Download 2.4 Chemical Reactions and Enzymes

2.4 Chemical Reactions and
Enzymes
Chemical Reactions
• Chemical reactions involve changes in the chemical bonds that join
atoms in compounds.
• Example: removing CO2 from body
(in bloodstream near tissues) CO2 + H2O > H2CO3 > CO2 + H2O (lungs)
(carbonic acid/more soluble)
Energy Changes
• Some chemical reactions release energy & others absorb it.
• Example of an energy releasing reaction is the burning of hydrogen
gas, in which hydrogen reacts with oxygen to produce water vapor.
• 2H2 + O2 > 2H2O
Reactants > Products
• The energy released is heat.
Energy Sources
• Every organism must have a source of energy to carry out chemical
reactions.
• Plants get that energy by trapping & storing the energy from sunlight
in energy-rich compounds.
• Animals get their energy when they consume plants or other animals.
• Humans release the energy needed to grow tall, to breathe, digest
food, & etc.
Activation Energy
• Activation energy – energy needed to get a reaction started.
• Ex. Your papers cannot burst into flames spontaneously, unless you light
them.
Enzymes (Nature’s Catalysts)
• Enzymes speed up chemical reactions that
take place in cells.
• Enzymes act by lowering the activation
energies.
• CO2 + H2O > H2CO3 (occurs in bloodstream)
• The reaction above is so slow that CO2 might
build up in the body faster than the
bloodstream could remove it. Our
bloodstream contains an enzyme called
carbonic anhydrase that speeds up the
reaction by a factor of 10 million. The
reaction takes place immediately & CO2 is
removed from the blood instantly.
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 substrates bind to a site on the enzyme called the active site. It is
compared to a lock and key since they have complementary shapes.
Enzyme-Substrate Complex
Regulation of Enzyme Activity
• Temperature, pH, and regulatory molecules can affect the activity of
enzymes.
• Enzymes work best at certain ionic conditions and pH value. For
example, stomach enzyme pepsin, which begins protein digestion,
works best under acidic conditions.