Proteins 蛋白质
Different proteins can appear very different and perform diverse functions (e.g. the water-soluble antibodies involved in the immune system and the water-insoluble keratin of hair, hooves and feathers). Despite this, each one is made up of amino acid subunits.
There about 20 different amino acids that all have a similar chemical structure but behave in very different ways because they have different side groups. Hence, stringing them together in different combinations produces very different proteins.
不同的蛋白质可以看起来非常不同，并发挥不同的功能（例如，参与免疫系统的水溶性抗体和头发、蹄子和羽毛的水不溶性角蛋白）。尽管如此，每一种都是由氨基酸亚单位组成的。
大约有20种不同的氨基酸，它们都有类似的化学结构，但由于它们有不同的侧基，所以表现得非常不同。因此，将它们以不同的组合串在一起，会产生非常不同的蛋白质。
Each amino acid has an amino group (NH2) and a carboxylic acid group (COOH). The R group is a different molecule in different amino acids which can make them neutral, acidic, alkaline, aromatic (has a ring structure) or sulphur-containing.
When 2 amino acids are joined together (condensation) the amino group from one and the acid group from another form a bond, producing one molecule of water. The bond formed is called a peptide bond.
Hydrolysis is the opposite of condensation and is the breaking of a peptide bond using a molecule of water.
每个氨基酸都有一个氨基（NH2）和一个羧基（COOH）。在不同的氨基酸中，R基是不同的分子，这可以使它们成为中性、酸性、碱性、芳香族（有环状结构）或含硫。
当2个氨基酸连接在一起时（缩合），其中一个的氨基和另一个的酸基形成一个键，产生一个水分子。形成的键被称为肽键。
水解与缩合相反，是用一个水分子打破一个肽键。
Due to the bonding and the shape and chemical nature of different amino acids, the shape of a whole chain of amino acids (a polypeptide or protein) is specific.
This will affect the properties of the protein, just as the type of a necklace depends on the type of beads and how they are strung together. Therefore, the primary structure depends on the order and number of amino acids in a particular protein.
For example:Haemoglobin is made up of 4 polypeptide chains, 2α chains and 2β chains, each with a haem group attached. There are 146 amino acids in each chain. If just one of these is wrong, serious problems can arise (e.g. sickle cell anaemia). The red blood cells become distorted, the amount of oxygen they can carry is reduced and blood capillaries can be blocked, leading to acute pains called crises.
由于不同氨基酸的结合以及形状和化学性质，一整条氨基酸链（多肽或蛋白质）的形状是特定的。
这将影响蛋白质的特性，就像项链的类型取决于珠子的类型和它们的串联方式。因此，主要结构取决于特定蛋白质中氨基酸的顺序和数量。
例如：血红蛋白是由4条多肽链组成的，2α链和2β链，每条链上都有一个血红素基团。每条链上有146个氨基酸。只要其中一个出错，就会出现严重的问题（如镰状细胞贫血）。红细胞变得扭曲，它们能够携带的氧气量减少，毛细血管可能被堵塞，导致被称为危机的急性疼痛。
This is the basic shape that the chain of amino acids takes on. The 2 most common structures are the α-helix and the β-pleated sheet.
这是氨基酸链所呈现的基本形状。两种最常见的结构是α螺旋和β褶皱片。
This has a regular coiled structure like a spring, with the R groups pointing towards the outside of the helix. Hydrogen (H) bonds are relatively weak but because there are so many, the total binding effect is strong and stable. The helix is flexible and elastic.
这有一个像弹簧一样的规则盘绕结构，R基团指向螺旋体的外部。氢（H）键相对较弱，但由于数量众多，总的结合效果很强且稳定。螺旋体是灵活和有弹性的。
This is composed of 'side by side' chains connected by H bonds. All the peptide linkages are involved in inter-chain H bonding so the structure is very stable.
这是由H键连接的 "并排 "链组成。所有的肽链都参与了链间H键的连接，所以结构非常稳定。
This is the overall 3-D structure of the protein.
The shape of the protein is held together by H bonds between some of the R groups (side chains) and ionic bonds between positively and negatively charged side chains. These are weak interactions, but together they help give the protein a stable shape. The protein may be reinforced by strong covalent bonds called disulphide bridges which form between two amino acids with sulphur groups on their side chains.
These interactions may be electrostatic attractions between charged groups e.g. NH3 and O- or van der Waal's forces.
