Enzymes
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- Created by: TaraCBeckworth
- Created on: 29-08-18 10:38
Lysozyme
Small enzyme, shape includes a cleft into which part of the bacterial cell wall can fit, causes bond between sugars 4 and 5 to be broken
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What do enzymes do to the activation energy of a reaction?
They lower the activation energy of a reaction
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Give 3 things enzymes do to help the binding of substrate
1) Proximity (Substrate molecules are held close together), 2) Orientation (Substrates are held in the correct relative orientation) 3) Strain (strain on bonds make it easier)
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What bond is formed when the substrate binds with the enzyme?
A temporary covalent bond
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How do you work out the initial reaction velocity (IRV, v)?
x/y on the graph
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Katal
1 Katal of enzyme activity produces 1 mole of product per second or utilises one mole of substrate per second (1 Katal = 1 mole/sec)
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Unit
1 Unit of enzyme activity produces 1 mmole of product per minute or utilises 1 mmole of substrate per min (1 Unit = 1 mmole/min)
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Turnover number (Kcat)
The number of substrate molecules that can be converted to product by 1 enzyme molecule in 1 second
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What bonds does a change in pH affect?
Electrostatic bonds
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pH will decrease enzyme activity if:
Overall active site shape changed, group involved in binding substrate or in the catalytic act changes charge, group on substrate involved in binding to the enzyme or in the catalytic act changes charge
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What are the 2 effects of the temperature change?
1) Gives more genetic energy so more collisions, 2) Denaturing
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Describe the denaturing effect of temperature
Proteins take on 3D structure on lowest potential energy, increased energy causes motion within molecule as well as between other molecules, weak bonds in 3' are broken and reformed in different positions, new 3D structure
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What happens to the rate of reaction at a low substrate concentration?
The rate of reaction will be a lot slower with a lower Vmax, the rate depends on the number of substrate molecules are present
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What happens to the rate of reaction at a high substrate concentration?
The rate of reaction is a lot faster with a higher Vmax, the number of enzyme molecules determines how fast the reaction takes place
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How do you workout IRV at a specified substrate concentration?
(Vmax X substrate concentration) / (Km + substrate concentration) -- Work Km from half Vmax
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How can you see the affinity of an enzyme for its substrate?
Work out the Km (High Km- low affinity, Low Km- high affinity)
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Features of Km
Measures stability of ES complex, is in units of concentration, the lower the ES stability the higher the Km (the more substrate you need to stabilise it), Km= the value of [S] that causes V (y on graph) = 1/2 Vmax
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What is an enzyme inhibitor?
Reduce the rate of an enzyme (competitive, non-competitive, reversible, irreversible)
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Irreversible inhibitors
Binds irreversible, covalent bond, bind to amino acid side chain at/ on active site (usually ser or cys), inactivates enzyme, usually prevents substrate binding
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DFP
Nerve poison, covalently binds to Ser residue in acetylchlorine esterase, prevents breakdown of neurotransmitter acetylcholine
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Penicillin
Antibiotic, covalently binds to Ser residue in glycopeptide transpeptidase, prevents synthesis of bacterial cell wall (peptidoglycan)
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Competitive inhibitors
Reversible, compete with substrate for access to active site, similar structure to substrate, can be overcome by increasing substrate concentration until it out-competes inhibitor, slower ROR but eventually meets Vmax as well, Km increases
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Non-Competitive inhibitors
Reversible, bind at allosteric site, prevents catalytic act from taking place not the binding of substrate, cannot be overcome by increasing [S], can be removed by repeated dialysis, Km remains unchanged, Vmax decreases
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Allosteric enzymes
Enzyme with 2 or more subunits allowing it to bind to more than 1 substrate
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Describe how allosteric enzymes work
Binding of substrate to 1 subunit initiates a change in form, allows 2nd substrate to bind to 2nd site and subsequently more sites are ready
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What increases an allosteric enzymes activity
Positive effector binding (changes active site for another substrate) allosteric activator
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What decreases activity?
Negative effector or an allosteric inhibitor
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Oxidoreductases
Oxidation/ reduction enzymes
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Transferases
Transfer of functional groups from one compound to another
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Hydrolase's
Splits bonds by addition of water
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Lyases
Add groups across double bond
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Isomerases
Catalyses isomerisation reactions
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Ligases
For new bonds with energy provided by cleavage of ATP
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Other cards in this set
Card 2
Front
What do enzymes do to the activation energy of a reaction?
Back
They lower the activation energy of a reaction
Card 3
Front
Give 3 things enzymes do to help the binding of substrate
Back

Card 4
Front
What bond is formed when the substrate binds with the enzyme?
Back

Card 5
Front
How do you work out the initial reaction velocity (IRV, v)?
Back

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