Lecture 9.1 and 9.2: Muscle Energy Metabolism Flashcards
Energy Transfer
Moving System Toward vs. Away From Equilibrium
- move system toward equilibrium: energy is produced
- move system away from equilibrium: energy is required (work)
- low thermodynamic stability in products and reactants
- high thermodynamic stability (lower energy) at equilibrium
Steady State Conditions
A → B
- there is a way to replenish ‘A’ at the same rate it is converted to ‘B’
- there is a way to remove ‘B’ at the same rate it is produced from ‘A’
In living cells, do reactions ever ‘finish’?
no – kept from reaching equilibrium
- reactions are always at some point away from equilibrium, but moving towards equilibrium
- if equilibrium is reached, cell dies
ATP Hydrolysis
ATP + H2O → ADP + Pi + H+
- amount of energy is proportional to the difference in thermodynamic stability of all reactants and all products
- hydrolysis products are more strongly bonded than reactants
ATP Hydrolysis
What is resonance stabilization?
there is greater resonance stabilization in products than reactants
ATP Hydrolysis
What are charge repulsion effects?
there is more ‘bond weakening’ by charge effects in reactants than in products
What are the 2 mechanisms through which ATP is generated?
- substrate level phosphorylation (SLP)
- oxidative phosphorylation (Ox Phos)
What are the 3 main substrates used for substrate level phosphorylation (SLP)?
- creatine phosphate
- glucose/glycogen
- lipid
How is ATP generated via SLP with creatine phosphate?
ATP generated via removal of phosphate, which can then be used in muscle contraction
How is ATP generated via SLP with glucose/glycogen?
ATP generated via oxidation
How is ATP generated via SLP with lipids?
ATP generated via oxidation
Describe the ATP yield for glucose oxidation.
glucose is converted into 2 pyruvate via glycolysis in cell cytosol
- produces 2 ATP
- substrate level phosphorylation
pyruvate is converted into 2 acetyl-CoA in mitochondrial matrix
- acetyl-CoA enters TCA cycle and produces 2 ATP
- substrate level phosphorylation (pyruvate is phosphorylated)
other products of glycolysis are used in electron transport in mitochondrial inner membrane
- produces various amounts of ATP
- oxidative phosphorylation
What is the actual vs. theoretical yield for glucose oxidation? Why?
actual ATP yield (32) is lower than the theoretical yield (36) due to involvement of H+ in pyruvate and ADP transport
Amount of Available Substrate in White Muscle (Fast Contraction)
creatine phosphate > glycogen > lipid > ATP > glucose
- ATP: muscle [ATP] = < 5 mmol/kg
- creatine phosphate: muscle [CrP] = around 40 to 50 mmol/kg
- glucose/glycogen: muscle glucose = 2 mmol/kg, muscle glycogen = 25 to 30 mmol/kg
- lipid: muscle triacylglycerol = 20 mmol/kg
Where are the sources of the main substrates that support ATP production?
muscles have stored sources for ATP production, or sources get transported through blood to muscle tissue
Source of Main Substrates that Support ATP Production
Where are carbohydrate sources?
- glucose from muscle stores of glycogen – main store
- glucose from blood
Source of Main Substrates that Support ATP Production
Where are lipid sources?
- fatty acids are stored in muscle and adipose tissues as triacylglycerol
- fatty acids from lipoproteins from the blood
What does mitochondrial beta-oxidation do?
breaks fatty acids into 2 carbon acetyl-CoA, which enter TCA and produce ATP
What substrate does glycolysis use?
only carbohydrates
What substrate does oxidative phosphorylation use?
can oxidize carbohydrates or lipids (or amino acids)
Carbohydrates vs. Lipids
Which substrate can be more rapidly mobilized?
glycogen
Carbohydrates vs. Lipids
Which substrate is a more dense source of energy?
lipids
- cell can produce approximately 10x more ATP from triglyceride droplets than from the same volume of glycogen granules
Carbohydrates vs. Lipids
Which substrate is associated with mitochondria?
- triglyceride droplets are always associated with mitochondria
- only some glycogen granules are associated with mitochondria, while others are dispersed within myofibrils
Carbohydrate Pathway: How are carbohydrates converted into ATP?
- glycogen is broken down into glucose 1-P by glycogen phosphorylase
- glucose 1-P is converted into pyruvate via glycolysis and yields ATP
- pyruvate is transported into mitochondria
- pyruvate dehydrogenase converts pyruvate into acetyl-CoA
- pyruvate may also sometimes be converted into lactate
- acetyl-CoA enters TCA cycle, which yields electrons that are used in oxidative phosphorylation to make ATP that is used in muscle contraction