Biological Mechanisms of Energy Requirement in Organisms | 生物体对能量需求的生物学机制

📚 Biological Mechanisms of Energy Requirement in Organisms | 生物体对能量需求的生物学机制

All living organisms require a continuous supply of energy to survive, grow and reproduce. This energy is used to drive chemical reactions, transport molecules across membranes and perform mechanical work. In most organisms, the energy ultimately comes from sunlight via photosynthesis, but it must be converted into a usable form, ATP, through cellular respiration.

所有生物体都需要持续的能量供应以生存、生长和繁殖。能量用于驱动化学反应、跨膜运输物质以及进行机械做功。在大多数生物体中，能量最终通过光合作用来自太阳光，但必须通过细胞呼吸转化为可用形式ATP。

1. Why Living Organisms Need Energy | 为什么生物体需要能量

Energy is required for anabolism, the synthesis of complex molecules such as proteins, nucleic acids, carbohydrates and lipids from simpler precursors. For example, amino acids are joined together to form polypeptides in a condensation reaction that requires energy.

能量用于合成代谢——由简单前体合成复杂分子，如蛋白质、核酸、糖类和脂质。例如，氨基酸在需要能量的缩合反应中连接形成多肽。

Energy is needed for active transport. Cells must transport ions such as Na⁺, K⁺ and Ca²⁺ against their concentration gradients, often using pumps such as the sodium-potassium ATPase.

能量用于主动运输。细胞必须逆浓度梯度运输Na⁺、K⁺和Ca²⁺等离子，通常利用钠钾ATP酶等泵蛋白。

Energy supports mechanical work, visible in muscle contraction, flagellar and ciliary movement, and the movement of chromosomes during mitosis and meiosis.

能量支持机械做功，体现在肌肉收缩、鞭毛和纤毛运动，以及有丝分裂和减数分裂过程中染色体的移动。

Energy is also released as heat, helping endothermic organisms maintain a stable body temperature. Even at rest, the heart, lungs and brain consume energy continuously.

能量还以热能形式释放，帮助恒温动物维持稳定的体温。即使在静息状态下，心脏、肺和大脑也不断消耗能量。

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2. ATP: The Universal Energy Currency | ATP：通用能量货币

Adenosine triphosphate (ATP) is the immediate source of energy for most cellular processes. Its role is to couple energy-releasing (exergonic) reactions with energy-requiring (endergonic) reactions.

三磷酸腺苷（ATP）是大多数细胞过程的直接能量来源。其作用是将释放能量的（放能）反应与需要能量的（吸能）反应偶联起来。

ATP is a small, water-soluble molecule that can diffuse easily within cells. It is not a long-term energy store; instead, it is continuously recycled from ADP and inorganic phosphate.

ATP是一种小分子水溶性物质，能在细胞内自由扩散。它不是长期能量储存形式，而是不断由ADP和无机磷酸再生。

The ATP/ADP cycle links catabolism and anabolism. Catabolic reactions such as respiration regenerate ATP, while anabolic reactions and other endergonic processes hydrolyse ATP to ADP and Pi.

ATP/ADP循环将分解代谢与合成代谢联系起来。呼吸作用等分解代谢反应再生ATP，而合成代谢及其他吸能过程将ATP水解为ADP和Pi。

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3. Structure and Hydrolysis of ATP | ATP的结构与水解

ATP is a nucleotide derivative. It consists of adenine (a purine base), ribose (a pentose sugar) and three phosphate groups attached to the 5′ carbon of ribose.

ATP是一种核苷酸衍生物，由腺嘌呤（嘌呤碱基）、核糖（戊糖）和连接在核糖5′碳上的三个磷酸基团组成。

The phosphate groups are linked by anhydride bonds. These bonds are described as high-energy because their hydrolysis releases a relatively large amount of free energy under cellular conditions.

磷酸基团之间通过酸酐键连接。这些键被称为高能键，因为在水解时，它们在细胞条件下释放相对大量的自由能。

In living cells, ATP is usually complexed with Mg²⁺ ions, which stabilise the molecule and aid the action of ATP-dependent enzymes.

