KPE264 - ATP, Enzymes, and Muscle Contraction

Module 1

• Adenosine Triphosphate (ATP) is the primary energy currency.
• Enzymes control reactions and increase the rate of chemical reactions, acting as catalysts.
• Substrate and product concentrations are key regulators of enzymes.
• Modulators, like ADP, control processes and facilitate breakdown when needed.
• Negative feedback can halt enzyme function.
• Stimulators can amplify enzyme activity.
• Ca2+ ATPase actively pumps calcium ions (Ca²⁺) out of the cytoplasm using ATP hydrolysis.
  • Important for muscle relaxation by decreasing cytosolic calcium levels.
  • Present in the sarcoplasmic reticulum in muscle cells and the plasma membrane in other cells.
  • Maintains low cellular calcium concentrations to prevent constant muscle contraction.
• Myosin ATPase hydrolyzes ATP to power muscle contraction.
  • Located in the myosin head.
  • Facilitates crossbridge formation.
  • Powers myosin movement along actin filaments during contraction.
• Na+/K+ ATPase uses ATP to pump sodium (Na⁺) out and potassium (K⁺) in to maintain the cell's ion gradient.
  • Provides energy to transport sodium.
  • Crucial for maintaining resting membrane potential and cellular function.
• Type I fibers are slow twitch fibers.
  • Can sustain exercise for extended durations.
  • Depend on oxygen for ATP production.
  • Recruited during low-intensity aerobic activities and daily tasks.
  • Heavily relied on.
• Type II fibers are fast twitch fibers.
  • Experience fatigue rapidly due to poor aerobic endurance.
  • Generate more force.
  • Produce ATP anaerobically.
  • Type IIa is more aerobic, while Type IIx is rarely recruited and more explosively activated.

Module 2

• Phosphocreatine immediately buffers ATP decreases, limiting continuous system use, and it’s not reliable long-term.
• Creatine Kinase catalyzes the conversion of creatine and ATP to creatine phosphate and ADP.
  • Provides a quick source of energy for muscle contraction.
  • Found in muscle cells, brain, and heart.
  • Important for short bursts of intense activity.
• The “GLUT” transporter is a membrane protein allowing glucose entry into muscle cells during exercise.
• Hexokinase traps glucose in muscle and is an enzyme converting glucose to glucose-6-phosphate, using ATP.
• Phosphofructokinase (PFK) is a key enzyme that catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate in glycolysis.
• Substrate-level phosphorylation is a process of ATP generation in the absence of oxygen.
• NADH is an important high-energy substrate used in the electron transport chain to generate ATP.
• Lactate dehydrogenase (LDH) reversibly converts pyruvate to lactate during anaerobic metabolism.
  • Helps regenerate NAD⁺ in anaerobic conditions.
  • Important in muscle cells during intense exercise.
• Pyruvate dehydrogenase (PDH) is an enzyme complex converting pyruvate to acetyl-CoA, linking glycolysis to the citric acid cycle.
  • Requires cofactors like NAD⁺ and CoA.
  • Active under aerobic conditions for energy production.
  • Located in mitochondria.
• Acetyl coA is a molecule that carries acetyl groups to the citric acid cycle for energy production.
  • Formed from pyruvate, fatty acids, or amino acids.
  • Essential for cellular respiration.
• Citrate synthase catalyzes the initial step of the citric acid/Krebs cycle, combining acetyl-CoA and oxaloacetate to form citrate and found in mitochondria.
• Cytochrome oxidase in the electron transport chain transfers H+ to O2, forming H2O.
  • Involved in aerobic respiration.
  • Crucial for producing ATP in the mitochondria.
• ATP synthase synthesizes ATP from ADP and inorganic phosphate at the end of the ETC, using energy from a proton gradient.
  • Located in the inner mitochondrial membrane.
  • Essential for energy production in oxidative phosphorylation.
• Albumin is a protein in the blood that carries FA and hormones to skeletal muscle.
• Hormone-sensitive lipase (HSL) stimulates the breakdown of triglycerides into FFAs and glycerol.
  • Located in adipose tissue and muscle.
  • Activated by epinephrine and glucagon during fasting or exercise.
• Fatty acetyl-CoA is recognizable by mitochondria.
  • Formed from fatty acid breakdown.
  • Used in the citric acid/Krebs cycle for energy production.
  • Involved in ketogenesis when carbohydrate supply is low.
• Carnitine palmitoyl transferase (CPT) shuttles fatty acids into mitochondria for beta-oxidation.

Module 3

• A hormone is a chemical substance secreted into bodily fluids, exerting specific effects on local or distant target tissues.
• Nonsteroid hormones are derived from proteins, peptides, or amino acids.
  • Not lipid-soluble, water-soluble, and unable to cross cell membranes.
  • Released from the pancreas, hypothalamus, pituitary gland, and adrenal medulla.
  • Includes insulin, proteins, and epinephrine.
• Steroid hormones are derived from lipids (cholesterol) and are lipid-soluble.
  • Lipid-soluble and able to cross cell membranes.
  • Released from ovaries, testes, and the adrenal cortex.
  • Examples include testosterone, estrogen, and cortisol.
• Insulin, a gluco-regulatory hormone from pancreatic beta cells, promotes glucose uptake into cells.
• Glucagon is a gluco-regulatory hormone from pancreatic alpha cells that raises blood glucose levels by stimulating the liver to release glucose.
• Epinephrine (adrenaline) is a hormone and neurotransmitter from the adrenal medulla that prepares the body for "fight or flight".
  • Increases heart rate, blood flow, and glucose release; increases muscle and liver glycogenolysis.
• Norepinephrine, similar to epinephrine, is released by SNS fibers and the adrenal medulla in the "fight or flight" response.
  • Regulates blood pressure, promotes vasoconstriction and lipolysis, and increases cardiorespiratory function.
• Adenylate cyclase converts ATP to cyclic AMP (cAMP) in response to activation by G-protein-coupled receptors (GPCRs).

