Part III and Chapter 8

BiologySixth Edition

Raven/Johnson

(c) The McGraw-Hill Companies, Inc.

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.

All Energy on Earth Comes From the Sun!

* 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.

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).

Flow of energy

• 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

Low entropy (hi energy)

High entropy (Low energy)

Breakdown of glucose results in a loss of potential energy and an increase in entropy

Entropy and Molecules

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+

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

Photosynthesis: H2O + CO2 + energy (solar) Glucose

•Free energy, G, is the amount of energy available to do work after a reaction has occurred:

•ΔG (change in free energy) is calculated by subtracting the free energy of reactants from that of products.

RespirationPhotosynthesis

Positive G

Negative G

Endergonic reaction - requires energyExergonic reaction - releases energy

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)

• 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 CofactorsEnzyme 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)

Consists of adenine, ribose and 3 phosphate groups

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.

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

EF+ G

H

DEF+ G

H

CDEF+ G

H

Evolution of a biochemical pathway that produces H

A

B

D

C

E

Feedback inhibition

Shape change

The End.