📚 IB Biology: Proteins Key Points | IB 生物：蛋白质考点精讲
Proteins are diverse and indispensable macromolecules that carry out an immense array of functions in living organisms. This revision guide distils the essential concepts you need for IB Biology, from amino acid chemistry to quaternary structure, with key examples such as haemoglobin, rubisco and collagen, and explains how structure dictates function.
蛋白质是生命体中种类繁多且不可或缺的大分子，承担着极其多样的功能。这份考点精讲凝练了IB生物中你必须掌握的核心概念，从氨基酸的化学性质到四级结构，涵盖血红蛋白、Rubisco和胶原蛋白等关键实例，并阐释结构如何决定功能。
1. Amino Acids: The Building Blocks of Proteins | 氨基酸：蛋白质的构建模块
All proteins are polymers constructed from 20 standard amino acid monomers. Each amino acid has a central α-carbon bonded to an amine group (—NH₂), a carboxyl group (—COOH), a hydrogen atom, and a variable R group (side chain).
所有蛋白质都是由20种标准氨基酸单体构成的聚合物。每个氨基酸都有一个中心α-碳原子，其上连接着一个氨基(—NH₂)、一个羧基(—COOH)、一个氢原子以及一个可变的R基（侧链）。
The R group determines the amino acid’s chemical properties: non‑polar, polar uncharged, or electrically charged (acidic and basic). The nature of the side chains governs how the polypeptide folds in water.
R基决定了氨基酸的化学性质：非极性、极性不带电或带电荷（酸性和碱性）。侧链的性质支配着多肽在水中的折叠方式。
2. Peptide Bond Formation | 肽键的形成
A peptide bond is a covalent bond formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of another. One water molecule is released, and the resulting link is an amide bond (—CO—NH—).
肽键是一个氨基酸的羧基与另一个氨基酸的氨基之间通过缩合反应形成的共价键。反应释放一分子水，形成的连接为酰胺键（—CO—NH—）。
The peptide bond exhibits partial double-bond character due to resonance, which restricts rotation around the C—N bond and gives the backbone a planar geometry.
由于共振作用，肽键具有部分双键性质，限制了C—N键的旋转，使主链具有平面几何构型。
The repeating backbone of a polypeptide is —N—Cα—C—, with the R groups projecting as side chains that interact with each other and with water.
多肽主链的重复单元为—N—Cα—C—，R基作为侧链突出，彼此之间以及与溶剂水相互作用。
3. Diversity of Polypeptides | 多肽的多样性
The 20 amino acids can be linked in any order and in any length. For a chain of n amino acids, the theoretical number of sequences is 20ⁿ, generating an astronomically large molecular variety.
20种氨基酸可以任意顺序、任意长度连接。对于含有n个氨基酸的链，可能的多肽序列达20ⁿ种，产生天文学般巨大的分子多样性。
In cells, the actual sequence of a polypeptide is specified by a gene through the genetic code. Ribosomes translate mRNA codons into a precise chain of amino acids.
在细胞中，一条多肽的实际序列由基因通过遗传密码决定。核糖体将mRNA上的密码子翻译成精确的氨基酸链。
4. Primary Structure: The Sequence of Amino Acids | 一级结构：氨基酸序列
The primary structure is the linear sequence of amino acids held together by peptide bonds. It is encoded by the DNA sequence of the corresponding gene and is unique to each protein.
一级结构是通过肽键连接在一起的氨基酸线性序列。它由相应基因的DNA序列编码，对每种蛋白质而言独一无二。
A change in just one amino acid can have drastic consequences. In sickle cell anaemia, a single substitution (glutamic acid → valine) in the β‑chain of haemoglobin causes the protein to polymerise, distorting red blood cells.
一个氨基酸的改变就可能引起严重后果。在镰状细胞贫血中，血红蛋白β‑链上一个谷氨酸被缬氨酸取代，导致蛋白质发生聚合，红细胞变形。
5. Secondary Structure: Alpha‑Helices and Beta‑Pleated Sheets | 二级结构：α-螺旋和β-折叠
Secondary structure refers to regularly repeating local conformations of the polypeptide backbone, stabilised by hydrogen bonds between the carbonyl oxygen (—C=O) and the amide hydrogen (—NH) of the peptide bond.
二级结构是指多肽主链上规则重复的局部构象，由肽键中羰基氧(—C=O)与酰胺氢(—NH)之间的氢键维持稳定。
The α‑helix is a right‑handed coil in which the R groups point outward, preventing steric clashes. The hydrogen bonds are parallel to the helix axis, making the structure spring‑like and elastic.
