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
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
A Representation of
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
Equation for Photosynthesis
carbon dioxide + water →
glucose + oxygen
organelles that carry on photosynthesis in green plant cells
the variety of green pigments within the chloroplasts
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 →
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
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
processes, both breakdown (hydrolysis) and synthesis, are made possible by 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
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?
substrate: molecules upon which an enzyme
acts. The enzyme is shaped so that it can only lock up with a
specific substrate molecule.
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
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.
enzyme may unhook from the substrate, it may be reused
Influencing Enzyme Activity
pH: 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
- 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.