IB Biology: Cellular Respiration Key Points | IB 生物：呼吸作用 考点精讲

📚 IB Biology: Cellular Respiration Key Points | IB 生物：呼吸作用 考点精讲

Cellular respiration is the cornerstone of energy metabolism in living organisms. It is a series of metabolic pathways that convert chemical energy stored in organic molecules, such as glucose, into adenosine triphosphate (ATP), the universal energy currency of the cell. Understanding respiration is essential for IB Biology, as it ties together concepts of biochemistry, cell structure, and physiological adaptation.

细胞呼吸是生物体能量代谢的基石。它是一系列代谢途径，能将储存在葡萄糖等有机分子中的化学能转化为三磷酸腺苷（ATP），即细胞的通用能量货币。理解呼吸作用对于IB生物至关重要，因为它将生物化学、细胞结构和生理适应等概念紧密联系在一起。

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

The overall equation for aerobic respiration is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (as ATP). This exergonic process involves the oxidation of glucose and the reduction of oxygen. Respiration can be divided into four main stages: glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation (which includes the electron transport chain and chemiosmosis).

有氧呼吸的总反应式为：C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 能量（以ATP形式）。这一放能过程涉及葡萄糖的氧化和氧的还原。呼吸作用可分为四个主要阶段：糖酵解、链接反应、克雷布斯循环以及氧化磷酸化（包括电子传递链和化学渗透）。

In eukaryotic cells, glycolysis occurs in the cytoplasm, while the remaining stages take place in the mitochondria. The process couples exergonic electron transfer to endergonic ATP synthesis via chemiosmosis. IB students should be able to explain how the structure of the mitochondrion enables this compartmentalisation.

在真核细胞中，糖酵解发生在细胞质中，其余阶段发生在线粒体内。该过程通过化学渗透将放能的电子传递与吸能的ATP合成偶联起来。IB学生应能解释线粒体的结构如何实现这种区室化。

2. Glycolysis: Breaking Down Glucose | 糖酵解：分解葡萄糖

Glycolysis occurs in the cytosol and does not require oxygen. It breaks down one molecule of glucose (6C) into two molecules of pyruvate (3C). The process consists of ten enzyme‑catalysed steps and can be divided into an energy‑investment phase and an energy‑payoff phase.

糖酵解发生在细胞质中，且不需要氧气。它将一分子葡萄糖（6碳）分解为两分子丙酮酸（3碳）。该过程包含十步酶促反应，可分为耗能阶段和放能阶段。

During the energy‑investment phase, two ATP molecules are used to phosphorylate glucose, forming fructose‑1,6‑bisphosphate. This molecule is then split into two triose phosphates. In the energy‑payoff phase, each triose phosphate is oxidised, producing two molecules of ATP (substrate‑level phosphorylation) and one molecule of NADH. Since each glucose yields two triose phosphates, the net gain is 2 ATP and 2 NADH per glucose.

在耗能阶段，消耗两分子ATP将葡萄糖磷酸化，形成果糖-1,6-二磷酸。然后该分子裂解为两个三碳糖磷酸。在放能阶段，每个三碳糖磷酸被氧化，通过底物水平磷酸化产生两分子ATP和一分子NADH。由于每个葡萄糖生成两个三碳糖磷酸，最终每分子葡萄糖净得2 ATP和2 NADH。

Phosphofructokinase (PFK) is a key regulatory enzyme in glycolysis, inhibited by high levels of ATP and citrate, and activated by AMP. This feedback ensures that glycolysis proceeds only when the cell’s energy status is low.

磷酸果糖激酶（PFK）是糖酵解中的关键调节酶，受高浓度ATP和柠檬酸抑制，被AMP激活。这种反馈机制确保仅在细胞能量不足时糖酵解才会进行。

3. The Link Reaction: Pyruvate Oxidation | 链接反应：丙酮酸氧化

Upon entering the mitochondrial matrix, each pyruvate undergoes oxidative decarboxylation, catalysed by the pyruvate dehydrogenase complex. This irreversible reaction removes one carbon atom as CO₂, oxidises the remaining two‑carbon fragment to an acetyl group, and attaches it to coenzyme A (CoA) to form acetyl‑CoA. One molecule of NAD⁺ is reduced to NADH + H⁺ per pyruvate.

丙酮酸进入线粒体基质后，在丙酮酸脱氢酶复合体催化下发生氧化脱羧。这一不可逆反应脱去一个碳原子生成CO₂，将剩下的二碳片段氧化成乙酰基，并将其连接到辅酶A（CoA）上形成乙酰辅酶A。每分子丙酮酸还将一分子NAD⁺还原为NADH + H⁺。

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