这是蛋白质的整体3-D结构。
蛋白质的形状是由一些R基（侧链）之间的H键和带正负电荷的侧链之间的离子键固定在一起。这些都是弱的相互作用，但它们共同帮助赋予蛋白质稳定的形状。蛋白质可能被称为二硫桥的强共价键加强，二硫桥在两个侧链上有硫基的氨基酸之间形成。
这些相互作用可能是带电基团之间的静电吸引，如NH3 和O-或范德瓦尔力。
Fibrous proteins are made of long molecules arranged to form fibres (e.g. in keratin). Several helices may be wound around each other to form very strong fibres. Collagen is another fibrous protein, which has a greater tensile strength than steel because it consists of three polypeptide chains coiled round each other in a triple helix. We are largely held together by collagen as it is found in bones, cartilage, tendons and ligaments.
Globular proteins are made of chains folded into a compact structure. One of the most important classes are the enzymes. Although these folds are less regular than in a helix, they are highly specific and a particular protein will always be folded in the same way. If the structure is disrupted, the protein ceases to function properly and is said to be denatured. An example is insulin, a hormone produced by the pancreas and involved in blood sugar regulation.
A globular protein based mostly on an α-helix is haemoglobin.
A globular protein based mostly on a β-pleated sheet is the immunoglobulin antibody molecule.
纤维蛋白是由长分子排列形成纤维（如角蛋白）。几个螺旋体可以相互缠绕，形成非常坚固的纤维。胶原蛋白是另一种纤维蛋白，它的抗拉强度比钢铁大，因为它是由三条多肽链以三螺旋的方式相互缠绕而成。我们在很大程度上是由胶原蛋白支撑的，因为它存在于骨骼、软骨、肌腱和韧带中。
球状蛋白是由链状物折叠成一个紧凑的结构。其中最重要的一类是酶。尽管这些折叠不如螺旋结构那么有规律，但它们具有高度的特异性，一种特定的蛋白质总是以同样的方式折叠的。如果结构被破坏，蛋白质就会停止正常功能，被称为变性。一个例子是胰岛素，一种由胰腺产生的、参与血糖调节的激素。
一个主要基于α-螺旋的球状蛋白是血红蛋白。
主要以β-褶皱片为基础的球状蛋白是免疫球蛋白抗体分子。
If a protein is made up of several polypeptide chains, the way they are arranged is called the quaternary structure. Again, each protein formed has a precise and specific shape (e.g. haemoglobin)
如果一个蛋白质是由几个多肽链组成的，它们的排列方式被称为四级结构。同样，形成的每个蛋白质都有一个精确而具体的形状（如血红蛋白）。
Prosthetic groups 修复基团The majority of proteins are assisted in their functions by a prosthetic group. This may a simple metal ion such as zinc in the enzyme carboxypeptidase, or it may be a complex organic molecule, such as the haem group in haemoglobin.
大多数蛋白质在其功能中都有一个修复基团的帮助。这可能是一个简单的金属离子，如羧肽酶中的锌，也可能是一个复杂的有机分子，如血红蛋白中的血族。
- Virtually all enzymes are proteins.
- Structural: e.g. collagen and elastin in connective tissue, keratin in skin, hair and nails.
- Contractile proteins: actin and myosin in muscles allow contraction and therefore movement.
- Hormones: many hormones have a protein structure (e.g. insulin, glucagon, growth hormone).
- Transport: for example, haemoglobin facilitates the transport of oxygen around the body, a type of albumin in the blood transports fatty acids.
- Transport into and out of cells: carrier and channel proteins in the cell membrane regulate movement across it.
- Defence: immunoglobulins (antibodies) protect the body against foreign invaders; fibrinogen in the blood is vital for the clotting process.
几乎所有的酶都是蛋白质。
结构性蛋白：如结缔组织中的胶原蛋白和弹性蛋白，皮肤、头发和指甲中的角质蛋白。
收缩性蛋白：肌肉中的肌动蛋白和肌球蛋白允许收缩，从而实现运动。
激素：许多激素具有蛋白质结构（如胰岛素、胰高血糖素、生长激素）。
运输：例如，血红蛋白促进了氧气在身体周围的运输，血液中的一种白蛋白可以运输脂肪酸。
进入和离开细胞的运输：细胞膜上的载体和通道蛋白调节跨膜运动。
防御：免疫球蛋白（抗体）保护身体免受外来入侵；血液中的纤维蛋白原对凝血过程至关重要。
Biochemical test 生物化学试验：
The reagent used to test for proteins is called biuret reagent. It can be used as two separate solutions of copper sulphate and potassium or sodium hydroxide or as a ready-made biuret solution. In either case, a purple colour indicates a positive result.
用于检测蛋白质的试剂被称为生物雷特试剂。它可以作为硫酸铜和氢氧化钾或氢氧化钠的两个独立溶液使用，也可以作为现成的比勒特溶液使用。在这两种情况下，出现紫色表示阳性结果。
知识点回顾：
「干货整理」A-level生物A*知识点笔记：生物分子——碳水化合物
A-level生物笔记：Biological Molecules生物分子——Lipids 脂质
,
