Cell Contents | 细胞内容物

📚 Cell Contents | 细胞内容物

Cell contents refer to all substances and structures enclosed within the plasma membrane. In A-Level Biology, a detailed knowledge of cellular components and their functions is essential for understanding everything from respiration to protein synthesis. This article covers eukaryotic and prokaryotic cell contents, including organelles, the cytoskeleton, and inclusions, along with experimental techniques.

细胞内容物是指质膜内包裹的所有物质和结构。在A-Level生物学中，详细掌握细胞组分及其功能对于理解从呼吸作用到蛋白质合成的所有过程至关重要。本文涵盖了真核和原核细胞内容物，包括细胞器、细胞骨架和内含物，以及相关的实验技术。

1. Overview of Cell Contents | 细胞内容物概览

All living cells contain a complex mixture of water, ions, macromolecules, and organised structures. The nature of these contents distinguishes prokaryotic cells, which lack membrane-bound organelles, from eukaryotic cells, where compartmentalisation is a defining feature.

所有活细胞都含有水、离子、大分子和有组织结构构成的复杂混合物。这些内容物的性质区分了缺乏膜包被细胞器的原核细胞与以区域化为标志的真核细胞。

Key eukaryotic cell contents include the nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, peroxisomes, ribosomes, the cytoskeleton, and various inclusions. Each contributes to cell maintenance, growth, and division.

真核细胞的关键内容物包括细胞核、内质网、高尔基体、线粒体、溶酶体、过氧化物酶体、核糖体、细胞骨架以及各种内含物。每部分都参与细胞的维持、生长和分裂。

Prokaryotic cell contents are simpler but equally vital: a circular DNA molecule, ribosomes, storage granules, and sometimes plasmids, flagella, and a capsule.

原核细胞内容物更简单但同样重要：一个环状DNA分子、核糖体、储存颗粒，有时还有质粒、鞭毛和荚膜。

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2. The Cytoplasm and Cytosol | 细胞质与细胞溶胶

The cytoplasm comprises all cell contents except the nucleus. Within it, the fluid component is called cytosol, a viscous aqueous solution containing enzymes, amino acids, nucleotides, and inorganic ions.

细胞质包括除细胞核外的全部内容物。其中液体组分被称为细胞溶胶，是一种粘稠的水溶液，含有酶、氨基酸、核苷酸和无机离子。

Many metabolic reactions, such as glycolysis, occur in the cytosol. The cytosol also serves as a medium for the movement of molecules and organelles, aided by the cytoskeleton.

许多代谢反应（如糖酵解）在细胞溶胶中进行。细胞溶胶还作为分子和细胞器运动的介质，这一过程由细胞骨架辅助。

The pH of the cytosol is typically around 7.2, and it contains dissolved proteins that buffer changes. The cytosol’s viscosity is higher than that of water, which influences diffusion rates.

细胞溶胶的pH通常约为7.2，并含有可缓冲变化的溶解蛋白质。其粘度高于水，这影响着扩散速率。

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3. Endoplasmic Reticulum (ER) | 内质网

The endoplasmic reticulum is a network of membrane-bound sacs and tubules continuous with the nuclear envelope. Rough ER is studded with ribosomes and is the site of protein synthesis for secretion or membrane insertion.

内质网是由与核被膜相连的膜包被囊泡和管道构成的网络。粗面内质网上附着核糖体，是分泌蛋白或膜蛋白合成的场所。

Proteins synthesised on rough ER enter its lumen, where they fold and undergo modifications such as glycosylation. Smooth ER lacks ribosomes and is involved in lipid synthesis, carbohydrate metabolism, and detoxification of drugs and poisons.

在粗面内质网上合成的蛋白质进入其内腔，在其中折叠并进行糖基化等修饰。滑面内质网无核糖体，参与脂质合成、碳水化合物代谢以及药物和毒物的解毒。

In muscle cells, the smooth ER stores and releases calcium ions essential for contraction. In liver cells, it plays a major role in breaking down stored glycogen.

在肌肉细胞中，滑面内质网储存并释放收缩所必需的钙离子。在肝细胞中，它在分解储存的糖原中起主要作用。

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4. Golgi Apparatus | 高尔基体

The Golgi apparatus consists of flattened membrane sacs called cisternae. It receives proteins and lipids from the ER, modifies them, and sorts them for transport to their final destinations.

