Enzymes

1
Enzymes

• Topic 3.6 and 7.6

2
Enzymes

• Proteins
• Biological catalysts
• May break a substrate molecule down into simpler
  molecules, or join two or more substrate
  molecules chemically together.
• Enzyme itself is unchanged in reaction its used
  to speed up the reaction.
• Animation- http//highered.mcgraw-hill.com/sites/0
  072495855/student_view0/chapter2/animation__how_en
  zymes_work.html

3
Activation energy

• Required to enable substrate to change into the
  product
• 50 chance that the reaction will proceed,
  otherwise it goes back to a stable form of the
  reactant again.

4
Active site

• Active site
• Part of the enzymes surface into which the
  substrate is bound and undergoes and reaction.
• Made of different parts of the polypeptide chain
  folded in a specific shape.
• Specificity the complexity of the binding site
  is such that only one type of substrate will
  bind.

5
How enzymes work

• Lock and Key model
• Model proposed earlier this century that
  suggested that the substrate was simply drawn
  into a closely matching cleft on the enzyme
  molecule
• Induced Fit Model
• more recent studies have revealed that the
  process more likely involves an induced fit,
  where the enzyme or reactants change their shape
  slightly.
• reactants bond to enzymes via weak chemical bonds
  which weaken bonds within the reactant, allowing
  the reaction to proceed more readily

6
Induced Fit Model

• An enzyme fits to its substrate somewhat like a
  lock and key.
• The shape of the enzyme changes when the
  substrate fits into the cleft
• (1) The substrate molecules are drawn into the
  cleft of the enzyme
• (2) The enzyme changes shape, forcing the
  substrate molecules to combine
• (3) the resulting end product is released by the
  enzyme which returns to its normal shape, ready
  to receive more.

7
Animation- http//www.sumanasinc.com/webcontent/an
imations/content/enzymes/enzymes.html
8
Catalysts

• Catalysts speed up reactions by influencing the
  stability of bonds in the reactants
• May also provide an alternative reaction pathway,
  lowering the activation energy.
• The presence of an enzyme simply makes it easier
  for a reaction to take place.

9
Catabolic Reactions

• Some enzymes can cause a single substrate
  molecule to be drawn into the active site.
• Chemical bonds are broken, causing the substrate
  molecule to break apart to become two separate
  molecules.
• Example digestion, cellular respiration

10
Anabolic Reactions

• Some enzymes can cause two substrate molecules to
  be drawn into the active site.
• Chemical bonds are formed, causing the two
  substrate molecules to form bonds and become a
  single molecule
• Examples protein synthesis, photosynthesis

11
Enzyme Reaction Rates

• Enzymes are sensitive molecules.
• Often have narrow range of conditions under which
  they operate properly.
• Temperature
• At low temperatures, there is little activity. As
  temperature increases until the point is reached
  when the temperature is so high it damages the
  protein (denaturation). This causes the enzyme to
  stop working.

12
(No Transcript)
13
Enzyme Reaction Rates

• Poisons can cause enzymes to cease functioning
• Cofactors such as vitamins and trace elements are
  required for many enzyme to function
• pH
• Extremes in acidity (pH) can also cause the
  protein structure of enzymes to denature.

14
Enzyme Cofactors

• Cofactors
• Enhance enzyme activity
• Nonprotein component of an enzyme and may be
  organic molecules (coenzymes) or inorganic ions
  (Ca2, Zn2)

15
Enzyme Inhibitors

• May also be deactivated, temporarily or
  permanently, via inhibitors.
• Reversible inhibitors
• Used to control enzyme activity
• Often an interaction between the substrate or end
  product and the enzymes controlling the reaction.
• Build up of the end product or a lack of
  substrate may serve to deactivate the enzyme.
• May be competitive, noncompetitive, or allosteric
  inhibitor

16
Enzyme Inhibitors

• Competitive inhibition
• Enzyme deactivation may be result of competitive
  inhibitor blocking the active site.
• Noncompetitive inhibition
• Enzyme deactivation may be results of
  noncompetitive inhibitor binding to another site
  on the enzyme.
• Substrate can still bind to active site, but
  slows the speed of reaction

17
(No Transcript)
18
Enzyme inhibitors

• Allosteric inhibitors
• Noncompetitive inhibitor binds to enzyme in
  another site other than active site, which causes
  the active site to be distorted. The substrate
  cannot bind to the active site.

19
Enzyme Inhibitors

• Irreversible Inhibitors
• Poisons
• Certain heavy metals bind tightly and permanently
  to the active sites of enzymes, destroying their
  catalytic properties.
• Examples Cadmium (Cd), lead (Pb), mercury (Hg),
  and arsenic (As)
• Generally non-competitive inhibitors, except Hg
• Heavy metals are retained in the body, and lost
  slowly.