Biology Energy Processes and ATP

Energy

• Energy is essential for multiple processes in living organisms, including anabolic reactions like protein synthesis and DNA replication.
• Active transport mechanisms, such as the sodium-potassium pump, rely on energy.
• Mechanical functions, including muscle contraction and movement via flagella or cilia, require energy.
• Organisms use energy to maintain homeostasis, support bioluminescence, and transmit nerve impulses.

ATP as Energy Currency

• ATP (adenosine triphosphate) hydrolysis releases energy through the conversion to ADP (adenosine diphosphate) and AMP (adenosine monophosphate).
• Energy release from ATP hydrolysis is characterized by the values: 30.6 kJ mol⁻¹ for ATP to ADP, 30.6 kJ mol⁻¹ for ADP to AMP, and 14.2 kJ mol⁻¹ for AMP to adenosine.
• ATP is small, water-soluble, and easily transported within cells, making it an immediate energy source.
• Phosphate (Pi) is an effective leaving group, allowing ATP synthesis via ATP synthase to be reversible and efficient.
• ATP maintains a high turnover rate and acts as a link between anabolic (energy-consuming) and catabolic (energy-releasing) reactions.

ATP Synthesis

• ATP can be synthesized through glycolysis and the Krebs cycle, with oxidative phosphorylation occurring during aerobic respiration.
• Only oxidative phosphorylation necessitates oxygen, which combines with electrons and protons in the final electron acceptor stage of respiration.
• Absence of the electron transport chain (ETC) prevents chemiosmosis and ATP synthesis.

Respiration Overview

• Respiration processes utilize organic molecules as fuel, proceeding through glycolysis, link reaction, Krebs cycle, and oxidative phosphorylation.

Glycolysis

• Glycolysis breaks down glucose to form two molecules of pyruvate and occurs in the cytoplasm.
• The initial step involves the phosphorylation of glucose using 2 ATP to provide activation energy.
• The phosphorylation process involves conversions from glucose to glucose phosphate, then to fructose phosphate, and ultimately onto fructose bisphosphate.

Link Reaction

• Takes place in the mitochondrion matrix, requiring active transport of pyruvate into the matrix.
• Decarboxylation removes CO₂, and dehydrogenation removes hydrogen.
• Generates a net gain of 2 ATP and 2 reduced NAD from 2 pyruvate molecules.

Coenzyme A

• Coenzyme A, composed of a nucleoside and vitamin, carries acetyl groups (CH3-CO) into the Krebs cycle.

Krebs Cycle

• The Krebs cycle is a closed pathway of enzyme-controlled reactions in the mitochondrial matrix.
• Acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6C), resulting in the release of CO₂ and reduction of NAD and FAD.
• Oxaloacetate is regenerated to perpetuate the cycle, and the net gain of CO₂ and reduced NAD is double that from one cycle due to two pyruvate molecules.

Oxidative Phosphorylation and Electron Transport Chain (ETC)

• This stage occurs in the inner mitochondrial membrane (cristae) and involves chemiosmosis.
• Reduced NAD and FAD donate hydrogen atoms to the ETC, splitting into protons (H⁺) and electrons (e⁻).
• Electrons move down an energy gradient, facilitating the pumping of H⁺ ions from the matrix to the intermembrane space, creating a proton gradient.
• Protons flow back into the matrix through ATP synthase, generating ATP from ADP and Pi via electrical potential energy.
• Oxygen serves as the final electron acceptor, combining with electrons and protons to form water (H₂O).

This quiz covers essential concepts related to energy in biological systems, focusing on ATP as the primary energy currency. Topics include energy used in anabolic processes, active transport, and mechanical functions such as muscle contraction. Test your understanding of how ATP hydrolysis and synthesis play crucial roles in cellular functions.