1. Multiple Choice
Which of the following biomolecules consists of monomers of amino acids:
A) carbohydrates B) Proteins C) Nucleic acids
Which of the following biomolecules consists of monomers of nucleotides:
Which of the following biomolecules is not used to store biological information:

2. LEQ: How do enzymes help cells perform chemical reactions?
Reading: 2.5, 12.3; Unit 2 Test mon
Activator: Reaction Acrostic
Term, phrase, idea using R-E-A-C-T-I-O-N
Key terms – bond energy, activation energy, enzyme,

3. Bonds break and form during chemical reactions.
Chemical reactions change chemicals into different ones
breaking old bonds
forming new bonds
O2 + C6H12O CO2 + H2O
Reactants Products
A chemical reaction transforms the chemical arrangement of its reactants into new products by breaking and forming new chemical bonds.
Bond energy:
Energy is added to break bonds.
released when bonds form.

4. Organisms require energy for a cell to maintain homeostasis.
“Products must be generated”
Reversible reactions can reach equilibrium - generally fatal to cells (no way to generate products)*
CO2 + H2O H2CO3
All living things require certain chemical reactants to produce the molecules necessary to maintain homeostasis. Therefore certain chemicals are a necessity to produce the biomolecules necessary to sustain life.
Organisms also require energy to produce these molecules. The reactants that organisms acquire through their diets or synthesize with the aid of inorganic chemicals and/or sunlight also contain an assoicated energy in their chemical bonds (chemical bonds).
Energy must be added to break chemical bonds during reactions (this displaces the arrangement of electrons in a bond, separating atoms from each other), but energy is also released from a bond when electrons reposition themselves, radiating heat, and sometimes emitting visible light.
Due to the nature of chemical reactions, there is a likelihood that the products may rearrange themselves back into the original reactants. We say that reactions are reversible and if reactants reform at the same rate that they are consumed, the reaction reaches equilibrium. This is generally fatal to cells because the chemical reactions necessary to maintain homeostasis must have specific products to continue sustaining life.

5. Chemical reactions release or absorb energy.
Activation energy needs to be absorbed to start a chemical reaction.
Significantly delay rate of reaction
The obstacle that must be overcome in any chemical reaction is the energy required to displace atoms from their arrangement in a bond to get the reaction started. This is called activation energy and a characteristic of the reaction to proceed.
Since this energy can be greater than the energy available in a chemical system, many reactions will not proceed without additional energy added to the reaction. If if a reaction can occur spontaneously, this should not be confused with it happening often. A cell could wait years for a bond to break on its own and would surely die without a means of reducing the activation energy necessary to carry out reactions to sustain life.

6. Exothermic reactions release more energy than they absorb.
Products have lower bond energies
Reactions generally fit two profiles:
Exothermic reactions are characterized by a net release in energy when the reactants rearrange themselves into resulting products. Remember, energy is still required to initiate the reaction, but as the reaction proceeds the amount released is greater. Products tend to simpler in arrangement when compared to their original reactants.

7. Endothermic reactions absorb more energy than they release.
Products have higher bond energies.
Endothermic reactions are characterized by a net increase in energy: energy is invested in creating new high energy bonds while the reactants rearrange themselves into products. This is typical of the reactions that produce polymers from monomers since new bonds are created to join them together.
Interestingly, these reactions can only proceed if an energy source is available to an organism, hence the need for constantly replenishing energy and sources of chemical reactants. Exothermic reactions can fill this energy need if an organism can obtain high energy reactants in suitable amounts.
The trick is to get the energy from an exothermic reaction to an endothermic reaction before it is lost as heat from the system. More on a chemical that assists in this transfer called ATP later.

8. A catalyst lowers activation energy.
Catalysts are substances that speed up chemical reactions.
decrease activation energy; increase reaction rate
Even if organisms can obtain suitable amounts of high energy reactants like carbohydrates or fats, the reactions themselves still require an energy investment to get them started (drag).
Organisms have uniformly evolved biological catalysts that reduce the activation energy demand and increase the rate of a reaction many-fold. Reactions that ordinarily take years if not longer can be accelerated to rate that results in many molecules of product in fractions of a second. Now that’s efficiency! This is also one of the most essential events that makes the life any organism leads possible.

9. Enzymes are proteins that catalyze chemical reactions without being consumed.
Enzyme terms:
Substrate
Reactant(s)
Active site
Binds substrates
Substrate specific
substrates (reactants)
enzyme
Substrates bind to an enzyme at certain places called active sites.
The biological catalysts used in the vast majority of reactions are proteins called enzymes. Enzymes catalyze reactions by accepting a reactant(s) (from here referred to as a substrate) into a specialized pocket or active site that is substrate specific. This specificity is a direct result of the unique amino acid sequence found in these proteins allowing each type of enyzme to catalyze a specific chemical reaction without necessarily interfering with or being interfered by other reactions in its vicinity (In AP, you will find that biological chemistry did evolve mechanisms to block these active sites to better control the rate of chemical reactions).

10. The lock-and-key model helps illustrate how enzymes function.
Substrates bind to an enzyme at certain places called active sites.
The enzyme brings substrates together and weakens their bonds.
The catalyzed reaction forms a product that is released from the enzyme.
Enzymes and their substrates work like a lock-and-key:
The substrate fits in the active site like a key in a door lock
The sound of the lock and key sliding into its fit is the activation energy barrier dropping
3) The lock is free to turn (react) with a simple turn of the key and wrist!
Note: enzymes can catalyze a reaction that joins two reactants and also breaks a reactant down. We’ve covered some of the basic of chemical reactions, but we’re truly just getting started. Many more mysteries lie ahead. Where did these enzymes come from? What reactions do they catalyze? Are they all made of protein or just most?

11. Questions
Chemical reactions tend to reach equilibrium when they are left to proceed on their own. Why is this dangerous for a cell (Hint: how will this affect the production of biomolecules)?
Biological catalysts are essential for cells to function as systems. Do you think cells could produce polymers by using uncatalyzed reactions? Why or why not?
Consider exothermic and endothermic reactions. How do cells find the energy to perform an endothermic reaction?

12. Summary:
How is the structure of an enzyme’s binding site related to its function?
When a chemical reaction reaches equilibrium describe what is happening to reactants and products.
What prevents a chemical reaction from occurring spontaneously?
Speculate: why has evolution produced nothing but cells that specialize in catalyzed chemical reactions?
How do catalyzed chemical reactions aid in homeostasis?
How can exothermic and endothermic reactions be considered a system?
The process below is exothermic. What must be true about the bond energies of the reactants and the products? Explain:
6O2 + C6H12O6  6CO2 + 6H2O

13. Answers:
Catalysts reduce the activation energy required to start a chemical reaction - easier to rearrange chemical bonds to form product.
Enzymes bring substrates close together so that they can react and slightly alter the bonds within the substrates by changing the shapes of the molecules (lowers the activation energy barrier).
Endothermic reactions absorb energy and their products have higher bond energy (energy goes into bond formation). Exothermic reactions release energy and their products have lower bond energy (energy leaves the reaction site when bonds break).
Bond energies must be higher in reactants than those of products: energy is released