BIOL 1541L Lecture Notes - Lecture 7: Exergonic Reaction, Adenosine Diphosphate, Exergonic Process

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Chapter 6 SB Notes
6.1 Life and the Flow of Energy
I. Energy: the ability to do work or bring about change
A. To maintain their organization and carry out metabolic activities, cells (as well as
organisms) need a constant supply of energy
B. Carries on the process of life, growth, development, response to stimuli, and
reproduction
C. Majority of organisms gets their energy from organic nutrients produced by
photosynthesizers (algae, plants, and some bacteria)
D. Life on Earth is dependent on solar energy
II. Forms of energy
A. Kinetic energy: the energy of motion
1. A ball rolling down a hill
B. Potential energy: stored energy - has the capacity to accomplish work that is not
being used at the moment
C. Chemical energy: contains energy in the chemical bonds of organic molecules
D. Mechanical energy: type of kinetic energy associated with the position, or motion
of an object
1. A moose walking is converting chemical energy into a type of kinetic energy
III. Two Laws of Thermodynamics
A. Explains why energy flows in ecosystems and in cells
B. First law(The law of conservation of energy) explains the ability of organisms to
convert chemical energy to mechanical energy
1. Energy cannot be created or destroyed but it can be changed form one form
to another
C. The second law states that energy cannot be changed from one form to another
without a loss of usable energy
1. No process requiring a conversion of energy is over 100% efficient
2. Much of the energy is lost in the form of hear
3. Glucose tends to break apart carbon dioxide and water
IV. Cells and Entropy
A. Second law can be stated in another way: every energy transformation makes
the universe less organized and more disordered.
B. Entropy: used to indicate the relative amount of disorganization
1. Processes that occur in cells are energy transformations, the second law
means that every process that occurs in cells always does so in a way that
increases the total entropy of the universe
2. Then any of these processes makes less energy available to do useful work
in the future
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6.2 Energy Transformations and Metabolism
C. Cellular metabolism: the sum of all chemical reactions that occur in a cell
1. A significant part of cellular metabolism involves the breaking down and the
building up of molecules
D. Catabolism: refers to the breaking down of molecules
E. Anabolism: refers to the building up(synthesis) of molecules
F. Reactants: in a chemical reaction, they are substances that participate in a
reaction
G. Products: substances that form a a result of a reaction
1. Example: in the reacting A + B -> D, A and B are the reactants and C and D
are the products
H. Free energy: the amount of energy available, that is, energy that is still “free”to
do work after a chemical reaction has occurred.
1. The change in free energy after a reaction occurs is calculatedly subtracting
the free energy content of the reactants from that of the products
2. A negative result means that the products have less free energy than the
reactants and the action will go forward
I. Exergonic reactions: spontaneous and release energy
J. Endergonic reactions: require an input of energy to occur
1. In the body, many reactions, such as protein synthesis, nerve impulse
conduction, or muscle contraction, are endergonic and they are driven by the
energy released by exergonic reaction
2. ATP is a carrier of energy between exergonic and endergonic reactions
V. ATP: Energy for Cells
A. ATP: the common energy currency of cells
1. All cells require energy, and they spend ATP
B. ADP (Adenosine diphosphate): a molecule of inorganic phosphate
C. Figure 6.3 The ATP Cycle
1. In cells, ATP carries energy between exergonic reactions and exergonic
reactions. When a phosphate group is removed by hydrolysis, ATP releases
the appropriate amount of energy for most metabolic reactions
VI. Function of ATP
A. In living systems:
1. Chemical work: ATP supplies the energy needed to synthesize
macromolecules (anabolism) that make up the cell, and therefore the
organisms
2. Transport work: ATP supplies the energy needed to pump substances across
the plasma membrane
3. Mechanical work: ATP supplies the energy needed to permit muscles to
contract, cilia, and flagella to bind chromosomes to move and so forth
VII. Coupled Reactions
A. Coupled reactions: the energy released by exergonic reaction is used to drive an
endergonic reaction
1. ATP breakdown is often coupled to cellular reactions that require an input of
energy
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