Chapter 5: Enzymes. Enzymes are Biological Catalysts What are enzymes? Biological catalysts made up...
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Transcript of Chapter 5: Enzymes. Enzymes are Biological Catalysts What are enzymes? Biological catalysts made up...
Chapter 5: Enzymes
Enzymes are Biological Catalysts
What are enzymes?
Biological catalysts made up of protein which alter rate of chemical reaction without themselves being
chemically changed at the end of reactions
Catalysts : Substance that increase rate of reaction without being used up.
Enzymes are Biological Catalysts Enzymes are made up of protein Denatures (enzyme loses it shape and
function) if exposed to high temperature or extreme changes in pH
Speeds up reaction without the need to increase temperature.
Mode of actions of enzymes
Body cannot withstand high temperatures Energy is required to start breaking down
fats – activation energy Enzymes lower activation energy >
Required to start chemical reaction.
Enzymes-catalysed Reactions1. Digestion Process whereby large insoluble food
substances are broken down into small soluble molecules
Carbohydrates MonosaccharidesProtein Amino Acids
Fats Fatty Acids + Glycerol
Enzymes-catalysed Reactions2. Synthesis of complex substances from
simpler ones. Synthesis of proteins Synthesis of glycogen for storage in the
body Synthesis of fats
Enzymes-catalysed Reactions3. Oxidation of Glucose Release of Energy to do work Involves a series of enzyme catalysed
reactions
4. Breakdown of toxic materials Hydrogen peroxide to water and oxygen
catalysed by catalase.Enzymes catalyse almost all reactions in body.
There are many different types of enzymes and eachis specific and will be produced only when required.
Classifying Enzyme• According to chemical reaction they catalyse• Usually ends up with –ase• Example:
• Breaking down of starch = amylase• Breaking down of Protein = Protease• Breaking down of Lipids/Fats = Lipase
• Enzyme combine with molecules it acts upon (substrate) to form an enzyme-substrate complex.
• Enzyme controlled reaction can be either• Anabolic : building up larger molecules• Catabolic: breaking down large molecules into smaller molecule
Characteristics of Enzymes• Speeds up rate of chemical reactions• Required in minute amount (small) – (itself not
breakdown)• Specific (Lock & Key hypothesis)
Lock & Key Hypothesis• Substrate which the enzyme acts on is called substrate• Example: Breaking down of starch, amylase is the
enzyme and starch is substrate. End-product = Maltose
• Enzyme molecules are usually larger than substrate• Small part of enzyme, called active site comes into
contact with substrate• Enzyme (lock) and substrate(key)
Enzyme(lock) Substrate (Key) Product
Amylase Starch Maltose
Lipase Lipid Fatty acids + glycerol
Protease Protein Amino acids
amylase
Active site
starch
Enzyme substrate complex
amylase 2 maltose
units
Enzyme are affected by temperature
• Enzyme and substrate in constant motion• Increase temperature results in increased kinetic
energy• Molecules move faster• Rate of enzyme colliding with substrate is higher• Rate of enzyme-substrate complex formed higher• Only up to an optimum temperature• Low temperature = enzymes are inactive
Enzyme are affected by temperature
• Around 37 ℃ in mammals• Too high a temperature will result in protein being
denatured• Active sites change shape and activity gradually decline• Different enzymes can withstand different temperature
range• Most enzymes will be completely denatured above 60
℃• Molecules move slower and rate of collision lower
Q: How does temperature affect Enzyme activity
What happens at low temperature?Enzyme are inactive at low temperature
What happens as temperature increase?As temperature increase, enzymes gain more kinetic energy causing them to move faster. When they move faster, chances of colliding into a substrate is higher. Hence, rate of forming enzyme-substrate complex is higher. Rate of reaction increases
What happens at optimum temperature?At optimum temperature, enzyme are most active
What happens above optimum temperature?Enzymes loses active sites, denatured.
0 ℃ 50 ℃ 100 ℃
Activeness of enzymes
Enzymes are affected by temperature:
Enzyme are affected by pH
• Enzyme usually work efficiently within a narrow pH range.
• Some enzymes works best in slightly acidic conditions (pepsin and rennin) while others in slightly alkaline conditions.
• Extreme pH will result in denaturation of enzymes
LowLow HighHigh
TemperatureTemperature InactiveInactive DenaturedDenatured
pH valuepH value DenaturedDenatured denatureddenatured
pH 1 pH 7 pH 14
Activeness of enzymes
Enzymes are affected by pH:
Enzyme are affected by Enzyme concentration
• Increase enzyme concentration, increased rate of reaction
• Temperature and pH are at optimum values• Substrate level must be high.
Enzyme are affected by substrate concentration
• Concentration of enzyme remains the same• Increased substrate concentration doesn’t necessarily
increase rate of reaction• Active sites become saturated, therefore could not work
any faster
5
4
3
2
1
42 86 10
No. of patties(Rate ofReaction)
Number of buns(substrate)
For example, you are making burgers with buns and the number of patties you have is limited.
Buns = Substrate, Patties = Rate of reaction
Enzyme are affected by substrate concentration
• How do you know that substance is not enough?• When I increase number of substance, I can produce
more burgers (Also: When I increase number of that substance, there is an increase of rate of reaction)
Limiting Factors
• Any factor that directly affects the rate of reaction if its quantity is changed
• Value of this factor has to be increased in order to increase rate of reaction
Reversible Reactions
• Most reactions in living cells are reversible.
• Enzyme can catalyse reversible reactions• Usually not allowed as products formed are used up or
transported away.
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