enzymes what are they? why do we need them? name some examples ?
TRANSCRIPT
Enzymes
What are they?
Why do we need them?
Name some examples ?
EnzymesGlobular proteins that catalyse chemical
reactions in living organisms
EnzymesGlobular proteins that catalyse chemical reactions in living organisms
Properties
Specific
Increase rate of the reaction
Unchanged at the end of the reaction
Enzymes
Need them because...
Reactions too slow to maintain life
Can’t increase temperatures/pressure in cells (fatal)
Enzymes Are Proteins
The enzyme binds to the substrates by its active site
The active site is a pocket formed by the folding of the protein
where the substrates bind.
Enzymes Are ProteinsThe enzyme binds to the substrates by its active site
The active site is a pocket formed by the folding of the protein
where the substrates bind.
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
Lock and Key
Enzyme reactions
enzyme + substrate enzyme-substrate complex
Enzyme reactions
enzyme + substrate enzyme-substrate complex
E +S ES
Enzyme reactions
enzyme + productenzyme-substrate complex
E +PES
enzyme + substrate enzyme-substrate complex
E +S ES
How do enzymes work?
An Example
An Example
Sucrose + H2O
Glucose + Fructose
An Example
Sucrose + H2O
Glucose + Fructose
Substrates
Products
For a reaction to occur the sucroseand water would have to collide with
enough energy to break and form bonds
This is the activation energy
Sucrose + H2O Glucose + Fructose
++
Substrates Products
Energy
Progress of reaction
Energy
Progress of reaction
Substrates
Energy
Progress of reaction
Substrates Products
Energy
Progress of reaction
Substrates Products
High energy intermediate
Energy
Progress of reaction
Substrates Products
High energy intermediate
Activation energy
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
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.
Enzyme activity
Four Variables
Temperature
pH
Enzyme Concentration
Substrate Concentration
Rat
e of
Rea
ctio
n
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 protein
ACTIVE SITE CHANGES SHAPE SO SUBSTRATE NO LONGER FITS
Even if temperature lowered – enzyme can’t regain its correct shape
Rat
e of
Rea
ctio
n
pH
1 3 42 5 6 7 8 9
Narrow pH optima
Disrupt Ionic bonds - Structure
Effect charged residues at activesite
Rat
e of
Rea
ctio
n
Enzyme Concentration
Enzyme Concentration
Rat
e of
Rea
ctio
n
Substrate Concentration
Substrate Concentration
Active sites full- maximum turnover
What is digestion?Breaking down large, insoluble molecules into smaller, soluble molecules that can be absorbed through the wall of the small intestine
What breaks down the large molecules?Digestive enzymes made by specialised cells inside glands
Some enzymes are...
Amylase Carbohydrates
Protease Proteins
Lipase Lipids
The enzymes break down...
Carbohydrates Simple sugars
Proteins Amino acids
Lipids (fats) Fatty acids + glycerol
Digestion animation
What does bile do?
• Bile is produced in the liver and stored in the gall bladder.
• The enzymes in the small intestine need an alkaline pH to work best, so bile passes into the small intestine and neutralizes acid from the stomach.
• Bile also emulsifies fat droplets to increase their surface area
Why do you think there is acid in the stomach?
• Kills bacteria in food – protects us• Denatures proteins – makes digestion easier• Activates stomach enzymes – these only
work in acidic conditions
• Ever wondered why PEPSIN (stomach enzyme) doesn’t digest our own stomach?
• Pepsin is inactive when first made and is only activated by HCL to start digesting proteins.
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