Cellular Respiration Overview

Cellular Respiration

• Cellular respiration is the process by which cells break down glucose to release energy in the form of ATP. This occurs in the mitochondria.
• Three main stages of cellular respiration: glycolysis, the Krebs cycle, and the electron transport chain.
• Glycolysis occurs in the cytoplasm and involves the breakdown of glucose into two molecules of pyruvate. This process yields a small amount of ATP and NADH.
• The Krebs cycle, also known as the citric acid cycle, occurs in the mitochondrial matrix. Pyruvate is converted into Acetyl CoA, which enters the cycle. The cycle releases carbon dioxide and produces NADH, FADH2, and more ATP.
• The electron transport chain is the final stage of cellular respiration. It occurs in the inner mitochondrial membrane. Electron carriers (NADH and FADH2) release electrons, which are passed along a chain of proteins. This movement of electrons establishes a proton gradient, which drives ATP synthesis through chemiosmosis. Oxygen is the final electron acceptor.
• Anaerobic respiration (fermentation) is an alternative pathway to produce ATP in the absence of oxygen. This process yields less ATP than aerobic respiration. Examples include lactic acid fermentation (in animals) and alcoholic fermentation (in yeast).

Photosynthesis

• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy in the form of glucose.
• Photosynthesis occurs in chloroplasts, specifically within the thylakoid membranes and stroma.
• Two main stages of photosynthesis: the light-dependent reactions and the Calvin cycle.
• The light-dependent reactions occur in the thylakoid membranes. Light energy is absorbed by chlorophyll and other pigments, which excites electrons. These electrons move along electron transport chains, generating ATP and NADPH. Water is split to replace lost electrons, releasing oxygen as a byproduct.
• The Calvin cycle occurs in the stroma. ATP and NADPH from the light-dependent reactions provide the energy and reducing power to convert carbon dioxide into glucose. This process is sometimes called carbon fixation.

Enzymes

• Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed in the process.
• Enzymes are proteins with specific shapes that bind to substrates at an active site.
• The induced fit model describes how an enzyme's active site changes shape slightly when it binds to a substrate to better facilitate the reaction.
• Factors affecting enzyme activity include:
  • Temperature: optimal temperature exists where enzymes operate most efficiently. Higher temperatures can denature enzymes.
  • pH: Each enzyme has a specific optimal pH where it works best. Changes in pH can alter the enzyme's shape.
  • Substrate concentration: Increasing substrate concentration increases enzyme activity until maximum velocity is reached.
  • Enzyme concentration: Increasing enzyme concentration increases the reaction rate until saturation.
  • Inhibitors: Substances that can bind to an enzyme and decrease its activity. Competitive inhibitors bind to the active site, noncompetitive inhibitors bind to a different site on the enzyme.
• Enzyme function is crucial for all metabolic processes.

Energy and Chemical Reactions

• Energy is the capacity to do work.
• Energy can take many forms, including kinetic (motion) and potential (stored).
• Chemical reactions involve changes in energy. Exergonic reactions release energy, endergonic reactions require energy input. Energy coupling occurs when the energy released from an exergonic reaction is used to power an endergonic reaction.
• ATP (adenosine triphosphate) is the primary energy currency of cells. ATP hydrolysis (breaking down ATP) releases energy that can be used for cellular processes. ATP is a nucleoside triphosphate synthesized from ADP and inorganic phosphate during cellular respiration.
• Free energy is a measure of energy available to perform work in a chemical reaction. A negative change in free energy ($\Delta G$) indicates a spontaneous reaction.

Redox Reactions

• Redox reactions involve the transfer of electrons between molecules.
• Oxidation is the loss of electrons, reduction is the gain of electrons.
• Oxidation and reduction reactions occur simultaneously in a redox reaction.
• Examples of redox reactions are crucial in cellular respiration and photosynthesis. For example, in cellular respiration, glucose is oxidized and oxygen is reduced.

Metabolic Pathways

• Metabolic pathways are series of linked biochemical reactions that convert substrates into products.
• These pathways are important for synthesis, degradation, and energy conversion in biological systems.
• They are highly regulated and involve various enzymes.
• Feedback inhibition is a method to regulate metabolic pathways, where the products of a pathway inhibit the activity of enzymes early in the pathway.

This quiz covers the essential processes of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport chain. Learn how cells convert glucose into ATP and the significance of each stage in energy production. Test your understanding of the mitochondria's role in this vital biological process.