1．Describe the similarities and differences in the cycling of Gs
and Ras between the active and inactive forms.
2. Some integral membrane enzymes depend upon the lipids in their microenvironment not only for scaffolding, but for enzymatic activity. The Na+-K+ ATPase is one example. Please design an experiment to test the influence of membrane fluidity on the velocity of the Na+-K+ ATPase.
3. a. The average molecular weight of proteins in the cell is about 30,000 daltons. A few proteins, however, are very much larger. The largest known polypeptide chain made by any cell is a protein called titin (made by muscle cells), and it has a molecular weight of 3,000,000 daltons. Estimate how long it will take a muscle cell to translate an mRNA coding for titin (assume the average molecular weight of an amino acidto be 120, and a translation rate of two amino acids per second for eucaryotic cells).
b. Transcription occurs at a rate of about 30 nucleotides per second. Is it possible to calculate the time required to synthesize a titin mRNA from the information given here?
4. What is the advantage of having an extracellular signal transmitted by a cascade of sequential events?
5. Heating of calf type I collagen fibers to 450C denatures the triple helices and separates the three chains from each other. Collagen that has been treated in this way does not renature to form a normal collagen triple helix. Why?--
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