AP Biology Lecture #12 Metabolism: Energy & Enzymes

Energy Definition: The Capacity to do work Types of Energy: Potential: Stored energy, measured as a capacity to do work. example: stretched spring Kinetic: Energy of motion, released potential energy. example: releasing of a stretched spring Thermal: Energy released as heat Chemical: Potential energy stored in molecules. Measured as Kilocalories (Kcal) aka Calories (C) (1 calorie (c) = heat req’d to raise 1g of H 2 O 1  C)

Energy Movement

Why do cells need energy? Chemical work, build, rearrange, tear apart compounds Mechanical work, move cilia, flex a muscle Electrochemical work, nerve impulses

From food webs to the life of a cell energy

Flow of energy through life Life is built on chemical reactions – transforming energy from one form to another organic molecules  ATP & organic molecules sun solar energy  ATP & organic molecules

9 Flow of Energy

Laws of Thermodynamics First Law of Thermodynamics – energy cannot be created or destroyed -energy can only be converted from one form to another For example: sunlight chemical energy photosynthesis energy

Laws of Thermodynamics Second Law of Thermodynamics: disorder is more likely than order entropy: disorder in the universe The 2 nd Law of Thermodynamics states that entropy is always increasing.

Laws of Thermodynamics Free energy: the energy available to do work -denoted by the symbol G (Gibb’s free energy) enthalpy: energy contained in a molecule’s chemical bonds free energy = enthalpy – (entropy x temp.) ΔG = ΔH - TΔS

Laws of Thermodynamics Chemical reactions can create changes in free energy:  G =  H - T  S When products contain more free energy than reactants –  G is positive. When reactants contain more free energy than products –  G is negative.

Chemical reactions & energy Some chemical reactions release energy – exergonic – digesting polymers – hydrolysis = catabolism Some chemical reactions require input of energy – endergonic – building polymers – dehydration synthesis = anabolism digesting molecules= less organization= lower energy state building molecules= more organization= higher energy state

Endergonic vs. exergonic reactions exergonicendergonic - energy released - digestion - energy invested - synthesis -G-G  G = change in free energy = ability to do work +G+G

Energy in energy-poor reactants glucose - a product with more energy + 6O 2 A Closer Look: Endergonic Reactions Photosynthesis Very endergonic – where does the plant get the energy? The SUN

A Closer Look: Exergonic Reactions glucose - energy-rich starting substance products with less energy Cellular Respiration

Laws of Thermodynamics Chemical reactions can be described by the transfer of energy that occurs: endergonic reaction: a reaction requiring an input of energy -  G is positive exergonic reaction: a reaction that releases free energy -  G is negative

Energy & life Organisms require energy to live – where does that energy come from? coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy) ++ energy + +

Coupling Reactions

ATP is the cell’s energy currency nearly all energy in a cell is stored within the ATP molecule Energy releasing rxns→ ATP→ Energy requiring rxns Cells cleave ATP into ADP & Pi releasing energy This energy can be used to do work such as synthesize other molecules or move muscles Adenosine Triphosphate (ATP)

How is ATP synthesized? ATP are renewable and are recycled by cells: