(a) Is amylose or amylopectin more likely to be a long-term storage carbohydrate
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Question
(a) Is amylose or amylopectin more likely to be a long-term storage carbohydrate in plants? Why?
(b) The active site of an enzyme is shown by chemical labeling experiments to contain a reactive lysine residue. Assuming that this is the only polar residue in that micro-environment, what would you expect to be the micro-pH of that active site pocket in the enzyme if this amino acid were 50% dissociated ?
(c) What are two differences in the carbohydrate – involved structures between Gram positive and Gram negative bacteria?
Explanation / Answer
* Amylose is more linear than amylopectin, and it takes up less space. It crystalizes more readily; high amylose starch is comparatively more resistant to digetion. Moreover, amylose is not soluble in cold water, and so is a preferred long term storage carbohydrate in plants.
* Lysine has a pKa greater than 10 in aqueous environment. However, in nonpolar environment, the pKa shifts to less than 6. Hence, the micro-pH is extected to be around 6 as pH = pKa when exactly half of the molecule has dissociated.
* The cell wall of Gram positive bacteria is composed of a polymer of repeated subunits of N-acetyl glucosamine a 1-4 N acetyl muramic acid. To the muramic acid, a tetra peptide or a penta peptide is attached.
In Gram negative bacteria, a lipopolysaccharide is present (LPS) outside the cytoplasmic membrane. This is also called Outer membrane. It is composed of lipid A, core polysaccharide, and O-antige.
Both core polysaccharide and O-antigen are righ in carbohydrates, the structures are composed of sugars like Heptulose, 3-deoxy D mannooctulosonic acid, glucose, galactose, mannonse, rhamnose, and abequose. LPS is not present in Gram positive bacteria.
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