Enzymes
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Enzymes. Characteristics of Enzymes. Proteins Monomer is: _______ ______ Catalysts Start or speed up chemical reactions without being used up. In case you wondered…How do enzymes work?. Lower Activation Energy to speed up rates of reaction

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Enzymes

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Enzymes

Enzymes


Characteristics of enzymes

Characteristics of Enzymes

  • Proteins

    • Monomer is: _______ ______

  • Catalysts

    • Start or speed up chemical reactions without being used up


In case you wondered how do enzymes work

In case you wondered…How do enzymes work?

  • Lower Activation Energy to speed up rates of reaction

    • Reactions require energy to begin…enzymes lower the amount of energy required.


Naming

Naming

  • Often end in “–ase”

  • Usually relates to the reaction they help start

    • Examples: lactase, sucrase,

      protease, carboxypeptidase


Catalyzing process

Catalyzing Process

  • A unique 3-D shape of an enzyme determines which chemical reaction it catalyzes

  • Important Vocab:

    • SUBSTRATE: A specific reactant that an enzyme acts on is called a substrateof the enzyme.


Enzymes

  • Important Vocab (cont.):

    • ACTIVE SITE: A substrate fits into a region of the enzyme called an active site.

      • An active site is typically a pocket or groove on the surface of the enzyme.


The enzyme and substrate form a complex

The enzyme and substrate form a complex

substrate

Active site

enzyme

Enzyme-substrate complex


Lock and key model

Lock and Key Model

+ +

Enzyme + Substrate  ES complex Enzyme + Products

P

S

S

P


Enzymes

Enzymes can be used to break down molecules


Enzymes

Enzymes can also be used to

bond two substrates into one product


Enzymes

In this lab- there are three reagents:

Turnip peroxidase

Hydrogen peroxide

Guiacol

Which is the enzyme?

Which is the substrate?

What is the other reagent then?!?


Enzymes

What kind of reaction is being started in this reaction (breaking down or building up?)

What are the products of this reaction?

H2O2 H20 + O


Enzymes

How will we know if the reaction occurred?

H2O2 H20 + O

Guiacol turns brown when oxidized. (and it gets more and more brown as more of the guiacol is oxidized).


Enzymes

How do we quantify “how brown” it is?

With a spectrophotometer!


Enzymes

Results of the lab (graph)


Structure

Structure

  • If an enzyme’s shape is changed so that it is no longer able to catalyze reactions, we call it…

    DENATURED

    • What kinds of things do you think could denature a protein?


Denaturation

Denaturation

  • Disruption of protein structure by

    • Heat: Break apart H bonds and disrupt hydrophobic attractions

    • Acids/ bases: Break H bonds between polar R groups and ionic bonds

    • Heavy metal ions: React with S-S bonds to form solids

    • Agitation: Stretches chains until bonds break


Applications of denaturation

Applications of Denaturation

  • Hard boiling an egg

  • Wiping skin with alcohol swab for injection

  • Cooking food to destroy E. coli

  • Autoclave sterilizes instruments


Think about it

Think about it

Tannic acid is used to form a scab on a burn. An egg becomes hard boiled when placed in hot water. What is similar about these two events?

Solution

Acid and heat cause a denaturation of protein. They both break bonds in the structure of protein.


Factors affecting enzyme action

Factors Affecting Enzyme Action

  • Temperatureaffects molecular motion

    • An enzyme’s optimal temperature produces the highest rate

    • Most human enzymes work best at 35-40 ºC.

WATCH OUT!!!

If the temperature gets too high, the enzyme may be denatured!


Temperature cont

Temperature (cont.)

Optimum temperature

Reaction

Rate

Low High

Temperature


Ions salt concentration ph influence enzyme activity

Ions:Salt concentration & pH influence enzyme activity.

  • SALT: The salt ions interfere with some of the chemical bonds that maintain protein structure

  • pH: The same is true of the extra hydrogen ions at very low pH

    • Optimal pH for most enzymes near neutral


Substrate concentration

Substrate Concentration

  • Increasing substrate concentration increases the rate of reaction initially (enzyme concentration is constant) Why?

  • Maximum enzyme activity will be reached when all of enzyme combines with substrate.

  • What would a graph of the above look like?


Substrate concentration cont

Substrate Concentration (cont.)

Maximum activity

Reaction

Rate

substrate concentration


Enzyme inhibition

Enzyme Inhibition

  • Inhibitors: cause a loss of catalytic activity

    • May change the protein structure of an enzyme

    • May be competitive or noncompetitive

    • Some effects are irreversible


Competitive inhibition

Competitive Inhibition

  • Acompetitive inhibitor

    • Has a structure similar to substrate

    • Occupies active site

      • “Competes” with substrate for active site

    • Effects can be reversed by increasing substrate concentration


Competitive inhibition image

Competitive Inhibition Image


Noncompetitive inhibition

Noncompetitive Inhibition

  • A noncompetitive inhibitor

    • Does not have a structure like substrate

    • Binds to the enzyme (not at active site) & changes the shapeof enzyme & active site

      • Substrate cannot fit altered active site

    • No reaction occurs

    • Effect is not reversed by adding substrate


Noncompetitive inhibition image

Noncompetitive Inhibition Image


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