Biological Science 101 – General Biology
Lecture Six: Cell Energy and Enzymes
Ch. 8, Pgs. 142-160
Cell Energy and ATP
Cell Energy (Metabolism):
- All of the chemical reactions in the body.
- Breakdown of complex molecules to simple ones = Catabolism (Cellular
Cellular respiration -> Energy produced.
- Build-up of complex molecules from simple ones = Anabolism, energy is required.
Complex molecules -> Catabolism -> Energy is produced (exergonic) -> Energy
captured -> Anabolism -> Energy is used (endergonic).
Energy Captured -> Cells use energy.
E.g. DNA replication, Protein synthesis and Membrane
Energy captured -> ATP (Adenosine triphosphate)
Exergonic reaction -- ATP --> Endergonic
ATP + H 02-> ADP + Pi (7.3 kcal/mole energy) Exergonic Muscle Cells -> require 10 million ATP/sec when
- Energy from foods is converted to energy through
- Glucose + O 2> CO +2H2O (686 kcal/mole)
Another energy molecule: NAD (Nicotinamide
Oxidation -- Electrons --> Reduction
- “High-energy foods”
- Involved in catabolism.
- Food broken down.
- Energy released.
- Catalytic proteins that speed up the rate of a
reaction, without altering the end products or change
Chemical reaction to start requires initial energy
(activation energy), usually heat energy.
Enzyme reduces the activation energy required. Characteristics of Enzymes:
1) Substrate Specific
- Sucrase -> Sucrose
- Sucrose binds to an active site on the enzyme.
- Form enzyme + substrate complex.
- Products released (glucose + fructose)
- Reaction occurs at 1000 x per second.
2) Affected by Environment (Sensitive)
- Temperatures can affect enzymes ability to function.
- Each enzyme has its own optimal temperature.
- pH can also affect enzymes.
- Each enzyme has its own optimal pH.
3) Requires Cofactors or Co-enzymes
- Assist with the catalytic activity.
E.g. Zn, Cu, Co-enzyme A, Vitamins (function as
cofactors or co-enzymes)
4) Activity of Enzymes are affected by Chemicals
- This may cause enzymes to stop.
- It can be reversible or irreversible:
a) Competitive Inhibition:
- Chemical inhibitor.
- Competes for active site.
- Reaction stop.
- Reversible. b) Non-competitive Inhibition:
- Chemical molecule binds to enzyme.
- Alters active site.
- Enzyme nonfunction