 7 giving each intermediate a negative charge
- plasma membrane impermeable to charged molecules meaning intermediates cant diffuse out of cell
P groups conserve energy from one compound to another
Help lower activation energy and increase specificity
Hexokinase and Glucokinase
Glucose is trapped inside cell by action of hexokinase and glucokinase Hexokinase - in most tissues - low Km and Vmax - insensitive to plasma Glucokinase - mainly in liver and pancreatic B-cells - high Km and Vmax - sensitive to plasma - clears glucose from high levels in blood
Pyruvate can be used in reactions other than the production of Lactate. What are two others?
Acetyl CoA in most organisms
Ethanol in yeast and microbes
Regulation of Glycolysis
Enzymes - hexokinase - phosphofructokinase - pyruvate kinase Substrate supply Hormonal control of enzymes
Does low or high ATP stimulate or inhibit glycolysis?
Low ATP - stimulates
High ATP - inhibits
Glycogenolysis
Break down of glycogen
Involves four enzymes:
1. Phospholyase - releases glucose-1-phosphate
2. Debranching enzyme - releases glucose from branch point
3. Phosphoglucomutase - transforms glucose-1-phosphate to glucose-6-phosphate
4. Glucose-6-phosphatase - transforms glucose-6-phosphate to glucose
What are the 2 general phases of Glycolysis?
Preparatory - investment of 2 ATP to help set up glucose for subsequent oxidation reactions for next phase
Payoff - return of 4 ATP molecules from oxidation of intermediates of glucose
Glycolysis and Cancer
Cancer cells have high rate of glycolysis
- need for anaerobic glycolysis due to poor vascularisation around tumor