高尔基体由扁平的膜囊（潴泡）组成。它接受来自内质网的蛋白质和脂质，对其进行修饰，并将其分选转运到最终目的地。

Modifications include further glycosylation, phosphorylation, and proteolytic cleavage. The Golgi also synthesises certain polysaccharides and forms lysosomes by budding off vesicles containing digestive enzymes.

修饰包括进一步的糖基化、磷酸化和蛋白酶切。高尔基体还合成某些多糖，并通过出芽形成含有消化酶的囊泡来产生溶酶体。

Vesicles leaving the trans face of the Golgi can fuse with the plasma membrane for exocytosis, or with other organelles. The cis face receives vesicles from the ER.

离开高尔基体反面膜囊的囊泡可与质膜融合进行胞吐，或与其他细胞器融合。顺面膜囊接收来自内质网的囊泡。

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5. Mitochondria | 线粒体

Mitochondria are double-membrane organelles responsible for aerobic respiration. The inner membrane is highly folded into cristae, which increase the surface area for ATP production via the electron transport chain and ATP synthase.

线粒体是双膜细胞器，负责有氧呼吸。内膜高度折叠成嵴，增加了通过电子传递链和ATP合酶产生ATP的表面积。

The mitochondrial matrix contains enzymes for the Krebs cycle, mitochondrial DNA, and ribosomes. Mitochondria are found in large numbers in metabolically active cells such as muscle fibres and sperm.

线粒体基质含有参与Krebs循环的酶、线粒体DNA和核糖体。线粒体在代谢活跃的细胞（如肌纤维和精子）中大量存在。

According to the endosymbiotic theory, mitochondria originated from free-living aerobic bacteria that were engulfed by ancestral eukaryotic cells.

根据内共生学说，线粒体来源于被祖先真核细胞吞噬的自由生活的需氧细菌。

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6. Lysosomes and Peroxisomes | 溶酶体与过氧化物酶体

Lysosomes are membrane-bound vesicles containing hydrolytic enzymes such as proteases, lipases, and nucleases. They digest worn-out organelles, engulfed pathogens, and cellular debris in a process called autophagy.

溶酶体是含有蛋白酶、脂肪酶和核酸酶等水解酶的膜包被囊泡。它们通过自噬过程消化老化的细胞器、被吞入的病原体和细胞碎片。

The internal pH of lysosomes is around 5.0, maintained by proton pumps, which provides the optimal environment for their enzymes. Peroxisomes contain oxidases that produce hydrogen peroxide, which is then broken down by catalase.

溶酶体内部pH值约为5.0，由质子泵维持，为其酶提供最适环境。过氧化物酶体含有氧化酶，可产生过氧化氢，后者随后被过氧化氢酶分解。

Peroxisomes are particularly abundant in liver and kidney cells, where they detoxify harmful substances. Unlike mitochondria, they are not thought to have arisen by endosymbiosis.

过氧化物酶体在肝和肾细胞中尤为丰富，用来解毒有害物质。与线粒体不同，它们并非通过内共生起源。

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7. Ribosomes | 核糖体

Ribosomes are the sites of protein synthesis, translating messenger RNA into polypeptides. They consist of two subunits made of ribosomal RNA and proteins.

核糖体是蛋白质合成的场所，将信使RNA翻译为多肽。它们由核糖体RNA和蛋白质组成的两个亚基构成。

Eukaryotic ribosomes are 80S (composed of 60S and 40S subunits), while prokaryotic ribosomes are 70S (50S and 30S). This difference is exploited by antibiotics that selectively target bacterial ribosomes.

真核生物核糖体为80S（由60S和40S亚基组成），而原核生物核糖体为70S（50S和30S）。这一差异被抗生素利用，可选择性地靶向细菌核糖体。

Ribosomes can be free in the cytosol, synthesising proteins for intracellular use, or bound to the rough ER, producing proteins destined for secretion or membranes.

核糖体可游离于细胞溶胶中，合成胞内使用的蛋白质；或结合在粗面内质网上，生产用于分泌或膜结合的蛋白质。

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8. The Cytoskeleton | 细胞骨架

The cytoskeleton is a dynamic network of protein filaments that extends throughout the cytoplasm. It provides mechanical support, maintains cell shape, and enables cell movement and intracellular transport.

