AP Bio Unit 3 pt 2
Certainly! Let's continue with the next set of terms in detail.
Glucose
Definition: A six-carbon sugar (C₆H₁₂O₆) and a primary energy source for cells.
Key Point: Glucose is broken down in cellular respiration to generate ATP, and is a key intermediate in both glycolysis and the citric acid cycle.
Example: Glucose is used in both aerobic and anaerobic processes, such as glycolysis and fermentation, to produce energy.
Pyruvate
Definition: A three-carbon molecule produced during glycolysis.
Key Point: Pyruvate is the end product of glycolysis and can be further processed into either acetyl CoA (for the citric acid cycle) or lactate/ethanol (via fermentation) depending on oxygen availability.
Example: In aerobic conditions, pyruvate enters the mitochondria and is converted into acetyl CoA for the citric acid cycle.
Electron Transport Chain (ETC)
Definition: A series of protein complexes and other molecules in the inner mitochondrial membrane that transfer electrons from electron donors (e.g., NADH, FADH₂) to electron acceptors (e.g., oxygen).
Key Point: The ETC is the final stage of aerobic respiration, where most ATP is produced via oxidative phosphorylation.
Example: In the ETC, electrons pass through complexes I-IV, and the energy released is used to pump protons into the intermembrane space, creating a proton gradient that drives ATP synthase.
Chemiosmosis
Definition: The process by which ATP is synthesized by the movement of protons (H⁺) across a membrane through ATP synthase.
Key Point: Chemiosmosis occurs in both cellular respiration (in mitochondria) and photosynthesis (in chloroplasts), driven by a proton gradient.
Example: During oxidative phosphorylation in the ETC, protons are pumped across the inner mitochondrial membrane, and as they flow back through ATP synthase, ATP is produced.
ATP Synthase
Definition: An enzyme complex that synthesizes ATP from ADP and inorganic phosphate (Pi) using the energy from a proton gradient.
Key Point: ATP synthase is driven by the flow of protons through the enzyme, a process known as chemiosmosis.
Example: ATP synthase is found in the inner mitochondrial membrane and the thylakoid membrane of chloroplasts, playing a central role in ATP production in both cellular respiration and photosynthesis.
Oxidative Phosphorylation
Definition: The production of ATP through the transfer of electrons from NADH and FADH₂ to oxygen via the electron transport chain, coupled with the chemiosmotic synthesis of ATP.
Key Point: Oxidative phosphorylation is the final stage of cellular respiration and is the primary source of ATP in aerobic organisms.
Example: In the mitochondria, oxidative phosphorylation generates most of the ATP used by cells, contributing to energy production during aerobic respiration.
Substrate-level Phosphorylation
Definition: The direct transfer of a phosphate group from a high-energy substrate to ADP to form ATP.
Key Point: This type of phosphorylation occurs in glycolysis and the citric acid cycle, in contrast to oxidative phosphorylation, which occurs in the electron transport chain.
Example: During glycolysis, the enzyme phosphoglycerate kinase catalyzes the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, producing ATP in the process.
Photophosphorylation
Definition: The process by which light energy is used to convert ADP and Pi into ATP during the light reactions of photosynthesis.
Key Point: Photophosphorylation occurs in the thylakoid membranes of chloroplasts and is driven by the energy from photons absorbed by chlorophyll.
Example: In the light reactions, photons excite electrons in chlorophyll, which are passed through the electron transport chain to drive ATP production via chemiosmosis.
Photosystem I
Definition: A protein complex in the thylakoid membrane that absorbs light energy to produce NADPH during the light reactions of photosynthesis.
Key Point: Photosystem I absorbs light at a wavelength of 700 nm and is involved in the final stages of the light reactions, where electrons are transferred to NADP⁺ to form NADPH.
Example: Photosystem I is involved in the linear electron flow, where it passes electrons to NADP⁺, producing NADPH, which is used in the Calvin cycle.
