Energy and Enzymes- BIO 1113

OSU Ball/Mackey

Metabolism 

All of the chemical reactions that occur within an organism that are necessary for the maintenance of life

Catabolic Reactions

Breakdown complex molecules and release energy

Anabolic Reactions

Use energy to build complex molecules

Energy

The capacity to do work

Kinetic Energy

Energy of motion

• Heat- kinetic energy associated with random movement of molecules

Potential Energy

Energy stored in position 

• Chemical- potential energy available for release in chemical reaction (breakdown of food)

Thermodynamic

Study of the energy transformations that occur in a collection of matter

1st Law of Thermodynamic

Energy can be transferred/transformed but not destroyed

• Principle of Conservation of Energy

2nd Law of Thermodynamics

Every energy transformation or transfer increases the entropy of the universe

• Entropy= measure of disorder/randomness

Gibbs Free energy (G)

portion of a system’s energy that can perform work

If deltaG is negative

reaction is spontaneous (energetically favorable)

• Loss of free energy, final state is more stable

• Exergonic Reaction (energy is EXiting)

• Catabolic Reaction

If deltaG is positive

reaction requires energy input

• Endergonic Reaction (energy is entering)

Equilibrium

state of maximum stability

• Lowest possible G value

• Any change will require energy therefore systems never spontaneously move away from equilibrium (can do no work)

Energy Coupling

• Use of exergonic reactions to drive endergonic reactions

• Usually happens through transfer of electrons or phosphate group

Redox Reactions

• Transfer of electrons releases energy stored in organic molecules

• Oxidation-reduction reactions

Oxidation

Loss of electrons (LEO)

Reduction

Gain electrons (GER)

Adenosine Triphosphate (ATP)

Bonds between phosphate groups can be broken by hydrolysis

Regeneration of ATP

Reverse reaction must be endergonic

• ADP + P_i → ATP + H₂O = deltaG + 7.3 kcal/mol

Exergonic reactions provide necessary energy

• Cellular respiration

• Light energy

If ATP could not be regenerated we would use up our body weight in ATP each day

• Working muscle cell=10 million molecules of ATP consumed and regenerated per second

Role of Enzymes

Just because a reaction is spontaneous does not mean it occurs quickly

Enzymes are proteins (mostly) which act as catalysts and speed up reactions

• Not consumed by the reaction

• Act by lowering the activation energy (E_A)

Substrate

Reactant acted on by the enzyme

Active site

• Region that actually binds the substrate

• Only specific substrate can fit in active site

Induced fit

• Binding of substrate causes the enzyme to slightly change shape

• Brings chemical groups of active site into optimal position to catalyze reactions

Activation energy

• Reactants absorb energy from their surroundings to reach state where bonds can change 

How do enzymes lower E_A?

• Act as a docking station to bring reactants together in proper orientation

• Stretch reactants toward transition-state form, stressing and bending chemical bonds

• Provide a microenvironment more favorable to a particular reaction

• Participate directly in the chemical reaction

Steps of substrate and enzyme reacting

1. Substrates enter active site

2. Substrates are held in active site by weak interactions

3. Active site can lower E_A and speed up a reaction

4. Substrates are converted to products

5. Products are released

6. Active site is available for two new substrate molecules

Do enzymes work alone?

Cofactors

• Inorganic ions

Coenzymes

• Organic molecules

Prosthetic groups

• Molecules permanently attached to the enzyme

Factors that Affect Enzyme Activity

• Proteins function best under specific conditions

Temperature

• once you reach a temperature so high you denature enzymes so the enzyme no longer functions

• optimal temperature is different based on each enzyme, depends on environment 

pH

Enzyme Regulation

Enzyme function is tightly regulated 

• Regulatory binding is usually reversible

Competitive Inhibition

Molecule resembles substrate and binds to active site

• molecule close enough to compete for active site, blocking substrate

Allosteric Regulation

Regulatory molecule binds away from active site and causes change in shape

• Can either activate or inhibit activity

Enzyme Inhibitors

toxins, poisons, and drugs

• sarin gas= binds to active site of acetylcholinesterase

• HIV 

• ACE inhibitors

• Prilosec

• Penicillin=blocks active site of enzyme necessary for cell wall formation in bacteria

Other methods of regulating enzyme activity

Cleavage

• Trypsinogen to trypsin

Phosphorylation

• Causes conformational change

Regulating Metabolic Pathways

Enzymes often catalyze a series of related reactions

• Metabolic pathway

Feedback Inhibition

• End product of a pathway can bind to an enzyme that acts earlier in the pathway and inhibit it

• Prevents cell from wasting energy to make excess product