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Enzymes - PowerPoint PPT Presentation

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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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Presentation Transcript
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.
  • 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.
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


Active site


Enzyme-substrate complex

lock and key model
Lock and Key Model

+ +

Enzyme + Substrate  ES complex Enzyme + Products





Enzymes can also be used to

bond two substrates into one product

In this lab- there are three reagents:

Turnip peroxidase

Hydrogen peroxide


Which is the enzyme?

Which is the substrate?

What is the other reagent then?!?

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

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).

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


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


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.


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

temperature cont
Temperature (cont.)

Optimum temperature



Low High


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



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
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