Upload
dina-smith
View
230
Download
4
Tags:
Embed Size (px)
Citation preview
2.4 Chemical Reactions and Enzymes
Everything that happens in an organism is based on chemical
reactions
Chemical reactions
• A chemical reaction is a process that changes, or transforms, one set of chemicals into another
• The elements or compounds that enter into a chemical reaction are known as reactants
• The elements or compounds produced by a chemical reaction are known as products
Baking soda + vinegar chemical reaction
Chemical reactions
• Chemical reactions always involve changes in the chemical bonds that join atoms in compounds
Energy in reactions
• Energy is released or absorbed whenever chemical bonds form or are broken. Because chemical reactions involve breaking and forming bonds, they involve changes in energy.
Energy changes
• Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy will not occur without a source of energy.
• An example of an energy releasing reaction is hydrogen gas burning, or reacting, with oxygen to produce water vapor.
• 2H + O ₂ ₂ 2H O₂
Hindenberg
Energy changes
Energy changes
Energy changes
Activation energy
• Even chemical reactions that release energy do not always occur spontaneously. If they did, the paper you are writing on might burst into flames.
• Chemists call the energy that is needed to get a reaction started the activation energy.
Activation energy
Enzymes
• A catalyst is a substance that speeds up the rate of a chemical reaction. Catalysts work by lowering a reaction’s activation energy.
• Enzymes are proteins that act as biological catalysts. Enzymes speed up chemical reactions that take place in cells.
• Enzymes work by lowering the activation energies.
Enzyme action
Enzyme action
• For a chemical reaction to take place, the reactants must collide with enough energy so that existing bonds will be broken and new bonds will be formed.
The Enzyme-Substrate Complex
• Enzymes provide a site where reactants can be brought together to react. Such a site reduces the energy needed for reaction
• The reactants of enzyme-catalyzed reactions are known as substrates
The Enzyme-Substrate Complex
Regulation of Enzyme Activity
• Many enzymes are affected by changes in temperature. Enzymes produced by human cells generally work best at temperatures around 37℃, the normal temperature of the human body.
• Enzymes also work best at certain pH values and solute concentrations
Regulation of enzyme activity
Regulation of enzyme activity