Biochemistry/Enzymes

• Enzymes: Biological protein molecules that can speed up the rate of all the chemical reactions that take place within cells without being changed itself.

How they work

Enzymes work by lowering a reaction's activation energy, thus allowing the reaction to start more quickly. They help speed up or catalyze chemical reactions that would be too slow at cellular temperatures. Enzymes can not make a reaction occur that would not normally occur, they can only change the activation energy of a reaction.

Enzyme-substrate complex

• Activation Energy: The amount of energy required to start a chemical reaction.

Enzymes work by binding to a substance called a substrate. Enzymes have an active site, which is the groove/space where the substrate will fit. The active site and shape of an enzyme determines its function--Enyzme function was first described through the lock and key hypothesis which states that an enzyme and a substrate must fit perfectly in order for the reaction to work.

Today, we know that the fit does not have to be perfect, but close to it. The new hypothesis for enzyme function is known as the induced fit hypothesis. The induced fit hypothesis is the idea that an enyzme can slightly change its shape to better fit or mold around a substance.

Effect of pH and Temperature

Temperature and Kinetic Energy

1. The optimum (the point at which the enzyme works best) temperature for enzymes is between a range of 35° to 40°.
2. If the temperature drops below this point, enzyme activity will slow down because molecules are not moving fast enough (decrease in kinetic energy).
3. If the temperature goes above this range, the enzymes will denature or loose their shape. They can't return to their normal shape after they are denatured.

pH

1. Enzymes work best at a pH range of 6-8.
2. Going above or below the optimum pH will cause enzymes to denature, lose their shape, and not function.

Substrate Concentration

If the amount (concentration) of substrate increases, enzyme activity will increase gradually and then decrease since there are not enough enzymes to take in all of the substrates.

Enzyme Concentration

If the amount (concentration) of enzyme increases, enzyme activity will increase and then level off as it utilizes all of the enzymes avaliable.

Examples

The names of most enzymes end with -ase which makes them easy to recognize. Just remember that there are some enzymes that do not end with -ase.

Characteristics

1. Enzymes are substrate specific, which means that only ONE substrate will fit with ONE enzyme.
2. Enzymes can be used more than once.

Chemical Reactions and Enzymes

1. What is a chemical reaction? A process that changes one set of chemicals into another set of chemicals.

Types of chemical reactions

• Exothermic: Reactions that release energy
• Endothermic: Reactions that absorb energy

See also

Suggested Reading:

Biochemistry Textbook:

• Chapter 14 [[1]]
• Chapter 15 [[2]]
• Chapter 16 [[3]]
• Chapter 17 [[4]]

• w: Transferase
• w: EC number
• w: List of enzymes
• w: List of EC numbers

• Biochemistry for Biology Return to Homepage
• Biochemistry for Novices
• Portal:Food chemistry
• Topic:Biochemistry
• Khan Academy's lesson on Enzymes

External links

Free Lectures available at ITunes U

{{Chemistry resources}}{{Phosphate biochemistry}}