Chapter 6
Biology
Energy1. Capacity to do work.
2. Kinetic energy is energy of motion.
3. Potential energy is stored energy.
Types of energyUsed by humans:• Gravitational (e.g., hydro, tidal)• Kinetic (e.g., wind, waves)• Geothermal• Nuclear• Solar• Chemical (combustion of petroleum, coal, gas, wood,
H2) Often converted to electricity
Used by cells:• Chemical energy
– Breaking of covalent bonds in complex molecules like glucose and ATP
Cell Energy
Two Laws of Thermodynamics
• 1. First law of thermodynamics– energy cannot be created or destroyed.
• 2. Second law of thermodynamics– energy cannot be changed from one form
into another without a loss of usable energy
– Entropy – measure of disorder (ie. the more random a collection of matter, the greater it’s entropy)
Does Life violate the Second law of
Thermodynamics?
Life ...
"define life not by it's substance but by its organization … life in all it's forms has a
mechanism for processing energy and information that emerge from some fundamental
order in the universe, a new natural law that shapes those forms out of chaos."
Byte 1/95 p45
Metabolic Reactions and Energy Transformations
Metabolism• 1. Sum of all the biochemical
pathways.
• 2. Reaction A + B = C + D
• 3. Free energy (G) is the amount of energy that is free to do work after a chemical reaction.
Chemical Reactions
• Exothermic (exergonic)
• Endothermic (endergonic)
ATP: Energy for Cells
ATP (adenosine triphosphate) is the energy currency of cells.
When cells require energy, they "spend" ATP.
Structure of ATP
• ATP is called a "high-energy" compound because a phosphate group is easily removed.
• In cells, about 7.3 kcal per mole is released when ATP is hydrolyzed to ADP + P
Structure of ATP
• ATP is a nucleotide made of base adenine, sugar ribose, and three phosphate groups.
Function of ATP
• 1. Chemical work: ATP supplies energy to synthesize macromolecules that make up the cell.
• 2. Transport work: ATP supplies energy needed to pump substances across the plasma membrane.
• 3. Mechanical work: ATP supplies energy to move muscles, cilia and flagella, chromosomes, etc.
Metabolic Pathways and Enzymes
Reactions in Cells Are Orderly
• Metabolic pathways are orderly sequence of chemical reactions; each step is catalyzed by a specific enzyme.
• Reactants Products
• A + B = C + D
Reactions in Cells Are Orderly
• Metabolic energy is captured more easily if it is released in small increments.
• Each step in a series of chemical reactions is assisted by an enzyme.
Cell Enzyme
Reactions in Cells Are Orderly
• Enzymes are catalysts that speed chemical reactions without the enzyme being changed.
• Every enzyme is specific in its action and catalyzes only one reaction or one type of reaction.
• A substrate is a reactant in an enzymatic reaction.
Enzymes Lower the Energy of Activation
• Almost no metabolic reaction occurs in a cell unless its own enzyme is present.
Enzymes
Enzyme-Substrate Complexes
• Every cell reaction requires its specific enzyme;
–they are named for substrates by adding the ending "-ase "
Enzyme Synthesis.avi
Factors That Affect Enzymatic Speed
• 1. Moderate Temperature
• 2. Optimal pH
• 3. Amount of Active Enzyme
Factors That Affect Enzymatic Speed
• Competitive inhibition, another molecule is similar to enzyme's substrate, competes with true substrate for enzyme's active site, resulting in decreased product formation.
• Non-competitive inhibition, a molecule binds to allosteric site, a site other than active site, hereby changing the three-dimensional structure of enzyme and ability to bind to its substrate.
Factors That Affect Enzymatic Speed
• Feedback inhibition regulates activity of most enzymes; product produced by an enzyme binds to enzyme's active site. – when product is abundant, active
sites are full and enzyme activity drops.
Cell End Product Inhibition
Factors That Affect Enzymatic Speed
• Cofactors Help Enzymes– many enzymes require an inorganic
ion or nonprotein cofactor to function.
The End.