ATP Synthesis and Respiration

ATP Synthesis in Respiration

• Glycolysis occurs in the cytoplasm. Glucose (6C) is phosphorylated to glucose-6-phosphate using 2 ATP. Glucose splits into two triose phosphate molecules. Oxidation to pyruvate releases 2 NADH and 4 ATP (net gain of 2 ATP).

• Link Reaction takes place in the mitochondrial matrix. Pyruvate loses CO2 and forms NADH, producing acetyl-CoA.

• Krebs Cycle involves acetyl-CoA (2C) combining with oxaloacetate (4C) to form citrate (6C). Decarboxylation and dehydrogenation reactions produce 2 CO2, 3 NADH, 1 FADH2, and 1 ATP per cycle, regenerating oxaloacetate.

• Oxidative Phosphorylation happens in the inner mitochondrial membrane. Electrons from NADH and FADH2 travel along the electron transport chain (ETC), creating a proton gradient. H+ ions flow through ATP synthase, producing ATP. Oxygen is the final electron acceptor, creating water.

Anaerobic Respiration

• Animals use pyruvate reduction to lactate, regenerating NAD+ for glycolysis.

• Plants/Microorganisms convert pyruvate to ethanol and CO2, oxidizing NADH to NAD+.

Photosynthesis

Light-dependent Reactions

• Non-cyclic Photophosphorylation: Light excites electrons in photosystem II (PSII); electrons pass down an electron transport chain (ETC), pumping H+ into the thylakoid lumen. H+ flow through ATP synthase produces ATP. Electrons from PSII replenish PSI. Electrons from PSI reduce NADP+ to NADPH.

• Cyclic Photophosphorylation involves only photosystem I (PSI). Electrons cycle back to PSI via the ETC, creating ATP, but no NADPH or oxygen.

Light-independent Reactions (Calvin Cycle)

• Location: Stroma of chloroplasts.

• Stages:

  • Carbon Fixation: CO2 combines with RuBP (5C) to form two molecules of 3-PGA (3C), catalyzed by rubisco.
  • Reduction: 3-PGA gets reduced to triose phosphate (TP) using NADPH and ATP.
  • Regeneration: Some TP regenerates RuBP for further carbon fixation, using ATP.

• Products: Glucose, other carbohydrates, and organic molecules are produced from TP.

Homeostasis

Regulation of Blood Glucose

• Hyperglycemia: Beta cells in the pancreas detect high blood glucose and release insulin, promoting glucose uptake and glycogen formation (glycogenesis) in the liver.

• Hypoglycemia: Alpha cells in the pancreas detect low blood glucose and release glucagon. Glucagon promotes glycogen breakdown (glycogenolysis) and glucose synthesis (gluconeogenesis).

Regulation of Temperature

• High Temperature: Vasodilation (widened blood vessels), sweating, and reduced metabolic rate help cool the body.

• Low Temperature: Vasoconstriction, shivering (muscle contractions), and increased metabolic rate with adrenaline and thyroxine aid in heat production.

Osmoregulation

• Water Loss: Osmoreceptors in the hypothalamus detect low water levels and trigger the release of ADH from the posterior pituitary, increasing water reabsorption in the collecting duct.

• Water Excess: Reduced ADH secretion decreases water reabsorption, promoting water excretion.

Control and Coordination

Nervous Transmission

• Resting Potential: Sodium-potassium pump maintains a negative internal charge (-70 mV) by actively transporting 3 Na+ out and 2 K+ in.

• Depolarization: Stimulation opens Na+ channels, allowing Na+ influx causing a less negative membrane potential.

• Repolarization: Opens K+ channels causing K+ efflux, restoring the negative membrane potential.

• Hyperpolarization: Excess K+ outflow results in a potential drop below resting potential, re-established by the sodium-potassium pump.

Synaptic Transmission

• Arrival of an action potential at the synaptic knob triggers Ca2+ channels opening and Ca2+ influx. Causing neurotransmitter vesicles release neurotransmitters (e.g., acetylcholine) into the synaptic cleft. Neurotransmitters bind to receptors on the postsynaptic membrane, triggering an action potential in the postsynaptic neuron.

Hormonal Coordination

• Endocrine System: Hormones are released into the bloodstream, targeting specific cells with matching receptors. Examples include adrenaline (fight-or-flight) and insulin (blood glucose regulation).