📚 The Need for Energy in Living Organisms | 生物体对能量的需求
All living organisms require a continuous supply of energy to maintain their highly ordered state. Energy is needed for movement, growth, reproduction, active transport, and countless biochemical reactions. Without a constant input of usable energy, cells cannot maintain homeostasis and life ceases.
所有生物体都需要持续的能量供应来维持其高度有序的状态。能量用于运动、生长、繁殖、主动运输以及无数生化反应。没有持续可用的能量输入，细胞无法维持稳态，生命就会停止。
1. Why Living Organisms Need Energy | 生物为什么需要能量
Living organisms are open systems that must constantly take in energy from their surroundings to maintain organisation. Energy is required to carry out essential life processes such as active transport, synthesis of macromolecules, movement, and reproduction. Without energy, metabolic reactions cannot proceed at a useful rate and cells lose their ability to respond to the environment.
生物体是开放系统，必须不断从环境中获取能量以维持组织化结构。能量用于执行主动运输、大分子合成、运动和繁殖等基本生命过程。没有能量，代谢反应无法以有效速率进行，细胞也会失去对环境作出反应的能力。
In heterotrophs such as animals and fungi, this energy comes from the chemical potential energy stored in organic nutrients, especially glucose. Autotrophs such as plants capture light energy and convert it into chemical energy during photosynthesis.
在动物和真菌等异养生物中，这种能量来自有机营养物质（尤其是葡萄糖）中储存的化学势能。植物等自养生物则捕获光能，并在光合作用中将其转化为化学能。
2. ATP as the Universal Energy Currency | ATP：通用的能量货币
Cells do not use glucose directly to power most reactions. Instead, energy from respiration or photosynthesis is used to synthesise adenosine triphosphate (ATP), which is the immediate energy donor for nearly all cellular work.
细胞并不直接利用葡萄糖为大多数反应供能。相反，呼吸作用或光合作用释放的能量被用来合成三磷酸腺苷（ATP），它是几乎所有细胞活动的直接能量供体。
ATP is called the universal energy currency because it links energy-releasing catabolic reactions with energy-requiring anabolic reactions. It is small, water-soluble, and easily moved around the cell, so it can deliver energy precisely where it is needed.
ATP 被称为通用的能量货币，因为它将放能的分解代谢反应与需能的合成代谢反应联系起来。它分子小、溶于水且易于在细胞内运输，因此能把能量精确输送到需要的地方。
- Active transport – 主动运输
- Muscle contraction – 肌肉收缩
- Biosynthesis of macromolecules – 大分子的生物合成
- Cell division – 细胞分裂
- Nerve impulse transmission – 神经冲动传导
- Maintenance of body temperature – 维持体温
3. Structure and Hydrolysis of ATP | ATP 的结构与水解
ATP consists of the nitrogenous base adenine, the pentose sugar ribose, and three phosphate groups. The three phosphate groups are linked by phosphoanhydride bonds, and the terminal phosphate bond is easily hydrolysed.
ATP 由含氮碱基腺嘌呤、五碳糖核糖和三个磷酸基团组成。三个磷酸基团通过磷酸酐键连接，末端磷酸键很容易水解。
Hydrolysis of ATP is catalysed by ATP hydrolase (ATPase):
ATP 的水解由 ATP 水解酶（ATPase）催化：
ATP + H₂O → ADP + Pᵢ + energy
This reaction releases about 30.5 kJ mol⁻¹ of energy under standard conditions, but in the cell the actual free energy change is often higher because reactant and product concentrations are far from standard.
该反应在标准条件下释放约 30.5 kJ mol⁻¹ 的能量，但在细胞内实际自由能变化往往更大，因为反应物和产物浓度远非标准状态。
The released inorganic phosphate (Pᵢ) can be transferred to other molecules, leading to phosphorylation and a change in their shape or reactivity.
释放出的无机磷酸（Pᵢ）可转移给其他分子，引起磷酸化并改变它们的形状或反应活性。
4. Energy Coupling and Phosphorylation | 能量偶联与磷酸化
ATP hydrolysis is an exergonic reaction, meaning it releases free energy. Cells couple this exergonic reaction to endergonic reactions that require an input of energy, allowing otherwise unfavourable processes to occur.
ATP 水解是一个放能反应，即释放自由能。细胞将这种放能反应与需要输入能量的吸能反应偶联，使原本不利的过程得以进行。
Energy coupling usually involves phosphorylation: a phosphate group from ATP is transferred to a substrate or enzyme, increasing its free energy and enabling conformational change or formation of a new bond.
