Humboldt State University ® Department of Chemistry

Richard A. Paselk

VUB Biology

Fall 2001

Lecture Notes:: 8 October

© R. Paselk 2001
 
     
 

Metabolism

Catabolism: degradation of molecules to provide energy.

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

Metabolic Pathways: (overhead/handout - Interactions of Metabolic Pathways) sequences of consecutive enzyme catalysed reactions which are readily studied and traced.

Characteristics of pathways:

The flux through a metabolic pathway is invariably controlled or regulated, most commonly by Feedback Inhibition, but also through Feed-forward activation. Regulation is one of the things that makes biochemistry "biological."

The Stages of Catabolism (overhead/handout): For convenience we can breakdown catabolism into four hierarchical levels:

 

DIGESTION

For food taken into the body, digestion accomplishes Stage I, as outlined below. (Breakdown of substances in cells etc. will of course be done somewhat differently.)

 

GLYCOLYSIS

Glycolysis is going to be our first pathway, and it is arguably the most important and universal of the metabolic pathways.

First if we look at the Glycolysis Pathway (overhead/handout), we can break it into three phases:

 

GLUCONEOGENESIS

In order to provide glucose for vital functions such as the metabolism of RBC's and the CNS during periods of fasting (greater than about 8 hrs after food absorption in humans), the body needs a way to synthesis glucose from precursors such as pyruvate and amino acids. This process is referred to as gluconeogenesis. It occurs in the liver and in kidney. Most of Glycolysis can be used in this process since most glycolytic enzymes are reversible. However three irreversible enzymes must be bypassed in gluconeogenesis vs. glycolysis (overhead/handout): Hexokinase, Phosphofructokinase, and Pyruvate kinase. Phosphofructokinase, and/or hexokinase must also be bypassed in converting other hexoses to glucose.

 

Overview of Glucose Metabolism in the Tissues: Diagram (overhead/handout)

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Last modified 16 October 2001
© R Paselk