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Lecture 4

BIOL 3113 Lecture Notes - Lecture 4: Kinetic Energy, Chemical Bond, Cell Metabolism

Course Code
BIOL 3113
Barbara S

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Metabolism is the sum total of all of the chemical reactions that occur in living cells.
Cell Metabolism
Cell- chemical factory- performs millions of reactions every second
Two sets of reactions:
-reactions that break down complex molecules
-release energy that can be used by the cell
-provides building blocks
Anabolism (Biosynthesis)
-reactions that synthesize new molecules using energy and molecules released by
catabolic reactions
*Anabolism + Catabolism = Metabolism
Insert diagram
There is a universal tendency of things to become disordered
Second Law of Thermodynamics:
-states that the degree of disorder (entropy) in the universe can only increase
-The movement toward disorder is a spontaneous process and requires a periodic effort to
reverse it
-The creation of order in living systems is energetically unfavorable (add energy to
organize) and is made possible only by the release of heat from chemical reactions, which
increases the disorder (entropy) of the rest of the universe
*cell takes energy from food molecules to carry rxn that order molecules inside----->
releases heat that increases disorder in the cell environment
First law of thermodynamics:
-states that energy can be converted from one form to another, but it cannot be created or
destroyed, e.g.:
*Chemical bond energy heat energy
*Light (electromagnetic) energy chemical bond energy
*Chemical bond energy electrical energy kinetic energy
*Kinetic energy heat energy
The cell can not derive any benefit from the heat energy it produces unless the heat -
generating reactions inside the cell are directly linked to the processes that maintain
molecular order coupling of heat production to an increase in order

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A direct linkage of the “burning” of food molecules to the generation of biological order
is necessary for cells to be able to create and maintain an island of order in the universe
tending toward disorder
Light from the sun is the ultimate source of all energy for humans and animals - Plants
trap energy from sunlight
Photosynthesis light energy converted into chemical bond energy in plant cell
Atoms from inorganic sources + energy formation of chemical bonds between atoms
production of sugars
Sugars are used as a source of chemical bond energy and as a source of substrates to
make other molecules like amino acids, nucleotides and fatty acids that are converted into
macromolecules serve as food for animals
In plants and animals, energy is extracted from food molecules by a process of gradual
oxidation of organic molecules Respiration
Photosynthesis and respiration - complementary processes - C, O, H, N cycle
between different living organisms and inorganic world
Oxidation and Reduction
Some chemical reactions involve the transfer of electrons from one molecule to another
Oxidation - partial or complete loss of electrons
Reduction - partial or complete acquisition of electrons
Complete Oxidation and Reduction
Fe++ Fe+++ + 1e-
Cl2 + 2e- 2Cl-
Oxidation and reduction reactions occur simultaneously. The molecule being oxidized
gives up its electrons to the molecule being reduced.
Terms “oxidation” and “reduction” also apply when there is only a partial shift of
electrons between atoms linked by a covalent bond.
Partial Oxidation and Reduction
2H2 + O2 2H2O
Protons (H+) are often transferred simultaneously with electrons (hydrogenation)
A + e- + H+ AH
Oxidation of Carbon
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