Regents Prep: Living Environment: Homeostasis:
Biochemical Processes
The energy for life comes primarily from the Sun. Photosynthesis is the major way the energy of the Sun is converted to sugars which provide for the energy needs of living systems.

Plants and many microorganisms use solar energy to combine the inorganic molecules carbon dioxide and water into energy-rich organic compounds such as glucose sugar and release oxygen to the environment.

A Representation of Photosynthesis

The overall process of photosynthesis in a plant or algal cell is shown in the graphic below.   Plants use use water and the energy provided by sunlight to combine carbon dioxide into glucose sugar with oxygen being released as a waste product.


Equation for Photosynthesis

carbon dioxide + water →  glucose + oxygen
  (sunlight) (enzymes)

Picture of Completed Chromatographychloroplasts: organelles that carry on photosynthesis in green plant cells

chlorophylls: the variety of green pigments within the chloroplasts

While chlorophyll is the chief pigment responsible for photosynthesis in green plants, many plants contain other colored pigments as well.   These chlorophyll and colored pigments may be separated according to their various chemical charges by a technique known as chromatography.  In this technique, a mixture of plant pigments is separated by placing a drop or two of pigment on a special paper called chromatography paper which is dipped in a chemical allowing the different plant pigments to move based on their charges. A picture of a completed chromatography may be viewed in the graphic at the right.

In all organisms, organic compounds such as glucose can be used to make other molecules.  These molecules include proteins, DNA, starch, and fats.  The chemical energy stored in bonds can be used as a source of energy for life processes.

Stored energy is released when chemical bonds are broken during cellular respiration and new compounds with lower energy bonds are formed. Cells usually transfer this energy temporarily in phosphate bonds of a high-energy compound called ATP. (adenosine triphosphate)

Equations for Cell Respiration

glucose + oxygen → 

 carbon dioxide  + water  + 36 ATP

The energy from ATP is then used by the organism to obtain, transform, and transport materials, and to eliminate wastes.

water + ATP → 

 ADP + P + Energy

Note:  ADP is adenosine diphosphate.

 This reaction is reversible and ADP can be converted back to ATP in cellular respiration.

Types of Reactions
hydrolysis: reaction in which large molecules are broken down into smaller molecules. Chemical digestion is an example of a hydrolysis reaction

synthesis: the combining of simpler molecules to form a more complex molecule

Biochemical processes, both breakdown (hydrolysis) and synthesis, are made possible by enzymes.  Enzymes and other molecules, such as hormones and antibodies, have specific shapes that influence both how they function and how they interact with other molecules.

Enzyme Structure and Function
catalyst: inorganic or organic substance which speeds up the rate of a chemical reaction without entering the reaction itself.

enzymes: organic catalysts made of protein.

  • most enzyme names end in -ase
  • enzymes lower the energy needed to start a chemical rx. (activation energy), thus speeding the reaction

How do enzymes work?
: molecules upon which an enzyme acts. The enzyme is shaped so that it can only lock up with a specific substrate molecule.

substrate -------------> product


Lock and Key Theory

Each enzyme is specific for one and ONLY one substrate (one lock - one key)

active site: part of the enzyme that fits with the substrate

Note that the active site has a specific fit for this particular substrate and no other.

This theory has some weaknesses, but it explains many basic things about enzyme function.  

Since the enzyme may unhook from the substrate, it may be reused many times.

Factors Influencing Enzyme Activity
: the optimum (best) in most living things is close to 7 (neutral). High or low pH levels usually slow enzyme activity

Temperature: strongly influences enzyme activity

  • optimum (best) temperature for maximum enzyme function is usually about 35-40 C.
  • reactions proceed slowly below optimal temperatures
  • above 45 C. most enzymes are denatured (change in their shape so the enzyme active site no longer fits with the substrate and the enzyme can't function)

Concentrations of Enzyme and Substrate

When there is a fixed amount of enzyme and an excess of substrate molecules the rate of reaction will increase to a point and then level off.

This leveling off occurs because all of the enzyme is used up and the excess substrate has nothing to combine with.

If more enzyme is available than substrate, a similar reaction rate increase and leveling off will occur. The excess enzyme will eventually run out of substrate molecules to react with.


Created by James M. Buckley, Jr.
Copyright 1999-2003 Oswego City School District Regents Exam Prep Center
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