Enzymes

1
Enzymes

• Chapter 24

2
Goals

• Understand functions of enzymes
• Know the difference between activators and
  inhibitors
• Understand enzyme activity

3
Enzyme Function

• Catalysts (inorganic and biological)
• Increase speed of reaction by lowering energy
  required
• No net change of the catalyst in a reaction
• Can be reused
• Cant cause a reaction, only enhance it.
• Biological catalysts are better because
• Catalytic power is greater
• Increase reaction speed 109 to 1020 times
• They are specific react with one substrate only
  and only make one isomer of product.
• Activity is regulated by inhibitors and coenzymes

4
Activation energy and catalysts

• catalyst lowers activation energy

5
Speed of Enzymatic Reactions

• Enzymes are proteins denatured by same means.
• Temperature higher temp, faster reaction.
• Temp too high, denature
• pH enzyme wont function if its not at its
  ideal pH
• Concentration rate increases if we increase
  enzyme concentration or substrate concentration
  (until all enzyme is in use)

6
How Enzymes Work

• Enzyme may need to be activated by the addition
  of a cofactor or coenzyme
• A specific substrate enters the active site
  (think of a key and a lock. My house key will
  not operate your car)
• Shape of active site dictated by the chemistry
• What residues present (usually acid/base), what
  are hydrogen bonded
• Enzyme-substrate complex
• Enzyme releases product

7
Enzyme Models

• Used lock and key model so far
• Problems-
• enzymes are dynamic
• If active site didnt change, no reason to
  release product. Complex would be too stable
• Does not account for non-competitive inhibition
• Induced Fit - active slightly changes size and
  shape as substrate enters
• Glove (enzyme) and hand (substrate) idea

8
Activators and Inhibitors

• Activators increase activity of enzyme
• Mg2 and Zn2
• Inhibitors- slow reaction or stop it, both
  reversible or irreversible.
• Competitive- compete against substrate for spot
  in active site.
• Non-competitive bind to enzyme at a location
  other than the active site, but change the shape
  of the active site so the substrate no longer
  fits.
• To reverse reversible inhibition, add more
  substrate.
• Irreversible inhibition cannot be overcome by
  adding more substrate

9
Poisons

• Inhibitors- can be beneficial or not.
• Penicillin inhibits the formation of cell walls.
• Cyclic AMP inhibits uncontrolled cell growth.
• Organic phosphates (bug and weed killers)
• Irreversibly inhibit cholinesterase
• Cholinesterase breaks down acetylcholine in brain
• Acetylcholine jumps the gap in nerve cells to
  allow communication
• Too much acetylcholine makes neurons fire
  repeatedly
• Convulsions, rapid irregular heart beat, death.

10
Apoenzymes and Coenzymes

• Apoenzyme coenzyme ? functioning enzyme
• apoenzyme protein part
• coenzyme non-protein part
• - B vitamins, coenzyme Q10
• Zymogens are inactive enzymes that need the
  addition of apoenzyme or coenzyme to work.
• This protects you from excessive blood clotting
  or digestion of your stomach.

11
Drawing Enzymatic Reactions

• Figure 24-3 p. 427 Follow the hydrogen/
  electrons
• a1 b1
• A ? B ? C
• Feedback control

12
Nomenclature

• Name of the substrate or the type of reaction
  catalyzed with ase at end.
• Some common names not useful - insulin
• Six most common classes of enzymes
• Oxidoreductases - oxidation/reduction rxns
• Transferases - transfer atoms from one molecule
  to another (add phosphate to glucose in
  glycolysis)
• Hydrolases - break up a substance using water
• Lyases - make or break a double bond
• Isomerases - create isomers of substrate
• Ligases - join two molecules together

13
Oxidoreductases

• What were oxidation reduction reactions?
• Make ATP
• Dehydrogenases remove hydrogen
• Catalases catalyze decomposition of hydrogen
  peroxide to water and oxygen
• Peroxidases decompose organic peroxides to
  hydrogen peroxide and water

14
Hydrolases

• Carbohydrases
• Salivary amylases breaks starch into sugar
• Sucrase breaks sucrose into glucose and
  fructose
• Maltase breaks maltose into glucose
• Lactase breaks lactose to glucose and galactose
• Proteases
• Pepsin
• trypsin
• Peptidases
• Nucleases

15
Lyases

• Remove functional groups by forming double
  bonds.
• fumarase
• Fumaric acid ?L-malic acid

16
Types of Chemotherapy

• Antibiotics
• Antimetabolites

17
Antibiotics

• Bacteria require cell wall, animal cells no wall.
• Antibiotics inhibit one enzyme that forms the
  wall.
• Without wall, bacterial cells burst.
• Not effective against viruses.
• Bacterial life cycle faster than human, bacteria
  are mutating to make antibiotics ineffective.

18
Antimetabolites

• Look very similar to substrate.
• Enzyme tries to convert it to product, but cant
  release the substrate.
• Commonly used in the treatment of cancer

19
Enzymes in Blood Used to Diagnose Disease

• Diagnosis

• Enzyme

20
Isozymes

• Enzymes with the same function, but slightly
  different structure.
• LDH1, LDH2, LDH3, LDH4, LDH5

21
Allosteric Regulation

• Change the activity of an enzyme by bonding
  something to the enzyme at a place other than the
  active site.
• Activity may be increased or decreased.

22
Therapeutic Enzymes

• Insulin administered to control absorption of
  glucose
• Lactase can be taken when eating dairy products
  for individuals with lactose intolerance.
• European population less than 10 lactose
  intolerant.
• Chinese population greater than 90 lactose
  intolerant.