Download NME2.26 - Introduction to Metabolic Pathways

NME2.26: INTRODUCTION TO METABOLIC PATHWAYS
29/02/08
IMPORTANT DEFINITIONS



Anabolism is the synthesis or generation of a substance
Catabolism is the degradation or destruction of a substance
Metabolism is the sum of the biochemical changes undergone by a substance in the body
LEARNING OUTCOMES
Describe the metabolic pathways involved in storing and generating energy




Daily energy consumption from food is between 2000-3000kcal/day
o A kilocalorie is defined as the amount of energy required to raise the temperature of 1kg of
water by 1˚C
The majority of this energy is used to maintain the basal metabolic rate (BMR) and in exercise
o Excess energy is stored in the form of fats and glycogen
In the fed state dietary glucose is:
o Oxidised directly to generate ATP
o Stored as glycogen and triglycerides
In the fasted state, glycogenolysis and lipolysis provide energy from stores
Describe the main energy reserves of the body




Energy is stored in the body mainly as fats and glycogen
Fat is the major energy store of the body making up more than 7kg total body weight
o Mainly stored in adipocytes as triglycerides
o High calorific content – 5 times more energy efficient than carbohydrates
o Water-insoluble – does not require water for storage
Glycogen is a carbohydrate store in liver and muscle
o Can be rapidly degraded to glucose
o Liver glycogen reserves (20%) used in blood glucose maintenance
o Muscle glycogen reserves (80%) used to provide energy for exercise
Fat provides the most calories per unit weight; protein and carbohydrates provide less
Understand the role of ATP and reducing equivalents (e.g. NADH)




ATP (adenosine triphosphate) is a coupling molecule for energy transfer between energy producing
and energy consuming processes
One mole of ATP provides:
o 7.3kcal of energy when hydrolysed to ADP
o 10.9kcal of energy when hydrolysed to AMP
The primary objective of metabolism is to maintain a steady supply of ATP
ATP synthesis occurs during substrate oxidation







Adenylate kinase is catalyses the reversible reaction:
o ATP + AMP ↔ 2ADP
NADH is generated during carbohydrate oxidation
FADH is generated during carbohydrate and fatty acid oxidation
Catabolic pathways generate ATP e.g. substrate oxidation
Anabolic pathways consume ATP e.g. biosynthesis
Substrate oxidation converts large molecules into smaller molecules
o NAD is reduced to NADH
o NADH is re-oxidised to NAD in oxidative phosphorylation generating ATP
Biosynthesis converts small molecules into larger molecules using ATP
Understand how enzymes control flux through metabolic pathways



Flux through catabolic pathways is determined by ATP turnover (anabolic pathways?)
Metabolic pathways are highly regulated to:
o Maintain intracellular homeostasis
o Match ATP supply to demand
Enzymes control and regulate metabolism through catalysis of irreversible intermediary reactions
Understand the mechanisms by which enzyme activity is regulated

Enzymatic activity is regulated by:
o Allosteric control through feedback of products and ‘feed-forward’ of precursors
o Hormonal control through enzymatic modification, induction or repression