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Enzymes
Honors Biology
2009
Hydrogen Peroxide
H2O2
H-O-O-H
Antiseptic – kills infective organisms?
Cells produce as a waste (poison)
Body enzymes (chemicals) can break it down, make it
harmless
Produced by?
Liver
Liquid (liver added)
bubbles (gas) + liquid
H2O2
H20
+
O2
(toxic) Enzyme
(harmless)
Hydrogen peroxide in tooth whitening products
Oxygen reacts with deposits on teeth to remove them
Types of Chemical Reactions
(changes)
Decomposition – break down; break molecules apart
Examples:
H2O + O2
A. H2O2
B. Starch to what?
glucose, using salivary mouth enzyme amylase; also
produced by pancreas
C. Lipid (fat) to what?
fatty acids + glycerol, using lipase produced
by pancreas and small intestine
D. Proteins to what?
amino acids, using pepsin produced by stomach
finished in small intestine using proteases
Synthesis – join small molecules to
make larger ones
What type of chemical reaction is often
involved?
Dehydration synthesis (water removal)
Examples:
A. amino acids
B. glucoses
protein
di- and poly-saccharides
(maltose, starch)
C. fatty acids + glycerol
lipid (fat)
D. photosynthesis (light/to join)
CO2 + H2O
C6H12O6 + O2
Decomposition or Synthesis?
Synthesis
Dehydration
Decomposition
Hydrolysis
Catalysts and Enzymes
Some chemical reactions can be speeded up by heating; not
always possible in an organism
Catalyst - Something that can speed up a chemical reaction
Chemical reactions often need a “boost” (energy input) to occur Activation Energy
What acted as catalysts in our lab and demos?
Manganese dioxide MnO2 (inorganic)
Liver
Enzyme – catalyst of living origin - organic (cells)
Catalysts and enzymes can lower the activation energy allowing
reactions to occur, often at a lower temperature (Ex: 98.60)
Enzymes for decomposition of Hydrogen Peroxide
Plant - peroxidase
Liver – catalase
Characteristics of Enzymes
1. Organic (living things) origin
Lab Results:
“New” Liver + “New” peroxide Reaction?
Yes
“Old” Liver + “New” peroxide
Reaction?
Yes
2. Enzymes are not changed by the reaction in which
they participate; can be reused
Lab Results:
“New” Liver + “old” Liquid (O2 and H2O)
Reaction?
No
Why not?
Peroxide already broken down
3. Enzymes can speed up both decomposition and
synthesis reactions. Can break apart or join things together
(Judge – can marry or divorce)
Sometimes, not always, one enzyme can
do both.
Ex. A (glucose) + B (fructose)
enzyme #1
AB (sucrose)
synthesis
Ex. AB (sucrose)
Enzyme # 1 or another?
A (glucose) + B (fructose)
decomposition
If enzyme # 1 can do both……..
AB (sucrose)
A (glucose) + B (fructose)
4. Enzymes are
themselves, made of
protein.
Huge chains of amino
acids that coil into
specific shapes with a
specific bonding areas
called: Active Sites (like
one piece of a puzzle)
5. Enzymes are specific (picky) about what
chemicals they act upon (specificity)
(again, two puzzle pieces)
Called: Lock and key hypothesis
Chemicals acted upon = substrate
Ex. Enzyme that could decompose sucrose
into glucose and fructose has an active
site that only fits/bonds to sucrose,
not starch, protein or fat, etc.
Ex. Enzyme that joins glucose and fructose to
make sucrose
When enzyme and substrate bond for the
reaction, forms enzyme-substrate complex
6. Usually, not always, enzymes are
named after the substrate upon which
they react, followed by suffix - ase
Ex. Peroxidase – acts on peroxide
Sucrase – acts on sucrose
Lipase – acts on lipids
Proteases – act on proteins
Ex. An exception
Amylase – acts on starch
7. Enzymes act best at specific temperatures.
Lab Results:
A. Liver + peroxide at room temperature
Reaction?
B. Liver + peroxide at high (65 degree) temperature
Reaction?
C. Liver + peroxide at body (37 degree) temperature
Reaction?
D. Liver + peroxide at cold (0 to 5 degree) temperature
Reaction?