细胞骨架是贯穿细胞质的动态蛋白质纤维网络。它提供机械支撑、维持细胞形状，并使细胞运动和胞内运输成为可能。

Three main types of fibres exist: microfilaments (actin), about 7 nm in diameter, involved in contraction and cell division; microtubules (tubulin), 25 nm, which form the spindle and tracks for motor proteins; and intermediate filaments (e.g. keratin), 10 nm, providing tensile strength.

存在三种主要纤维：微丝（肌动蛋白），直径约7 nm，参与收缩和细胞分裂；微管（微管蛋白），25 nm，形成纺锤体并作为马达蛋白的轨道；中间丝（如角蛋白），10 nm，提供抗张强度。

Microtubules also make up centrioles, cilia, and flagella. The sliding of microtubules drives the beating of cilia and flagella in a ‘9+2’ arrangement.

微管还构成中心粒、纤毛和鞭毛。微管的相对滑动以“9+2”排列的形式驱动纤毛和鞭毛的摆动。

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9. Cellular Inclusions | 细胞内含物

Inclusions are non-living, temporary components of the cell, not bounded by membranes. They often serve as storage of nutrients, secretory products, or pigment granules.

内含物是细胞中非生命的、临时的组成成分，无膜包被。它们通常用于储存营养物质、分泌产物或色素颗粒。

Common inclusions in plant cells are starch grains in chloroplasts or amyloplasts. Animal cells may contain glycogen granules, lipid droplets in adipocytes, and melanin in skin cells.

植物细胞常见的内含物是叶绿体或淀粉体中的淀粉粒。动物细胞可能含有糖原颗粒、脂肪细胞中的脂滴，以及皮肤细胞中的黑色素。

Unlike organelles, inclusions are not involved in active metabolism but represent accumulated products that can be mobilised when the cell requires energy or building blocks.

与细胞器不同，内含物不参与活跃代谢，而是代表积累的产物，当细胞需要能量或原料时可被动员。

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10. Prokaryotic Cell Contents | 原核细胞内容物

Prokaryotic cells, such as bacteria, have no membrane-bound nucleus. Their genetic material consists of a single circular DNA molecule located in a region called the nucleoid.

原核细胞（如细菌）无膜包被的细胞核。它们的遗传物质由位于类核区的单个环状DNA分子组成。

Plasmids, small extra-chromosomal DNA circles, often carry genes for antibiotic resistance and can be exchanged between bacteria. The cytoplasm contains 70S ribosomes, storage granules, and enzymes, but no ER, Golgi, or mitochondria.

质粒是额外的染色体外DNA小环，常携带抗生素抗性基因，并可在细菌间交换。细胞质含有70S核糖体、储存颗粒和酶，但没有内质网、高尔基体或线粒体。

Many prokaryotes possess a rigid cell wall of peptidoglycan, a capsule for protection, and flagella for motility. Some also have pili for attachment. Respiration occurs across the cell membrane.

许多原核生物具有由肽聚糖构成的坚硬细胞壁、用于保护的荚膜，以及用于运动的鞭毛。有些还有用于附着的菌毛。呼吸作用跨细胞膜进行。

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11. Studying Cell Contents | 研究细胞内容物

To investigate cellular contents, light microscopes reveal basic structures, while transmission electron microscopes (TEM) resolve organelles down to the nanometre scale. Cell fractionation is the key experimental technique for isolating components.

为研究细胞内容物，光学显微镜可显示基本结构，而透射电子显微镜（TEM）可分辨纳米级别的细胞器。细胞分级分离是分离各组分的关键实验技术。

In cell fractionation, tissues are homogenised in a cold, isotonic buffer with a pH buffer to prevent enzyme denaturation and osmotic damage. The homogenate is then subjected to differential centrifugation.

在细胞分级分离中，组织在冷的等渗缓冲液和pH缓冲剂中匀浆，以防酶变性和渗透损伤。然后对匀浆进行差速离心。

At low speeds, nuclei and debris pellet; higher speeds yield mitochondria and lysosomes; ultracentrifugation isolates microsomes (ER fragments) and ribosomes. Purity can be assessed using marker enzymes or electron microscopy.

低速离心时，细胞核和碎片沉淀；较高速度得到线粒体和溶酶体；超速离心可分离微粒体（内质网碎片）和核糖体。纯度可用标志酶或电子显微镜评估。

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