制作临时的样本#

• Cut thin sections of the material to be examined 切片
• Stain 染色
• Mount the specimen on a clean glass slide 放到载玻片上
• Lower the coverslip over the specimen (to prevent the specimen drying out) 覆盖

光学显微镜和电子显微镜的对比

There are two types of electron microscope 有两种电子显微镜:

• Transmission Electron Microscope 穿透电子显微镜: 2D image, can see interior details 可以呈现出 2D 的图像，并且可以看到细胞内的结构。

• Scanning Electron Microscope 扫描电子显微镜: 3D image, can only see surface structures 可以看到细胞表面的 3D 结构。

Magnification and Resolution#

Magnification 放大倍数: the number of times larger an image is compared to the object’s size. 图像比实物大多少倍。

Resolution 分辨率: The ability to distinguish between two separate points. 能分辨出两个很近的物体的能力。

The maximum resolution can be calculated from the wave length of radiation used to view the specimen.

最大的分辨率（分辨率的极限）能通过观察光的波长计算出来，例如使用波长为 500nm 的光观察一个物体，那么这个物体的最大分辨率为 250nm。

Cell Surface Membrane / plasma Membrane 细胞膜#

• Partially permeable / semi-permeable 半透的

• Control the exchange of materials between the cell and its environment

  控制进出细胞的物质

Cell Wall 细胞壁#

• Fully permeable 全透的 - All the substances can pass through it 全部物质都可以通过

• Protect and prevent the cell from bursting when water enters by osmosis

  防止细胞内水分太多时破裂

• Resist turgor pressure 抵抗膨压

• Cell wall is relatively rigid and gives the cell a definite shape

  细胞壁相对而言比较坚固，可以给细胞提供一个稳定的形状

• Cell wall of plant cells is made of cellulose

  植物的细胞壁由纤维素*(C₆H₁₀O₅)n*构成

Plasmodesma (plural: plasmodesmata) 胞间连丝#

• A pore-like structure 孔状的结构

• Plant cells are linked to neighbouring cells by plasmodesmata

  相邻的植物细胞通过胞间连丝相连

• Contain fine strands of cytoplasm, allowing the controlled passage of materials from one cell to the other

  含有细小的细胞质链，可以控制物质在细胞间的传输

Cytoplasm 细胞质#

The contents of a cell inside the cell surface membrane, excluding the nucleus. Cytoplasm contains organelles, e.g. ribosomes or mitochondrion

细胞质指的是细胞内除了细胞核之外的所有物质以及细胞器，像是 mitochondrion 和 robosome 之类的细胞器就被包括在细胞质里。

Cytosol is the solution of the cytoplasm, in which the organelles are suspended.

细胞溶质是细胞质中的溶液，其中的细胞器都属于悬浮的状态。

如果把一个细胞想象成一杯珍珠奶茶，那么…

• 奶茶杯 = Cell Surface Membrane
• 奶茶以及加料 = Cytoplasm
• 奶茶本身 = Cytosol
• 加料 = Organelles

Nucleus (plural: nuclei) 细胞核#

• Contain the genetic material (DNA, chromatin and chromosome)

  包含遗传物质：DNA、染色质和染色体

• DNA contains the instructions / genes that control the activities of the cell, e.g. control protein synthesis

  DNA 含有细胞活动的指令（或基因），可以控制包括蛋白质合成等一系列活动

• Contains nucleolus (plural: nucleoli), one or more may be present in one nucleus

  包含一个或多个核仁

• Nucleolus is the place of making ribosome 核仁负责生产核糖体

When a cell is not dividing/not during nuclear division, the material containing DNA is called chromatin. Chromatin is loosely coiled and thread-like. It’s long, thin and in a loose form.

when a cell is dividing/during nuclear division, the material containing DNA is called chromosomes. Chromosomes are condensedfrom chromatin. They are short and thick and in a condensed form.

通常来说一个细胞只会有一个细胞核，但是每个细胞的情况不一样，例如：

• 血红细胞为了运输氧气没有细胞核
• 肝脏里的细胞有多个细胞核
• Skeletal muscle cells 有多个细胞核
• 部分真细胞有多个细胞核

The nucleus is surrounded by two membranes called the nuclear envelope, the nuclear envelope has many small pores called nuclear pores.

