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Agenda• Attendance• Review chart of mutations• Enzyme interactive website• Notes• Practice• Tooth pick activity

Enzymes and Metabolism!!!

Lets speed up some reactions!!

Vocab you need to know by the end of this Unit

Vocabulary:activation energy, biochemical reaction, coenzyme, competitive inhibitor, enzyme, enzyme activity, enzyme concentration, heavy metal, induced fit model, metabolism, non-competitive inhibitor, pH, proteins, substrate, substrate concentration, thyroid, thyroxin, vitamins

First you need to know:• What are acids?

• What are bases?

• What are buffers?

• Why do we Care?

2-5

• Acids are molecules that release hydrogen ions in solution.

HCl H+ + Cl-

2-6

• Bases are molecules that either take up hydrogen ions or give off hydroxide ions in solution.

NaOH Na+ + OH-

2-7

• Concentrations of hydrogen ions or hydroxide ions can be represented using the pH scale.

moles/liter1 x 10 –6 [H+] = pH 6 1 x 10 –7 [H+] = pH 7 1 x 10 –8 [H+] = pH 8

2-8

• Buffers are substances that help to resist change in pH.

Describe the importance of pH to biological systems in the human body.

6-11

Metabolic Reactions and Energy Transformations

• Metabolism is the sum of all the chemical reactions that occur in a cell.

• Reactants are substances that participate in a reaction; products are substances that form as a result of a reaction.

• A reaction will occur spontaneously if it increases entropy.

• Biologists use the term “free energy” instead of entropy for cells.

6-12

• Free energy, G, is the amount of energy 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.

• A negative ΔG means the products have less free energy than the reactants, and the reaction will occur spontaneously.

6-13

• Exergonic reactions have a negative ΔG and energy is released.

• Endergonic reactions have a positive ΔG and occur only if there is an input of energy.

• Energy released from exergonic reactions is used to drive endergonic reactions inside cells.

• ATP is the energy carrier between exergonic and endergonic reactions.

6-14

ATP: Energy for Cells• ATP (adenosine triphosphate) is the energy

currency of cells. • ATP is constantly regenerated from ADP

(adenosine diphosphate) after energy is expended by the cell.

• ATP is coupled to endergonic reactions in such a way that it minimizes energy loss.

6-15

• ATP is a nucleotide made of adenine and ribose and three phosphate groups.

• ATP is called a “high-energy” compound because a phosphate group is easily removed.

• The amount of energy released when ATP is hydrolyized is 7.3 kcal per mole.

6-16

The ATP cycle

6-17

Coupled Reactions

• In coupled reactions, energy released by an exergonic reaction drives an endergonic reaction.

6-18

Coupled reactions

6-19

Function of ATP

• Cells make use of ATP for:• Chemical work – ATP supplies energy to

synthesize macromolecules, and therefore the organism

• Transport work – ATP supplies energy needed to pump substances across the plasma membrane

• Mechanical work – ATP supplies energy for cellular movements

6-20

Metabolic Pathways and Enzymes

• Cellular reactions are usually part of a metabolic pathway, a series of linked reactions, illustrated as follows:

• E1 E2 E3 E4 E5 E6

A → B → C → D → E → F → G

A-F are reactants or substrates B-G are the products in the various reactionsE1-E6 are enzymes.

6-21

• An enzyme is a protein molecule that functions as an organic catalyst to speed a chemical reaction.

• An enzyme brings together particular molecules and causes them to react.

• The reactants in an enzymatic reaction are called the substrates for that enzyme.

6-22

Energy of Activation• The energy that must be added to cause

molecules to react with one another is called the energy of activation (Ea).

• The addition of an enzyme does not change the free energy of the reaction, rather an enzyme lowers the energy of activation.

6-23

Energy of activation (Ea)

6-24

Enzyme-Substrate Complexes• Every reaction in a cell requires a specific

enzyme.

Enzymes are named for their substrates:Substrate EnzymeLipid LipaseUrea UreaseMaltose MaltaseRibonucleic acid Ribonuclease

6-25

• A small part of an enzyme, called the active site, complexes with the substrate(s).

• The active site may undergo a slight change in shape, called induced fit, in order to accommodate the substrate(s).

• The enzyme and substrate form an enzyme-substrate complex during the reaction.

• The enzyme is not changed by the reaction, and it is free to act again.

6-26

Enzymatic reaction

6-28

Induced fit model

6-30

Factors Affecting Enzymatic Speed• Enzymatic reactions proceed with great speed

provided there is enough substrate to fill active sites most of the time.

• Enzyme activity increases as substrate concentration increases because there are more collisions between substrate molecules and the enzyme.

Menu31

Substrate Concentration

Rat

e of

Rea

ctio

n Enzyme Active Site is Saturated

Menu32

6-33

Temperature and pH• As the temperature rises, enzyme activity

increases because more collisions occur between enzyme and substrate.

• If the temperature is too high, enzyme activity levels out and then declines rapidly because the enzyme is denatured.

• Each enzyme has an optimal pH at which the rate of reaction is highest.

Menu34

Effect of pH on Enzyme Activity

2 3 4 5 6 7 8 9

Rat

e of

Rea

ctio

n

pH

Pepsin Trypsin

Each enzyme has its own optimum pH.

Menu35

Effect of Temperature on Enzyme Activity

30 40 50

Rate

of

Reacti

on

Temperature

Menu36


30 40 50

Rate

of

Reacti

on

Temperature

Increasing the temperature causes more collisions between substrate and enzyme molecules. The rate of reaction therefore increases as temperature increases.

Menu37


30 40 50

Rate

of

Reacti

on

Temperature

Enzymes denature when the temperature gets too high. The rate of reaction decreases as the enzyme becomes nonfunctional.

Menu38

Regulation of Enzymes

· The next several slides illustrate how cells regulate enzymes. For example, it may be necessary to decrease the activity of certain enzymes if the cell no longer needs the product produced by the enzymes.

Menu39

Regulation of Enzymes

geneticregulation

regulation of enzymesalready produced

competitiveinhibition

noncompetitiveInhibition

(next slide)

Cell can turn on DNA genes to build more enzymes when needed

Cells can use certain chemicals to slow down existing enzymes

6-40

Enzyme Inhibition• Enzyme inhibition occurs when an active enzyme

is prevented from combining with its substrate.

• When the product of a metabolic pathway is in abundance, it binds competitively with the enzyme’s active site, a simple form of feedback inhibition.

• Other metabolic pathways are regulated by the end product binding to an allosteric site on the enzyme.

Menu41

Competitive Inhibition

In competitive inhibition, a similar-shaped molecule competes with the substrate for active sites.

Menu42

Competitive Inhibition

Active site is being occupied by competitive inhibitor

This substrate cannot get into active site at this time

Menu43

Noncompetitive InhibitionActive site Inhibitor Altered active site

Enzyme

Menu44

Noncompetitive Inhibition

· The binding of an inhibitor to an allosteric site is usually temporary. Poisons are inhibitors that bind irreversibly. For example, penicillin inhibits an enzyme needed by bacteria to build the cell wall. Bacteria growing (reproducing) without producing cell walls eventually rupture.

6-45

Feedback inhibition

6-48

Enzyme Cofactors• Presence of enzyme cofactors may be necessary

for some enzymes to carry out their functions.

• Inorganic metal ions, such as copper, zinc, or iron function as cofactors for certain enzymes.

• Organic molecules, termed coenzymes, must be present for other enzymes to function.

• Some coenzymes are vitamins.

Enzyme Enzyme

Coenzyme