Biology 107
Introduction to Metabolism I
September 9, 2005
Introduction to Metabolism I
Student Objectives: As a result of this lecture and the assigned
reading, you should understand the following:
1. Despite the organized structure of cells, all living things tend toward
disorder. To maintain order, living things and the cells they are
made up of depend on a continual flow of energy from the
environment.
2. Metabolism is the sum total of an organism's chemical processing;
some chemical processes degrade complex molecules into simpler
molecules (catabolic pathways), and some chemical processes
synthesize complex molecules from simpler molecules (anabolic
pathways).
Introduction to Metabolism I
3.
Energy can only be described and measured by how it affects
matter. Energy is the capacity to perform work - all organisms
require energy to stay alive, and all organisms transform energy.
4.
There are two (2) forms of energy: potential energy and kinetic
energy.
5.
The first law of thermodynamics (law of energy conservation) =
the total amount of energy in the universe is constant and energy
can be transferred and transformed, but it cannot be created or
destroyed.
Introduction to Metabolism I
6.
The second law of thermodynamics = energy conversions reduce
the order of the universe. Heat, which is due to random molecular
motion, is one form of disorder. The second law has direct
applications to cellular activities - as explained in this law, energy
cannot be transferred or transformed by the cell with 100%
efficiency.
7.
Chemical reactions in living organisms - the starting substances
of chemical reactions are called reactants; reactants interact with
one another to form new substances called products.
8.
Chemical reactions, including those in cells, are of two types:
endergonic (energy-requiring) and exergonic (energy-releasing).
Introduction to Metabolism I
9.
In an endergonic biosynthetic reaction, the electrons forming the
chemical bonds of the product are at a higher energy level than
the electrons of the reactants (i.e., the reaction requires input of
energy).
10.
Cells supply the energy for endergonic reactions through coupled
reactions in which endergonic reactions are linked to exergonic
reactions.
11.
ATP is the cell's main energy carrier. Most frequently, coupled
reactions use ATP as the energy source, and ATP is renewable
energy that cells regenerate from exergonic reactions.
Metabolic
Pathways
Reactions occur in a
stepwise fashion
Pathways are
interconnected
Chemical reactions
are catalyzed by
enzymes
Free Energy And Capacity To Do Work
Need For Continual Flow Of Energy Into Systems
A Cell Does Three Main Kinds of
Work
Mechanical work, such as the beating of cilia (Chapter 6),
the contraction of muscle cells, and the movement of
chromosomes during cellular reproduction
Transport work, the pumping of substances across
membranes against the direction of spontaneous
movement (Chapter 7)
Chemical work, the pushing of endergonic reactions,
which would not occur spontaneously, such as the
synthesis of polymers from monomers (the focus of this
chapter, and Chapters 9 and 10)
Energy Profile For a Chemical Reaction
Energy Profiles For Energy-requiring and Energyreleasing Reactions
Enzymes Lower Activation Energy But They
Do Not Change the Overall Energy Profile
Coupling Of Energy-releasing Reactions With
Energy-requiring Reactions
ATP, GTP, UTP, CTP
All nucleotide triphosphates contain high energy
bonds. Although ATP is the primary cellular energy
carrier, other nucleotide triphosphates may provide
energy to specific chemical reactions.