(c) The McGraw-Hill Companies, Inc. Part III and Chapter 8 Biology Sixth Edition Raven/Johnson (c) The McGraw-Hill Companies, Inc.

All Energy on Earth Comes From the Sun! Energy – the capacity to do work - two basic forms* are potential or kinetic Potential energy is stored energy (eventually transferred to kinetic energy). Kinetic energy is the energy of motion. * Other forms include solar, heat, and electrical energy

Two Laws of Thermodynamics First Law: Energy cannot be created or destroyed, but it can be changed from one form to another. Second Law: Energy cannot be changed from one form to another without loss of usable energy.

Flow of energy First law Second law When energy transformations occur, energy is neither created nor destroyed (1st Law) but there is always loss of usable energy, usually as heat (2nd Law).

Due to the two laws of thermodynamics, all living things depend on an outside source of energy. Energy exists in several different forms and the ultimate source of energy for ecosystems is the sun.

Entropy a measure of disorder High entropy = high disorder It takes energy to keep an organized room (fight entropy)!

Cells and entropy Entropy and Molecules Low entropy (hi energy) High entropy (Low energy) Breakdown of glucose results in a loss of potential energy and an increase in entropy

Energy can be transferred from one molecule to another: Oxidation – loss of an electron and/or H+ (~energy) Reduction – gain of an electron and/or H+ (~energy) Electrons are usually paired with a H+

Free energy, G, is the amount of energy available to do work after a reaction has occurred: Photosynthesis: H2O + CO2 + energy (solar)  Glucose Respiration: Glucose  H2O + CO2 + energy (ATP) H2O + CO2 have less energy than glucose, so energy is either consumed or released, depending on which direction the reaction is going ΔG (change in free energy) is calculated by subtracting the free energy of reactants from that of products.

Endergonic reaction - requires energy Respiration Photosynthesis Negative G Positive G Endergonic reaction - requires energy Exergonic reaction - releases energy

Activation energy is necessary to break the bonds of the reactant Activation energy is necessary to break the bonds of the reactant – otherwise reactants would never be around!

Catalyst – substance that increases the rate of a chemical rxn, but is unchanged by the rxn. Enzyme – protein molecule that acts as a biological catalyst (*not all biological catalysts are proteins* - see page 151)

Enzyme-Substrate Complex An enzyme brings together particular molecules and causes them to react to produce a product. Substrates - The reactants in an enzymatic reaction. Enzyme + Substrate Enzyme-Substrate Complex Enzyme + Product

Multienyme Complexes – loose association of a group of enzymes involved in a sequence of reactions Benefits: -reduces randomness -reduction of unwanted side reactions -can be controlled as a unit

Enzyme Cofactors Enzyme function is often assisted by additional components known as cofactors, which often function in electron transfer Examples: -Inorganic metal ions, such as copper, zinc, or iron Non-protein organic cofactors (vitamins) are called coenzymes Enzymes that require a cofactor CANNOT function without them!

Adenosine Triphosphate (ATP) Energy in ATP lies in the bonds between each of the phosphate groups, which are highly negatively charged. The is a strong electrostatic charge pulling on the covalent bonds between the phosphate groups (‘coiled springs’). A lot of energy is released when those bonds are broken. Consists of adenine, ribose and 3 phosphate groups

What are good long-term energy storage molecules? ATP can provide most of the energy a cell needs Because of the instability of ATP (phosphate bonds) ATP is not a good long-term energy storage molecule. What are good long-term energy storage molecules? Most cells only have a few seconds supply of ATP and therefore they must continually produce ATP

Metabolism – total of all chemical reactions carried on by an organism Anabolism – the expenditure of energy to make or transform chemical bonds Catabolism – the harvesting of energy from breaking chemical bonds Many reactions within a cell occur in sequences. This sequence is called a biochemical pathway. E1 E2 E3 E4 A → B → C → D → E

F + G  H Evolution of a biochemical pathway that produces H EF + G  H DEF + G  H CDEF + G  H

A B D C E

Feedback inhibition Shape change

The End.