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Kinetics of biological processes

Kinetics is popular term applied loosely to systems in which an object moves or event occurs over time.

Kinetics is commonly used in biology in relation to any cellular process e.g. enzyme kinetics, protein complex formation, vesicle fusion, actin polymerization.

Enzyme kinetics: The molecular mechanism of the enzyme determines the rate at which it catalyzes a given reaction. Enzymatic mechanisms are commonly described in terms of the types of interactions the enzyme has with other molecules. These interactions include non-covalent binding to substrate, product or modifiers (co-factors). Co-factors can decrease (inhibit) or increase (activate) enzyme activity. Enzymes are commonly classified as unregulated or regulated.

Enyzme kinetics tend to occur rapdily at temporal scales of microseconds to seconds (Streyer, 3rd ed, p6.). Other biological processes may be observed over larger time scales such as protein synthesis, vesicle transport, or cytoskeletal re-organization. The temporal aspects of these macroscopic kinetic events may be monitored via time-lapse microscopy or sequential samples at fixed intervals.

Unregulated enzymes:

Enzymes that are not regulated are easily modeled with mass action kinetics. The rate at which they catalzye a reaction when they are not near saturating conditions can be described as a function of the concentration of substrate (S) and the speed of the enzymatic reaction (Vmax or k).

Facilitated diffusion through membrane transporters is another "unregulated" biological process.

Regulated enzymes:

Regulated enzymes, enzymes involving co-factors, inhibition or activation by other molecules maye not be modeled accurately by mass action kinetics. The enzyme's kinetic behavior may be better characterized by Michaelis-Menten or Hill type kinetic models.

Michaelis-Menten is the root of many kinetic models for enzymes. It can be used to model reversible or irreversible reactions that involve:



Reference Materials and Links:

Modeling Networks of Signaling Pathways, U.S. Bhalla, Computational Neuroscience 2001 ed. E. De Schutter
This chapter provides easy to understand approaches to developing models of "well, stirred" systems. Rules and hints are provided for describing the kinetics of a few common enzymatic reactions and deciding if it is feasible to develop a complete numerical model for your system.

"THE Medical Biochemistry Page": Online materials for biochemistry including sections on enzyme kinetics. Developed by Dr. Michael W. King, Indiana State University School of Medicine

"An Introduction to Enzyme Kinetics" by Dr. Peter Birch, Department of Biological Sciences, University of Paisley.

revised 01/14/2006