Questions and Answers
What is activation energy?
How do catalysts, such as enzymes, affect activation energy?
Which of the following statements about ATP is true?
What happens to the activation energy when the phosphate groups are removed from ATP?
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What is essential for reversible reactions in biological processes?
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What role does the Sun play in energy for cellular processes?
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Why are the bonds linking phosphate groups in ATP considered unstable?
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Which of the following describes the energy released from ATP hydrolysis?
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What is the role of ADP in the ATP cycle?
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What process is catalysed by ATP synthase to convert ADP and inorganic phosphate into ATP?
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During which of the following processes does photophosphorylation occur?
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Which statement best describes the role of ATP in cells?
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What is the main purpose of chemiosmosis in ATP synthesis?
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What happens during substrate-level phosphorylation?
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What is a key characteristic of ATP as an energy source?
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In mitochondria, what drives the synthesis of ATP during oxidative phosphorylation?
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Which statement correctly describes the fate of protons in the mitochondria during ATP synthesis?
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What is a necessity for the completion of oxidative phosphorylation in cellular respiration?
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Which enzyme is primarily responsible for catalyzing the reaction that converts ADP and inorganic phosphate into ATP?
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What is the initial step required for glycolysis to begin?
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How many molecules of reduced NAD are produced from one molecule of glucose during glycolysis?
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What is the end product of glycolysis?
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Which of the following statements about the energy yield of glycolysis is correct?
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What happens to pyruvate in the absence of oxygen?
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Which coenzyme is primarily responsible for carrying hydrogen ions during respiration?
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Study Notes
Activation Energy
- Activation energy is the energy required for a chemical reaction to proceed by increasing the energy of the substrate.
- Catalysts, such as enzymes, reduce activation energy, allowing reactions to occur faster and at lower temperatures.
- The energy released during reactions results in the formation of products, and reactions can be reversible but often require external energy input for the reverse process.
- Biological processes are predominantly cycles of reversible reactions needing energy from the Sun.
Role of ATP
- Adenosine triphosphate (ATP) serves as the universal energy currency for cells, utilized in nearly all energy-requiring cellular processes.
- ATP is water-soluble and easily transported, ensuring efficient energy delivery within cells.
- It provides immediate energy through a one-step reaction and is hydrolyzed easily to release energy.
- ATP can be recycled quickly from adenosine diphosphate (ADP) through phosphorylation, allowing constant ATP availability.
- Each of the three phosphate groups in ATP is negatively charged, leading to unstable covalent bonds that release substantial energy (30.5 kJ/mol for the first two phosphates and 14.2 kJ/mol for the last).
ATP Synthesis
- ATP synthesis from ADP involves three mechanisms:
- Photophosphorylation in chloroplasts during photosynthesis.
- Oxidative phosphorylation across mitochondrial membranes during electron transport.
- Substrate-level phosphorylation during metabolic reactions, like glycolysis.
Chemiosmotic Theory
- In mitochondria, hydrogen ions are pumped across membranes, creating a proton gradient that drives ATP synthesis via ATP synthase.
- Protons flow back through ATP synthase, converting ADP and inorganic phosphate into ATP, with electrons combining with protons and oxygen to form water.
ATP Usage
- ATP is not suitable for long-term energy storage; fats and carbohydrates serve that purpose more effectively.
- ATP is used in diverse cellular functions, including:
- Anabolic processes: building macromolecules (e.g., polysaccharides, proteins).
- Movement: muscle contraction and intracellular transport.
- Active transport: moving molecules against concentration gradients.
- Secretion: formation of vesicles.
- Activation of chemicals: enhancing reactivity via phosphorylation.
Glycolysis
- Glycolysis occurs in the cytoplasm, converting one glucose molecule into two pyruvate molecules through ten enzyme-controlled reactions, grouped into four stages:
- Activation of glucose: phosphorylation using ATP increases reactivity.
- Splitting of sugar: fructose 1,6-bisphosphate is divided into two triose phosphates.
- Oxidation: NAD+ is reduced to form NADH as hydrogen is removed from triose phosphates.
- Production of ATP: converting triose phosphates into pyruvate yields a net gain of two ATP and two NADH.
Link Reaction
- Pyruvate from glycolysis enters mitochondria, undergoing decarboxylation and oxidation.
- Each pyruvate loses a carbon (as CO2), is oxidized to reduce NAD+ to NADH, and forms acetyl coenzyme A (acetyl CoA) for entry into the Krebs cycle.
Coenzymes
- Coenzymes like nicotinamide adenine dinucleotide (NAD) and flavine adenine dinucleotide (FAD) aid in carrying hydrogen atoms and electrons in respiration.
- NAD is crucial for the function of dehydrogenase enzymes that facilitate oxidation reactions in the metabolic pathway.
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Description
This quiz explores the concept of activation energy in chemical reactions. Learn how substrates transform into products and the role of catalysts, such as enzymes, in lowering activation energy. Understand the importance of activation energy for the rate and feasibility of chemical processes.
