ENERGY AND METABOLISMCH 8

• Metabolism: all of an organism’s chemical reactions

• Metabolic pathways: series of chemical reactions

• Catabolic pathways: break down large molecules releasing energy

• Anabolic pathways: build large molecules using energy

I. Energy and living things

• Energy = the ability to cause change• Kinetic energy = energy of motion• Potential energy = stored energy• Chemical energy: potential energy available

for release in chemical reactions• Thermal energy: kinetic energy due to

movement of atoms•

A. Laws of Energy Transformations• Thermodynamics: study of energy

transformations1. 1st Law of Thermodynamics: energy can’t be created or destroyed only transformed or transferred

2. 2nd Law of Thermodynamics: every energy transfer or transformation increases entropy (disorder) of universeduring energy transfers or transformations, energy is often lost as heat or other unusable form

• energy enters an ecosystem as light and exits as heat

• Organisms are ordered and have low entropy. But they use large molecules thus increasing entropy of universe by releasing heat

B. Free energy and chemical reactions

• Free Energy = the energy available to do work• All molecules have a certain amount of free

energy = G• All chemical reactions result in a change in

free energy = ∆G• ∆G = Gproduct – G reactant

1. Endergonic reactions

• Are not spontaneous• Require input of energy to occur• ∆G is positive• Products have a greater G than reactants• Example: glucose production during

photosynthesis•

2. Exergonic reactions

• Are spontaneous• Release energy• ∆G is negative• Products have lower G than reactants• Example glucose breakdown during

respiration•

II. ATP: The energy molecule

• The chief energy molecule for all cells is ATP• ATP is used for:– Chemical work– Transport work– Mechanical work

• To do work, cells couple exergonic processes to drive endergonic ones

A. Structure and hydrolysis of ATP

• Made of a 5 carbon ribose sugar, three phosphates and an adenine base

• When the last phosphate bond in ATP is broken by hydrolysis a HUGE amount of energy is released

B. How ATP performs work

• Hydrolysis of ATP is exergonic• This energy released is used to drive an

endergonic reaction

C. Regeneration of ATP

• Forming ATP is endergonic• It is coupled to a catabolic reaction

III. Enzymes and chemical Reactions

A. Activation Energy• The input energy needed to get a reaction started• The existing bonds in a molecule are stable• In order to break those bonds to form new ones, an

input of energy (activation energy) is required

B. Enzymes

Protein catalysts that speed up chemical reactions by lowering the activation energy

C. Structure of an enzyme

• Usually globular in shape• Has an active site where substrate binds and

chemical reaction occurs. • Once substrate enters active site, induced fit

allows chemical reaction to occur• Many have allosteric site that regulates

activity at the active site

• The shape of the enzyme (its active site and allosteric site) is determined by the way that enzyme folds

• The primary structure of the enzyme determines its secondary and tertiary structure which determines shape and ultimately function

• If the shape of the enzyme is altered then it can no longer carry out chemical reactions

Mechanism of enzyme action:

http://www.stolaf.edu/people/giannini/flashanimat/enzymes/enzyme.swf http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter2/animation__how_enzymes_work.html

D. Factors affecting enzyme activity

The more substrate, the faster the rate of reaction due to increased rate of collision with active site, till all active sites are occupied with substrate and the rate of reaction plateaus

1. Amount of substrate:

2. Temperatureoptimal temperature: where rate of reaction is greatest• Below the optimal temp:

Increasing temp increases molecular motion and rate of collision with active site

• Above the optimal temp:Weak interactions holding enzyme’s shape break and enzyme unfolds

http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter2/animation__protein_denaturation.html

3. pH• Below or above the

optimal pH, charges on the ionic amino acids are altered.

• This alters the ionic interactions in the active site

• The active site loses its shape and unfolds

4. Inhibitors

what would happen if more substrate was added to reaction with competitive inhibitor? Noncompetitive inhibitor?

http://bcs.whfreeman.com/thelifewire/content/chp06/0602001.html

IV. Allosteric Regulation of Metabolic Pathways

Product becomes allosteric inhibitor and shuts off an early enzyme in the pathway

http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter2/animation__feedback_inhibition_of_biochemical_pathways.html