Testing and Thinkingl. (True/False) There is no fundamentaldistinction betweensignaling molecules that bind to cell-surface receptors andthose that bind to intracellular receptors. Explain youranswer.2. How is it that different cells can respond in different waysto exactly the same signaling molecule even when they haveidenticalreceptors?3. Why do you suppose that别构或变构phosphorylation/dephosphorylation, as opposed to allostericbinding of small molecules,for example,plays such aprominent role in switching proteins on and off in signalingpathways?
1 Testing and Thinking 1. (True/False) There is no fundamental distinction between signaling molecules that bind to cell-surface receptors and those that bind to intracellular receptors. Explain your answer. 2. How is it that different cells can respond in different ways to exactly the same signaling molecule even when they have identical receptors? 3. Why do you suppose that phosphorylation/dephosphorylation, as opposed to allosteric binding of small molecules, for example, plays such a prominent role in switching proteins on and off in signaling pathways? 别构或变构
Testing and Thinking1.Thehormoneglucagon（胰高血糖素）stimulatesthebreakdownofstoredglycogen（糖原）in liver and muscle cells by the followingenzymes.Whichis the first enzyme that must be activated?(a.Protein kinaseAb.Phosphorylasekinased.Protein phosphatasec.Glycogenphosphorylasee.Proteinphosphataseinhibitor-l2.Fillin the blanks with the appropriateterms:isanintracellularproteinthatbinds calciumand activates(a)enzymes.(b)A substance that fits intoa specificbinding site on the surface of aproteinmoleculeis calleda2
2 Testing and Thinking 1. The hormone glucagon（胰高血糖素） stimulates the breakdown of stored glycogen（糖原） in liver and muscle cells by the following enzymes. Which is the first enzyme that must be activated? ( ) a. Protein kinase A b. Phosphorylase kinase c. Glycogen phosphorylase d. Protein phosphatase e. Protein phosphatase inhibitor-1 2. Fill in the blanks with the appropriate terms: (a) is an intracellular protein that binds calcium and activates enzymes. (b) A substance that fits into a specific binding site on the surface of a protein molecule is called a
ANSWER1.A2.(a) calmodulin (b) ligand3
3 ANSWER 1.A 2.(a) calmodulin (b) ligand
第4节酶联受体信号传递途径Signalingviaenzyme-linked receptor★特点：不需要信号偶联蛋白（G-蛋白），而是通过受体自身的酪氨酸蛋白激酶的活性来完成信号跨膜转换；该通路对信号的反应比较慢（通常要几小时）并且需要许多细胞内的转换步骤；通常与细胞分裂相关
4 第4节 酶联受体信号传递途径 Signaling via enzyme-linked receptor 特点： ◆不需要信号偶联蛋白(G-蛋白), 而是通过受体自 身的酪氨酸蛋白激酶的活性来完成信号跨膜转 换； ◆该通路对信号的反应比较慢(通常要几小时)， 并且需要许多细胞内的转换步骤； ◆通常与细胞分裂相关
enzyme linked receptor、分为两种情况：一本身具有激酶活性，如EGF，PDGF，CSF等的受体；一本身没有酶活性，但可以连接激酶（非受体酪氨酸)，如细胞因子受体超家族。5
5 • 分为两种情况： – 本身具有激酶活性，如EGF，PDGF，CSF等的受 体； – 本身没有酶活性，但可以连接激酶(非受体酪氨 酸)，如细胞因子受体超家族。 enzyme linked receptor