Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 438

Introductory Biochemistry

Spring 2007

Lecture Notes: 7 March

© R. Paselk 2006
 
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Vitamins and Cofactors, cont.

Note the relationships of the various cofactors to their vitamin precursors. Chapter 7 of your text has images of the various cofactors and vitamins, as well as example chemistries. You should keep it in mind to refer back too during our studies.

Nucleotide Functions: Most involve use of the nucleotide as a recognition molecule, e.g. ATP (Figure 7.4)

Nicotinamide Adenine Dinucleotide (NAD+) (Figure 7.8) uses ADP (bolded) as a recognition "handle." (Note the two nitrogenous bases each attached to a ribose and linked through a phosphoric acid anhydride linkage:

Similarly adenosine with a modified ribose (reduced to the alcohol - ribitol) is used in Flavin Adenine Dinucleotide = FAD (Figure 7.10; not truly a dinucleotide since ribitol instead of ribose!):

Coenzyme A (Figure 7.12) has an ADP attached to an arm of pantothenic acid, which in turn is attached to beta-mercaptoethylamine. Acetyl groups can be carried on the sulfhydryl group:

Three vitamins give cofactors with long "arms" which enable the cofactors to shift an attached substrate between adjacent active sites on a single enzyme. (Note attachment of biotin and lipoate to lysine side-chain to give 10 atom arms.)

Introduction to Metabolism

Catabolism: degradation of molecules to provide energy.

Anabolism: reactions using energy to synthesize new molecules for growth etc.

Metabolic Pathways

(overhead - Interactions of Metabolic Pathways; Figures 10.5 and 10.6) sequences of consecutive enzyme catalysed reactions which are readily studied and traced. A more rational definition is that of Newsholme and Leach (Biochemistry for the Medical Sciences, Wiley, 1983: pg.42)

"[A] metabolic pathway is a series of enzyme-catalyzed reactions, initiated by a flux-generating step and ending with either the loss of products to the environment, to a stored product (a metabolic 'sink') or in a reaction that precedes another flux-generating step (that is, the beginning of the next pathway)." Where a flux generating step is a non-equilibrium reaction that generates the flux going through the pathway and to whose rate all other reactions of the pathway conform. Note that by this definition some pathways may be inter-organ while others may take place in single compartment. We will explore this definition/concept as we look at metabolism.


Pathway Diagrams

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Last modified 7 March 2007