Chapter 2 Enzymes

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Chapter 2Enzymes
AP 151
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All Cells need Energy to do Work

• Cells use energy to
• grow, make new
• parts, and reproduce.

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Biological Work

• Energy an be defined as the capacity to do work
• Biological work has three basic forms
• Chemical work
• Growth
• Protein synthesis
• Information storage
• Transport work
• Move molecules across plasma membrane
• Maintain concentration gradients
• Mechanical work
• Positioning movement of organelles
• Cell shape
• Beating of cilia flagella
• Muscle contraction

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Activation Energy and theNet Free Energy Change
of the Reaction

• Activation energy is the energy needed to get the
  reaction started.
• The net free energy change is the difference in
  free energy between the reactants and products.

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Exergonic and Endergonic Reactions

• Exergonic reactions release energy or are energy
  producing reactions. The products have a lower
  free energy than the reactants
• C6H12O6 6O2 ? 6H2O 6CO2 36 ATP heat
• Endergonic reactions are energy utilizing
  reactions where part or all of the activation
  energy is retained or trapped in the chemical
  bonds of the products.
• CO2 H2O Radiant energy ? C6H12O6 6O2

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Enzymes

• Means in yeast 1st described by Buchner
• Proteins are biological (organic) catalysts
• promote rapid reaction rates
• Substrate - substance an enzyme acts upon
• Naming Convention
• named for substrate with -ase as the suffix
• amylase enzyme digests starch (amylose)
• Lowers activation energy energy needed to get
  reaction started
• enzymes facilitate molecular interaction

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Enzymes and Activation Energy
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Characteristics of Enzymes

• 1. Lower the activation energy of a reaction.
• - Activation energy is the energy needed to get
  a reaction started.
• 2. Increases the rate of a reaction but does not
  cause a reaction to occur that would not occur in
  its absence.
• - Enzymes are biological catalysts
• 2H2O2 -gt 2H2O O2 One molecule of
  catalase can break 40 million molecules of
  hydrogen peroxide each second.
• 3. Are not used up or changed by the reaction.
• 4. Exhibit specificity, competition, and
  saturation.

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How do enzymes increase the rate of a chemical
reaction?

• Enzymes bind to their substrates and bring them
  together in the proper orientation for the
  reaction to begin.
• The binding and aligning of the substrates lowers
  the activation energy of the reaction.

enzyme A B ? C D enzyme
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Substrate Binding

• Lock and Key Model
• Induced Fit Model

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Cofactors

• Enzyme activity relies on the binding of certain
  inorganic molecules before substrate binding can
  occur. Examples are Ca2 and Mg2.

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Coenzymes

• Coenzymes are organic molecules.
• Do not alter the enzymes binding site.
• Accept electrons from an enzyme in one metabolic
  pathway and transfer them to an enzyme in
  another.
• They are not needed in large amounts.
• The water soluble vitamins (thiamine (B1) niacin,
  riboflavin (B2)) are all good examples of
  cofactors.
• NAD (nicotinamide adenine dinucleotide)
• FAD (flavine adenine dinucleotide)

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Coenzyme NAD

• NAD transports electrons from one metabolic
  pathway to another

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Temperature pH Modulation

• Enzymes are proteins, and all proteins have a
  native configuration which gives them a
  particular function (activity) or structure.
• Changes in temperature and pH greatly affect the
  enzymes confirmation and results in loss of
  activity. We say it is denatured.

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Proteolytic Activation

• Some enzymes are produced in an inactive form
  called proenzymes or zymogens.
• The pro- prefix and -ogen suffix signifies that
  the molecule is inactive.
• Chymotrypsinogen
• Pepsinogen
• Angiotensinogen
• Prothrombin

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Temperature pH Modulation

• Small changes in temperature, pH, or salt can
  increase or decrease enzyme activity.
• Once a critical level is exceeded, then the
  change in confirmation is irreversible and the
  enzyme forever looses its activity.

Pepsin pH of 1-2 Trypsin pH of 8-9.5
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Isozymes

• Any of a group of enzymes that catalyze the same
  reaction
• Have different structures and physical and
  biochemical properties.
• Lactate dehydrogenase (LDH) - widely distributed
  through- out the body
• Cellular damage causes an elevation of the total
  serum LDH
• Diagnostic usefulness is in the determination of
  which fraction of LDH is elevated
• LDH-1 is found mainly in heart muscle and RBCs
• LDH-2 in white blood cells
• LDH-3 is highest in the lung
• LDH-4 is highest in the kidney, placenta, and
  pancreas
• LDH-5 is highest in the liver and skeletal muscle
• For future reference http//www.nlm.nih.gov/medli
  neplus/ency/article/003471.htm

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Effect of Enzyme or Substrate Concentration on
Reaction Rate

• The reaction rate is directly related to enzyme
  concentration.
• What is the independent variable in this graph?
• The reaction rate can reach a maximum (Vmax) when
  the enzyme is saturated.
• What is the independent variable in this graph?

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Feedback Inhibition

• Occurs when the product of a series of enzymatic
  reactions begins to accumu- late within the cell
• Product may then inhibit the action of the first
  enzyme in its synthesis
• Further production of the enzyme is then halted

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