Need help with my writing homework on Some Issues in Molecular Cell Biology. Write a 1250 word paper answering; Membrane lipids possess a critical common structural theme: membrane lipids are amphipathic molecules (amphiphilic molecules), most of which form bilayers. Membrane lipid contains both a hydrophilic (water-loving) and a hydrophobic moiety. In essence, hydrophilic molecules dissolve readily in water because they contain charged groups or uncharged polar groups that can form either favorable electrostatic interactions or hydrogen bonds with water molecules. Hydrophobic molecules, by contrast, are insoluble in water because all, or almost all, of their atoms, are uncharged and nonpolar and therefore cannot form energetically favorable interactions with water molecules.
(a) What type of secondary structure is adopted by the polypeptide segments Met 1–Ala 11 and Thr 50–Ala 59? (2 marks)
(b) What type of secondary structure is adopted by the polypeptide segment Ile 93–Arg 102? (1 mark)
(c) How many chiral centers are present in the C-terminal amino acid residue? (1 mark)
(d) At the normal cellular pH, what will be the charge of amino acid residue 62? (1 mark)
(e) In this model of isolated, purified protein none of the cysteine residues has formed disulphide bonds. Assuming that Ras adopts the same conformation within the cell, give two reasons why internal disulphide bonds are unlikely to form in this protein. (2 marks)
(f) The guanine base of the GDP forms hydrogen bonds with Asp 119 in Ras.
(i) How many hydrogen bonds are shown in the model between GDP and Asp 119? (1 mark)
(ii) What functional group of the amino acid forms the bonds? (1 mark)
(iii)One hydrogen bond is formed between the nitrogen atom N1 in the guanine base and the oxygen atom OD1 in the Asp residue (N—H—O). What is the distance between the nitrogen and oxygen atoms? (1 mark)
(g) Is this form of Ras active or inactive? Explain your reasoning. (2 marks)
(h) If site-directed mutagenesis was carried out on H-Ras to change Lys 16 to Tyr 16, what effect do you think this would have on the function of the protein? Explain your reasoning. (2 marks)
(i) Outline what effect interaction of Ras with an appropriate GEF (guanine nucleotide exchange factor) would have on the structure and function of Ras. (2 marks) (You need to upload the relevant data).