Photosystem II
Definition: A protein complex in the thylakoid membrane that absorbs light energy to produce ATP and splits water molecules, releasing oxygen.
Key Point: Photosystem II absorbs light at a wavelength of 680 nm and is the first protein complex in the light reactions, initiating the process of electron transport and photophosphorylation.
Example: Photosystem II splits water molecules into oxygen, protons, and electrons, generating the electrons that are passed through the electron transport chain to Photosystem I.
NADH
Definition: The reduced form of nicotinamide adenine dinucleotide (NAD⁺), an electron carrier involved in redox reactions.
Key Point: NADH carries electrons to the electron transport chain during cellular respiration, where it donates its electrons to generate ATP.
Example: NADH is produced during glycolysis, the citric acid cycle, and fatty acid oxidation, and is used in oxidative phosphorylation to produce ATP.
NAD⁺
Definition: The oxidized form of NADH, an electron carrier molecule involved in cellular respiration and other redox reactions.
Key Point: NAD⁺ accepts electrons during glycolysis and the citric acid cycle, becoming reduced to NADH, which then donates electrons to the electron transport chain.
Example: NAD⁺ is regenerated during fermentation to ensure that glycolysis can continue in the absence of oxygen.
FADH₂
Definition: The reduced form of flavin adenine dinucleotide (FAD), another electron carrier molecule used in cellular respiration.
Key Point: FADH₂ is produced during the citric acid cycle and donates electrons to the electron transport chain, contributing to the production of ATP.
Example: FADH₂ is produced when succinate is converted to fumarate in the citric acid cycle.
FAD
Definition: The oxidized form of FADH₂, an electron carrier used in cellular respiration.
Key Point: FAD accepts electrons during the citric acid cycle and is reduced to FADH₂, which then contributes electrons to the electron transport chain.
Example: FAD is reduced to FADH₂ in the conversion of succinate to fumarate during the citric acid cycle.
NADP⁺
Definition: Nicotinamide adenine dinucleotide phosphate, an electron carrier in photosynthesis.
Key Point: NADP⁺ is reduced to NADPH during the light reactions of photosynthesis, and NADPH is used in the Calvin cycle for carbon fixation.
Example: NADP⁺ accepts electrons at the end of the light reactions in the thylakoid membrane, becoming NADPH.
NADPH
Definition: The reduced form of NADP⁺, an electron carrier in photosynthesis.
Key Point: NADPH provides the reducing power needed for the Calvin cycle, where carbon dioxide is fixed into glucose and other organic molecules.
Example: NADPH is used to reduce 3-phosphoglycerate to glyceraldehyde-3-phosphate during the Calvin cycle.
Oxygen
Definition: A diatomic molecule (O₂) that acts as the final electron acceptor in the electron transport chain during aerobic respiration.
Key Point: Oxygen is essential for oxidative phosphorylation, where it accepts electrons and combines with protons to form water.
Example: Oxygen is essential for the production of ATP in aerobic organisms, and its consumption in the electron transport chain is why we breathe in oxygen.
Carbon Dioxide
Definition: A waste product of cellular respiration and a key reactant in photosynthesis.
Key Point: In cellular respiration, carbon dioxide is produced during the citric acid cycle and is exhaled by organisms. In photosynthesis, carbon dioxide is fixed into organic molecules.
Example: In aerobic respiration, glucose is oxidized to produce carbon dioxide, water, and energy (ATP). In photosynthesis, carbon dioxide is converted into glucose through the Calvin cycle.
Citric Acid Cycle / Krebs Cycle
Definition: A series of enzymatic reactions that take place in the mitochondria, where acetyl CoA is oxidized to produce CO₂, NADH, FADH₂, and ATP.
Key Point: The citric acid cycle is a key step in aerobic respiration, completing the oxidation of glucose and generating high-energy electron carriers for the electron transport chain.
Example: Acetyl CoA reacts with oxaloacetate to form citric acid, which is then converted through a series of reactions, producing ATP, NADH, FADH₂, and CO₂.