Human body (98.60 F or 370 C)
Enzymes are protein which denatures (unravels)
at non ideal temperatures, destroys active site
Why do high fevers make us feel so sick and can be
fatal?
8. Enzymes function best at specific
pH levels.
Lab results:
A. Liver + peroxide with pH of 4
pH? Should be acid
Reaction?
B. Liver + peroxide with pH of 7
pH? Should be neutral
Reaction?
C. Liver + peroxide with pH of 10
pH? Should be basic/alkaline
Reaction?
Ideal pH can vary greatly from one enzyme to another
Ex: Stomach enzymes need acidic pH of about 1-2
Some stomach cells are modified to secrete acid
Can secrete too much and cause acid reflux into food pipe (esophagus)
May need drugs to reduce acid production – Prilosec, Nexium, Zantac
Or, take a base to neutralize the acid – Tums, Rolaids (Antacids)
Small intestine enzymes won’t function in acid
What would need to be added to the food as it moves into intestine from stomach?
Base – added by pancreas and small intestinal cells
Ex: Enzymes in blood like a pH of 7.4 (Blood clotting proteins)
Cut E1
E2
E3 etc....................................E13 Clot
Most hemophiliacs (bleeding disorder) are missing enzyme # 8
9. Some enzymes need a “helper” and
cannot function without it.
May be non protein and non organic, called cofactors
Ex: ions of Zinc, Iron, Copper
If organic (contain Carbon), called coenzymes
Most are vitamins themselves or made from
vitamins
Ex: Vitamin B6 needed for enzymes to convert one amino acid to
another
Ex: Coenzyme Q 10 helps cells produce energy
Protects cell membranes from damage that
can lead to aging or even cancer
It decreases in bodies as we age
Supplements
10. Enzymes can
sometimes be “shut
down” by other chemicals
called: Inhibitors.
Ex: Many insecticides
contain inhibitor chemicals
to shut down enzymes used
for transmitting nervous
messages.
Ex: Some drugs to treat HIV
infection contain inhibitors
to stop the virus from
reproducing
Summary of Enzyme Function
Enzymes and Human
Digestion
Four main stages of food processing
1. Ingestion – to take into body
2. Digestion – to chemically decompose
3. Absorption – to take into bloodstream
4. Elimination – to remove waste (feces)
What needs to be digested?
Carbohydrates, Lipids, Proteins
Human Digestive Anatomy
Pathway of Food
Mouth – Ingestion
(Salivary Glands) – dump enzymes into mouth;
Digestion
Esophagus
Stomach – Digestion by producing enzymes
(Pancreas) – dumps enzymes and buffer base into
small intestine
(Liver) – dumps bile into small intestine
Small Intestine – Digestion (produces enzymes) and
Absorption
Large Intestine – Absorption of water and
elimination
Accessory Digestive Organs
Food Pathway and Enzymes
Mouth salivary glands secrete:
Salivary amylase – starts polysaccharide breakdown into
disaccharides
Ex: starch to maltose
Stomach cells secrete:
Acid – Why?
Lowers pH and kills bacteria
Mucus – Why?
Protects stomach lining
Pepsinogen which is converted to pepsin
in acid
Begins protein digestion
Stomach takes 2-6 hours to empty
Chyme = stomach contents
Liver
Dumps bile into small intestine (stored in gall bladder)
Bile begins Lipid break down into droplets (emulsify)
Small Intestine cells secrete:
A base (buffer)
Why?
Neutralize acidic chyme
Pancreas
Dumps enzymes into small intestine
Small intestine and pancreas both produce various
Enzymes:
I. Pancreatic amylase – continues starch breakdown
II. Maltase – breaks maltose into 2 glucoses
III. Lactase – breaks lactose into glucose and galactose
(Lactose intolerance)
IV. Sucrase – breaks sucrose into glucose and fructose
V. Proteases – continue protein break down into amino acids
VI. Lipases – continue lipid breakdown into fatty acids and glycerol
Small intestine absorbs small particles
Large Intestine
No enzymes secreted
Absorbs most of the water to form feces
Absorbs tiny ions like calcium (Ca++) and
sodium (Na+) – electrolytes
Elimination of feces through rectum and
anus