能量偶联通常涉及磷酸化：ATP 上的磷酸基团转移到底物或酶上，增加其自由能，使构象改变或新键形成得以发生。
For example, in glycolysis, glucose is phosphorylated to glucose-6-phosphate using ATP, trapping glucose inside the cell and making it more reactive for subsequent breakdown.
例如，在糖酵解中，葡萄糖利用 ATP 被磷酸化为 6-磷酸葡萄糖，从而将葡萄糖限制在细胞内，并使其更容易参与后续分解。
5. Active Transport | 主动运输
Active transport moves ions or molecules across membranes against their concentration gradient, from a region of lower concentration to a region of higher concentration. This requires energy because it decreases entropy and often works against an electrochemical gradient.
主动运输将离子或分子逆浓度梯度跨膜转运，即从浓度较低的一侧运往浓度较高的一侧。这需要能量，因为它降低熵，且通常逆电化学梯度进行。
The sodium-potassium pump is a key example. For every ATP hydrolysed, it exports three Na⁺ ions and imports two K⁺ ions. This maintains resting potential in neurones and controls cell volume.
钠钾泵是一个典型例子。每水解一分子 ATP，它泵出三个 Na⁺ 并泵入两个 K⁺。这维持了神经元的静息电位并控制细胞体积。
- Sodium-potassium pump in animal cells – 动物细胞中的钠钾泵
- Proton pumps in plant root cells – 植物根细胞中的质子泵
- Co-transport of glucose in the small intestine – 小肠中葡萄糖的协同转运
6. Anabolic Reactions and Biosynthesis | 合成代谢与生物合成
Anabolic reactions build complex molecules from simpler precursors, including proteins from amino acids, polysaccharides from monosaccharides, and nucleic acids from nucleotides. All require an input of ATP or an equivalent nucleotide triphosphate.
合成代谢反应从较简单的前体构建复杂分子，包括由氨基酸合成蛋白质、由单糖合成多糖以及由核苷酸合成核酸。所有这些都需要输入 ATP 或等效的三磷酸核苷酸。
For example, protein synthesis involves amino acid activation by tRNA synthetases using ATP, followed by peptide bond formation powered by GTP during translation.
例如，蛋白质合成涉及氨酰-tRNA 合成酶利用 ATP 活化氨基酸，随后在翻译过程中由 GTP 提供能量形成肽键。
Plants also use energy from ATP and reduced NADP in the Calvin cycle to convert carbon dioxide into triose phosphate and eventually glucose.
植物在卡尔文循环中还利用 ATP 和还原型 NADP 的能量，将二氧化碳转化为磷酸丙糖并最终生成葡萄糖。
7. Movement and Muscle Contraction | 运动与肌肉收缩
Movement at the cellular level, such as ciliary beating, flagellar motion, and cytoplasmic streaming, depends on ATP. In animals, skeletal muscle contraction is a major consumer of ATP.
细胞层面的运动，如纤毛摆动、鞭毛运动和细胞质环流，都依赖 ATP。在动物体内，骨骼肌收缩是 ATP 的主要消耗者。
During muscle contraction, myosin heads bind to actin and perform a power stroke. ATP binding to myosin releases the head from actin, and ATP hydrolysis re-energises the myosin head for the next cycle. Without ATP, muscles remain locked in rigor.
在肌肉收缩过程中，肌球蛋白头部与肌动蛋白结合并完成动力冲程。ATP 与肌球蛋白结合使头部与肌动蛋白解离，ATP 水解为肌球蛋白头部重新供能以进入下一循环。没有 ATP，肌肉将僵直锁定。
ATP is also needed to pump Ca²⁺ back into the sarcoplasmic reticulum during muscle relaxation, so active transport is essential to end contraction.
肌肉舒张时，还需要 ATP 将 Ca²⁺ 泵回肌质网，因此主动运输对终止收缩至关重要。
8. Maintenance of Body Temperature | 维持体温
In mammals and birds, a large proportion of the energy released by respiration is converted to heat. This is because energy transfers in living systems are never 100% efficient, and much of the free energy from glucose oxidation is lost as thermal energy.
在哺乳类和鸟类中，呼吸作用释放的能量有很大一部分转化为热量。这是因为生物系统中的能量传递永远不会达到 100% 的效率，葡萄糖氧化释放的自由能大部分以热能形式散失。
This heat is not wasted in endotherms. It is used to maintain a constant core body temperature, allowing enzymes to work at their optimum even when the external environment is cold.
