单选题真核生物的TATA盒是

单选题呼吸链中起电子传递作用的金属是

单选题下述哪种物质含高能磷酸键

单选题对于糖酵解的叙述哪项是不正确的

单选题脑中氨的主要去路是(1991年，2004年)

单选题含载脂蛋白B 48 的血浆脂蛋白是

单选题基本表达的表述中错误的是

单选题关于单加氧酶错误的是

单选题RNA聚合酶催化转录，其底物是

单选题DNA复制与转录过程有许多异同点中，描述不正确的是

单选题All animals must rest, but do they really sleep as we know it? The answer to this question seems obvious. If an animal regularly stops its activities and stays quiet and unmoving—if it looks as though it is sleeping—then why not simply assume that it is in fact sleeping? But how can observers be sure that an animal is sleeping? They can watch the animal and notice whether its eyes are open or closed, whether it is active or lying quietly, and whether it responds to light or sound. These factors are important clues, but they often are not enough. Horses and cows, for example, rarely close their eyes, and fish and snakes cannot close them. Yet this does not necessarily mean that they do not sleep. Have you ever seen a cat dozing with an eye partly open? Even humans have occasionally been observed to sleep with one or both eyes partially open. Animals do not necessarily lie down to sleep either. Elephants, for example, often sleep standing up, with their tusks resting in the fork of a tree. Finally, while "sleeping" animals often seem unaware of changes in the sounds and light and other stimuli around them, that does not really prove they are sleeping either. Observations of animal behavior alone cannot fully answer the question of whether or not animals sleep. The answers come from doing experiments in "sleep laboratories" using a machine called the electroencephalograph (EEC). The machine is connected to animals and measures their brain signals, breathing, heartbeat, and muscle activity. The measurements are different when the animals appear to be sleeping than when they appear to be awake. Using the EEC, scientists have confirmed that all birds and mammals studied in laboratories do sleep. There is some evidence that reptiles, such as snakes and turtles, do not truly sleep, although they do have periods of rest each day, in which they are quiet and unmoving. They also have discovered that some animals, like chimpanzees, cats, and moles (who live underground), are good sleepers while others, like sheep, goats, and donkeys, are poor sleepers. Interestingly, the good sleepers are nearly all hunters with resting places that are safe from their enemies. Nearly all the poor sleepers are animals hunted by other animals: they must always be watching for enemies, even when they are resting.

单选题血浆中具有氧化酶活性的蛋白质是

单选题对于磷酸戊糖途径的叙述恰当的是

单选题不参加脂酸β－氧化的辅因子是

单选题脂酸β-氧化的循环步骤是

单选题启动子(promoter)是指

单选题A.生酮氨基酸B.生糖氨基酸C.两者都是D.两者均否

单选题A．已糖激酶B．磷酸烯醇式丙酮酸羟激酶C．丙酮酸脱氢酸D．α-酮戊二酸脱氢酶E．乙酸CoA羟化酶 (1988年)

单选题生物素是哪个酶的辅酶

单选题下列哪种反应可用于检测蛋白质的水解程度