ATP of Skeletal Muscles Energy of Skeletal Muscles Lecture -3 Lecture -3.
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Transcript of ATP of Skeletal Muscles Energy of Skeletal Muscles Lecture -3 Lecture -3.
ATP of Skeletal Muscles
Energy of Skeletal Muscles Lecture -3
Objectives
• Recognize the importance of ATP as energy source in skeletal muscle.
• Understand how skeletal muscles derive and utilize ATP for energy.
• Differentiate between energy metabolism in red and white muscle fibers.
ATP or adenosine triphosphate is the energy currency used by our body everyday to perform a number of tasks:
ATP
•Maintain body temperature
•Repair damaged cells
•Digestion of food
•Mechanical work – movement
ATP ↔ ADP+ Energy
• ATP is the most important form of chemical energy stored in cells
• Breakdown of ATP into ADP+PO4 releases energy.
• Muscles typically store limited amounts of ATP – enough to power 4-6 seconds of activity
• So resting muscles must have energy stored in other ways.
ATP
Systems of generation of ATP
1- ATP-Ctreatine Phosphate system
2- Glycolytic system
3- Oxidative system
The process that facilitates muscular contraction is entirely dependent on body’s ability to provide & rapidly replenish ATP
INTERACTION OF ENERGY SYSTEMS
Immediate Short-term Long-term
100%%
Cap
acit
y o
f E
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Sys
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10 sec 30 sec 2 min 5+ min
Energy Transfer Systems and Exercise
Aerobic Energy System
Anaerobic Glycolysis
ATP – Creatine Phosphate
Exercise Time
Energy systems for muscular exercise
Energy Systems Mole of ATP/min
Time to Fatigue
Immediate: ATP-CP(ATP & creatine phosphate)
4 5 - 10 sec
Short Term: Glycolytic(Glycogen-Lactic Acid)
2.5 1 - 2 min
Long Term: Oxidative1 Unlimited time
Energy requirements
The three energy systems often operate simultaneously during physical activity
HOWEVERRelative contribution of each system to total energy requirement differs
depending on exercise intensity & duration
Magnitude of energy from anaerobic sources depends on person’s capacity and tolerance for lactic acid accumulation
(Athletes are trained so that they will have better tolerance for lactic acid)
As exercise intensity diminishes & duration extends beyond 4 minutes, energy more dependent on aerobic metabolism
Fatigued muscle no longer contracts due to:
1 -Accumulation of lactic acid (low pH of sarcoplasm)2 -Exhaustion of energy resources ( ADP & ATP)
3 -Ionic imbalance: muscle cells is less responsive to motor neuronal stimulation
Muscle Fatigue
What are the mechanisms by which muscle fibers obtain energy to
power contractions?
Muscles and fiber types
White muscle : (glycolytic)mostly fast fiberspale (e.g. chicken breast)
Red muscle: (oxidative)mostly slow fibersdark (e.g. chicken legs)
Most human muscles are:
Mixed fiberspink
Fast Vs. Slow Fibers
Type I
Type II
• Abundant mitochondria• Extensive capillary supply• High concentrations of myoglobin• Can contract for long periods of time• Fatigue resistant• Obtain their ATP mainly from fatty acids oxidation by TCA cycle & ETC (oxidative phosphorylation)
Slow fibers
• Large glycogen reserves• Relatively few mitochondria• Produce rapid & powerful contractions BUT of short duration• Easily fatigued• Obtain their ATP mainly from anaerobic glycolysis
Fast fibers
ENERGY REQUIREMENTS AND SOURCE OF ENERGY FOR SKELETAL MUSCLE
( Resting vs. Working)
ATP use in the resting muscle cell
During periods of muscular rest ATP is required for:
1- Glycogen synthesis (glycogenesis) i.e. storage form of glucose to be used during muscular exercise
2- Creatine phosphate production i.e. energy storage compound to be used at
the beginning of muscular contraction
Source of ATP in resting muscle fibers
• Resting muscle fibers takes up free fatty acids from blood.
• Fatty acids are oxidized (in the mitochondria) to produce acetyl CoA & molecules of NADH & FADH2
• Acetyl CoA will then enter the citric acid cycle (in the mitochondria) ATP, NADH, FADH2 & CO2
• NADH & FADH2 will enter the electron transport chain. synthesis of ATP
Figure 10–20a
RESTING MUSCLE FIBERS METABOLISM
ATP sources in working muscle
• At the beginning of exercise, muscle fibers immediately use stored ATP
• For the next 15 seconds, muscle fibers turn to the creatine phosphate.
This system dominates in events such as the 100m dash or lifting weights.
ATP sources in working muscle cont .
• After the phosphagen system is depleted, the process of anaerobic glycolysis can maintain ATP supply for about 45-60s
Glycogen stored in muscles Glucose 2 pyruvic acid + 2 ATPs 2 Pyruvic acid 2 lactic acid Lactic acid diffuses out of muscles blood liver Glucose (by
gluconeogenesis) blood muscles
* It usually takes a little time for the respiratory and cardiovascular systems to catch up with the muscles and supply O2 for aerobic metabolism.
Figure 10–20c
WORKING MUSCLE FIBERS METABOLISM
Anaerobic metabolism is inefficient:1- Large amounts of glucose are used for very small ATP returns.2- Lactic acid is produced leading to muscle fatigue
Type of sports uses anaerobic metabolism?
Sports that requires bursts of speed and activity e.g. basketball.
ATP sources in working muscle cont .
• Aerobic metabolism occurs when the respiratory & cardiovascular systems have “caught up with” the working muscles. • During rest and light to moderate exercise, aerobic
metabolism contributes 95% of the necessary ATP.• Compounds which can be aerobically metabolized
include: Fatty acids, pyruvic acid (made from glucose via
glycolysis) & amino acids.
ATP sources in working muscle cont .
WORKING MUSCLE FIBERS METABOLISM
Aerobic Vs. Anaerobic sources of energy
Aerobic
Require oxygen
Source of energy :mainly fatty acids, then
carbohydrate
End Products:CO2, H2O & ATP
Anaerobic
No requires oxygen
Source of energy :ONLY Carbohydrate
(anaerobic glycolysis)
End Products:Lactate & ATP
The Cori cycle&
The glucose-alanine cycle
The Cori cycle
• Liver converts lactate into glucose via gluconeogenesis
• The newly formed glucose is transported to muscle to be used for energy again
The glucose-alanine cycle• Muscles produce: 1- Pyruvate from glycolysis during exercise 2- NH2 produced from normal protein degradation
Pyruvate + NH2 Alanine
• Alanine is transported through the blood to liver• Liver converts alanine back to pyruvate
Alanine – NH2 = Pyruvate
• Pyruvate is converted to glucose (gluconeogenesis).• Glucose is transported to muscle to be used for energy
again.• Liver converts NH2 to urea for excretion (urea cycle)