对恒温动物而言，这些热量并非浪费。它被用来维持恒定的核心体温，使酶即使在寒冷的外界环境中也能处于最适温度下工作。
In cold conditions, shivering involves rapid muscle contractions, and non-shivering thermogenesis in brown fat uses uncoupling proteins to increase ATP-independent respiration and heat production.
在寒冷条件下，战栗涉及快速的肌肉收缩；棕色脂肪中的非战栗产热利用解偶联蛋白，增加不依赖 ATP 的呼吸作用并提高产热。
9. Nerve Impulse Transmission | 神经冲动传导
Neurones transmit information using action potentials, which depend on the unequal distribution of Na⁺ and K⁺ ions across the membrane. The sodium-potassium pump uses ATP to maintain these gradients, so without ATP, nerve signalling quickly fails.
神经元通过动作电位传递信息，而动作电位依赖 Na⁺ 和 K⁺ 在膜两侧的不均匀分布。钠钾泵利用 ATP 维持这些梯度，因此没有 ATP，神经信号传导会迅速失效。
ATP is also needed for the synthesis, packaging, and release of neurotransmitters at synapses. Vesicular transport and exocytosis of synaptic vesicles require energy derived from ATP hydrolysis.
突触处神经递质的合成、包装和释放也需要 ATP。突触囊泡的转运和胞吐作用依赖 ATP 水解释放的能量。
In sensory receptors, ATP is required to restore ionic balance after stimulation, and in the visual cycle it helps regenerate rhodopsin after light absorption.
在感觉受体中，ATP 用于在刺激后恢复离子平衡；在视觉循环中，ATP 帮助光吸收后视紫红质的再生。
10. Bioluminescence and Other Specialised Processes | 生物发光及其他特殊需能过程
Some organisms, such as fireflies and certain marine bacteria, use ATP to produce light. The enzyme luciferase catalyses the oxidation of luciferin, and ATP is required to activate luciferin before light is emitted.
一些生物，如萤火虫和某些海洋细菌，利用 ATP 产生光。荧光素酶催化荧光素的氧化，而荧光素在发光前需要 ATP 活化。
Other specialised processes include the generation of electric fields by electric eels, production of defensive chemicals, active uptake of mineral ions by root hairs, and excretion of wastes against concentration gradients.
其他特殊过程包括电鳗产生电场、防御性化学物质的合成、根毛对矿质离子的主动吸收以及逆浓度梯度排泄废物。
Cell division also has a high energy demand. ATP is needed for spindle fibre movement, chromosome separation, and re-formation of nuclear membranes and the cell membrane during cytokinesis.
细胞分裂对能量需求也很高。纺锤丝运动、染色体分离以及胞质分裂中核膜和细胞膜的重新形成都需要 ATP。
11. Overview: Respiration and Photosynthesis Supply ATP | 呼吸作用与光合作用提供 ATP
Heterotrophs obtain ATP mainly through aerobic respiration in mitochondria. The complete oxidation of one glucose molecule can yield up to about 32 ATP molecules, although the exact number depends on the shuttle system and proton leak.
异养生物主要在线粒体中通过有氧呼吸获得 ATP。一分子葡萄糖完全氧化最多可产生约 32 分子 ATP，但具体数量取决于穿梭系统和质子泄漏。
Respiration includes glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation. In oxidative phosphorylation, electrons are transferred through the electron transport chain, and chemiosmosis uses the resulting proton gradient to drive ATP synthase.
呼吸作用包括糖酵解、连接反应、克雷布斯循环和氧化磷酸化。在氧化磷酸化中，电子通过电子传递链传递，化学渗透利用由此形成的质子梯度驱动 ATP 合酶。
Autotrophs generate ATP during the light-dependent reactions of photosynthesis. Light energy excites chlorophyll, drives photophosphorylation, and produces ATP along with reduced NADP for use in the Calvin cycle.
自养生物在光合作用的光依赖反应中生成 ATP。光能激发叶绿素，驱动光合磷酸化，产生 ATP 和还原型 NADP，供卡尔文循环使用。
12. Energy Flow and Loss as Heat | 能量流动与热散失
Energy enters most ecosystems as sunlight, is converted to chemical energy by producers, and is passed to consumers through feeding. At each trophic level, much energy is lost as heat through respiration and as undigested waste
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