第七章酶 扇第 节酶的概念及特
Enzyme 第一节酶的概念及特 点
An Introduction to Enzymes 酶的概念 Much of the history of biochemistry is the history of enzyme research. Biological catalysis was first recognized and described in the late 1700s, in studies on the digestion of meat by secretions of the stomach and research continued in the 1800s with examinations of the conversion of starch to sugar by saliva and various plant extracts. In the 1850s, Louis Pasteur concluded that fermentation of sugar into alcohol by yeast is catalyzed by"“ ferments
An Introduction to Enzymes Much of the history of biochemistry is the history of enzyme research. Biological catalysis was first recognized and described in the late 1700s, in studies on the digestion of meat by secretions of the stomach, and research continued in the 1800s with examinations of the conversion of starch to sugar by saliva and various plant extracts. In the 1850s, Louis Pasteur concluded that fermentation of sugar into alcohol by yeast is catalyzed by “ferments.” 一、 酶的概念
An Introduction to Enzymes He postulated that these ferments were inseparable from the structure of living yeast cells; this view, called vitalism(活力论, prevailed for decades. THen in1897 Eduard buchner discovered that yeast extracts could ferment sugar to alcohol, proving that fermentation was promoted by molecules that continued to function when removed from cells. frederick w. kuhne called these molecules enzymes. As vitalistic notions of life were disproved, the isolation of new enzymes and the investigation of their properties advanced the science of biochemistry
An Introduction to Enzymes He postulated that these ferments were inseparable from the structure of living yeast cells; this view, called vitalism(活力论), prevailed for decades. Then in 1897 Eduard Buchner discovered that yeast extracts could ferment sugar to alcohol, proving that fermentation was promoted by molecules that continued to function when removed from cells. Frederick W. Kühne called these molecules enzymes. As vitalistic notions of life were disproved, the isolation of new enzymes and the investigation of their properties advanced the science of biochemistry
An Introduction to Enzymes The isolation and crystallization of urease by James Sumner in 1926 provided a breakthrough in early enzyme studies. Sumner found that urease crystals consisted entirely of protein, and he postulated that all enzymes are proteins. In the absence of other examples, this idea remained controversial for some time. Only in the 1930s was Sumner's conclusion widely accepted, after John Northrop and Moses Kunitz crystallized pepsin trypsin, and other digestive enzymes and found them also to be proteins
An Introduction to Enzymes The isolation and crystallization of urease by James Sumner in 1926 provided a breakthrough in early enzyme studies. Sumner found that urease crystals consisted entirely of protein, and he postulated that all enzymes are proteins. In the absence of other examples, this idea remained controversial for some time. Only in the 1930s was Sumner’s conclusion widely accepted, after John Northrop and Moses Kunitz crystallized pepsin, trypsin, and other digestive enzymes and found them also to be proteins
An Introduction to Enzymes During this period, J. B. S. Haldane wrote a treatise entitled Enzymes. Although the molecular nature of enzymes was not yet fully appreciated Haldane made the remarkable suggestion that weak bonding interactions between an enzyme and its substrate might be used to catalyze a reaction. This insight lies at the heart of our current understanding of enzymatic catalysis
An Introduction to Enzymes During this period, J. B. S. Haldane wrote a treatise entitled Enzymes. Although the molecular nature of enzymes was not yet fully appreciated, Haldane made the remarkable suggestion that weak bonding interactions between an enzyme and its substrate might be used to catalyze a reaction. This insight lies at the heart of our current understanding of enzymatic catalysis
酶的概念 Most Enzymes Are Proteins With the exception of a small group of catalytic RNA molecules, all enzymes are proteins. Their catalytic activity depends on the integrity of their native protein conformation. If an enzyme is denatured or dissociated into its subunits, catalytic activity is usually lost. If an enzyme is broken down into its component amino acids, its catalytic activity is always destroyed. Thus the primary secondary, tertiary, and quaternary structures of protein enzymes are essential to their catalytic activity
一、 酶的概念 With the exception of a small group of catalytic RNA molecules, all enzymes are proteins. Their catalytic activity depends on the integrity of their native protein conformation. If an enzyme is denatured or dissociated into its subunits, catalytic activity is usually lost. If an enzyme is broken down into its component amino acids, its catalytic activity is always destroyed. Thus the primary, secondary, tertiary, and quaternary structures of protein enzymes are essential to their catalytic activity. Most Enzymes Are Proteins
酶的概念 酶的概念酶是由生物细胞产生的以蛋白质为 主要成分的生物催化剂。 生物体内的反应是在很温和的条件(如温和的 温度、按近中性的pH)下进行的,而同样的反 应若在非生物条件下进行,则需要高温、高压、 强酸、强碱等剧烈的条件
一、 酶的概念 生物体内的反应是在很温和的条件（如温和的 温度、接近中性的pH）下进行的，而同样的反 应若在非生物条件下进行，则需要高温、高压、 强酸、强碱等剧烈的条件。 酶的概念—酶是由生物细胞产生的以蛋白质为 主要成分的生物催化剂
question?-- Keeping the Sweet Taste of Corn The sweet taste of freshly picked corn(maize)is due to the high level of sugar in the kernels. Store bought corn (several days after picking is not as sweet, because about 50%of the free sugar is converted to starch within one day of picking. To preserve the sweetness of fresh corn, the husked ears can be immersed in boiling water for a few minutes (<blanched )then cooled in cold water. Corn processed in this way and stored in a freezer maintains its sweetness. What is the biochemical basis for this procedure
The sweet taste of freshly picked corn (maize) is due to the high level of sugar in the kernels. Storebought corn (several days after picking) is not as sweet, because about 50% of the free sugar is converted to starch within one day of picking. To preserve the sweetness of fresh corn, the husked ears can be immersed in boiling water for a few minutes (“blanched”) then cooled in cold water. Corn processed in this way and stored in a freezer maintains its sweetness. What is the biochemical basis for this procedure? question?-- Keeping the Sweet Taste of Corn
酶的概念 但酶发挥其催化作用并不局限于活细胞内,在许 多情况下,细胞内产生的酶需分泌到细胞外或转移到 其它组织器官中发挥作用,如胰蛋白酶、脂酶、淀粉 酶等水解酶。把由细胞内产生并在细胞内发挥作用的 酶称为胞内酶,而将细胞內产生后分泌细胞外起作用 的酶叫胞外酶
一、 酶的概念 酶是但酶发挥其催化作用并不局限于活细胞内，在许 多情况下，细胞内产生的酶需分泌到细胞外或转移到 其它组织器官中发挥作用，如胰蛋白酶、脂酶、淀粉 酶等水解酶。把由细胞内产生并在细胞内发挥作用的 酶称为胞内酶，而将细胞内产生后分泌细胞外起作用 的酶叫胞外酶
酶的概念 在本章节中把酶所催化的反应称作酶促反应 ,发生化学反应前的物质称底物( substrate), 而反应后生成的物质称产物( product)
一、 酶的概念 在本章节中把酶所催化的反应称作酶促反应 ，发生化学反应前的物质称底物（substrate）， 而反应后生成的物质称产物（product）