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Aim: explore and the structure and function of enzymes Objectives: List the main properties of enzymes Explain the terms active site, specificity and catalysts Discuss how enzyme activity is affected by temperature and pH
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ENZYMES 1
Jorge Melo
DNA nucleotide recap
OO=P-O O
N
CH2
O
C1C4
C3 C2
5
Phosphate Group
Sugar(deoxyribose)
Nitrogenous base (A, G, C, or T)
DNA double helix
P
P
P
O
O
O
1
23
4
5
5
3
3
5
P
P
PO
O
O
1
2 3
4
5
5
3
5
3
G C
T A
DNA Double helix
Antiparallel (5’-3’) (3’-5’)
Complementary rule
Chargaff’s rule
A-T C-G
Hydrogen bonds
DNA vs RNA The sugars
Uracil instead of thymine
RNA –usually single stranded
RNA mRNA
tRNA rRNA
RNA- recap
DNA double helix unwind (helicase)
RNA polymerase
Ligase
Nucleic acids recap
Helicase
RNA polymerase
Ligase
tRNA
Transcription
Translation
Gene
Name given to some stretches of DNA and RNA that encode for a peptide
Stands for:Ribonucleic acid
What am I? I am important to life
I am affected by temperature
I am a globular molecule
I am involved in biochemical reactions
I am involved in the breakdown of molecules
I am an Enzyme
Aims and objectives
Aim: explore and the structure and function of enzymes
Objectives: List the main properties of enzymes Explain the terms active site, specificity
and catalysts Discuss how enzyme activity is affected
by temperature and pH
Mind Map Enzymes: facts and functions
Enzymes: chemical structure
Enzymes: properties
Names of enzymes
How enzyme works (theories)
Activation energy and Rate of reaction
The effect of temperature and pH on the enzyme
Facts about enzymes Enzymes are chemicals that
control the reactions in cells.
They are the caretakers of cells and tissues.
They make sure that cell chemistry is kept in good shape.
Each one has a particular job to do.
Examples of enzyme functions
Clear the fat out the blood stream after a meal
Detection of glucose level in the body
Break down the alcohol in beer or wine (liver)
Enzymes
Thousands of chemical reactions take place in the body every second.
These make up the metabolism.
Enzymes control the metabolism by determining when and how chemical reactions take place.
Enzymes
Enzymes are catalysts that speed up the rate of metabolic reactions.
These reactions will take place without enzymes, but they would take years rather milliseconds.
Enzymes Which of the following reactions break
molecules down and which build molecules up?
A glycogen molecule formed from glucose molecules.
The digestion of starch to maltose.
Urea formed from ammonia and carbon dioxide.
Enzyme
Example of a reaction that you already know:
Hydrolysis Condensation
Enzyme Enzyme
Enzymes the Chemical Structure
globular proteins.
long chains of amino acids.
In a globular protein, the amino acid chain is folded and wound into a spherical or globular shape.
Enzyme
Tertiary structure
Enzymes the Chemical Structure
Specific three-dimension shape (tertiary structure)
This is Important: if it is altered , the enzyme cannot function
Three dimension shape is maintained by hydrogen bonds and ionic forces
Properties of Enzymes
Specific.
Not used up in reactions.
Combine to form enzyme/substrate complexes.
Only small amount of enzyme needed
Properties of Enzymes
Are fast acting – high turnover number.
Affected by temperature and pH.
Some only able to work if a cofactor is present.
Can be slowed down or stopped by inhibitors.
Specificity Each enzyme can only catalyse one
particular reaction.
This is because an enzyme can only react with a specific substrate molecule.
Amylase can only catalyse the hydrolysis of starch into smaller disaccharide maltose molecules.
This is because amylase can only react with starch molecules.
Properties of enzymes
An enzyme acts on a chemical known as a substrate and the new substance that is formed is the product
Substrate product
The name of the enzyme often comes from substituting or adding -ase in the name of the substrate
Enzyme
Names of Enzymes
The name of an enzyme comes from the particular substance on which it acts.
Lactase acts on the milk sugar lactose.
Amylase works on starch – proper name amylose.
Cellulase breaks down cellulose.