α‑螺旋是右手螺旋，R基朝外，避免了空间位阻。氢键平行于螺旋轴，使结构呈弹簧状，具有弹性。
The β‑pleated sheet consists of extended polypeptide strands aligned side by side. Hydrogen bonds form between strands; the R groups alternately project above and below the plane of the sheet. The strands can run parallel or antiparallel.
β‑折叠由多条伸展的多肽链并排而成。链之间形成氢键；R基交替伸向折叠片平面的上方和下方。链的走向可以是平行或反平行。
Silk fibroin is rich in β‑sheets, producing long, insoluble, flexible fibres with high tensile strength. In contrast, keratin in hair and nails contains α‑helices bundled into coiled coils.
丝素蛋白富含β‑折叠，形成长而不溶、柔韧且抗张强度高的纤维。而毛发和指甲中的角蛋白则含有盘绕成螺旋束的α‑螺旋。
6. Tertiary Structure: 3D Folding and Bonds | 三级结构：三维折叠与化学键
The tertiary structure is the overall three‑dimensional shape of a single polypeptide chain. It results from interactions among the R groups and is stabilised by several types of bonds and forces.
三级结构是单条多肽链的整体三维形状，由R基之间的相互作用决定，并通过多种化学键和力来稳定。
Key interactions include: hydrophobic interactions (non‑polar side chains cluster in the interior, away from water), hydrogen bonds, ionic bonds (salt bridges between oppositely charged side chains), and covalent disulfide bridges formed between cysteine residues.
关键的相互作用包括：疏水作用（非极性侧链聚集在内部，避开水）、氢键、离子键（带相反电荷侧链之间的盐桥）以及半胱氨酸残基之间形成的共价二硫键。
The final 3D conformation determines the protein’s specific function, such as the precise shape of an enzyme’s active site or the binding pocket of a receptor.
最终的三维构象决定了蛋白质的专一性功能，例如酶活性部位的精确形状或受体的结合口袋。
7. Quaternary Structure: Multiple Polypeptide Chains | 四级结构：多条多肽链的组合
Quaternary structure occurs when two or more polypeptide subunits assemble to form a functional protein. The subunits are held together by the same types of interactions found in tertiary structure, and the assembly can be symmetrical or asymmetrical.
四级结构发生在两条或多条多肽亚基组装成功能性蛋白质时。亚基之间依靠与三级结构中相同的相互作用结合在一起，组合形式可以是对称或非对称的。
Haemoglobin is a classic example: it is a tetramer consisting of two α‑globin and two β‑globin subunits, each with a haem group that binds oxygen. The quaternary structure enables cooperative binding.
血红蛋白是一个典型例子：它是一种四聚体，由两条α‑珠蛋白和两条β‑珠蛋白亚基组成，每条含有一个能结合氧的血红素基团。四级结构使其具备协同结合能力。
Another example is collagen, which is formed from three α‑chains wound into a triple helix, with extensive hydrogen bonding and covalent cross‑links enhancing tensile strength.
另一个例子是胶原蛋白，它由三条α‑链缠绕成三螺旋，大量的氢键和共价交联增强了抗张强度。
8. Globular vs. Fibrous Proteins: Form and Function | 球状蛋白与纤维状蛋白：形式与功能
Proteins can be broadly classified by shape. Globular proteins are roughly spherical and soluble in water, with hydrophobic residues buried inside and hydrophilic residues on the surface. Fibrous proteins are long, elongated, and often insoluble, providing structural support.
蛋白质可根据形状大致分类。球状蛋白大致呈球形，可溶于水，疏水残基埋入内部，亲水残基位于表面。纤维状蛋白细长，通常不溶，主要提供结构支撑。
The table below summarises key differences supported by IB examples.
下表总结了关键差异并辅以IB示例。
| Property / 性质 | Globular / 球状 | Fibrous / 纤维状 |
| Shape / 形状 | Roughly spherical / 大致球形 | Long and narrow / 细长 |
| Solubility / 溶解性 | Usually soluble / 通常可溶 | Usually insoluble / 通常不溶 |
| Function / 功能 | Catalysis, transport, regulation / 催化、运输、调控 | Structure, support / 结构、支撑 |
| Examples / 实例 | Haemoglobin, rubisco, insulin / 血红蛋白、Rubisco、胰岛素 | Collagen, keratin, silk fibroin / 胶原蛋白、角蛋白、丝素蛋白 |
9. Denaturation: Loss of 3D Structure | 变性：三维结构的丧失
Denaturation is the process in which a protein loses its tertiary and secondary structure, and consequently its function, due to the disruption of non‑covalent bonds and disulfide bridges. The primary structure (peptide bonds) remains intact.
