Question

2. Under physiological conditions, the Na+-K+ pump transports sodium and potassium across the membrane through the hydrolysis of ATP. This occurs in a sequence of steps.

A. (5pts) Beginning with the START step, put the other steps a-e (currently listed in random order) of the Na+-K+ pump’s mechanism in order to complete a full cycle of transport.

START – The protein is phosphorylated open to the extracellular side, and contains 2 K+ ions.

a. ATP hydrolysis, protein phosphorylation, and ADP release open the protein to the extracellular side.
b. The protein binds ATP which opens the protein to the cytoplasmic side.
c. The protein closes & dephosphorylates.

d. 3 Na+ exit into the extracellular space, and 2 K+ enter into the protein.
e. 2 K+ exit into the cytoplasm, 3 Na+ enter into the protein, and the protein closes.

Order of steps: START ______ ________ ______ ______ _____
B. (3pts) Describe a condition in which the cycle would proceed in the reverse order.

1. Short answer (8pts each, 2 sentences max)
A. How does the saturation of lipid tailgroups affect a membrane’s fluidity?

B. Why don’t cells have membrane transporters to build gradients of O2?

C. Your lab recently purchased a 30-inch monitor, & your friend claims now they can enlarge all images obtained using a light microscope to distinguish objects that are less than 0.1 μm apart. Is she right? Please provide your reasoning.

D. Why is C. elegans a useful model organism for studying cell development?

3. (6pts) Suppose you a treating a patient who isn’t expert in cell biology. How would you explain to them how their disease is caused by specific cellular and molecular defects? You can choose either a patient with multiple sclerosis OR a patient with cystic fibrosis. (2-4 sentences)

Answer 1

1. (A) Saturation of lipid tail groups affect a membrane’s fluidity because fatty acid that are saturated contain only single bond so that at room temperature it would pack with tight condition and responsible for making it a solid at room temperature.

(B) Oxygen being, non-polar molecule that is able to pass the membrane freely. Hence, oxygen is passively transported across the membrane. That is why cells do not have membrane transporters to build gradients of oxygen.

(c) Yes, she is right as light microscope is able to distinguish object less then o.1 μm apart . Because light microscope has a good resolution.

(D) C. elegans is used as model organism because

(i) It is found very easily as it is easily found in various part of the world.

(ii) Its average life span is small i.e 2-3 weeks.

(iii) C. elegans has many similarity in cellular structure with human and other organism.