Carbohydrate metabolism 1-3 (wk4) Flashcards
Describe what ATP (adeno triphosphate)
-1 ATP molecule is used per actin-myosin power stroke
-There are 100’s of myosin heads within each sarcomere
-There are 100’s of thousands sarcomeres within each muscle fibre
-There are approx 250,000 muscle fibres in the biceps brachii
-Assuming all fibres are engaged, a single twitch requires ~7.5 billion ATP molecules
-The demand for ATP hydrolysis during strenuous whole-body exercise can be as high as 12 hexillion molecules of ATP per minute or 1kg of ATP per minute
How the ATP-ADP cycle relates to anabolism and catabolism
-ATP-ADP cycle
-ATP-ADP cycle -> ATP is a high energy nucleotide with three phosphate groups attached to a ribose sugar. The negative charge on the terminal oxygen of the phosphate group (PO4-) acts like a compressed spring, as it repels the rest of the molecule. Chemical energy is released from ATP when it’s hydrolysed, losing a phosphate group (∆G=-6.4Kcal/mol)
How the ATP-ADP cycle relates to anabolism and catabolism
-Anabolic reactions
-Anabolic reactions -> Anabolic reactions (+∆G, endergonic) are coupled to the hydrolysis (catabolism) of ATP to ADP + Pi (inorganic phosphate) + energy (-∆G, exergonic) to perform cellular work.
How the ATP-ADP cycle related to anabolism and catabolism
-Catabolic reactions
-Catabolic reactions -> Catabolic reactions (-∆G, exergonic) release energy which can be used for ATP synthesis. The net energy from ATP breakdown/synthesis is ‘manipulated’ by cells in order to allow both anabolic and catabolic reactions to proceed.
Describe the turnover of ATP-ADP cycle during exercise
-ATP supplies the demand of energy from skeletal muscle and other tissues during exercise
-A human w/ energy expenditure of 2000kcal per day turns over ~ 45kg of ATP
-The demand for ATP hydrolysis during strenuous exercise can be as high as 1kg per minute
-The metabolic pathways used to resynthesize ATP vary for different types of exercise
Describe the utilisation of ATP during exercise
- Mechanical energy -> muscle contraction
- Electrical energy -> electrical nerve impulses (Na+ - K+ pump and Ca2+ pump)
Explain changes in skeletal muscle (ATP) during maximal exercise
-Stored ATP in muscle would last ~3 seconds during maximal exercise
-Muscle can keep on going through accumulating breakdown products of ATP -> ADP, AMP and PCr
How myokinase can replenish ATP
-Myokinase adds phosphate groups
-Myokinase reaction is anaerobic and maintains ATP during hard exercise
-The reaction is favoured because of:
* Reduced ATP
* Increased ADP
* AMP is broken down into the liver and then excreted via the kidneys by adenylate deaminase (urea cycle) to favour more ATP formation
Explain changes in skeletal muscle (PCr) during maximal exercise
-PCr has highest phosphoryl transfer potential
-Creatine kinase rapidly drives ATP synthesis during hard exercise
-PCr outweighs Cr in muscle (2:1) to favour the conversion to Cr and ATP
-Although PCr stores are 3-4 times larger than ATP, the resynthesis of PCr stores is slower than ATP
-PCr stores last ~7 seconds during maximal exercise
-CK maximal rate of ATP resynthesis is 2.6 mmol/kg/s
Describe the enzymatic pathway converting Pcr to ATP
-Integration: ATP regeneration during exercise -> ATP is ~8mmol/kg, but the maximal demand during exercise is ~3mmol/kg/sec. ATP doesn’t drop below 60% of resting levels during exercise, due to the enzymes myokinase and creatine kinase.
-PCr provides the initial demand of ATP (~7 sec). Cr levels increase.
-Pi increases and ADP increases modestly because myokinase reutilised ADP to generate more ATP
-Beyond these anaerobic pathways, ATP is supplies through the breakdown of carbohydrates and fats – anaerobic and aerobic metabolism.
How ATP is hydrolysed and resynthesized during maximal exercise
How ATP is hydrolysed and resynthesized during maximal exercise:
-Resynthesis of ATP is optimised for different activities by utilising different energy systems
-These vary in maximal rates and sustainability
Describe and draw the relationship between the breakdown of glucose and Gibbs free energy
-Carbohydrates as a source of energy -> Glucose is rich in C-H bonds that can yield energy. The breakdown of glucose is associated with a negative change in Gibbs free energy (-∆G)
Describe the basic process of carbohydrate digestion and absorption
-Digestion -> Carbohydrate digestion begins in the mouth (saliva) and then small intestine (pancreatic juices), where the enzyme (alpha)-amylase hydrolyses (alpha)(1-4)-glycosidic bonds in starch to short-chain carbohydrates (oligosaccharides). Oligosaccharides are then broken down into disaccharides in the villi of the small intestine.
-Specific enzymes such as lactase, maltase and sucrase then breakdown disaccharides to monosaccharides
-Absorption -> Monosaccharides are then absorbed into cytosol of enterocytes and transported into capillaries that empty into venous blood and the portal vein that supplies the liver
Key steps regulating glycogen synthesis and breakdown
-Glycogen content of liver and muscle
-Glycogen content of liver and muscle -> Glycogen is mainly stored in the liver (3-7%) and muscle (1-1.5%). A lean female weighing 62kg will have approximately 233g of muscle glycogen and 70g of lover glycogen. In muscle, these are optimally located between thick and thin filaments and near the mitochondria. Glycogen is stored in the granules containing enzymes needed for its breakdown and storage. ATP provision in muscle is enhanced by the breakdown of liver glycogen during exercise – communication between these 2 tissues.
Describe the synthesis and breakdown of glycogen (reaction, process and enzymes)