Muscles Tissues Part 3 Flashcards
What are the sources of ATP for muscles?
- Stored in muscle fibers before contraction begins as 3mmol ATP, 20mmol CP (creatine phosphate) and 100mmol glycogen
- Generated in three ways in muscle cell
a) direct phosphorylation ADP by creatine phosphate
creatine phosphate + ADP <-> Creatine + ATP
at rest: skeletal fiber produces more ATP and CP than it needs
at us: more ATP is made through
b) aerobic metabolism and c) glycolysis (anaerobic metabolism)
What are the sources of energy stored in a typical muscle fiber?
ATP, Creatine Phosphate, Glycogen
Energy source: ATP
Initial Quantity: 3mmol
Utilization process: ATP -> ADP + P
Number of twitches supported by each energy source alone: 10
Duration of isometric tetanic contraction supported by each energy source alone: 2 sec
Why is glucose the primary energy source for cells?
- Glucose is a small, soluble molecule that is easily distributed through body fluids
- Glucose can provide ATP anaerobically through glycolysis. Although only a small amount is produced, glycolysis is important during peak levels of physical activity, in red blood cells, or when a tissue is temporarily deprived of oxygen
- Glucose can be stored as glycogen, which forms compact, insoluble granules
- Glucose can easily be mobilized because the breakdown of glycogen occurs very quickly and involved only a single enzymatic step. Mobilization of other intracellular reserves involves much more complex pathways and takes considerably more time
What are the roles of other fuel molecules besides glucose?
Can be chopped up, modified, and enter aerobic pathway -> ATP
- Fatty acids liberated from adipose tissue
- Glucose broken down into pyruvic acid in glycolysis
- Oxygen from hemoglobin in blood or from myoglobin muscle fibers
- Amino acids from protein breakdown
> > cellular respiration in mitochondria
duration of energy provided: minutes -> hours
Explain the process of cellular respiration
1. Glycolysis (Occurs in the cytoplasm)
- breakdown of glucose into pyruvate
2 molecules of pyruvate (3 carbons each)
2 molecules of ATP (net gain)
2 molecules of NADH (electron carriers)
Oxygen requirement: Anaerobic (does not require oxygen)
2. Citric Acid Cycle (Krebs Cycle) (Occurs in the mitochondria)
Starting molecule: Pyruvate (converted to Acetyl-CoA)
Products (per 1 Acetyl-CoA):
3 molecules of NADH
1 molecule of FADH₂
1 molecule of ATP
2 molecules of CO₂ (carbon dioxide as waste)
Oxygen requirement: Aerobic (requires oxygen)
3. Electron Transport Chain (ETC) (Occurs in the inner mitochondrial membrane)
- established proton (H+) gradient used to supply ATP synthase protein channel
Starting molecules: NADH and FADH₂ (from previous stages)
Process: Electrons are transferred through protein complexes in the mitochondrial membrane, creating a proton gradient.
End products:
ATP: Large amounts generated by ATP synthase (about 34 ATP per glucose molecule)
Water: Oxygen accepts electrons and combines with protons to form water (H₂O).
Oxygen requirement: Aerobic (oxygen is the final electron acceptor)
How much of ATP generation does aerobic respiration account for?
95%
What is glycogenosis and glycogenolysis?
Anabolism and catabolism of glycogen -> glucose
How is glucose broken down into pyruvate?
Glycolysis
What is lipolysis and lipogenesis?
Catabolism and anabolism of triglyceride -> fatty acid
What is gluconeogenesis?
Formation of new glucose from non-carbohydrate
-ex. converted from fatty acids of amino acid to form new glucose
What is beta-oxidation?
Converting fatty acids to 2 carbon chains
What to do in the absence of O2?
Anaerobic respiration: glycolysis followed by lactic acid production
Muscle glycogen
>
Glucose (from blood)
> (undergoes glycolysis, produces 2 ATP)
2 pyruvic acid
>
2 Lactic acid -> diffuses into blood
What are the limits on use of anaerobic respiration?
- Lowered pH will disable key enzymes necessary for contraction and decrease Ca++ binding to troponin. Muscles will not be able to generate as much of a contraction
- Depletion of metabolic reserves within muscle fibers
- Damage to the sarcolemma and SR
- Muscle fatigue
What are the advantages of aerobic respiration?
- Produces 32 ATP / glucose molecule instead of 2
- No lactic acid produced
What are the limiting factors on using aerobic respiration?
Availability of O2 that can diffuse into muscle fiber
Describe energy use and the 3 levels of muscle activity: At rest
Mostly fatty acids and glucose used as fuel to generate ATP (aerobic) ATP used to build reserves of creatine phosphate and glycogen
Fatty acids are catabolized; the ATP produced is used to build energy reserves of ATP, CP, and glycogen
Describe energy use and the 3 levels of muscle activity: Moderate activity
Glucose and fatty acids used as fuel in aerobic respiration
- 32 molecules of ATP / molecules of glucose
Glucose and fatty acids are catabolized; the ATP produced is used to power contraction
Describe energy use and the 3 levels of muscle activity: Peak activity
Most (2/3) ATP through glycolysis (anaerobic)
- buildup of H+ ions leads to fatigue once sarcoplasm buffer system reaches its limit (enzymes become less functional)
- when blood pH drops = metabolic acidosis (or lactic acidosis)
Most ATP is produced through glycolysis, with lactic acid as a by-product. Mitochondrial activity now produces only about one-third of ATP consumed
Glycolysis and skeletal muscle contraction:
Enables skeletal muscles to continue contracting even when insufficient oxygen is available
Production of lactate during peak activity and its conversion to glucose in the liver, and rebuilding of glycogen reserves in muscles during recovery
This process continues after exertion has ended, because lactate levels within muscle fibers remain relatively high, and lactate continues to diffuse into the bloodstream. After the absorbed lactate is converted to pyruvate in the liver, roughly 30% of the new pyruvate molecules are broken down in the mitochondria, providing the ATP needed to convert the remaining 70% of the pyruvate molecules into glucose. The glucose molecules are then released into the circulation, where they are absorbed by skeletal muscle fibers and used to rebuild their glycogen reserves