Energy Transformation, Cellular Energy & Enzymes (Outline)
• Energy conversions and recycling of matter in the ecosystem. • Forms of energy: potential and kinetic energy • The two laws of thermodynamic and definitions • Chemical reactions and energy transformation • Biochemical metabolic reactions and pathways • Coupling energy consuming biochemical reactions with the energy releasing reaction of ATP dissociation • Types of cellular work that require energy (ATP) • Role of enzymes in catalyzing biochemical reactions • Biochemical composition of enzymes and the physical and chemical factors that regulate their activity • Competitive and non-competitive inhibitors of enzymes. Figure 1.4-0
ENERGY FLOW
Sun
Inflow of Outflow of light energy heat
Consumers (animals) Producers (plants)
Chemical energy Leaves take up in food Decomposers such CO2 from air; roots as worms, fungi, absorb H2O and and bacteria return minerals from soil chemicals to soil Figure 1.4-1
ENERGY FLOW
Sun
Inflow of Outflow of light energy heat
Consumers (animals) Producers (plants)
Chemical energy Leaves take up in food Decomposers such CO2 from air; roots as worms, fungi, absorb H2O and and bacteria return minerals from soil chemicals to soil Energy is the capacity to do work
– Kinetic energy is the energy of motion
– Potential energy is stored energy that can be converted to kinetic energy
• Chemical bonds are a form of potential energy that can be transformed to energize cellular work
The field of study of energy transformations is Thermodynamics
• The First Law of Thermodynamics Energy can not be created or destroyed, it can be transformed from one form to another
• The Second Law of Thermodynamics Energy transformations increase disorder or entropy of the universe, and some energy is lost as heat.
Energy transformation is not 100% efficient Heat
Chemical reactions Carbon dioxide + Glucose + ATP ATP
water Oxygen Energy for cellular work
Figure 5.2B Chemical reactions either store or release energy Endergonic reactions absorb energy and form products rich in potential energy
Products
Amount of energy Energy required required
Reactants Potential energy of molecules
Figure 5.3A Exergonic reactions release energy and yield products that contain less potential energy than their reactants
Reactants
Amount of energy Energy released released
Products Potential energy of molecules
Figure 5.3B Cells carry out thousands of chemical reactions some exergonic and others endergonic
Cellular metabolism is the sum of all chemical reactions that take place inside the cell
Energy coupling uses exergonic reactions to fuel endergonic reactions
– ATP powers cellular work by shuttling chemical energy – The energy in an ATP molecule lies in the bonds between its phosphate groups
Adenosine Triphosphate Adenosine diphosphate
Phosphate
groups H2O
P P P P P + P Energy Hydrolysis + Adenine
Ribose ATP ADP Figure 5.4A ATP hydrolysis is the main exergonic reaction used in cellular energy coupling
ATP hydrolysis transfers a phosphate group to a molecule (phosphorylation).
A phosphorylated molecule has a higher potential energy making it possible for the reaction to take place. ATP is a renewable resource that cells regenerate
ATP
Energy from Energy for exergonic endergonic reactions reactions ADP + P
Figure 5.4C Types of Cellular Work
ATP
Chemical work Mechanical work Transport work Membrane protein Solute
P + Motor protein P
Reactants P
P P
Product P Molecule formed Protein moved Solute transported
Figure 5.4B ADP + P ENZYMES • Proteins that function as catalysts for biochemical reactions
• Have a conformation (3D shape) that determines their specific binding to reactants (substrates)
• Lower the energy barriers of chemical reactions For a chemical reaction to begin reactants must absorb some energy, called the energy of activation
EA barrier Enzyme
Reactants
1 Products 2
Figure 5.5A A protein catalyst called an enzyme can decrease the energy of activation needed to begin a reaction
EA without enzyme
EA with enzyme
Reactants Net
Energy change in energy
Products
Progress of the reaction Figure 5.5B Enzymes, as proteins, have unique three- dimensional shapes that determine which chemical reactions occur in a cell
Each enzyme catalyzes a specific cellular reaction
The catalytic cycle of an enzyme
1 Enzyme available with empty active site Active site Substrate (sucrose)
2 Substrate binds to enzyme with induced fit Enzyme Glucose (sucrase)
Fructose
H2O 4 Products are released 3 Substrate is converted to products Figure 5.6 The cellular environment affects enzyme activity
– Temperature, salt concentration, and pH
– Some enzymes require non-protein components Cofactors- metal ions Coenzymes- organic molecules (vitamin derivatives) – Enzyme inhibitors interfere with an enzyme’s activity
– A competitive inhibitor takes the place of a substrate in the active site – A noncompetitive inhibitor alters an enzyme’s function by changing its shape
Substrate Active site
Enzyme
Normal binding of substrate
Competitive Noncompetitive inhibitor inhibitor
Enzyme inhibition Figure 5.8 Many poisons, pesticides, and drugs are enzyme inhibitors