The Ramachandran plot is a visual description of the combinations of ϕ and ψ dihedral angles that are permitted in a peptide backbone and those that are not permitted due to steric constraints. Dihedral angles that define the α helix and the β conformation are found only within certain regions of the plot.

拉氏构象图是一种可视化描述：它标出肽主链中哪些 ϕ、ψ 二面角组合是被允许的，哪些因空间位阻而不被允许。定义 α 螺旋和 β 构象的那些二面角，只落在图中某些特定的区域之内。

These and other major advances gave rise to the central dogma of molecular biology, comprising the three major processes in the cellular utilization of genetic information. The first is replication, the copying of parental DNA to form daughter DNA molecules with identical nucleotide sequences. The second is transcription, the process by which parts of the genetic message encoded in DNA are copied precisely into RNA. The third is translation, whereby the genetic message encoded in messenger RNA is translated on the ribosomes into a polypeptide with a particular sequence of amino acids.

这些以及其他重大进展催生了分子生物学的中心法则，它包含细胞利用遗传信息的三大过程。第一是复制，即拷贝亲代 DNA，形成核苷酸序列完全相同的子代 DNA 分子。第二是转录，即把 DNA 中编码的部分遗传信息精确地拷贝成 RNA。第三是翻译，即把信使 RNA 所编码的遗传信息在核糖体上译成具有特定氨基酸序列的多肽。

Hydrogen bonds are strongest when the bonded molecules are oriented to maximize electrostatic interaction, which occurs when the hydrogen atom and the two atoms that share it are in a straight line—that is, when the acceptor atom is in line with the covalent bond between the donor atom and H (Fig. 2-5). This arrangement puts the positive charge of the hydrogen ion directly between the two partial negative charges. Hydrogen bonds are thus highly directional and capable of holding two hydrogenbonded molecules or groups in a specific geometric arrangement.

当成键的两个分子取向使静电作用最大化时，氢键最强；这发生在氢原子与共用它的两个原子处于一条直线上时，也就是受体原子与供体原子和 H 之间的共价键共线时（图 2-5）。这种排布把氢离子的正电荷正好置于两个部分负电荷之间。因此氢键具有高度的方向性，能够把两个成氢键的分子或基团固定在特定的几何取向上。

For macromolecules, the most stable (that is, the native) structure is usually that in which these weak interactions are maximized. The folding of a single polypeptide or polynucleotide chain into its three-dimensional shape is determined by this principle. The binding of an antigen to a specific antibody depends on the cumulative effects of many weak interactions. The energy released when an enzyme binds noncovalently to its substrate is the main source of the enzyme’s catalytic power. The binding of a hormone or a neurotransmitter to its cellular receptor protein is the result of multiple weak interactions.

对大分子而言，最稳定的（也就是天然的）结构，通常就是这些弱相互作用被最大化的那种结构。单条多肽链或多核苷酸链折叠成其三维形状，就是由这一原理决定的。抗原与特异性抗体的结合，取决于许多弱相互作用的累加效应。酶与底物非共价结合时释放的能量，是酶催化能力的主要来源。激素或神经递质与其细胞受体蛋白的结合，也是多重弱相互作用的结果。

An advantage of nuclear magnetic resonance (NMR) studies is that they are carried out on macromolecules in solution, whereas x-ray crystallography is limited to molecules that can be crystallized. NMR can also illuminate the dynamic side of protein structure, including conformational changes, protein folding, and interactions with other molecules.

核磁共振（NMR）研究的一个优点，是它在溶液中的大分子上进行，而 X 射线晶体学则只限于能够结晶的分子。NMR 还能揭示蛋白质结构动态的一面，包括构象变化、蛋白质折叠以及与其他分子的相互作用。

Protein folding is a problem particularly well-suited for computational biochemists. Protein-folding landscapes can be complex, and nearly an infinite number of possible peptide conformations are theoretically available for the protein to sample as it folds. However, to understand how folding happens efficiently and by only sampling a small portion of all possible conformations requires computers that can quickly test tens of thousands of possible folding trajectories in a brief time. Sometimes these calculations are carried out on powerful supercomputers, but in other instances research groups have taken to crowdsourcing these problems to thousands of citizen scientists.

蛋白质折叠是一个特别适合计算生化学家来做的问题。蛋白质折叠的能量地貌可以很复杂，理论上蛋白质在折叠时可供采样的肽构象数目近乎无穷。然而，要理解折叠何以能高效完成、且只采样了全部可能构象中极小的一部分，就需要计算机能在很短时间内快速检验成千上万条可能的折叠轨迹。这类计算有时在强大的超级计算机上进行，但在另一些情况下，研究组会把这些问题众包给成千上万的公民科学家。