细胞核被一种叫做核被膜的“双膜”结构所包围，核被膜上的小孔成为核孔。

Mitochondrion (plural: mitochondria) 线粒体#

• surrounded by two membranes (a mitochondrial envelope).

  被线粒体包膜（一种双膜结构）包围

• The inner membrane is folded to form cristae (singular: crista) to increase surface area

  内层的膜会折叠成cristae（一种凸起的结构），用于增加表面积

• the interior of the mitochondrion is called the matrix

  线粒体中的内部区域被称为matrix，是主要进行有氧呼吸的场所

• The space between the two membranes is called the intermembrane space

  两层膜之间的空间被称为膜间空间

Cells with a high demand for energy, such as liver and muscle cells, contain large numbers of mitochondria.

在需要大量能量的细胞（例如肝脏细胞和肌肉细胞）中含有大量的线粒体。

Mitochondria carry out aerobic respiration to release energy/produce ATP.

线粒体会通过有氧呼吸释放能量/产生ATP。

注意：能量不可以被产生，只能转化。Energy can only be released, not produced

ATP 是能量的载体，能量在 ATP 中被储存为化学势能（Chemical Potential Energy）

ATP produced in mitochondria is used for energy consuming activities in cells, such as muscle contraction, protein synthesis, exocytosis and active transport.

在线粒体中产生的 ATP 会在肌肉收缩、蛋白质合成、胞吐或主动运输等需要能量的细胞活动中消耗掉。

ATP 分子遇到水分子时会发生水解反应（Hydrolysis）：To break bonds between phosphate groups and release energy. 当分子间的化学键断裂时会释放能量。

在图片中线粒体有不同的形状，有的是圆形的，有的是胶囊形的，这是因为两个原因：

1. Mitochondria can change shape. 线粒体可以改变形状
2. They are cut at different angles. Some are cut through transverse section and some through longitudinal section. 展示的角度不一样，有的展示的是横切面，有的则是纵切面。

Many mitochondria are sausage-like. But they can change shape and divide.

大多数线粒体都是胶囊形（或者说“香肠形”的），但是它们仍然可以变换形状

Chloroplast 叶绿体#

Inside the chloroplast 叶绿体的内部

• Chloroplast envelope 叶绿体包膜
• 70S ribosome 核糖体
• Circular DNA in stroma 基质中的环状 DNA
• grana made of thylakoid membranes 由类囊体膜构成的颗粒
• Starch grains 淀粉粒

Thylakoids 类囊体 - fuild-filled sacs

Chloroplasts carry out photosynthesis to produce glucose / carbohydrate. 叶绿素会通过光合作用生产葡萄糖 / 碳水化合物。

Not all plant cells have chloroplast. For example, plant cells in the root have no chloroplast.

并不是所有的植物细胞都有叶绿体，比如不需要光合作用的根毛细胞就没有。

ATP produced in chloroplast is used in photosynthesis.

ATP 也会在叶绿体中产生，但是这里产生的 ATP 会被主要用于光合作用。

Vacuole 液泡#

Animal cells may possess small, temporary vacuoles, or called vesicle

动物细胞中也有类似于液泡的结构，被称为囊泡。只不过囊泡不是永久存在的，而且相对于液泡来说非常小

• Surrounded by tonoplas 被液泡膜所覆盖

Functions:

• Support 里面的液体会撑起整个细胞
• Lysosomal activity - Plant vacuoles may contain hydrolases and act as lysosomes. 提供和 lysosome 类似的功能
• Secondary metabolites 有一些生长相关，但比较次要的物质可以储存在液泡中
• Food reserves 溶解了的果糖和矿物离子会储存在液泡中
• Waste products 暂时储存一些没有用的东西
• Growth in size 水通过渗透作用进入细胞会增大细胞的体积

The solution in the vacuole is called cell sap, it contains:

• pigments
• enzymes
• sugars (glucose)
• minieral ions
• oxygen
• carbon dioxide
• …

液泡中的溶液被称为细胞液，它包含了：

• 色素
• 酶
• 糖（葡萄糖）
• 矿物离子
• 氧气
• 二氧化碳
• ……

Vacuoles help to regulate the osmotic properties fo cells (the flow of water inwards and outwards by osmosis) and support the stems of the plants.

