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Unformatted text preview: w well the
pump binds its substrate, in this case Ca2+. The higher the affinity of a transport
protein for Ca2+ (in this case), the more specific that transporter is for transporting
(c) Using the initial rate data below, calculate the Vmax and Km for each Ca2+ pump. 7.06 Spring 2004 80 PS 1 key 5 of 11 Ca2+ pump A
Ca2+ pump B
Ca2+ pump C Initial rate of Ca2+ export into liposome, Vo 70 Ca2+ pump D 60 50 40 30 20 10 0
1 2 3 4 5 6 7 8 9 10 11 12 2+ External [Ca ] uM Answer: For pumpA, Vmax=75 and Km=2.2mM. PumpB, Vmax= 37.5 and Km=
3.5mM. PumpC, Vmax= 15 and Km= 4.5mM. PumpD, Vmax=2 and Km=6mM
(d) Based on this data, which Ca2+pump would you recommend to your graduate student
and why? Also, why would some do some Ca2+ pumps have higher Kms than others?
Answer: Based on this data, the best pump is Ca2+ pumpA. This pump has the
highest maximal rate and is the most specific for Ca2+. Your initial isolation
experiment didn’t test for Ca2+ specific pumps, just for transport proteins that
were capable of transporting Ca2+. Therefore the primary function of some of
these pumps might not be Ca2+ transport. However, because of their structure they
are still capable of transporting Ca2+ when its true substrate is absent, or when the
concentration of Ca2+ is high enough to out-compete the true substrate.
(e) Ca2+ pumps fall under the category of ATP-powered pumps. Explain how ATPpowered pumps work. Also explain how ion channels work, what the three types of
transporters are and how each one works.
Answer: ATP-pumps use the energy of ATP hydrolysis to transport ions or small
molecules against their electrochemical gradient. Ion channels allow specific ions
(determined mostly by the structure of the channel) to flow down their
electrochemical gradient (no extra energy is required). The three types of
transporters are: uniporters, which utilize conformational changes to transport
specific molecules down their concentration gradient; symporters and antiporters
drive the transport of one molecule against its concentration gradient by
transporting a second molecule down its concentration gradient. Symporters 7.06 Spring 2004 PS 1 key 6 of 11...
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This note was uploaded on 01/23/2012 for the course LSM lsm1301 taught by Professor Seow during the Spring '11 term at National University of Singapore.
- Spring '11