Cell Energetics Concept Review
Energy: Big Idea in Science
• Energy flows in one direction,
energy never cycles back to its
source
What is energy?
• Energy is the capacity to do work
• Work is the transfer of energy
• Using the definition, explain how ATP is a form of energy.
There are different forms of energy:
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Light
Chemical
Heat
Potential Energy: Stored energy
Kinetic Energy: Energy of motion
The 1st Law of Thermodynamics
• The total amount of energy in the universe is constant. Energy
can’t be created or destroyed, it can only change forms.
• EVERY energy transfer results in some energy being lost to the
environment as heat. Energy transfers are NEVER 100%
efficient.
Example in Biology
The 2nd Law of Thermodynamics (The Law of
Entropy)
• In the absence of energy inputs, an organized system becomes
more disorganized over time.
• Organized Disorganized
• Concentrated Diffuse
• Complex Simple
Example in Biology
Energy Reactions
Endergonic Reactions
Exergonic Reactions
• Net increase of usable energy
(energy in), transforming CO2
and H2O to glucose.
• Net decrease of usable energy
(energy out), transforming
glucose to CO2 and H2O.
• A + B + energy AB
• AB Energy + A + B
Metabolic Pathways
Biosynthetic Pathway (Anabolic)
• Metabolic pathway where small molecules are used to build larger
molecules of higher bond energy.
• Example: The synthesis of carbohydrates in photosynthesis.
Degradative Pathway (Catabolic):
• Exergonic pathways that breaks down large molecules to smaller
ones.
• Example: Cellular respiration
Coupled Reaction
• The use of an exergonic reaction to drive an endergonic reaction.
ATP is responsible for mediating most energy coupling in cells.
• Example: Energy from ATP is transferred to glucose to initiate
glycolysis
The Structure of Adenosine Triphosphate (ATP)
• ATP (adenosine triphosphate) is
the cell’s energy shuttle
• ATP is composed of ribose (a
sugar), adenine (a nitrogenous
base), and three phosphate groups
How is Energy Released from ATP?
•Energy is released when the
terminal phosphate bond is
broken during hydrolysis
ATP Energy Transfer
• Enzymes couple the energy of ATP hydrolysis directly to
endergonic reactions by transferring a phosphate group from
ATP to another molecule.
• The recipient of the phosphate group has been “phosphorylated”.
Substrate Level Phosphorylation
• Enzymes directly transfer a phosphate group from a substrate of
a reaction to ADP.
• Example: The formation of ATP from PGAL during glycolysis.
Electron Transfer or Oxidative Phosphorylation
• The production of ATP using energy derived from the redox
reactions of and electron transport chain.
• The combined processes of chemiosmosis and electron transport
Chemiosmosis
• An energy coupling mechanism that uses energy stored in the
form of a hydrogen ion gradient across a membrane through
ATP Synthase to drive cellular work such as the synthesis of
ATP.
• What drives ATP synthase to form ATP
Enzyme Induced Fit Model
• There are weak interactions between an enzyme and its substrate
upon binding which induce change in the enzyme’s shape.