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Metabolism:   Energy and Enzymes. Chapter 6. Energy = the ability to do work. Kinetic Energy (energy of motion) Potential Energy (stored energy). First Law of Thermodynamics - the law of conservation of energy

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energy the ability to do work
Energy = the ability to do work

Kinetic Energy (energy of motion)

Potential Energy (stored energy)

First Law of Thermodynamics - the law of conservation of energy

Second Law of Thermodynamics - energy cannot be changed without a loss of usable energy (heat)

atp the energy currency of cells adenosine triphosphate
ATP - the energy currency of cells (adenosine triphosphate) 

Functions:1. CHEMICAL WORK - Supplies energy needed to make macromolecules that make up the cell (and organism)2. TRANSPORT WORK - Supplies energy needed to pump substances across the cell membrane3. MECHANICAL WORK - supplies energy needed to make muscles contract and other cellular parts to move (flagella)

metabolic pathways enzymes 6 3
Metabolic Pathways & Enzymes (6-3)

Enzyme - protein molecule that functions as an organic catalyst to speed reactions

Substrate - reactants in the enzymatic reaction, this is what an enzyme attaches to

Energy of Activation - the energy required to cause the reaction

properties of enzymes
Properties of Enzymes:
  • Enzymes are made of proteins.
  • They speed up chemical reactions inside the cytoplasm.
  • They are needed only in small amounts
  • They remain unchanged after each reaction and can therefore be reused
  • Each enzyme is specific for a substrate

Factors Affecting Enzymatic Speed

1. Substrate concentration2. Temperature & pH *3. Enzyme concentration

Enzymes can be denatured - they change shape so much that they are no longer effective. High temp or pH can cause denaturation. 


Siamese cats have an enzyme that works at lower temperatures only, causing the nose and ears to become a darker color than the rest of the body.


Enzymatic Inhibition - when a substance binds to an enzyme and decreases its activity. (Usually reversible)

Competitive Inhibition 

Noncompetitive Inhibition (allosteric site)

**Both are forms of feedback inhibition

Some inhibitors are NOT reversible - poisons like cyanide, lead poisoning all affect enzymes

QUESTION: What type of inhibition is pictured below?

Enzyme Animation (Tutorial)

Enzyme Quiz

enzyme lab s
Enzyme Lab(s)

  2H2O2 ----> 2H2O + O2

Hydrogen Peroxide is broken down by the enzyme: catalase within cells.   

KMNO4 (potassium permanganate) can be used to determine how much H2O2 is left within the flask after the reaction has stopped.   (Titration)


You slowly add KMnO4, which is purple, to the flask. The peroxide in the flask causes the KMnO4 to lose color when the solution is mixed thoroughly. When all the peroxide has reacted with KMnO4, any additional KMnO4 will remain light brown or pinkish even after you swirl the mixture. This is the endpoint. Record the amount of KMnO4 you have used. 

The more KMnO4 you use, the more peroxide is left in the flask.

the activity of catalase can be seen by the bubbling of oxygen during the reaction
The activity of catalase can be seen by the bubbling of oxygen during the reaction

Generally speaking, catalase reactions occur faster at warmer temperatures.

If temperature is too hot (boiling) then the enzyme becomes denatured


Virtual Labs with Enzymes

McGraw Hill Lab

Bio 114  Enzymes

Lab Bench Enzyme Catalysis