Enzymes 1

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What are the 6 classes of enzymes?
1.Oxidoreductases 2.Transferases 3.Hydrolases 4.Lyases 5.Isomerases 6.Ligases
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What do oxidoreductases do?
Add O2 or remove 2H, technically transferring electrons. example is Lactate dehydrogenase which reduces pyruvate to L-lactate
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What do transferases do?
Transfer functional groups to make an amino acid or from an aa. example- glutamate+pyruvate ->l-alanine + 2-ketoglutarate.
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What do hydrolases do?
hydrolytic reactions, adding water to break bonds. eg Trypsin reaction of breaking a peptide bond.
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What do lyases do?
Break C=C bond by adding groups or form it by removing them. The groups are; c-c, c-o or c-n. example. citrate --> oxaloacetate and acetate. making c=O and removing acetate. enzyme is citrate lyase.
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What do isomerases do?
Catalyse the transfer of functional groups within the same molecule.example is phosphoglucose isomerase which glucose-6P-->fructose 6P
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What do ligases do?
Formation of C-C or C-N bonds due to ATP cleavage.example is in DNA replication.
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What enzymes contain iron?
haem groups in other proteins eg. cytochrome oxidase. and iron containing centres such as flavin enzymes which sulfur coordinates from cystine residues.
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What are isoenzymes?
when two different enzymes have different protein structures but catalyse the same reaction
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What happens to order of reaction at high substrate conc?
It is zero order as an increase won't effect enzyme rate if it is already working at maximum.
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What are three assumptions of the michaelis-mentis equation?
1. substrate conce is always higher than enzyme conc. so [ES] is small. 2. [ES] doesn;t change with time at equilibrium. 3. Only initial velocities are used in the calculations
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What is the equation?
Vo(initial velocity) = Vmax[S]/Km[S]. km=[S] as if vo=0.5vmax then km=[S]. km =(k-1)+k2/k1
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What is initial velocity?
The rate of the reaction before the product formation begins to effect the rate.
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What is Km?
The [S] at which the initial velocity is half the maximum velocity.
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What is VMax?
the max rate of an enzyme reaction when all active sites are fully saturate
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How can you relate substrate affinity and Km?
When K2 is not rate limiting and is much larger than (k-1). then Km=k-1/k1. which is the dissociation constant. only here does km represent affinity.
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What is Kcat and what does it's values mean?
means the number of substrate conversion/time in one active site when the enzyme is saturated. high Kcat=velocity could be at max because it is at it's max diffusion rate. Kcat is low=velocity will depend on other factors.
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What is the specificity rate constant?
kcat/km. to find how the enzyme works.
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How can you use y=mx+c for the line-weacer burke plot?
1/Vo=km/Vmax[s] + 1/Vmax[S]
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Card 2


What do oxidoreductases do?


Add O2 or remove 2H, technically transferring electrons. example is Lactate dehydrogenase which reduces pyruvate to L-lactate

Card 3


What do transferases do?


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Card 4


What do hydrolases do?


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Card 5


What do lyases do?


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