quiz1_2_24

quiz1_2_24 - 7.014 Quiz I 2/25/05 Your Name: _ TA's Name:...

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7.014 Quiz I 2/25/05 Your Name : _________________________________ TA's Name: Write your name on this page and your initials on all the other pages in the space provided. This exam has 10 pages including this coversheet. Check that you have pages 1-10. The last page has the structures of the amino acids. This exam has 4 questions. Read all questions before starting to write. Write your answers as clearly and precisely as possible in the space provided. This is a closed book exam. Question Value Score 1 36 2 36 3 14 4 14 TOTAL: 100
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Name:________________________________________ TA:____________________ 2 Question 1 (36 points) Below is a ribbon representation of the K + channel, a membrane spanning protein made up of four copies of a single polypeptide. The K + channel allows K + ions to be shuttled through the membrane. Inside the cell Outside the cell a) What protein secondary structure is part of the K + channel protein as shown above? b) Does the K + channel have quaternary structure? If yes, describe it. c) Using as a schematic of a phospholipid, draw a cross-section of the membrane around the K + channel shown above. d) What type(s) of amino acids do you expect to find on the K + channel polypeptides i) next to the tails of the membrane lipids? (Circle all that apply) Polar Nonpolar Positively charged Negatively charged Why? ii) next to the heads of the membrane lipids? (Circle all that apply) Polar Nonpolar Positively charged Negatively charged Why?
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Name:________________________________________ TA:____________________ 3 Question 1, continued e) If you were trying to estimate the volume occupied by this protein, would the picture above provide all the information you need? Why or why not? The positively charged K + ion is a very small soluble molecule. f) Explain why K + cannot come across the membrane without a channel protein. You isolate a mutant of the K + channel that transports less K + than normal. You run both the wild-type and mutant proteins on a denaturing gel and get the following result: Wildtype Mutant g) From the gel data we can conclude that (circle all that apply): shorter than i) Each subunit of the mutant protein is the same length as in the wild-type protein. longer than Justify your answer(s) primary ii) The mutant and wild-type proteins could differ in their secondary structure. tertiary Justify your answer(s)
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Name:________________________________________ TA:____________________ 4 Question 1, continued The K + channel has several binding pockets in which K + ions may associate. Below is an image of one of the binding pockets of the K + channel shown from above.
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This note was uploaded on 05/02/2009 for the course BIOL 7.014 taught by Professor Walker during the Spring '05 term at MIT.

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quiz1_2_24 - 7.014 Quiz I 2/25/05 Your Name: _ TA's Name:...

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