Enzymes

What is an enzyme?

Biological catalyst

• Usually made of proteins

Why are enzymes important

• Speed up reactions

  • By lowering activation energy (easier for reactions to start)

• Breaks down food —→ usable nutrients

• Turns food —→ energy for cells to use

• Build and repair molecules

What do enzymes affect?

Rate of reaction —→ makes reactions happen faster

• By lowering activation energy needed

What molecules do enzymes act on?

Substrates

What is activation energy (AE)?

The minimum energy needed to start a chemical reaction

Do enzymes change ΔG?

No, they only lower activation energy (AE)

What is the transition state?

A high-energy unstable stage where:

• Old bonds break

• New bonds form

Enzymes help substrates reach this state more easily

What is enzyme specificity?

Means an enzyme usually works on…

• one specific substrate

OR

• One specific type of reaction

How are enzymes named/classified?

“-ase”

• Ends in -ase suffix

What is an active site?

Region on the enzyme where the substrate binds —→ reaction happens

What is the “Lock and Key Model?”

Enzyme active site has a FIXED shape that matches the substrate

What is the “Induced Fit Model?”

Enzyme CHANGES shape to better fit the substrate

Which matters more—shape or chemistry at the active site?

Chemistry

• The active site’s chemical interactions DRIVE the reaction

What happens in the active site?

Substrate binds active site (enzyme + substrate bond) —→ Substrate becomes unstable —→ activation energy decreases —→ product forms —→ product released

How do enzymes lower activation energy?

By…

• Holding substrates in the right position

• Strain the substrate bonds

• Form temporary covalent bonds

Stabilizing transition state = less energy needed to begin for reaction

How can the reaction rate be measured

By measuring…

• Decrease in substrate concentration

OR

• Increase in product concentration (over time)

What is enzyme kinematics

Study of reaction rates and factors affecting them

What happens when substrate concentration increases?

Reaction rate INCREASES —→ enzymes get full —→ rate stops increasing

• When all enzyme active sites become saturated/full

  • Saturated = All active sites are occupied by substrate

Effect of temperature on enzyme activity

• LOW temp (cold) —→ Slow activity

• Ideal temperature (depends on the organism) —→ Highest activity

• HIGH temp (hot) —→ enzyme denatures —→ Activity drops

Effect of pH on enzyme activity

Each enzyme has an optimum pH depending on the organism

• Too high/low pH

  • Changes charges on amino acids

  • Changes enzyme shape

  • REDUCES ACTIVITY

What are cofactors?

Non-protein helper molecules (NOT PROTEINS!!!)—- they’re extra molecules or ions

• Enzymes need in order to work

  • Attaches to the enzyme to activate it —→ lets the reaction happen

Types of cofactors (3)

• Activators

• Coenzymes

• Prosthetic groups

Coenzymes

Organic molecules that help carry electrons OR chemical groups during reactions

Prosthetic Groups

Organic molecules permanently attached to the enzyme

What are enzyme inhibitors?

A molecule that slows or stops an enzyme from working

• By blocking or reducing enzyme activity

Why do enzymes control metabolism instead of just speeding reactions?

Enzymes control metabolism because…

• They decide which reactions HAPPEN and WHEN

• Regulating them lets the cell control its chemical reactions

Why do enzymes lower activation energy but not ΔG?

Enzymes lower the energy needed to start a reaction, but they don’t change the total energy released or required

• ΔG is the energy difference between reactants and products

  • Enzymes don’t change the energy of reactants or products