1. Energy, ATP, and Enzymes

2. Energy
The ability to do work, that is, to move matter against opposing forces such as gravity and friction
Kinetic energy- energy of motion
Potential energy- stored energy, the capacity to do work

3. Study of energy transformation
Thermodynamics
Study of energy transformation
The First Law of Thermodynamics- energy can be transferred and transformed, but it can neither be created nor destroyed
The total energy of the universe is constant
Mass is a form of energy
The Second Law of Thermodynamics- every energy transfer or transformation increases the entropy of the universe
There is trend toward randomness
Energy must be spent to retain order- this spending of energy usually releases heat, increases the entropy elsewhere

4. Free Energy- the portion of a system’s energy that can perform work
It’s called “free” energy because this is the energy which can perform work, not because there is no energy cost to the system
Exergonic Reaction- a process with a net release of free energy
Sometimes called spontaneous, but that doesn’t mean that it will occur rapidly
Endergonic Reaction- a process which absorbs free energy from the surrounding
Most synthesis are endergonic
Energy Coupling- use of exergonic process to drive an endergonic process
The free energy released from the exergonic process is absorbed by the endergonic process

5. Types of Cellular Work
Mechanical- beating of cilia, muscle contractions, etc.
Transport- pumping of molecules and ions across a plasma membrane against their concentration gradient, etc.
Chemical- pushing endergonic reactions that would not occur spontaneously

6. ATP- Power to Drive Cellular Work
Adenosine triphosphate – a close relative to Adenine, a nucleotide found in DNA
Contains 3 phosphate groups connected to each other in sequence
The bonds can be broken by hydrolysis
When the terminal phosphate bond is broken, a molecule of inorganic phosphate (Pi) is formed
This forms adenosine diphosphate, ADP + Pi
This generates free energy, which can be used by the cell to do work

7. ATP

8. Enzymes and Chemical Reactions
Catalyst- a chemical agent that changes the state of a reaction without being consumed in the reaction
Substrate- reactants in an enzyme-catalyzed reaction
Intermediate- compounds formed between initial reactants and products (i.e. enzyme-substrate complex)
Products- products
Cofactors- helpers for enzymes
Energy Carriers- sources of quick energy (ATP)

9. Enzymes are protein catalysts
99% of all enzymes are proteins
Speed up reactions
Work for both forward and reverse reaction
They can become saturated
They are highly selective

10. How Energy Relates to Reaction
Initial State  transition state  final state
Substrate must overcome an energy barrier to react and form the products
An enzyme lowers the energy barrier, thus speeding up the reaction

12. Lock and Key Hypothesis
There is only one active site which precisely fits the reactants (more or less)

13. Enzymes are Substrate Specific
Enzymes bind to the substrate or substrates when there are two or more reactants
Catalytic action of the enzyme converts the substrate(s) to product(s)
Enzymes can distinguish its substrate from similar molecules and even isomers of the same molecules
Only a restricted region of the enzyme molecule actually binds to the substrate- active site
This is not perfect- as enzyme and substrate come together, a small conformation change occurs so that the action site fits even more snugly around the substrate  Induced Fit

16. Temperature: a measure of molecular motion
A Cell’s Physical and Chemical Environment Affect Enzyme Activity
Temperature: a measure of molecular motion
As temp increases, reaction rate will increase
However, as temp increases, the molecular motion of the enzyme also increases
Enzyme’s active site may become unstable and function poorly
Bond maintaining 2o, 3o, and 4o structure of protein collapse  denatured

17. Temperature optimum- temperature at which enzyme exhibits peak performance

18. pH- a measure of [H+] – acidic or basic
pH optimum- peak performance at a certain pH
Extreme pH, enzyme may denature

19. Cofactors A non-protein enzyme helper Aid in enzyme catalytic function
May be inorganic (Zn or Cu) or organic  coenzymes
Stabilize transition state
Most vitamins are coenzymes

20. Most Enzymes are Regulated 1. Competitive Inhibition
Other molecules is “competing” for space on the active site
Interfere with substrate binding…slow down reaction rate

21. 2. Allosteric Regulation
Regulatory molecules (ligands) may bind to a location other than the active site  allosteric site
Allosteric activation- shape change make active site available
Allosteric deactivation or non-competitive inhibition- shape change makes active site unavailable

22. 3. Feedback Inhibition (Negative Feedback)
When the product of a pathway acts as an inhibitor of the pathway
Prevents too much buildup of product
Provides a mean of self-regulating in a system