Chapter 6 Section 2 and 4Energy and Enzymes

I. The Flow of Energy in Living Systems

A. Thermodynamics: energy change;

thermo = heat dynamics = movement

B. Energy can take many forms

1. Energy: ability to do work

2. Kinetic energy: energy causing objects to move

3. Potential energy: energy stored in objects not moving.

Energy measured in kcal or joule

http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/energy/ce.html

C. The sun provides energy for living systems

1. Energy from sun captured by plants, algae, and bacteria in photosynthesis.

2. Energy used to turn CO2 and water into sugars or organic carbon.

D. Oxidation-reduction reactions transfer electrons while bonds are made or broken

1. Oxidation: an atom or molecule that loses an electron (e-)

2. Reduction: atom or molecule that gains an e-

3. Oxidation-reduction (redox) reaction: chemical reaction in which oxidation and reduction occur.

I. The Laws of Thermodynamics and Free Energy (Chapter 6 Section 2)

A. The First Law of Thermodynamics states that energy cannot be created or destroyed (amt. of energy is constant)

1. Heat: measure of motion of molecules. In organisms, energy is stored in chemical bonds. When energy is shifted to other chem. bonds, some of it is lost to the environment as heat.

B. The Second Law of Thermodynamics states that some energy is lost as disorder increases

1. Entropy: disorder or random movement of molecules increases. Energy converts matter from an ordered, less stable form to an unorganized, more stable form.

C. Chemical reactions (chem rxtn) can be predicted based on changes in free energy

1. Free energy – the amount of energy available to break & form chem bonds. Gibbs free energy = G

2. Enthalpy – energy stored in chemical bonds. H

Entropy – energy unavailable due to disorder. S

G = H – STFree energy = enthalpy – (entropy x temperature)

3. Endergonic – more energy to go INTO the rxtn. Products have more energy than reactants.

Energy + CO2 + H2O C6H12O6 + O2

4. Exergonic – more energy RELEASED from the rxtn. Reactants have more energy than products.

C6H12O6 + O2 Energy + CO2 + H2O

D. Spontaneous chemical reactions require activation energy

1. Activation energy: energy needed to start a chem rxtn.

a. Increasing the rate of a rxtn

i. Increase energy of reactants (incr. temp.)

ii. Lower activation energy

2. How catalysts work

a. Catalyst: substance that lowers activation energy (EA) to speed up a rxtn.

b. catalysis: increasing chem rxtn by adding a catalyst.

III. ATP: The Energy Currency of Cells (6.3) A. Adenosine triphosphate (ATP): nucleotide

that acts as “currency” for energy-requiring chem. reactions.

Supplies activation energy, active transport energy, energy for movement and growth.

High energy bonds

B. Cells store and release energy in the bonds of ATP

1. The structure of ATP has 3 parts:

1 five carbon sugar ribose

1 two carbon-nitrogen rings adenine

3 phosphate groups

2. How ATP stores energy

• The phosphate groups have a high neg. charge and repel. Hydrolysis breaks apart the phosphate groups. When ATP is hydrolyzed once it becomes

a. Adenosine diphosphate (ADP) and

b. Inorganic phosphate (Pi)

c. Adenosine monophosphate (AMP): forms when 2 phosphate groups are hydrolyzed from ATP.

C. ATP hydrolysis drives endergonic reactions

• When ATP hydrolysis is coupled with endergonic reactions, more energy is released that used.

• The group that receives the P group is phosphorylated.

D. ATP cycles continuously (unstable as ATP) • Cells use exergonic reactions to provided

energy to make ATP from ADP and Pi. The hydrolysis of ATP drives endergonic reactions.

IV. Enzymes: Biological Catalysts • Most enzymes are proteins that carry out

catalysis.

• They carry out a specific rxtn.

• Names of enzymes usually end in -ase

A. An enzyme alters the activation energy of a rxtn

1. Substrate: reactants in an enzyme catalyzed rxtn.

2. Product: chemicals at end of rxtn.

B. Active Sites of enzymes conform to fit the shape of substrates

1. Active sites: place where substrate fits into enzyme and a chem rxtn occurs.

2. Enzyme-substrate complex: when the substrate is in the active site.

3. Induced fit: enzyme slightly changes shape to better fit around substrate.

C. Enzymes occur in many forms • 1. Multienzyme

complexes: group of enzymes joined together catalyzing a series of rxtns.

• 2. Nonprotein enzymes: RNA can act like a catalyst.

D. Environmental and other factors affect enzyme function

1. Temperature: most enzymes work best at a specific temp or optimum temp. If the temp goes too far below or above the temp, they will denature and become inactive.

Human optimum temp 35C – 40C

2. pH: most enzymes work best at a specific pH or optimum pH. If the pH goes too far below or above the pH, they will denature and become inactive.

Human optimum pH usually 6-8 (stomach 2)

3. Inhibitors and activatorsa. Competitive inhibitors – compete with

and stop substrate from binding with the active site.

b. Noncompetitive inhibitor: stops substrate from reacting by binding with enzyme in a place other than the active site.

d. Allosteric enzyme: can be turned on or off

e. Allosteric site: switch

f. Allosteric inhibitor: turns off (inactivates) enzyme

g. Allosteric activator: turns on (activates) enzyme

http://www.dmcg.edu/phpbb2/index.php?showtopic=736&mode=threaded

http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swf

4. Enzyme cofactors and coenzymes

• Help enzymes carry out rxtns often by moving electrons.

V. Metabolism: The Chemical Description of Cell Function

A. Metabolism: all chemical reactions in an organism

B. Anabolism: chem rxtns that use energy to change chem bonds

C. Catabolism: chem rxtns that release energy when chem bonds are broken

D. Biochemical pathways organize chemical reactions in cells

1. Biochemical pathways: a sequence of chemical reactions carried out by enzymes in which the product of one reaction becomes the substrate for the next one. Each enzyme takes part in one step.

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120070/bio09.swf::A%20Biochemical%20Pathway

E. Biochemical pathways may have evolved in stepwise fashion

• In a biochem pathway, the final reactions evolved first then the first reactions evolved later.

F. Feedback inhibition regulates some biochemical pathways

1. Feedback inhibition: Regulates biochemical pathways. End product of pathway binds to an allosteric site on the enzhyme that catalyzes the first reaction in the pathway. This stops production when end products are at high levels.

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120070/bio10.swf::Feedback%20Inhibition%20of%20Biochemical%20Pathways