Lecture 7 - Energy and Enzymes pt. 2

What is metabolism?

Collection of chemical reactions within a cell

What do catabolic chemical reactions do?

Breakdown complex molecules into simpler compounds

What is an example of catabolic reactions?

Starch breaking down into glucose molecules

What do anabolic reactions do?

Use simple molecules to build more complex ones

What is an example of an anabolic reaction?

protein synthesis

What are the characteristics of anabolic reactions?

Endergonic

Use energy

Enthalpy (H) increases

Entropy (S) decreases

ΔG > 0

What are characteristics of exergonic reactions?

Exergonic

Release energy

Enthalpy (H) decreases

Entropy (S) increases

ΔG < 0

What is activation energy?

Initial energy invested and required to start a reaction

What is activation energy required for?

Substrates to achieve the transition state

What are enzymes?

A class of proteins that catalyze chemical reactions

What does catalysis do?

Increase rate of chemical reactions

Wha happens to enzymes after chemical reactions within"

They're reused many times since they're not destroyed during the chemical reaction

What do enzymes lower?

activation energy

What makes enzymes biological catalysts?

lowering the activation energy of biological reactions

Increasing the number of reactants that can reach the transition state

Does not change ΔG of the reaction

Increasing the rate of reaction

What is the first step in enzyme actions?

Initiation: substrates bind to the active site in a specific orientation, forming an enzyme-substrate complex

What is the second step in enzyme activation?

Transition state facilitation: interactions between enzyme and substrate lower the activation energy

What is the third step in enzyme activation?

Termination: products have lower affinity for active site and are released. Enzyme is unchanged after the reaction

What limits rate of catalysis?

Saturation of enzyme-catalyzed reactions

When do enzyme-catalyzed get saturated?

At high substrate concentration, enzyme-catalyzed reactions reach a maximum rate. Uncatalyzed reactions slowly increase as substrate concentration increases

When does reaction rate plateau?

When enzyme become saturated with substrate

When does reaction rate increase linearly?

With increasing enzyme concentration when substrates are in excess

How does an enzyme work?

1. Substrate molecule binds to the Active Site of the enzyme

2. Usually, a pocket or cleft on enzyme surface

3. A region where catalysis occurs

What is substrate specificity?

The shape of the enzyme at substrate site allows enzyme specifically recognize and bind substrate

What happens when ATP and glucose bind to the active site?

The enzyme changes shape

What does induced fit do?

Reorients substrates and bind them tighter to the active site

What are cofactors/enzymes

Non-protein component of an enzyme

What are cofactors?

Metal ions that support enzyme action

What are examples of cofactors?

zinc, iron, copper

What are coenzymes?

Organic compounds that support enzyme action

What are examples of coenzymes?

vitamins

What does the activity of an enzyme change as a function of?

Temperature, pH, modification, and interaction with regulators

What does protein modification change?

The shape and activity of proteins

What is the inactive form of protein

Unphosphorylated form

What is the unphosphorylated form the site of?

Phosphorylation

What is the active form of protein called?

Phosphorylated form

What causes inactive protein to become active?

Phosphate groups cause loops to move

What's one was of regulating enzymes?

Regulatory molecules

What are competitive interactions?

When molecules compete with normal substrate for active site

What are noncompetitive interactions?

When molecules don't compete with normal substrate for active site, but interact elsewhere on enzyme (allosteric site)

What are characteristics of competitive inhibition?

Inhibiting molecule binds to active site, preventing

binding of the substrate

Inhibiting molecule COMPETEs with substrate for

active site.

What happens in noncompetitive regulation?

Molecule binds to enzyme but NOT to the active

site-allosteric site

What are characteristics of allosteric control of enzyme activity

Non-competitive binding of molecules to enzyme

Increased affinity of substrate- enzyme interaction or induce the formation of substrate binding site.

Site of binding: allosteric site

Makes the enzyme more efficient

What is the function of intermediates in enzyme metabolic pathways?

They serve as both a product and a reactant.

What are the steps of feedback control of enzyme activity?

1. Product of enzyme 3 interacts Enzyme 1

2. Allosteric inhibition

3. Decrease activity of Enzyme 1

4. Decrease the rate of the reaction catalyzed by enzyme 1

5. Negative feedback regulation (feedback loop)

What does decrease of the reaction rate lead to?

Decrease reaction product