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."

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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.