Concept 6.4 - Enzymes speed up metabolic reactions by lowering energy barriers

Laws of thermodynamics

Determine what can and cannot happen under certain conditions not do not address the rate of processes

Spontaneous reactions

Occur without external energy but can be extremely slow

Role of enzymes

Can significantly speed up reactions

Enzyme function

• Macromolecules that act as catalysts, speeding up reactions without being consumed

• Crucial for regulating metabolic math ways and preventing congestion due to slow chemical reactions

Types of enzymes

• Protein enzymes

• Ribozymes (some RNA molecules that can function as enzymes)

What do chemical reactions involve?

Both bond breaking and bond forming

The hydrolysis of sucrose ________ the bond between glucose and fructose and a bond in a ________ molecule, forming _____ new bond(s).

Breaks, water, two

Reactant molecules must _________ energy to reach a highly unstable state before the reaction can proceed.

Absorb

Activation energy

Energy needed to push reactants to the top of an energy barrier so the reaction can proceed

What is activation energy often supplied by, and what does it accelerate and make more likely?

Often supplied by heat, accelerates reactant molecules and makes bond breakage more likely

What happens to reactants when they absorb enough energy?

Reach an unstable transition state where bonds can break

In an exergonic reaction, such as AB + CD = AC + BD, the reaction occurs…

Occurs spontaneously with negative △G

What does the activation energy barrier determine?

Rate of the reaction

What do reactants need to do before the actual reaction can occur?

Must absorb enough energy to reach transition state

Substrate specificity

The ability of an enzyme to select and bind to a specific substrate (the reactant molecule) due to the shape and chemical environment of its active site

Local conditions

• Temperature

• pH

• Substrate concentration