液泡中的液体会平衡细胞的“渗透”作用，并且里面的液体会撑起细胞，乃至于让植物的茎呈现挺立的状态。

The pigments colour the petals of certain flowers and the parts of some vegetables.

液泡中的色素会赋予某些花瓣和植物丰富的颜色。

Endoplasmic Reticulum 内质网#

The endoplasmic reticulum consists of flattened sacs of membrane called cisternae.

内质网由称为囊泡的扁平膜囊组成。

Use the full name when answer is endoplasmic reticulum and do not say ‘ER’

在考试的时候尽量不要使用 ER 这个简写，而是使用全称 Endoplasmic reticulum

There are two types of endoplasmic reticulum:

• Rough ER - covered with many ribosomes
• Smooth ER - lacks ribosomes

内质网分为两种：

• 粗面内质网 - 覆盖着许多核糖体
• 光滑内质网 - 缺乏核糖体

The membrane of rough endoplasmic reticulum is continuous with the outer membrane of the nuclear envelope, and covered by ribosomes. It’s responsible for making protein, transport protein or modify proteins (deal with proteins).

粗面内质网和细胞核的外层相连，并且上面有许多核糖体（核糖体的存在使这种内质网表面变得粗糙，这也是它名字的由来）。它负责生产蛋白质、运输蛋白质或者操作蛋白质（总之就是负责和蛋白质相关的一些事物）。

Smooth ER lacks ribosomes, the membrane of smooth ER is not continuous with the outer membrane of the nuclear envelope. It makes lipids and steroids, and it’s also the major storage site for calcium ions.

光滑内质网几乎没有核糖体，并且它的膜并不与细胞核相连。它负责生产脂质和类固醇，它还是储存钙离子的主要地方。

Golgi body / apparatus 高尔基体#

• Can be seen under a light microscope 可以在光学显微镜下观察到

Golgi body is made of cisternae, and constantly being formed at one end from vesicles which bud off from the rough ER, and are broken down again at the other end to form Golgi vesicles

高尔基体由囊泡构成，会在粗面内质网的一段生成，并且在另一端被分解成高尔基小泡

在 Goblet cell 中含有大量的Glogi bodies，Goblet cell 需要产生大量的分泌物

Functions:

• modify proteins from the rough ER (sugars are added to proteins to make glycoproteins)

  进一步操作来自 rough ER 的蛋白质

• Make glycolipid

• package and transprot proteins in Golgi vesicles to other parts of the cell or for secretion/exocytosis

  把蛋白质运输到细胞的其他地方

• some Golgi vesicles are used to make lysosome (remain in Golgi body)

  部分高尔基小泡会被用于制作溶酶体

Golgi vesicles can…

• carry the protein to the cell membrane for exocytosis 运输功能
• remain in the cell as lysosome 作为溶酶体留在细胞中

mRNA 在细胞核中产生，然后移动到 Rough ER 表面的核糖体上，并产生蛋白质。vesicle from rough ER 会携带蛋白质到 Golgi body。Proteins are modify in Golgi body and Golgi vesicle carries the modified proteins to the cell surface membrane for exocytosis.

• A: protein made on the ribosome is moving into the rough ER

  蛋白质在核糖体中产生，并移动到粗面内质网中

• B: rough ER buds of small vesicles, vesicles fuse to form the Golgi apparatus, therefore protein moves into Golgi apparatus. Protein may be modified / processed inside Golgi apparatus

  蛋白质通过运输小泡（Transport Vesicle）从粗面内质网移动到高尔基体，并在高尔基体中进一步加工

• C: Golgi apparatus buds off Golgi vesicles

  高尔基体分离出高尔基小泡

• D: Golgi vesicles travel to cell surface membrane, Golgi vesicle fuses with enzyme leaves cell or responsible for exocytosis

  蛋白质通过高尔基小泡移动到细胞膜上

• E: ribosome or mRNA leaves the nucleus

  核糖体或者 mRNA 来自细胞核

Ribosome 核糖体#

• Made of rRNA and proteins

• Have a large subunit and a small subunit

• Function: make proteins

• 25nm in diameter

70S ribosome has a smaller size, it can be found in mitochondria and chlroplasts.

