📚 Mitochondrial Structure and Function | 线粒体的结构与功能
Mitochondria are double-membrane-bound organelles found in the cytoplasm of most eukaryotic cells. They are central to aerobic respiration, producing the majority of ATP required for cellular work. In addition to ATP synthesis, mitochondria participate in apoptosis, calcium storage and metabolic regulation.
线粒体是大多数真核细胞质中存在的双膜细胞器。它们是有氧呼吸的核心场所，产生细胞活动所需的大部分 ATP。除 ATP 合成外，线粒体还参与细胞凋亡、钙储存和代谢调节。
1. Overview of Mitochondrial Structure | 线粒体结构概述
A mitochondrion typically has a rod-shaped or oval profile, about 0.5-1.0 μm in diameter and 2-8 μm in length. Its most distinctive feature is the presence of two membranes: a smooth outer membrane and a highly folded inner membrane. These membranes create two separate compartments: the intermembrane space and the matrix.
线粒体通常呈杆状或椭圆形，直径约 0.5-1.0 微米，长度约 2-8 微米。其最显著的特征是具有两层膜：光滑的外膜和高度折叠的内膜。这两层膜形成两个独立的区室：膜间隙和基质。
The number of mitochondria per cell varies with energy demand. Muscle and liver cells contain many mitochondria, whereas mature red blood cells have none.
每个细胞中的线粒体数量随能量需求而变化。肌肉细胞和肝细胞含有大量线粒体，而成熟红细胞没有线粒体。
Under the electron microscope, the inner membrane can be seen projecting into the matrix as cristae, giving the organelle a compartmentalised appearance. This compartmentalisation is essential for establishing proton gradients during oxidative phosphorylation.
在电子显微镜下，可以看到内膜以嵴的形式伸入基质，使该细胞器呈现区室化结构。这种区室化对于氧化磷酸化过程中建立质子梯度至关重要。
2. Outer Mitochondrial Membrane | 线粒体外膜
The outer mitochondrial membrane is a phospholipid bilayer that encloses the entire organelle. It contains many integral proteins called porins, which form large non-selective channels. As a result, the outer membrane is freely permeable to small molecules and ions up to about 5000 Da.
线粒体外膜是包围整个细胞器的磷脂双分子层。它含有许多称为孔蛋白的整合蛋白，形成大型非选择性通道。因此，外膜对分子量约 5000 Da 以下的小分子和离子具有自由通透性。
Larger proteins cannot pass through porins easily. Those destined for the intermembrane space or matrix must be imported by specific translocase complexes. The outer membrane also interacts with the endoplasmic reticulum at contact sites involved in lipid transfer and calcium signalling.
较大的蛋白质不容易通过孔蛋白。那些要进入膜间隙或基质的蛋白质必须由特定的转位酶复合体输入。外膜还在与内质网的接触位点发生相互作用，参与脂质转移和钙信号传导。
3. Inner Mitochondrial Membrane and Cristae | 线粒体内膜与嵴
The inner mitochondrial membrane is folded into numerous cristae, which greatly increase its surface area. It is rich in the phospholipid cardiolipin, which makes the membrane particularly impermeable to ions and protons. This impermeability is vital because a proton gradient must be maintained across the inner membrane.
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