Biochemistry Chapter 7 - Enzymes

What are the properties of enzymes?

• Biological catalysts

• Most are proteins

• Nomenclature: add ase

• Accelerate chemical reactions under physiological conditions

• Highly specific

What is an apoenzyme? What is a holoenzyme?

• Apoenzyme = catalytically inactive enzyme = enzyme without a cofactor

• Holoenzyme = catalytically active enzyme = enzyme with cofactor

What are the two types of cofactors

What kind of system is a cell in regard of thermodynamics?

They are open!!!

What are exergonic reactions? What are endergonic reactions?

Exergonic:

• reactions have a negative delta G (free energy is released) and are favorable/ spontaneous

Endergonic:

• reactions have a positive delta G (free energy input required) and are unfavorable

Note:

• When delta G is zero there is no net change in the concentration of reactants and products (equalibrium)

How do enzymes work? Do they alter the equalibrium?

Enzymes do NOT change the equalibrium of a reaction, only accelerate the reaction by decreasing the activation energy

Draw the energy diagram of a chemical reaction

What is the activation energy?

The energy required to form the transition state from the substrate is called the activation energy

How do enzymes affect the transition state

Enzymes facilitate the formation of the transition state

What are transition state analogs?

• Transition states are unstable arrangement of atoms that cannot be isolated

• Transition state analogs mimic this arrangement, inhibiting the enzyme

• Enzymes prefer to bind the transition state, because it represents the highest energy with the best binding

What are the two theories of enzyme substate binding?

• The lock and key theory

• The induced fit theory

Common features of active sites

• The active site is a three-dimesnional cleft or crevice created by amino acids from different parts of the primary structure

• The active site consitiutes a small portion of the enzyme volume

• Active sites create unique microenvironments

• The interaction of the enzymes and substrate at the active site involves multiple weak interactions

• Enzyme specificity depends on the molecular architecture at the active site

• The active site stabilizes