Enzymes Flashcards by Elizabeth .

Define enzyme

One or more polypeptide chains forming a catalytic active site

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Define substrate

Molecule which binds active site and undergoes a chemical reaction

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Define product

The result of the enzyme action

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What does a anabolic reaction mean?

Smaller reactants form larger products

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What does a catabolic reaction mean?

Larger products from smaller products

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What are the six classes of enzymes?

Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases

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What 2 things does reaction rate depend on?

Speed of reaction / Rate constant k

Number of reactions happening

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What are the advantages of enzymes?

Reusable
Specific
Efficient
Controllable

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How do enzymes ‘speed up’ reactions?

By lowering the activation energy

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What are the 2 proposed models for enzyme reactions?

Lock and Key- Fischer

Induced Fit -Koshland

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Each change in activation energy of 5kJ/mol= how many times faster?

10x

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What is the enzyme attachment theory?

Ogston’s 3 point binding theory

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What 2 things determines reaction specficity?

3D arrangement of residues

Chemical properties of the residues

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Define Co-Enzymes

Organic molecules which provide/remove groups for reaction

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What 3 things can you compare enzymes via?

Turnover number
Efficiency
Potency

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What is the catalytic triad?

Often only 3 amino acids perform the actual catalyst

What 3 things can an active site also contain?

Metal cofactors
COenzymes
Prosthetic groups

Define isozymes

Different enzymes same substrate

What does spectrophotometer measure?

Starting point is the measuring the change in [S] or [P] over the time after addition of enzyme

What is an indication of purity?

Enzyme activity/ total amount of protein

Describe what the role of an enzyme is ?

Provides an alternative route from substrate to products requiring less energy

So more molecules have that energy so more go from S to P per second and equilibrium is reached sooner

Reactions can be pushed backwards by what?

Increasing the [product]

Keq=

Keq= K forward/k reverse= [P]/[S]

V= Vmax x [S] / Km + [S]

which is also equal to Kwd x [S]

Overall rate depends on rate constants and concentrations. Which equations explain this?

Ks->p x [s] Kp->s x [P] Usually Ksp . Kps

What 2 assumptions do we make about enzyme reactions?

[ES] constant | [s] >[E] so [S] is constant

Vmax is set by what?

Number of enzyme molecules not number of substrate molecules. It is the maximum rate when all is [ES]

What is the equation of the Dissociation constant/ affinity for substance Kd?

K-1/K1= [E] X[S]/[ES]

What does a small Kd mean?

high affinity

What is Micheals constant?

Km= K-1 +Kcat/ K1

How do you measure V max ?

You cant measure it as its infinity so you find 1/2 V max

What are the x and y on Lineweaver-Burk plot? | Whhat doeds intersection of the X and Y axis mean?

X= 1/[S] y= 1/V Y intercept= 1/vmax X intercept= -1/Km

State the equation for V max?

Vmax= Kcat x[E]

# Define Km What does a low Km mean?

Km is [S] when half molecules are ES and its at half maximum rate Low Km means high affinity for the substrate

Kcat catalytic rate constant =

number of reactions per second

If Kcat/Km > 1x108 the V is limited by what?

Diffusion of the substrate to the enzyme not the ezyme itself