objectives students should know : that enzymes act as catalysts lowering activation energy through...
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Enzymes
ObjectivesStudents should know : That enzymes act as catalysts lowering activation energy
through the formation of enzymesubstrate complexes.The lock and key and induced fit models of enzyme action.Enzyme properties The properties of enzymes relating to their tertiary
structure. Description and explanation of the effects of temperature, competitive and non-competitive inhibitors, pH and substrate concentration.
Candidates should be able to use the lock and key model to explain the properties of enzymes. They should also recognise its limitations and be able to explain why the induced fit model provides a better explanation of specific enzyme properties
Enzymes are Biological catalystsMade of protein.Enzymes control chemical reactions that take place in the cytoplasm.
Not used up during the reaction.Are specific.Require optimum conditions at which they work best
The minimum amount of energy needed to start the reaction,
leading to the formation of a high energy intermediate
= The Activation energy
Energy
Progress of reaction
Substrates Products
High energy intermediate
Activation energy
Enzymes reduce the height of the energy
barrier
Lock and Key
enzyme + substrate enzyme-substrate complex enzyme + product
Active site
The active site involves a small number of key residues that actually bind thesubstrates
The rest of the protein structure is needed to maintain these residues in position
Enzymes can break substances down:
animation
Example: starch digestionStarch
Maltose
Or build larger molecules:
Active site
es
Induced Fit
The enzyme moulds itself around the substrate molecule
Enzyme activity
How fast an enzyme is workingRate of Reaction
Rate of Reaction = Amount of substrate changed (or amount product formed) in a given period of time.
Rate
of
React
ion
Enzyme activity
Variable you are looking at
Enzyme activity
Variables
Temperature
pH
Substrate Concentration
Rate
of
React
ion
Temperature
0 20 30 5010 40 60
40oC - denatures
5- 40oC Increase in Activity
<5oC - inactive
Effect of heat on enzyme activtyIf you heat the protein above its optimal temperature
bonds break meaning the protein loses it secondary and tertiary structure
Effect of heat on enzyme activty
Denaturing the proteinACTIVE SITE CHANGES SHAPE
SO SUBSTRATE NO LONGER FITS
Even if temperature lowered – enzyme can’t regain its correct shape
Rate
of
React
ion
pH
1 3 42 5 6 7 8 9
Narrow pH optima
Disrupt Ionic bonds - Structure
Effect charged residues at activesite
Rate
of
React
ion
Substrate Concentration
Substrate Concentration
Rate
of
React
ion
Substrate Concentration
Substrate Concentration
Active sites full- maximum turnover
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Digestive enzymes allow hydrolysis reactions to take place rapidly in the conditions found in the gut.Starch is broken down by amylases to
glucose
Proteins are broken down by proteases into amino acids
Fats are broken down into fatty acids and glycerol
Why can humans digest starch but not cellulose?
Lactose intoleranceAt birth babies make lactase to digest milk
sugarSome people stop making this enzyme when
they get olderThey become Lactose intolerant
ProblemsIf they eat milk products the lactose is not
broken downThe sugar stays in the gut.Water stays in the gut due to the sugarThe person develops diarrhoeaBacteria digest the lactose, producing gas
and causing painAffected individuals must avoid lactose
products
