Enzymes and the Regulation of Enzyme Activity

How do Exergonic Reactions work?

Proceeds w/ a net release of free energy and is spontaneous

How do Endergonic Reactions work?

Absorb free energy from surroundings and is non-spontaneous

How important is chemical bond breaking/formaion?

Involved in every reaction

What is Activation Energy (or Free Energy of Activation)?

Initial energy needed to start a chemical reaction

How is Activation Energy often supplied?

As thermal energy that reactants absorb from surroundings

What type of Reaction is this Energy Profile for?

Exergonic

What type of Reaction is this Energy Profile for?

Endergonic

What happens in Catalysis?

Catalysts speed up reactions by lowering Ea barrier

Do Enzymes affect free energy?

No, hasten reactions that would eventually occur

What is an Enzyme Substrate?

Reactant that an enzyme acts on

How is the Enzyme-Substrate Complex formed?

Enzyme binds to substrate, activity of the enzyme converts substrate to product

What is the Active Site?

Region on enzyme where substrate binds

What is Induced Fit of a Substrate?

Brings chemical groups of active site into positions that enhance their catalytical ability

How much of an Enzyme is needed?

Very small amounts can have substantial metabolic effects because they’re used repeatedly in catalytic cycles

How can Active Sites lower an Ea Barrier?

• Orienting

• Straining

• Microenvrionment

• Bonding

• Orienting substrates correctly

• Straining substrate bonds

• Providing favourable microenvironment

• Covalently bonding to substrate

What is the relationship between the rate of Enzyme-catalysed reactions and Substrate Conc?

Rate speeds up when substrate conc increases

What is the result of all Enzyme Active Sites being engaged?

Enzyme is saturated - reaction rate only increases by adding more enzyme

What happens after the Substrates enter the active site?

• Holding

• Conversion

• What happens to the AS?

• Substrates held in AS by weak interactions

• Substrates converted to products, products released

• AS available for new substrates

What Environmental Factors affect Enzymes?

Temperature and pH

What are Cofactors?

Inorganic/Organic non-protein enzyme helpers

How do Competitive Inhibitors work?

Bind to AS compete w/ substrate

How do Non-Competitive Inhibitors?

Bind to another part of enzyme causing to change shape and makes AS less effective

What are Examples of Enzyme Inhibitors?

Toxins, poisons, pesticides, antibiotics

What would result if Metabolic Pathways weren’t tightly regulated?

Chemical chaos

How does the cell regulate metabolic pathways?

Switching on/off genes that encode specific enzymes or by regulating enzyme activity

How does Allosteric Regulation affect Enzyme Activity?

Inhibit/stimulate it

When does Allosteric Regulation occur?

Regulatory molecule binds to a protein at 1 site and affects protein’s function at another

What does the binding of an activator do?

Stabilises inactive form of the enzyme

What is Cooperativity?

Form of allosteric regulation that can amplify enzyme activity

How do substrate prime enzymes?

1 substrate primes an enzyme to act on additional substrate molecules more readily

Why is cooperativity allosteric?

Binding by a substrate to 1 AS affects catalysis in a different AS

What happens in Feedback Inhibition?

End product of a metabolic pathway shuts down pathway

What does Feedback Inhibition prevent?

Prevents a cell from wasting chemical resources by synthesising more product than needed