lect8 - Bio 1A. Feb. 6, 2009 Lecture 8. Wilt Reconsidering...

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Lecture 8. Wilt Reconsidering the Enzyme I. Allostery A. Allosteric effectors may have positively, or negatively, on the functions of the active site. 1.It may stabilize an active conformation if the enzyme oscillates between an active and inactive form. 2. The interaction may produce cooperativity. Occupancy of one active site in a multi-subunit protein can enhance the activity of remaining site. For example, binding of one oxygen to a heme in Hb produces enhanced binding in remaining unoccupied sites. 3. Feedback lnhibition ( non-competitive) by the product of a metabolic sequence can regulate the flow of substrates through a sequence, as in the production of isoleucine from threonine. II. The binding site of an enzyhme A. It has exquisite specificty, due to molecular complementarity B. Catalysis can proceed by many different chemical mechanisms, such as acid-base catalysis, transitory covalent bonding, activity of metals and prosthetic groups. 1. pH and temperature can have big effects on the active site. Overview of Metabolism I. Metabolism consists of degradation of molecules (catabolism) obtained from food stuff, with the attendant capture of energy, and the formation (anabolism) of 60 building blocks necessary to form the macromolecules needed by cells for their maintenance and reproduction. A. An abbreviated way to show this is: 1. Complete oxidation to form energy glucose -------------------------------- CO 2 + H 2 O + (-686 kcal/mol) 2. Or incomplete oxidation to yield some energy and 2-3 carbon compounds, which can then be used, together with NH 3 and ATP for biosynthesiis. glucose ----+ NH 3 + ATP ------- 60 building blocks --------- macromolecules B. This is all accomplished with a series of enzymatically catalyzed reactions. The complete oxidation of glucose and capture of its energy takes place in 28 smaller steps. We shall sketch the general progress of these reactions, focusing on a few crucial steps. C. It is important to realize that these reactions are not only catalyzed by enzymes, but are also regulated ( i.e., rates controlled) by various kinds of mechanisms). We shall mention them here, and look at them in detail after we have investigated more thoroughly the metabolism of glucose. 1. Many carbohydrates found in food stuffs are first converted to glucose in
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lect8 - Bio 1A. Feb. 6, 2009 Lecture 8. Wilt Reconsidering...

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