Module 4

• Hemoglobin is a protein in red blood cells that binds oxygen in the lungs and releases it in tissues, transporting oxygen and returning carbon dioxide.
• Arterial blood, found in arteries, is oxygen-rich and delivered from the lungs.
• Venous blood returns to the heart from tissues, high in carbon dioxide and low in oxygen.
• Myoglobin in muscle cells stores and binds O2 more tightly than hemoglobin, shuttling O2 to mitochondria and only found in muscle.
• Bicarbonate ion (HCO3-) is a negatively charged ion formed when carbonic acid dissociates in the blood.
  • Main form of carbon dioxide transport.
  • Acts as a buffer to maintain blood pH.
• Carbaminohemoglobin is a compound formed when carbon dioxide binds to amino acids on hemoglobin in red blood cells and doesn't compete for the same binding site as O2.
• Carbonic acid (H2CO3) is a weak acid formed when carbon dioxide reacts with water.
• Carbonic anhydrase is an enzyme that catalyzes the conversion of CO2 and H2O into carbonic acid and vice versa.
  • Found in red blood cells, kidneys, and other tissues; speeds up CO2 transport and regulation of blood pH.
• Central chemoreceptors in the brainstem (medulla) detect changes in the pH of cerebrospinal fluid, which reflects CO2 levels in the blood.
  • Stimulated by increased CO2 & H+ in cerebrospinal fluid.
  • Increase rate and depth of breathing to remove excess CO2 from the body.
• Peripheral chemoreceptors in the aortic and carotid bodies detect changes in blood oxygen (O2) levels, CO2 levels, and pH.
  • Sensitive to changes in arterial blood PO2, PCO2, and H+.
    • Work within a tight range of values.
    • Sensitive to small changes.
• Mechanoreceptors/stretch receptors in the lungs detect mechanical changes like stretch or pressure in tissues.
  • Located in the pleurae, bronchiole, and alveoli.
  • Sense movement, especially during exercise.

Module 5

• Aortic valve allows blood to flow from the left ventricle.
• The mitral valve is a bicuspid valve.
• The pulmonary valve sends blood to the lungs for reoxygenation.
• The tricuspid valve receives deoxygenated blood.
• Semilunar valves include the aortic and pulmonary valves.
• Atrioventricular valves include the mitral and tricuspid valves.
• Atrioventricular (AV) valves regulate flow within the heart between the atria and ventricles with a one-way flow and the opening of the valve produces a "lub" sound.
• Semilunar (SL) valves regulate flow out of the heart into pulmonary and systemic circulation and the closing of the valve makes a "dub" sound.
• The SA node is the natural pacemaker of the heart, initiating electrical impulses and setting the heart's rhythm.
• The AV node is a cluster of cells that receives the electrical impulse from the SA node, delays it briefly, and passes it to the ventricles.
• The AV bundle is a pathway that carries the electrical impulse from the AV node to the ventricles.
• Purkinje fibers are specialized fibers that carry the electrical impulse to the heart muscle cells, causing the ventricles to contract.
• End Diastolic Volume (EDV) is the volume of blood in the ventricles at the end of diastole.
• Stroke Volume (SV) is the volume of blood ejected from the ventricles per beat.
• End Systolic Volume (ESV) is the volume of blood remaining in the ventricle at the end of systole.
• Ejection fraction is the fraction of blood pumped out of the ventricle in relation to the amount of blood in the ventricle before contraction.
• Muscle Pump refers to venous return to the heart promoted by contraction of skeletal muscles, which squeezes veins.
• The Frank-Starling Law of the Heart states that increased EDV leads to increased stretch on the walls, increasing the force of contraction and stroke volume.
• Chronotropic refers to the rate of contraction, i.e., heart rate (HR).
• Inotropic refers to the strength of contraction, i.e., stroke volume (SV).
• Acetylcholine is a neurotransmitter released by the vagus nerve in the PNS that decreases HR.
• The vagus nerve carries parasympathetic signals to the heart, lungs, and digestive organs.
  • Slows HR.
  • Plays a key role in the rest and digest response.
• Cardiac accelerator nerves carry sympathetic signals to the heart to increase heart rate and force of contraction.
• Arteries establish bulk flow and driving pressure, moving blood from the heart to arterioles.
• Arterioles regulate flow to specific regions, having the greatest control of circulation.
• Capillaries regulate surface area for exchange.
• Veins/venules regulate flow return, aided by the "muscle pump."

Module 6

• Vasodilation decreases pressure.
• Vasoconstriction increases pressure.
• Hematocrit is the percentage of blood volume occupied by red blood cells (RBCs).
• Plasma is the liquid component of blood, consisting mostly of water, electrolytes, proteins, hormones, and waste products.
• Red blood cells (RBC) are cells responsible for transporting oxygen and carbon dioxide in the blood.

Module 7

• Insulin sensitivity is how easily your cells respond to insulin's signal to take up glucose from the blood.
• Insulin resistance means your cells don't respond well, so your body needs more insulin to do the same job.