1. Things to look for in the metabolic process:
Cell Metabolism
Things to look for in the metabolic process:
1. Energy transformations
Kinetic energy
work
Potential energy
Examples:
Kinetic energy = energy of motion Potential energy = stored energy
Examples of kinetic energy might include brownian motion of molecules in solution or gas Examples might include: food energy (glycogen and fat); energy is stored in chemical bonds.
Examples of energy transformations might include:
Chemical work in the form of protein synthesis and any other anabolic process
Epithelial transport systems
Muscle contraction
Energy conversion is not 100% efficient. Some energy lost as heat during the conversion. Where does your internal heat come from?
Energy must follow the laws of thermodynamics – 1st law is constancy of total energy. No gain or loss, just conversions from one form to another
2nd law – everything is moving toward greater disorder
Chemical reactions transfer energy
Chemical reactions proceed based on several factors.
Reactions requiring energy are coupled to reactions releasing energy.
5. Many metabolic reactions are reversible; many are irreversible

2. What do they do to help reactions proceed?
ENZYMES
What are they?
What do they do to help reactions proceed?
THEY LOWER THE ACTIVATION ENERGY OF A REACTION
Activation Energy - The energy barrier that must be overcome during a collision of two potential reactants in order for a reaction to occur.
Enzymes are largely proteins that act as biological catalysts. They speed up the rate of a chemical reaction without being changed themselves.
Enzymes lower the activation energy for a reaction to proceed. By binding to substrates they bring them into optimal reaction positions.
Enzymes tertiary or quaternary structure has a specific location that substrate(s) bind to. This binding promotes the interaction of the reactants (substrates), while allowing them to be released from the enzyme active site after they are through.
This type of interaction is called the induced-fit model. The enzyme structure does change when the substrates bind, but it also reverts when the products are formed.
How do they do this? (induced fit)

3. Activation energy required for rxn to occur
Proportion of reactants that have reached sufficient energy to participate in the reaction

4. Some enzymes may also require Cofactors or Coenzymes
Cofactors are inorganic, or non-protein organic molecules
Coenzymes are organic molecules that act as receptors and carriers for atoms/functional groups
Cofactor – usually a metal; trace elements are often used
Coenzyme- organic molecule; most often NAD+ or FAD+

5. Enzyme activity may be modulated. Possible modulators include:pH
Temperature
Other molecules
competitive inhibitors
noncompetitive inhibitors
allosteric modulators
covalent modulators
Concentration of enzyme/substrate
pH changes enzyme activity because it changes the way that amino acids within the enzyme’s structure interact with one another. Thus, changes in pH can alter the tertiary/quaternary structure of the enzyme, resulting in a change in its function.
Temperature can work as a positive or negative modulator. Up to a certain temperature, warming results in an increase in the kinetic energy of both enzyme and substrate molecules, thus increasing their chances of interacting. Above a certain temperature, the heat will begin breaking hydrogen and other weak bonds within the protein and change it’s tertiary structure. This is called denaturation.
A competitive inhibitor is a molecule that binds to and blocks the active site on an enzyme. They may just block the site, without the enzyme altering them in any way. They may also be molecules that can act as a substrate for the enzyme, competing with the “natural” substrate. Ethylene glycol (antifreeze) is acted upon by alcohol dehydrogenase and made into the toxin oxalic acid. Treatment for ingestion is to give a person ethanol. Ethanol is also a substrate for alcohol dehydrogenase, thus competing with ethylene glycol for the binding site on alcohol dehydrogenase.
Noncompetitive inhibitors bind to the enzyme somewhere other than the active site. They don’t block substrate binding, but somehow inhibit normal catalysis. Some bind to cofactors.
Can you explain HOW/WHY each of these modulators results in a change in enzyme activity?

13. Km = affinity of substrate for enzyme; defined as [substrate] that elicits half-maximal reaction velocity Km

14. You have a mixture of several metabolic intermediates in a test tube
You have a mixture of several metabolic intermediates in a test tube. The intermediate compound A is the substrate of enzyme ZZ. Additional compounds include B, C, D, F, and G. Look at the following conditions and explain what is happening.
 Condition 1: A and B are in in the test tube in equal concentrations. A is found to occupy the active site 3X as often as B, but when both are present, the reaction rate slows down. Draw what the activity of the enzyme might look like in the presence of compound A, and then when A and B are both present.
Condition 2: Enzyme ZZ is in the test tube with intermediates A, C and F. The activity of the enzyme is lower than expected. What is possibly happening and how would you determine whether your theory is true or not? Graph your experimental results. 
Condition 3. Enzyme ZZ is in the test tube with intermediates B and D. The activity is higher than expected. What is possibly happening and how would you determine whether your theory is true or not? Graph your experimental results.
Activity of enzyme ?
[Substrate]