1. Energy and Enzymes
Ch. 6

2. Flow of energy Energy is the ability to do work or bring a change.
There are 2 types of energy
Kinetic- Energy of motion
Potential- Stored energy
Flow of energy

3. Laws of Thermodynamics
There is a constant flow of energy in biological systems.
The laws of thermodynamics explain why energy flows through ecosystems and cells.
First Law of Thermodynamics- Law of conservation of energy (Energy cannot be created or destroyed, but it can change forms)
Second Law of thermodynamics- Energy cannot change forms without a loss of usable energy.
Laws of Thermodynamics

4. The second law of thermodynamics can be restated as energy transformation make the universe less organized.
The term Entropy is used to indicate the relative amount of disorganization.
Entropy (s)

5. In cell biology, we use the concept of free energy instead of entropy.
Free energy (ΔG) is the amount of energy left to do work after a chemical reaction has occurred. “available energy”.
ΔG is determined by subtracting the free energy content of the reactants from that of the products.
A –ΔG mean that the products have less free energy than the reactants. This is a endergonic reaction- meaning energy is required.
A +ΔG is an exergonic reaction or spontaneous.
Metabolic reactions

6. Gibbs Free Energy ∆G= ∆H - T∆S
∆H = Change in Enthalpy (Heat content) Measured in KJ/mol.
T = Temperature in Kelvin
∆S = Change in Entropy
Gibbs Free Energy

7. ATP, or adenosine triphosphate, is the common energy currency of the cell.
ATP is constantly being generated from ADP (adenosine diphosphate) and an inorganic phosphate molecule.
ATP supplies come from the breakdown of glucose and other biomolecules. Only 39% of the free energy in glucose is converted to ATP.
ATP

8. ATP is a nucleotide of the base adenine and the 5-carbon sugar ribose (together called adenosine) and 3 phosphate groups.
ATP is a “high energy” molecule because the phosphate groups are easy to remove.
APT Structure

9. The ATP cycle

10. ATP hydrolysis is coupled to endergonic reactions so these reactions can have enough energy for the reaction to occur.
Coupled reactions

11. Example: Muscle Contractions

12. Enzymes are protein molecules that speed up a chemical reaction without being affected itself.
The reactants of enzymatically accelerated reactions are called substrates.
Ribozymes are RNA that also serve as biological catalyst.
enzymes

13. Enzymes Activation Energy
Reactants are generally reluctant to participate in a chemical reaction, unless energy is applied. This energy is called activation energy.
Enzymes lower the activation energy. They do this by bringing substrates into contact with each other.
Enzymes

14. Induced fit model Enzymes
The active site complexes with the substrates
Causes active site to change shape
Shape change forces substrates together or apart… initiating or breaking bonds
Enzymes

16. enzymes Factors affecting Enzyme Activity Substrate concentration
Enzyme activity increases with substrate concentration
More collisions between substrate molecules and the enzyme
Temperature
Enzyme activity increases with temperature
Warmer temperatures cause more effective collisions between enzyme and substrate
However, hot temperatures destroy enzyme pH
Most enzymes are optimized for a particular pH
enzymes

17. Denaturation

18. enzymes Factors affecting Enzyme Activity
Cells can affect presence/absence of enzyme
Cells can affect concentration of enzyme
Cells can activate or deactivate enzyme
Enzyme Cofactors - Non-protein molecules that assist enzymes. (often metal ions, Fe2+)
Coenzymes are organic cofactors, like some vitamins
Phosphorylation – some require addition of a phosphate
enzymes

19. Enzymes Enzyme Cofactors (or Coenzymes)
Some enzymes need cofactors to work; these are non-protein groups that attach to the enzyme. Ex. Minerals such as zinc or Mg
Many vitamins (because they are organic are important because they are called coenzymes
Enzymes

20. Reversible enzyme inhibition
When a substance known as an inhibitor binds to an enzyme and decreases its activity
Competitive inhibition – substrate and the inhibitor are both able to bind to active site
Noncompetitive inhibition – the inhibitor binds not at the active site, but at the allosteric site
Feedback inhibition – The end product of a pathway inhibits the pathway’s first enzyme
Enzymes

21. Enzymes Allosteric Enzymes- 2 binding sites
Active Site – substrate binds to
Allosteric Site – allosteric affecter binds
Allosteric Activator – molecule binds to allosteric site and ACTIVATES enzyme.
Creates active form of enzyme.
Allosteric Inhibitor - molecule binds to allosteric site and INHIBITS enzyme.
Creates inactive form of enzyme.
Enzymes

23. Metabolic pathways are a series of linked chemical reactions.
There can be many steps in metabolic pathway, in which each step requires a different enzyme to catalyze the reaction.
The product of one reaction becomes the reactant of the next reaction.
E E E3 E4 E5
A  B  C  D  E  F
Metabolic pathways

24. Enzyme Inhibitors
Inhibition is when the wrong molecule (an inhibitor) binds, blocking the active site; substrate can’t bind
Many poisons are inhibitors of essential enzymes (e.g. death cap mushroom, arsenic, cadmium)

25. Materials that irreversibly inhibit an enzyme are known as poisons
Cyanides inhibit enzymes resulting in all ATP production
Penicillin inhibits an enzyme unique to certain bacteria
Heavy metals irreversibly bind with many enzymes
Nerve gas irreversibly inhibits enzymes required by nervous system
Enzymes