APK 2105C Lecture Notes - Lecture 11: Cell Metabolism, Kinetic Energy, Pepsin
23 May 2018
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Chapter 3, Part 4
Cell Metabolism
• Enzymes increase rxn rate in the body
o Biological catalysts
o Substrate specific
▪ Substrate = whatever comes in and binds to enzyme
• Reversible binding—substrate is not necessarily changed
o Occurs at active site
▪ Lock and key model = the shape of the substrate complements the active
site of the enzyme
• Enzyme accepts substrate based on its shape
• Does not explain reverse reaction
o Product will not look the same—it will be similar
▪ Induced fit model = both the substrate AND the product can bind to the
active site on the enzyme, allowing the rxn to be reversible
o Enzymes do not change the nature of the rxn or the final product
▪ Enzymes just change the speed the rxn occurs at
o Enzymes themselves are not changed by the rxn
▪ Enzymes can be recycled and used repeatedly
o Enzyme + substrate → enzyme-substrate complex → product + enzyme
▪ Enzyme from the end can go back and start rxn over again
▪ Add more substrate? More product
▪ Enzyme rxns proceed in both direction
▪ Add more product? Make more substrate
• Factors that affect the rate of enzyme-catalyzed rxns
o Temperature
▪ Body temp is tightly regulated—changes in temp are rarely significant
▪ Enzymes have optimal temperature
• Don’t want it to be too cold or too hot
• Kinetic energy increases with heat but enzymes get denatured
with too much heat
o pH = hydrogen ion concentration
▪ Increasing acidity = lower enzyme activity
• Causes structural changes
• Alters the charge of the active site
o Enzymes have electrical affinity to draw substrates into the
active site
▪ Enzymes have optimal pH range
• Location of enzyme in the body may indicate where it operates
optimally
o Pepsin in the stomach
o Cofactors and coenzymes
▪ Cofactors = vitamin or mineral that acts, cooperates with an enzyme
• Enhances the fit of the active site
• Enhances the ability of the enzyme to bind to the substrate
▪ Coenzymes = vitamin-derived cofactors that function to carry chemical
groups from one rxn to another
• Unchanged by rxns—can be reused
• FAD from B12
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