ENERGY AND ENZYMES
I. The Role of Energy in
Living Systems
II. Using Energy from the
Controlled Combustion of Food
III. How Cells Speed Up
Chemical Reactions
I. The Role of Energy in
Living Systems
v All
biological processes require energy, which living organisms must extract from
their environment. This energy is used
to manufacture and transform the chemical compounds that make up living cells. The capture and use of energy by living
organisms involves thousands of chemical reactions, which together are known as
metabolism.
o
Chemical reactions can be grouped into
sequences called metabolic pathways.
v The
laws of thermodynamics apply to living systems.
o
First Law of Thermodynamics:
o
Second Law of Thermodynamics:
v The
flow of energy and the cycling of carbon connect living things with the
environment
o
Energy comes to photosynthetic organisms (PRODUCERS)
in the form of sunlight. Photosynthesis
is the process of building sugar molecules from carbon and water, utilizing
energy from the sun. The energy from the
sun is stored in the chemical bonds of the sugars. Organisms that do not undergo photosynthesis (CONSUMERS)
gain energy from the chemical bonds in food molecules, such as sugars and fats.
§ Remember
that plants themselves also utilize the sugars that they make by
photosynthesis, primarily at night.
§ Most
organisms produce CO2 as a byproduct of the energy-harvesting
process (called RESPIRATION), and this CO2 is a source of carbon for
photosynthesis. In this way, carbon
atoms are continually cycled from CO2 in the atmosphere to sugars
made by producers and back to CO2 by respiring producers and
consumers.
II. Using Energy from the
Controlled Combustion of Food
v Living
systems obtain energy from food by burning organic molecules such as sugars to
form CO2 and water. What
would happen if this occurred as a single reaction?
o
Wood
+ O2 CO2
+ H2O + energy (as heat and light)
o
Bomb Calorimeters
v Capturing
energy from foods requires the transfer of electrons
o
Oxidation is Loss
o
Reduction is Gain
o
Redox
reactions are oxidation-reduction reactions
§ Combustion
Reaction: Oxidation of Methane
§ Biological
Reaction: Oxidation of Methane
v Metabolism
is all the chemical reactions within living organisms that produce complex
macromolecules, such as sugar and proteins, and which break down those
macromolecules to yield smaller molecules and usable energy.
o
Anabolic Reactions create complex molecules
out of smaller compounds
o
Catabolic Reactions break down complex
molecules to produce usable energy
o
These reactions tend to be intimately
related.
§ Energy
in a living system is transferred via the universal energy carrier, ATP. ATP breaks down to ADP + P, releasing energy
in the break down.
v Chemical
reactions involve changing the arrangement of atoms in molecules and are
governed by simple transformations of energy.
Remember the basic chemical formula:
o
A +
B C + D
o
A and B are the starting materials, or
reactants
o
C and D are the end results, or products
o
A + B will not necessarily react just because
they are present together. They need to
be destabilized, or activated before a chemical reaction can begin and
proceed. This jumpstart is the
activation energy of the reaction.
v All
chemical reactions tend to proceed in the direction that will result in
products with greater stability and a lower energy state. Products whose energy state is lower than
that of their reactants have less energy stored in their chemical bonds; these products
are therefore in a less ordered state, as favored by the second law of
thermodynamics. This encourages chemical
reactions to proceed in a particular direction (“downhill”) energetically from
reactants to products.
III.
How Cells Speed up Chemical Reactions
v In
cells, can be acquired by random collisions of molecules in the cytosol
v Another
source of activation energy is enzymes: a specialized class of proteins that
catalyze reactions (increase the speed at which the reaction proceeds).
o
Enzymes bind to specific reactants, called
substrates and brings them together in an orientation that favors the making or
breaking of bonds required to form the products.
o
Enzymes are specifically tailored to promote
only one reaction.
o
Enzymes cannot make impossible reactions
happen nor promote a particular reaction by changing the amount of energy
associated with the reactants or products.
o
Enzyme activity can be affected by certain
variables:
§ Temperature
§ pH
§ Amount
of substrate in the environment
§ Amount
of product in the environment
§ Amount
of enzymes in the environment
v The
hydration of CO2 requires catalysis: Follow along with the reaction
of CO2 with H2O to produce bicarbonate.
v The
shape of an enzyme directly determines its activity
o
Each enzyme has an active site that fits only
substrates with the correct three-dimensional shape and chemical
characteristics. “Matchmaker,
matchmaker…”
o
Ex: Carbonic anhydrase
can bind molecules of both carbon dioxide and water to its active site,
promoting the hydration reaction.
v Sequences
of reactions have energetic advantages
o
Groups of enzymes catalize
multiple steps in a sequence of chemical reactions known as a metabolic pathway
§ This
enables the product of one reaction to immediately become a reactant in another
reaction.
§ Metabolic
pathways are how most chemical building blocks of the cell are built (ex: amino
acids and nucleotides).
§ Enzymes
are arranged in the cell so as to promote the multiple chemical reactions of
metabolic pathways.
Ø Metabolic
Rates and Lifespan
Ø Metabolism
and Healthy Living