变性是蛋白质因非共价键和二硫键被破坏而失去其三级和二级结构，继而丧失功能的过程。一级结构（肽键）保持完整。
Common denaturing agents include heat (breaks hydrogen bonds and increases kinetic energy), extreme pH (alters charges on R groups, disrupting ionic and hydrogen bonds), and heavy metal ions (bind to —SH groups or displace essential metals).
常见的变性因素包括高温（破坏氢键、增加动能）、极端pH值（改变R基电荷，破坏离子键和氢键）以及重金属离子（与—SH基团结合或置换必需金属）。
Cooking egg white illustrates irreversible denaturation: the soluble albumin protein unfolds and coagulates into a solid white mass.
煮蛋清是不逆变性的实例：可溶的清蛋白变性展开并凝固成白色固体。
10. Functions of Proteins in Living Organisms | 蛋白质在生物体内的功能
Proteins are arguably the most versatile biomolecules. Their functions are directly linked to their specific three‑dimensional conformations.
蛋白质可以说是功能最多样的生物分子。它们的功能直接与其特定的三维构象相关。
Catalysis: Enzymes are globular proteins that lower activation energy and speed up biochemical reactions with exquisite specificity.
催化作用：酶是球状蛋白，能降低活化能并以极高的特异性加速生化反应。
Transport: Haemoglobin transports oxygen in the blood; membrane proteins such as channel proteins facilitate the passage of ions and molecules.
运输：血红蛋白在血液中运输氧气；通道蛋白等膜蛋白协助离子和分子通过。
Structure: Collagen provides tensile strength in tendons and skin; keratin forms protective structures in hair and nails.
结构：胶原蛋白为肌腱和皮肤提供抗张强度；角蛋白构成毛发和指甲的保护结构。
Movement: Actin and myosin interact to cause muscle contraction.
运动：肌动蛋白和肌球蛋白相互作用引起肌肉收缩。
Defence: Antibodies (immunoglobulins) recognise and neutralise foreign antigens.
防御：抗体（免疫球蛋白）识别并中和外来抗原。
Signalling: Receptor proteins bind hormones and other signal molecules, triggering cellular responses.
信号传递：受体蛋白结合激素及其他信号分子，引发细胞应答。
11. Key Examples: Haemoglobin, Rubisco, and Collagen | 关键实例：血红蛋白、Rubisco和胶原蛋白
Understanding specific proteins required by the IB syllabus helps illustrate how structure relates to function.
理解IB大纲要求的具体蛋白质，有助于阐明结构如何与功能相关联。
Haemoglobin: A globular, quaternary protein (α₂β₂). Cooperative binding of oxygen results from a conformational change when one O₂ molecule binds, increasing the affinity of the remaining subunits. Its solubility and shape make it ideally suited for circulation in erythrocytes.
血红蛋白：一种具有四级结构的球状蛋白（α₂β₂）。当一个氧分子结合时引发构象变化，提高了其余亚基对氧的亲和性，从而实现协同结合。其溶解性和形状使其非常适合在红细胞中循环运输。
Rubisco (ribulose bisphosphate carboxylase/oxygenase): A globular enzyme essential for carbon fixation in photosynthesis. It catalyses the reaction of CO₂ with ribulose‑1,5‑bisphosphate. Its active site must accommodate the transition state with high specificity to avoid excessive oxygenation.
Rubisco（核酮糖‑1,5‑二磷酸羧化酶/加氧酶）：一种在光合作用碳固定中至关重要的球状酶。它催化CO₂与核酮糖‑1,5‑二磷酸的反应。其活性部位必须高特异性地容纳过渡态，以避免过多的加氧反应。
Collagen: An insoluble fibrous protein with a triple‑helix quaternary structure. Every third amino acid is glycine, allowing the three strands to pack tightly. Proline and hydroxyproline residues stabilise the helix. Covalent cross‑links between lysine residues give collagen its extraordinary tensile strength, making it a cornerstone of tendons, ligaments, and bone matrix.
胶原蛋白：一种不溶性纤维状蛋白，具有三螺旋四级结构。每隔两个氨基酸就有一个甘氨酸，使三条链能够紧密堆积。脯氨酸和羟脯氨酸残基稳定螺旋。赖氨酸残基之间的共价交联赋予了胶原蛋白卓越的抗张强度，使其成为肌腱、韧带和骨基质的根本组分。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导