Agenda: Thur 9/12

• Collect HW• Biomolecules Match-Up• Start Energy, Metabolism, and

Enzymes Lecture• Homework Energy, Metabolism, and

Enzymes Guided Reading (Chp.2&3)

• Due MONDAY

Energy, Metabolism, & Enzymes Notes

Chemical Reactions Make and/or Break Chemical Bonds

• Chemical reactions are the making and breaking of chemical bonds

• The starting molecules of a chemical reaction are called reactants

• The final molecules of a chemical reaction are called products

3

Example: Photosynthesis…a mighty important chemical reaction!

• Sunlight powers the conversion of carbon dioxide and water to glucose and oxygen

6 CO2 + 6 H2O → C6H12O6 + 6 O2

4

Metabolism/Bioenergetics

• Metabolism: The totality of an organism’s chemical processes; managing the material and energy resources of the cell– Catabolic pathways: degradative process such

as cellular respiration; releases energy–Anabolic pathways: building process such as

protein synthesis; photosynthesis; consumes energy

Strategies to regulate body temp and metabolism

• Endothermy = use of thermal E generated by metabolism to maintain homeostatic body temperatures

• Ectothermy = use of external thermal E to help regulate and maintain body temp

Thermodynamics = study of E transformations

• Energy (E)=capacity to do work; Kinetic energy~ energy of motion; Potential energy~ stored energy

• Thermodynamics~ 1st Law: conservation of energy; E transferred/transformed, not created/destroyed

• 2nd Law: transformations increase entropy (disorder, randomness)

• Combo: quantity of E is constant, quality is not

• Adenosine triphosphate (ATP) is the primary energy-transferring molecule in the cell

• ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups

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ATP: An Important Source of Energy for Cellular Processes

Energy Coupling & ATP

• E coupling: use of exergonic process to drive an endergonic one

• Adenosine triphosphate (ATP)

• ATP tail: high negative charge

• ATP hydrolysis: release of free E

The ATP cycleATP synthesis from ADP + P i requires energy

ATP

ADP + P i

Energy for cellular work(endergonic, energy-consuming processes)

Energy from catabolism(exergonic, energy yieldingprocesses)

ATP hydrolysis to ADP + P i yields energy

Free energy

• Free energy (G) = the energy available to do work

• DG = change in free energy

• Order is maintained by constant free energy input into a system– Loss of order or free energy flow results in death– Remember: excess acquired free energy versus

required free energy expenditure results in energy storage or growth!

In the previous example the initial state has more energy than the final state so that DG is a negative number

• If DG is a negative number, then the reaction is exergonic (releases energy)

• If DG is positive then DG is endergonic (absorbs energy).

Rule-Things tend to go from high energy to lower energy.

During this time bonds must be broken and remade.

The energy used to do this is called the energy of activation (EA).

Another exampleEndergonic reaction: ∆G is positive, reaction is not spontaneous

∆G = +3.4 kcal/molGlu Glu

∆G = –7.3 kcal/molATP H2O+

+NH3

ADP +

NH2

Glutamicacid

Ammonia Glutamine

Exergonic reaction: ∆ G is negative, reaction is spontaneous

P

Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/mol

Energy Concepts Video Clip• 2 min.

Enzymes = proteins (catalysts) that increases the rate of biochemical reaction.

Characteristics of enzymes:

a. Made of proteins

b. They are very specific and only work with a certain set of reactants or substrates that fit on their active site.

This is the space filling and ribbon model of the lysozyme. The groove is the active site where the substrate attaches

c. When an enzyme binds with the substrate, the substrate interacts with the enzyme causing it to change shape. This change in shape will facilitate the chemical reaction to occur. This is called the induced fit

Substrate: enzyme reactantActive site: pocket/groove on enzyme that binds to substrate

Example of an enzyme-catalyzed reaction: hydrolysis of sucrose by

sucrase

H2O

H

H

H

H

HO

OH

OH

OH

O

O OO OHH H H

H

H

H

CH2OH CH2OH

OHCH2OH

Sucrase

HOHO

OH OH

CH2OHH

CH2OH

H

CH2OH

H

O

Sucrose Glucose Fructose

C12H22O11 C6H12O6 C6H12O6

+HOH H

HO

d. It increases the reaction rate by lowering the energy of activation. They do not change D G.

e. Enzymes can be used over and over again

The graph represents the amount of product formed. At first amount of product formed increases, then the rate slows down until it reaches a constant maximum. The enzyme is becoming saturated. The fastest rate of product formation is at the beginning and is called the initial velocity. If the enzyme is kept constant and there is an increase in the amount of substrate, there will be an increase in the initial velocity until a saturation point is reached.

The previous experiment is repeated with the same amount of enzyme but increasing amount of substrate. The initial velocities increase because there is more substrate to attach the enzyme but the eventually there is no increase in initial velocity because all the enzymes have become saturated with substrate.

Effects on Enzyme Activity

• Temperature (denature)• pH• Cofactors:– inorganic, nonprotein helpers– ex.: zinc, iron, copper

• Coenzymes:– organic helpers– ex.:vitamins

Temperature- at first an increase in temperature will increase the reaction rate because of the kinetics of the reaction but after a certain temperature is reached, the hydrogen bonds fall apart and the enzyme will denature.

pH can affect the reaction rates. Most enzymes work best at a range of 6 to 8 but there are some exception such as pepsin. If the environment changes much from the optimum pH, again hydrogen bonds are affected, denaturing the enzyme.

Enzyme Inhibitors = Some chemicals inhibit the action of an enzyme.

• Irreversible (covalent) or reversible (weak bonds)

• Competitive: competes for active site (reversible); mimics the substrate

• Noncompetitive: bind to another part of enzyme (allosteric site) altering its conformation (shape); poisons, antibiotics

A competitive inhibitor is a molecule that resembles the substrate enough that it can bind to the active site in place of the substrate. This will slow down the reaction rate

A noncompetitive inhibitor is one that does not bind to the receptor site but to some other place on the molecule the allosteric site. This causes the active site to change shape so that substrate cannot bind. This also slows down the reaction rate.

Allosteric Regulation- These enzymes have two or more polypeptide chains each with its own active site. This enzyme also has two conformations-one with a functional active site and the other with a nonfunctional active site. This enzyme also has a place for the binding of an activator and an inhibitor. The activator will stabilize the conformation with the functional active site and the inhibitor will stabilize the inactive form of the enzyme.

Feedback inhibition- Usually enzymes work in biochemical pathway in which there is a series of intermediate chemical reaction that occur in order to get from point A (reactants) to point B (products). It is not unusual for an end product to act as an inhibitor to shut down the pathway when there is sufficient product present.

Feedback inhibition in isoleucine synthesis

Active siteavailable

Isoleucineused up bycell

Feedbackinhibition

Isoleucine binds to allosteric site

Active site of enzyme 1 no longer binds threonine;pathway is switched off

Initial substrate(threonine)

Threoninein active site

Enzyme 1(threoninedeaminase)

Intermediate A

Intermediate B

Intermediate C

Intermediate D

Enzyme 2

Enzyme 3

Enzyme 4

Enzyme 5

End product(isoleucine)

How Enzymes Work Video Clip

• 1 min.

QuickTime™ and aCinepak decompressor

are needed to see this picture.

After:

• Enzymes & Metabolism Worksheet