80S ribosome has a larger size, it can be found in cytoplasm and rough ER.

• Ribosomes are found in all types of cells

Lysosome 溶酶体#

• Simple sacs surrounded by a single membrane

• Contains digestive / hydrolytic enzymes, these enzymens must be kept seperate from the rest fo the cell to prevent damage. 溶酶体中包含消化酶/水解酶，这些酶必须和细胞的其他部分隔绝，不然细胞的其他部分有可能被溶酶体中的消化酶分解

  Digestive Enzymes:

  • Amylase
  • Maltase
  • Lactase
  • Lipase
  • Sucrase
  • Proteases

  hydrolases: hydrolytic enzymes,which carry out hydrolysis reactions

  水解酶：进行水解反应的酶

• Functions: breakdown / digest unwanted substances and structures such as old organelles or even whole cells. 分解不需要的物质，例如老旧的细胞器或者说一整个不用了的细胞

• The contents of lysosomes are acidic, pH 4 - 5 compared with 6.5 - 7.0 in the surrounding cytoplasm 溶酶体是酸性的，但属于是弱酸（pH 在 4 到 5 之间）

Centrosome 中心体#

There are two centrioles (not one as it appears under the light microscope) and they are at right angles to each other to form a centrosome.

中心体由两个中心粒构成，两个中心粒互相成直角排列。

It can only be found in animal cells but not plant cells 中心体只存在于动物细胞中，植物细胞里没有

Centrosome acts as microtubule organising centres (MTOCs) that make the microtubule spindle during nuclear division.

中心体作为微管组织中心（MTOCs），在细胞核分裂过程中形成微管纺锤体。(会在细胞分裂的过程中把分裂出去的部分推开)

Microtubules 微管#

Microtubules are made of a protein called tubulin. Tubulin has two forms, α-tubulin (alpha-tubulin) and β-tubulin (beta-tubulin). 微管由一种叫做微管蛋白的蛋白质构成，微管蛋白有两种形态，α 和 β。

1. α- and β-tubulin molecules combine to form dimers (double molecules) α-和 β-微管蛋白分子结合形成“二聚体”（一种双分子结构）

2. These dimers are then joined end to end to form long ‘protofilaments’. 这些“二聚体”随后端对端连接形成长的“原丝”。

   This is an example of polymerisation, the process by which giant molecules are made by joining together many identical subunits.

   这是一个“聚合反应”的例子，聚合反应就是许多个相同的小分子“汇聚到”一起然后形成一个大分子。

3. Thirteen protofilaments line up alongside each other in a ring to form a cylinder with a hollow centre. 十三个原纤维平行排列成环，形成一个中间空心的圆柱。

4. This cylinder is the microtubule. 这个圆柱体就是微管

Microtubules make up the cytoskeleton, which helps to determine cell shape. 微管构成细胞骨架，帮助决定细胞形状。

This diagram shows the arrangement of microtubules in two cells. The microtubules are coloured yellow.

微管相当于细胞的血管外加骨架，它对于细胞同时起到了物理上支撑的作用和功能上运输的作用。上图中的微管被标记成了黄色。

Functions of the microtubules 微管的功能：

• Support the cell structure 支撑细胞结构

• Transport secretory vesicles and other organelles and cell components 运输囊泡和其他细胞器

• Seperate the chromatids or chromosomes during the cell division 在细胞分裂期间分开染色单体或染色体

• Microtubules form part of the structure of centrioles 形成中心粒的部分结构

  Centriole’s structure:

  所以说：Tubulines → dimers → protofilaments → microtulube → centriole → centrosome

• Microtubules form an essential part of the mechanism involved in the beating movements of cilia and flagella. 微管是纤毛和鞭毛运动机制的重要组成部分。

During nuclear division, microtubule spindle (纺锤体) is used for the separation of chromosomes.

