biochemistry chapter 2

What role do enzymes play in biological reactions?

Enzymes act as biological catalysts that are unchanged and reusable.

What do oxidoreductases catalyze?

They catalyze oxidation-reduction reactions involving electron transfer.

What is the function of transferases?

Transferases move a functional group from one molecule to another.

How do hydrolases operate?

Hydrolases catalyze cleavage with the addition of water.

What distinguishes lyases from other enzymes?

Lyases catalyze cleavage without adding water or transferring electrons.

What is the role of isomerases?

Isomerases catalyze the interconversion of isomers.

What do ligases do?

Ligases join two large biomolecules, often of the same type.

What is an exergonic reaction?

It is a reaction that releases energy and has a negative (AG).

How do enzymes affect activation energy?

Enzymes lower the activation energy necessary for reactions.

Do enzymes alter the free energy of reactions?

No, enzymes do not alter (AG) or enthalpy, only the reaction rate.

What is the active site of an enzyme?

It is the site of catalysis where the substrate binds.

What does the lock and key theory suggest?

It hypothesizes that the enzyme and substrate are exactly complementary.

Explain the induced fit model.

It posits that both enzyme and substrate undergo conformational changes.

What may some enzymes require to be active?

Metal cation cofactors or small organic coenzymes.

What do enzymes experience regarding their kinetics?

Enzymes experience saturation kinetics where the reaction rate increases with substrate concentration until a maximum value is reached.

How are enzyme kinetics represented graphically?

Michaelis-Menten and Lineweaver-Burk plots represent enzyme kinetics as a hyperbola and a line, respectively.

What parameters can be used to compare enzymes?

Enzymes can be compared based on their Km (Michaelis constant) and vmax (maximum reaction velocity) values.

What characterizes cooperative enzymes?

Cooperative enzymes display a sigmoidal curve due to the change in activity with substrate binding.

How do temperature and pH affect enzymes in vivo?

Temperature and pH affect enzyme activity; changes can lead to denaturing and loss of activity due to structural changes.

What factors impact enzyme action in vitro?

Salinity can impact the action of enzymes in vitro.

What is feedback inhibition?

Feedback inhibition is when the catalytic activity of an enzyme is inhibited by the presence of high levels of a product in the same pathway.

What is reversible inhibition?

Reversible inhibition allows the replacement of an inhibitor with a stronger compound or removal via mild treatment.

Describe competitive inhibition.

In competitive inhibition, the inhibitor is similar to the substrate and binds at the active site; Vmax is unchanged, while Km increases.

Describe noncompetitive inhibition.

In noncompetitive inhibition, the inhibitor binds equally to the enzyme and the enzyme-substrate complex; Vmax decreases, Km is unchanged.

What is mixed inhibition?

Mixed inhibition occurs when the inhibitor binds unevenly to the enzyme and enzyme-substrate complex; Vmax decreases, Km varies.

What is uncompetitive inhibition?

Uncompetitive inhibition happens when the inhibitor binds only to the enzyme-substrate complex; both Km and Vmax decrease.

What is irreversible inhibition?

Irreversible inhibition renders the enzyme unavailable for a reaction and requires synthesis of new enzymes.

What are allosteric sites?

Allosteric sites are regulatory regions on enzymes where molecules can bind and influence enzyme activity.

What is phosphorylation in context of enzymes?

Phosphorylation is a covalent modification that can regulate the activity of enzymes.

What role do allosteric sites play?

Can be occupied by activators, increasing affinity or enzymatic turnover.

What is phosphorylation?

Covalent modification with phosphate that alters enzyme activity or selectivity.

Define glycosylation in enzymes.

Covalent modification with carbohydrates, altering enzyme activity or selectivity.

What are zymogens?

Inactive enzyme forms that are activated by cleavage.

What does covalent modification refer to?

Alteration of enzyme activity through phosphorylation or glycosylation.

How are enzymes activated from zymogens?

By cleavage, converting them from inactive to active forms.