Enzyme Properties/Regulation/Kinetics

Enzymes alter the position of equilibrium of a reaction

Reactions are energetically favourable when...

If a compound exists in two stereoisomer forms, an enzyme can act upon both of them.

Substrate specificity is the notion that enzymes [blank_start]catalyse[blank_end] one type of reaction dependent on substrate/active site [blank_start]complementarity[blank_end]. This means that multiple enzymes may be required to produce a particular product from a single substrate. Thus enzymes [blank_start]compartmentalise[blank_end] in cells.

What is the definition of an oxidoreductase?

What is the definition of a transferase enzyme?

What is the definition of a hydrolase enzyme?

Which type of bonds do ligases catalyse the formation of using energy from ATP?

The lock and key model of enzyme action states that the active site has a [blank_start]specific[blank_end] shape [blank_start]independent[blank_end] to that enzyme. The substrate is exactly [blank_start]complementary[blank_end] to the [blank_start]shape[blank_end] of that active site.

The modified lock and key model states that there is [blank_start]general[blank_end] complementarity between the enzyme and the substrate but not exact. As the substrate [blank_start]binds[blank_end] to the active site, the [blank_start]enzyme[blank_end] and [blank_start]substrate[blank_end] distort to become complementary. This increases the [blank_start]energy level[blank_end] of the substrate and reduces the [blank_start]transition energy[blank_end] required for the reaction.

In the induced fit model of enzyme action, what distorts to provide enzyme-substrate complementarity?

What is a cofactor?

What are isoenzymes?

In the catalysis of peptide bond hydrolysis by chymotrypsin, the polypeptide bind [blank_start]non-covalently[blank_end] with side chains in the hydrophobic pocket. A [blank_start]proton[blank_end] is tranferred from serine to histidine in the active site. This forms a [blank_start]tetrahedral[blank_end] transition state between the enzyme and the substrate. The [blank_start]C=O[blank_end] group in an amide bond of the substrate forms a single bond to the [blank_start]oxygen[blank_end] in serine. The [blank_start]proton[blank_end] is then transferred from histidine to the [blank_start]C-terminal[blank_end] fragment. This fragment is then released by cleavage of the [blank_start]C-N[blank_end] bond. A [blank_start]water[blank_end] molecule then binds to the histidine in place of the C-terminal fragment. The water molecule transfers a [blank_start]proton[blank_end] to histidine and the remaining [blank_start]hydroxide[blank_end] binds to the carbon of the N terminal fragment. [blank_start]A new tetrahedral[blank_end] transition state is formed. Cleavage of the [blank_start]acyl[blank_end] bond releases the N terminal fragment. Histidine's [blank_start]proton[blank_end] is transferred back to serine and the enzyme regains it's original structure.

At low substrate concentration, what is the order of reaction for an enzyme-catalysed reaction with respect to substrate concentration?

At high substrate concentration, what is the order of reaction of an enzyme-catalysed reaction with respect to substrate concentration?

K1 is the rate constant for the [blank_start]forward reaction[blank_end]. This is the [blank_start]formation of ES[blank_end]. K-1 is the rate constant for the [blank_start]reverse reaction[blank_end]. This is the [blank_start]breakdown of ES to E+S without catalysis[blank_end]. K2 is the rate constant for the [blank_start]breakdown of ES into E + P[blank_end].

In the Michaelis-Menten reaction model of enzyme kinetics, we use K-2 as the rate constant for the breakdown of the enzyme-product complex to the enzyme-substrate complex.

What are the assumptions of the Michaelis-Menten model of enzyme kinetics? Check all that apply

[blank_start]V0[blank_end] is the initial reaction velocity - the rate of reaction at the point of enzyme-substrate mixture. [blank_start]Vmax[blank_end] is the maximal velocity when all enzyme active sites are saturated. [blank_start]Km[blank_end] is the Michaelis constant.

The Michaelis constant is a measure of...

The lower the value of Km, the higher the affinity of the enzyme for the substrate.

What equation is this for?

What is the equation for Km, the Michaelis constant?

Km = [S] when...

What denotes the equilibrium constant for the formation of ES in terms of Michaelis-Menten kinetics?

If k2 is very small, the rate of reaction is...

What is the name given to the number of substrate molecules converted to product in a given unit of time on one enzyme molecule when enzyme is saturated with substrate?

The higher the Kcat number, the faster the rate of reaction

The specificity constant should be high to give a high efficiency of an enzyme-catalysed reaction. Therefore...

Lactate dehydrogenase consists of [blank_start]4[blank_end] monomers of either heart or [blank_start]muscle[blank_end] type. This allows the existence of [blank_start]5[blank_end] different isozymes. Lactate dehydrogenase catalyses the conversion of lactate to [blank_start]pyruvate[blank_end]. In the leg muscles there is a [blank_start]fast[blank_end] rate of lactate formation. Therefore, we need an enzyme with high [blank_start]sequestering[blank_end] ability. This means that lactate dehydrogenase in the leg muscles requires a [blank_start]low[blank_end] Km number. In the heart, lactate is toxic if left free so must be removed as quickly as possible. This means that lactate dehydrogenase in the heart requires a high [blank_start]Kcat[blank_end] number. During a [blank_start]myocardial infarction[blank_end], rupture of the heart endothelial cells causes lactate dehydrogenase enzymes to increase in levels in serum. These levels can therefore be used as a diagnostic tool.

What is the correct rearrangement of the Michaelis-Menten equation to give the Lineweaver-Burke equation?

1/Km on a Lineweaver-Burke plot is found by the x intercept. This value can be positive or negative.

A competitive inhibitor will alter the apparent Km value of an enzyme but not Vmax.

What will happen to the y intercept on the Lineweaver-Burke plot of a reaction taking place in the presence of a competitive inhibitor compared to the regular reaction?

What will happen to the x intercept on a Lineweaver-Burke plot of an enzyme-catalysed reaction in the presence of competitive inhibitor?

Non-competitive inhibitors do not alter the Km of an enzyme.

What happens to the gradient of a Lineweaver-Burk plot in the presence of a non-competitive inhibitor?

What is an allosteric binding site?

What is the name given to a molecule that binds to the site of an allosteric enzyme, causing a change in activity?

Which residues can phosphate be added or removed from? Check all that apply

Phosphorylation increases the activity of enzymes