生物化学名词解释.doc

生物化学名词解释第一章 白质结构与功能1肽单元（peptide unit）：参与肽键的6个原子C1，C， 蛋O，N，H，C2位于同一平面，C1和C2在平面上所处的位置为反式（trans）构型，此同一平面上的6个原子构成肽单元。2模体（motif）：由二个或三个具有二级结构的肽段，在空间上相互接近，形成一个特殊的空间构象, 并发挥特殊的功能，如锌指结构， 等。模体通常有其特征性的氨基酸序列。有的模体仅由几个氨基酸残基组成，如RGD (Arg-Gly-Asp)模体。3结构域（domain）：分子量较大的蛋白质常可折叠成多个结构较为紧密的区域，并各行其功能，称为结构域。4蛋白质等电点（Isoelectric point, pI）：在某一pH溶液中，蛋白质解离成正、负离子的趋势相等，即成为兼性离子，其所带的净电荷为零，此时溶液的pH值称为该蛋白质的等电点。5蛋白质的变性（denaturation of protein）：在某些物理和化学因素(如加热，强酸，强碱，有机溶剂, 重金属离子等)作用下，蛋白质的特定空间构象被破坏，从而导致其理化性质的改变和生物活性的丧失，称为蛋白质的变性。变性不涉及一级结构中氨基酸序列的改变。第二章 酶1酶的活性中心(active center of enzyme)：酶分子中与酶活性密切相关的基团(必需基团)在空间结构上彼此靠近，组成具有特定空间结构的区域，能与底物特异结合，并将其转变为产物，该区域称酶的活性中心。辅酶参与酶活性中心的组成。2同工酶(isoenzyme)：催化相同的化学反应，但酶蛋白的分子结构、理化性质及免疫学性质不同的一组酶。3变构酶和变构调节(allosteric enzyme and allosteric regulation)：一些代谢物（变构效应剂）可与酶蛋白分子活性中心外的某一部位可逆地结合，使酶发生变构而改变其催化活性。这种酶活性的调节方式称为变构调节。受变构调节的酶称为变构酶。变构酶常是由两个以上亚基组成的寡聚体,含有能与底物结合，起催化作用的催化亚基（部位）,以及能与变构效应剂结合而起调节作用的调节亚基（部位）。4酶的共价修饰调节(covalent modification)：在其他酶的催化作用下，酶蛋白肽链上的一些基团可与某种化学基团发生可逆的共价结合，从而改变酶的活性，此过程称为酶的共价修饰或化学修饰。以磷酸化和脱磷酸化修饰最为多见。5酶原与酶原激活(zymogen and zymogen activation)：有些酶在细胞中合成或初分泌时, 或在发挥其催化功能前只是酶的无活性的前体，这种无活性的酶的前体称为酶原。在一定条件下，酶原水解开一个或几个特定的肽键，使其构象发生改变，形成或暴露出活性中心，表现出酶的活性。这种由无活性的酶原转变为有活性的酶的过程称酶原激活。第三章 糖代谢1糖酵解途径(glycolytic pathway)：在胞质中由葡萄糖分解为丙酮酸的反应阶段为糖酵解和有氧氧化所共有，称为糖酵解途径。2底物水平磷酸化(substrate-level phosphorylation)：代谢物在脱氢或脱水过程中产生的高能磷酸键直接转移给ADP生成ATP的过程,例如磷酸烯醇式丙酮酸转变为丙酮酸。3糖异生(gluconeogenesis)：由非糖物质(乳酸、甘油、生糖氨基酸等)在肝脏和肾脏转变为葡萄糖或糖原的过程称为糖异生。4乳酸循环（lactate cycle or Cori cycle）：肌肉收缩（尤其是氧供应不足）时，糖原和葡萄糖通过糖酵解生成乳酸,乳酸进入血中运输至肝脏，在肝内乳酸异生成葡萄糖并弥散入血,又被肌肉摄取利用，构成的循环过程称为乳酸循环。其意义在于避免乳酸损失，防止乳酸堆积引起酸中毒。Chapter 1 Structure and Function of Proteins1Peptide unit: The partial double-bond character of the peptide bond makes C 1, C, O, N, H, C2 six atoms coplanar, C 1 and C2 are trans to each other, the semi-rigid plane composed of those six atoms is termed as peptide unit.2Motifs are grouping of more than two secondary structural elements that fold to near each other in space and have special functions, such as motif, zinc finger motif. Some motifs consist of only a few conserved functionally important AAs rather than super-secondary structures. e.g. RGD (Arg-Gly-Asp ) motif.3Domain: The tertiary structure of some proteins can be divided into one or more relatively independent compact regions that may be joined by a flexible segment of the chain, these compact units called domains. One protein may contain several domains, each of which has separate function.4pI of protein: pI is the pH at which protein molecular becomes electrically neutral, has no net electric charge.5Protein denaturation: Spatial structure of protein is sensitive to denaturing agents (high T, strong acids or bases, organic solvents, heavy metal ions). These agents result in unfolding and disorganization of protein spatial structure without change in primary structure, and loss of biological activity.Chapter 2 Enzyme1Active center of enzyme is a three-dimensional, local region of the enzyme, which is composed of several essential groups of AAs that has special spatial structure and specifically binds substrate and catalyzes it to become product. Coenzymes or prosthetic groups can be involved in the active site.2. Isozymes (isoenzymes) are a group of enzymes, which catalyze the same reaction but have different protein structure, physicochemical and immunological properties. 3Allosteric enzyme: They are oligomers containing allosteric site and catalytic site which are distinct and separated spatially on enzyme, whose activity can be modulated in the presence of allosteric effector at the allosteric site.Allosteric regulation of enzyme: Small allosteric effectors binding to allosteric site of the enzyme by non-covalent bonds triggers changes in enzyme conformation, then alters the catalytic activity of the enzyme. 4. Chemical (Covalent) modification of enzyme: The structure and activity of many enzymes can be altered reversibly through covalent modification by another enzyme. The most common modification is phosphorylation /dephosphorylation, which is reversible addition and removal of a phosphate at HO-group of Ser, Thr and Tyr.5Zymogen and zymogen activation: Some enzymes are synthesized and secreted as large inactive precursors before exerting their catalytic activity, called zymogens or proenzymes. Zymogens are activated by the irreversible hydrolysis of one or more peptide bonds and forming or exposing the active site in the enzyme molecule.Chapter 3 Metabolism of Carbohydrates1. Glycolytic pathway: One molecule of glucose is converted into two molecules of pyruvate in cytoplasm. This process is shared by glycolysis and aerobic oxidation.2. Substrate-level phosphorylation: ATP is formed by the direct transfer of a phosphate group from a high-energy substrate (eg. PEP to pyruvate) to ADP.3Gluconeogenesis: Formation of glucose or glycogen in liver or kidney from noncarbohydrates, such as lactate, amino acids and glycerol.4Lactate cycle (or Cori cycle): Extremely active muscles use glycogen as energy source, generating lactate via glycolysis. During recovery, some of this lactate is transported to the live