Enzymes and their substrates
Enzyme Substrate Reaction catalysed
Maltase Maltose Hydrolysis of maltose to glucose
Amylase Amylose Hydrolysis of starch to maltose
Alcohol dehydrogenase
Alcohol Removal of hydrogen from alcohol
DNA Ligase DNA Joining together 2 DNA strands
RNA polymerase Nucleotides that make RNA
Synthesis of mRNA to DNA molecule
Glycogen synthetase
Glucose Polymerisation of glucose into glycogen
ATPase ATP Synthesis or splitting of ATP
Names of Enzymes
Which substrate do you think each of these enzymes acts upon?
Sucrase.
Lipase.
Protease.
Task1
How enzymes work
There are two models that explain how enzymes work:
1. Lock and Key theory
2. Induced fit theory
Lock and Key Theory
Enzyme
SubstrateEnzyme Substrate complex
Products
Enzyme
Activation site
The Lock and Key Theory
This attempts to explain why enzymes are specific.
They are large molecules, usually much bigger than their substrates.
Only a relatively small part comes into contact with the substrate.
The Lock and Key Theory
This is called the active site.
Only 3-12 aa make the active site, but its shape is an exact fit for the substrate.
The substrate is the key that fits the enzymes lock.
Lock and Key Continued
The two molecules form a temporary structure called an enzyme/substrate complex
The products are formed at the active site
They then no longer fit and are repelled
The active site is then free to react with more substrate
The Lock and Key Theory
2 types of reactionCatabolic reaction: certain enzyme break a substrate down into two or more products
Substrate
EnzymeProducts
Enzyme
2 types of reactionAnabolic reaction: certain enzyme bond tow or more substrates together to assemble one product
Enzyme
Substrates Enzyme
Product
Induced fit theory
Induced fit theory The active site is a cavity of a particular
shape
Initially the active site is not the correct shape in which to fit the substrate
As the substrate approaches the active site, the site changes and this results in it being a perfect fit
After the reaction has taken place, and the products have gone, the active site returns to its normal shape
Rate of Reaction Most reactions in
cells would be very slow without enzymes.
The substrate may not be converted into the product unless it is given extra energy.
Heating the particles would increases their kinetic energy and they move about more quickly.
Rate of Reaction
This means that there is greater chance of collisions.
The rate of reaction then increases.
Activation EnergyThe energy needed to start a chemical reaction
It can be thought of as an energy barrier to get over before the reaction can get underway.This energy can be supplied in the form of heat.
But this is not practical in living systems.
Activation Energy By lowering the activation energy of a reaction,
the enzyme provides a different pathway for the reaction.
By lowering the activation energy, enzymes reduce the input of energy needed.
This allows reactions to take place at the at the lower temperatures found in the cells of organisms.
Activation Energy
Factors affecting enzyme activity
The factors that affect enzyme activity also affect the functions of the cell and ultimately the organism
enzymes are proteins and their functions is therefore altered by:
Temperature pH Substrate concentration Enzyme concentration Cofactors inhibitors
Activity
Work in pairs and think about how are the enzymes affected with the temperature and pH
Temperature High temp. reactions tend to take place faster
(more kinetic energy)
However if temp. is too high the enzyme may lose their shape Bonds that old the tertiary structure of the enzyme
molecule on shape tend to break When the active site of the enzyme loses its shape it
is no longer able to bond to the substrate Enzyme denatured Irreversible reaction
The temperature at which the enzyme works most rapidly is called optimum temperature
OT for plant enzymes 25 C
OT for Human body 37 and 40 C
OT some bacteria 80 C
Ph
Can have a direct effect on the bonding responsible for holding the enzyme molecule in its precise three-dimensional shape. If the active site is changed then enzyme action will be affected
Each enzyme has an optimum pH Extremes of pH can denature enzymes
and stop them from functioning as catalysts
Task2
Summary Six facts about enzymes Enzymes are globular proteins They reduce the activation energy needed for a
reaction to proceed and produce products Enzymes have a region called an active site.
The site is the "lock" into which a substrate "key" fits.
The enzyme then fits closely around the substrates. This is called induced fit.
Enzyme activity is affected by substrate type, temperature, pH and substrate concentration.