这是课本第五单元（第 128 页）的内容，现在可以不用细究，但是需要知道 microtubules 有这个功能。

Flagellum (plural: flagella) and cilium (plural: cilia) 鞭毛和纤毛#

这两个东西本质上是一样的（identical structure），但是由于这个东西被命名的时候还不知道它们内部的结构，所以被认为是两个不一样的东西。通常来说，它们一般是这样被区分的：

• Flagella are long and found usually one or two per cell

  鞭毛：比较长，而且一个细胞只有少量的鞭毛

• Cilia are short and often numerous

  纤毛：短而密

对于大多数真核细胞来说，它们的鞭毛有着相对来说比较复杂的“9+2”结构——即外圈有 9 的单元（每个单元由两个微管组成，组成一个叫 microtubule doublet 的东西，简称 MTD），内圈有两个单元（两个独立的微管）：

在正常情况下，一个 microtubule 是由 13 个 protofilaments 组成的，在组成外圈的 9 个 doublet microtubules 使会有 A 和 B 之分，A microtubule 有 13 个 protofilaments，而 B microtubule 只有 10 个 protofilaments。

不过中心的两个 microtubules 是常规的（有 13 个 protofilaments）。

Functions:

• locomotion 移动

• Cilia cells in lungs maintain a flow of mucus which removes debris such as dust and bacteria from the respiratory tract. 通过摆动纤毛使肺中的黏液往外移动。

  注意：不要把 cilia 和 microvilli 搞混了，二者虽然都是细胞器、也都是向外衍生出去的一部分，但是 cilia 是类似于“手臂”之类的东西，为的是移动之类的目的；而 microvilli 是用来增加细胞表面积来吸收更多物质的，并不能用来移动。

Microvillus (plural: microvilli) 微绒毛#

Found in epithelial cells of small intestine, which can greatly increase the surface area of the cell surface area. 位于小肠的表层细胞上，它能极大的增加细胞的表面积。

Functions：

• For reabsorption in the proximal convoluted tubules of the kidney

  在肾脏的近曲小管中进行再吸收

• For absorption of digested food into cells lining the gut

  将消化后的食物吸收进入肠道细胞

Cell surface membrane 细胞膜#

It has three layers (trilaminar structure) - two dark (heavily stained) layers surrounding a narrow, pale interior:

The membrane is partially permeable and controls exchange between the cell and its environment. 这层膜是半透的，它能控制细胞和外界的物质交换。

关于细胞膜的更多信息会在第四章中讲到

重点信息#

• Unicellular 单细胞的

• Generally 15 μm (diameter) 直径大约在 15 微米

• No nucleus 没有细胞核

• Peptidoglycan / murein cell walls 肽聚糖细胞壁

• Circular (chromosomal) DNA 环状的 DNA

• 70S ribosomes 核糖体（70S）

• No membrane-bound organelles (no mitochondria or chloroplasts)

  没有具有“膜”的细胞器

• Some have plasmids or flagellum 有的有质粒或者鞭毛

主要结构#

所有细菌细胞都有的结构：

• Murein cell wall 肽聚糖细胞壁
• Cell surface membrane 细胞膜
• Cytoplasm 细胞质
• Circular DNA 环状的 DNA
• Ribosome 核糖体

有时候会包括的结构：

• Flagellum with simple structure 结构简单的鞭毛

• Capsule of slime layer for additional protection 药囊或黏液状的保护层

• infolding of cell surface membrane 向内部折叠的细胞膜

  may form a photosynthetic membrane of carry out nitrogen fixation

• plasmid 质粒

  several small circle of DNA 可能会有一些环状的 DNA（质粒）

• Pili

  For attachment to other cells of surface; And involved in sexual reproduction.

  用于附着于其他细胞或其他表面；以及会参与有性繁殖。

Prokaryotes vs Eukaryotes#

Common structural features#

**Cell surface membrane:**essential because it forms a partially permeable barrier between the cell and its environment, regulating movement of materials into and out of the cell. This is necessary to maintain an environment inside the cell which is different from that outside the cell.

**Cytoplasm:**site of metabolic activity. It contains biochemicals in solution.

**Ribosomes:**sites of protein synthesis, an essential activity of all cells. (DNA controls cells by controlling which proteins are made.) Protein synthesis is a complex process involving the interaction of many molecules; the ribosome provides a site where this an happen in an organised way.

**DNA:**the genetic material. DNA contains the information which controls tha activities of the cell. It can replicate itself, enabling new cells to be formed.