在活细胞中，ATP通常与Mg²⁺离子结合，这样既能稳定分子结构，又有助于依赖ATP的酶发挥作用。

Hydrolysis of ATP to ADP and Pi has a standard free energy change (ΔG°′) of approximately −30.5 kJ mol⁻¹, but the actual value varies with pH and Mg²⁺ concentration.

ATP水解为ADP和Pi的标准自由能变化（ΔG°′）约为−30.5 kJ mol⁻¹，但实际值随pH和Mg²⁺浓度而变化。

ATP + H₂O → ADP + Pi + 能量 ΔG°′ ≈ −30.5 kJ mol⁻¹

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4. Overview of Cellular Respiration | 细胞呼吸概述

Cellular respiration is the controlled oxidation of organic compounds, usually glucose, to release chemical energy as ATP. It includes both aerobic and anaerobic pathways.

细胞呼吸是有机化合物（通常是葡萄糖）的受控氧化过程，释放化学能并合成ATP。它包含有氧呼吸和无氧呼吸两种途径。

The overall equation for aerobic respiration shows that glucose is completely oxidised to carbon dioxide and water, releasing large amounts of energy.

有氧呼吸的总方程表明葡萄糖被完全氧化为二氧化碳和水，释放大量能量。

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量（约 2870 kJ mol⁻¹）

Aerobic respiration is divided into four main stages: glycolysis in the cytoplasm; the link reaction and the Krebs cycle in the mitochondrial matrix; and oxidative phosphorylation on the inner mitochondrial membrane.

有氧呼吸分为四个主要阶段：细胞质中的糖酵解；线粒体基质中的连接反应和克雷布斯循环；线粒体内膜上的氧化磷酸化。

Anaerobic respiration involves only glycolysis, followed by fermentative pathways that regenerate NAD⁺. It produces far less ATP than aerobic respiration.

无氧呼吸仅包括糖酵解，随后通过发酵途径再生NAD⁺。它产生的ATP远少于有氧呼吸。

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5. Glycolysis | 糖酵解

Glycolysis occurs in the cytoplasm of all living cells and does not require oxygen. It is the first stage of glucose breakdown and consists of ten enzyme-catalysed reactions.

糖酵解发生在所有活细胞的细胞质中，不需要氧气。它是葡萄糖分解的第一阶段，由十步酶催化反应组成。

During glycolysis, glucose is first phosphorylated using two ATP molecules to form fructose-1,6-bisphosphate. The phosphorylated sugar is then split into two molecules of triose phosphate.

在糖酵解中，葡萄糖首先利用两分子ATP磷酸化，形成果糖-1,6-二磷酸。随后，磷酸化糖被裂解为两分子三碳糖磷酸。

Each triose phosphate is then oxidised in a series of reactions that produce pyruvate. The oxidation is coupled to the reduction of NAD⁺ to NADH, and substrate-level phosphorylation generates ATP.

随后，每个三碳糖磷酸在一系列反应中被氧化生成丙酮酸。这种氧化与NAD⁺还原为NADH相偶联，并通过底物水平磷酸化产生ATP。

For each glucose molecule, glycolysis yields a net gain of 2 ATP, 2 NADH and 2 pyruvate molecules, with no CO₂ released.

对于每分子葡萄糖，糖酵解净生成2个ATP、2个NADH和2个丙酮酸分子，不释放CO₂。

葡萄糖 + 2NAD⁺ + 2ADP + 2Pi → 2丙酮酸 + 2NADH + 2H⁺ + 2ATP + 2H₂O

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6. Link Reaction and Krebs Cycle | 连接反应与克雷布斯循环

In aerobic conditions, pyruvate enters the mitochondrial matrix and is converted to acetyl coenzyme A (acetyl CoA). This link reaction is catalysed by pyruvate dehydrogenase.

在有氧条件下，丙酮酸进入线粒体基质，转化为乙酰辅酶A（acetyl CoA）。这一连接反应由

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