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Topic ThreeTopic ThreeEnzymesEnzymes
Catalysts and EnzymesCatalysts and EnzymesWhy are enzymes important? • hundreds of chemical
reactions are in progress in a typical living cell at a given moment
• These reactions provide energy and substances needed for growth and repair
• Chemical reactions would not be possible without ENZYMES
33
CatalystsCatalysts
Catalyst = a chemical that speeds up the rate of a chemical reaction•Is not used up in the reaction
Watch a catalyst in action!
44
EnzymesEnzymesEnzyme = an organic catalyst•Made up of proteins•Allow chemical reactions to happen at room temperature•Speed up reactions without increasing temperature!
Enzymes are everywhere!
In saliva…
… stomach
… even mitochondria!
Draw the picture below to show how an enzyme works:
Substrate
Enzyme
Active Sites
Enzyme-Substrate Complex
Products
What type of reaction is this?
Hydrolysis or catabolic reaction.
• Chemical reactions normally occur very SLOWLY!
• Increasing temperature increases the rate of reaction
• But increasing temperature too much will denature proteins and damage our cells!
• Enzymes speed up the rate of a reaction without increasing the temperature
Why are enzymes necessary?
• Chemical reactions require an initial energy input to start
• Ex: Rock must be rolled up the hill before it is able to roll down the other side of the hill by itself
• Activation Energy = energy required to initiate (start) a chemical reaction
Activation EnergyActivation Energy
Activation EnergyActivation EnergyNo enzyme = higher activation energy
With enzyme =
lower activation energy
Enzymes do not change the amount
of energy available!
3-2 Enzymes are Substrate Specific3-2 Enzymes are Substrate Specific
• Substrate: a molecule which attaches to the active site of an enzyme
• Active site: Area of an enzyme that combines with a substrate molecule
• Each enzyme is specific for a particular substrate– - Like lock and key
Substrates
Active Site
Naming of enzymesNaming of enzymes• Enzymes are given unique names based on the specific substrates • Enzyme name = name of the substrate + ASE
Fructose + GlucoseSucrose + H2OSucrase
SubstrateSubstrate EnzymeEnzymeMaltoseMaltose
LactoseLactose
ProteinProtein
Starch Starch
LipidsLipids
Polypeptides Polypeptides
Naming Enzymes:Fill in the following table!!
Maltase
LactaseProtease
Amylase
Lipase
Peptidase
Not all enzymes end with “ase”!! Pepsin
and Trypsin are protein enzymesthat do not end
in “ase”
stomach
Not all enzymes end with “ase”!! Pepsin and Trypsin are protein enzymes that do not end in “ase.”
pancreas
3-3 Basic Mechanism of Enzyme Action
• Chemical reactions occur when molecules collide or bonds are broken
• Enzymes increase the probability of reactions occurring inside cells by bringing substrate molecules CLOSER together
• Enzymes can form bonds between molecules or break bonds
Lock and Key HypothesisLock and Key Hypothesis
• The active site of the enzymes fits the substrate molecules• This forms an enzyme substrate complex
and
Product
Enzyme – Lock and Key HypothesisEnzyme – Lock and Key Hypothesis
A
B
C
D B
E
A: substratesB: enzymeC: active siteD: enzyme-substrate complexE: productsF: enzyme to be used again
F
3-4 Coenzymes and Cofactors3-4 Coenzymes and Cofactors• Recall:
– Cofactors are inorganic molecules– Examples: iron, zinc, calcium, magnesium and
potassium– Coenzymes are organic molecules such as
vitamins
Enzymes may not act alone...Enzymes may not act alone...• Sometimes additional chemicals are necessary
ingredients to permit enzyme activity• Enzyme co-factors and co-enzymes are often linked with
enzyme activity• Coenzymes and cofactors change the shape of the active
site on the enzyme!• Where a co-enzyme is lacking, enzyme activity may be
reduced
Enzyme Action Enzyme Action
1. Enzyme
2. Co-enzyme3. Substrate 4. Products
• What happens when someone has a poor diet???– The chemical reactions requiring coenzymes
(vitamins) and cofactors (minerals) cannot work when someone has a poor diet!!
Coenzymes and CofactorsCoenzymes and Cofactors
Other factors affecting Enzyme Activity a) Temperature
• Enzymes have an optimum temperature where the greatest number of molecular collisions occurs
• An increase in temperature causes an increase in reaction rate– More molecules = more collisions
• Optimum temperature range of most human enzymes is 35-40oC
• Examples of optimum temperatures: – Hot springs bacteria = 85oC– Antarctic ice fish = 2oC
Temperature cont…Temperature cont…• High temperatures cause enzymes
to denature (change shape)– Why do you think high fevers for long
periods of time are dangerous?
Reaction rate
Temperature
Optimal temperature = highest rate of chemical
reactions
Enzyme denatures
37oC
Effects of pHEffects of pH• Optimal pH for most enzymes is pH 6-8 but some operate
at more extremes– The enzyme pepsin has a optimal pH of 2
• A pH above or below the optimal pH may cause denaturation– Enzyme activity will lower because the shape of the enzyme has
changed…
Effects of pHEffects of pH
Substrate ConcentrationSubstrate Concentration• As substrate concentration increases, enzyme activity increases • As enzyme active sites become full, if the number of substrate
molecules exceed the number of enzymes molecules, then the reaction levels off.
Reaction rate
Substrate concentration
No more enzymes available = reaction rate leveling off
More substrate for the enzyme
to use = increasing reaction rate
Competitive Inhibitors• Inhibitors have shapes very similar
to the substrate and also bind to the active site of the enzyme
• When an inhibitor combines with the enzyme it prevents it from functioning properly• Inhibitor must be removed for
normal functioning to occur• decreases enzyme activity by
filling the active site so substrates cannot join!
Examples of competitive inhibitors include carbon monoxide, cyanide and penicillin
Carbon Monoxide (CO)Carbon Monoxide (CO)
• Many poisons and drugs act as competitive inhibitors…
• CO for example competes with oxygen for the active site on the hemoglobin molecule. – In fact, it binds to
hemoglobin 200X faster than oxygen! Once CO fits itself in, it rarely is dislodged
CyanideCyanide• Cyanide attaches to enzyme in mitochondria,
preventing the breakdown of sugars for energy. Cell dies!!
• Without the energy needed for active transport, protein synthesis, transport of nutrients, and elimination of wastes, a cell dies almost instantly!
PenicillinPenicillin• Penicillin kills invading
bacteria• Blocks an enzyme necessary
for the synthesis of protective walls in bacteria
• No effect on human enzymes
Topic 3-6: Control of Enzyme ActivityTopic 3-6: Control of Enzyme Activity • Many substances in the cell are produced by a
metabolic pathway (a series of many chemical reactions involving enzymes)
• Feedback inhibition = High levels of a substance will result in a decrease in its production