Section 2.4 Chemical Reactions and

Enzymes Pay attention to the graphs

Standard

• LS1.5 Research examples that demonstrate the functional variety of proteins and construct an argument based on evidence for the importance for the importance of the molecular structure to its function. Plan and carry out a controlled investigation to test predictions about factors which should cause an effect on the structure and function of a protein.

I Can…

• LS 1.5 I can research examples that demonstrate the functional variety of proteins.

• LS 1.5 I can use evidence to relate the structure of a protein to its specific function.

• LS 1.5 I can plan and conduct a controlled investigation that tests factors affecting the structure and function of a protein.

Key Questions

1. What happens to chemical bonds during chemical reactions?

2. How do energy changes affect whether a chemical reaction will occur?

3. What role do enzymes play in living things, and what affect their function?

Vocabulary

• Chemical reaction

• Reactant

• Product

• Activation energy

• Catalyst

• Enzyme

• Substrate

Chemical Reactions

• A chemical reaction is a process that changes, or transforms, one set of compounds into another.

• Mass and energy are conserved during chemical transformations.

• Some chemical reactions occur slowly.• Ex. - combination of iron and oxygen to form an iron oxide called rust

• Some occur quickly.

Chemical Reactions

• The elements or compounds that engage in a chemical reaction are known as reactants.

• The elements or compounds produced by a chemical reaction are known as products.

• Chemical reactions involve changes in the chemical bonds that join atoms in compounds.

Energy in Reactions

• Energy is released or absorbed whenever chemical bonds are formed or broken…chemical reactions involve changes in energy.

• Chemical reactions that release energy often occur on their own, or spontaneously.

• Chemical reactions that absorb energy require a source of energy.

Energy in Reactions Example

• An example of an energy-releasing reaction is the burning of hydrogen gas, in which hydrogen gas reacts with oxygen to form water vapor.

2H2 + O2→ 2H20

• The energy is released in the form of heat, and sometimes—when hydrogen gas explodes—as light and sound.

• The reverse reaction requires energy to occur.

Energy Sources

• In order to stay alive, organisms need to carry out reactions that require energy.

• Plants get this energy by trapping and storing the energy from sunlight in energy-rich compounds.

• Animals consume plants or other animals, then break apart the food and capture its energy.

Activation Energy

• Chemical reactions that release energy do NOT always occur spontaneously.

• The energy needed to get a reaction started is called its activation energy.

• Activation energy is involved in chemical reactions regardless of whether the overall reaction releases or absorbs energy.

Activation Energy- DRAW THESE GRAPHS

Enzymes

• Some chemical reactions that are essential to life either occur too slowly or never occur on their own (because of high activation energies).

• These chemical reactions require enzymes (biological catalysts).

• A catalyst is a substance that speeds up a chemical reaction.

• Catalysts are not consumed by the reaction.

• Catalysts work by lowering a reaction’s activation energy.

DRAW THIS GRAPH

Enzymes

• Enzymes are proteins.

• Role is to speed up chemical reactions that take place in cells.

• Very specific, catalyzing only one chemical reaction. • Part of an enzyme’s name is usually derived from the reaction it catalyzes.

• Ex.- lactase is involved in the chemical reaction that breaks down lactose.

Enzyme-Substrate Complex

• Reactants must collide with enough energy to break existing bonds and form new bonds.

• Enzymes provide a site where reactants are brought together, lowering the energy needed for the reaction.

• The reactants of enzyme-catalyzed reactions are known as substrates.

• The substrates bind to a site on the enzyme called the active site.

• Substrates fit into the active site like a puzzle piece or a “lock and key”.

Enzyme-Substrate Complex

Regulation of Enzyme Activity

• Enzymes play essential roles in chemical pathways, making materials, that cells need, releasing energy, and transferring info.

• The function of an enzyme depends on its structure.

• High temperature and extreme pH weaken hydrogen bonds, causing proteins to unfold or denature.

Regulation of Enzyme Activity

• Enzymes in human cells generally work best at temperatures close to 37oC.

• The stomach enzyme pepsin works best under acidic conditions.

• Most enzyme activity is regulated by molecules that carry chemical signals within cells, switching enzymes “on” or “off” as needed.

Section 2.4 Exit Ticket

1. What changes occur to chemical bonds during a chemical reaction?

2. How does the change in energy of a chemical reaction predict whether or not the reaction will occur?

3. Explain the role of enzymes and how they affect the chemical reactions of living things.

The End ☺