Unit 3: Energy & Enzymes

• Key Components:

  • Substrate

  • Product

  • Enzyme (catalyst)

Student Learning Outcomes (SLOs)

• SLO1: Define and differentiate between potential energy and Gibb's free energy.

Definitions of Energy

• Energy: Capacity to do work or promote change.

• Potential Energy: Energy due to position.

  • Chemical Potential Energy: Energy in bonds (position of electrons).

  • Question: Do polar or nonpolar bonds have higher potential energy?

Glucose Structure

• Molecular Composition of Glucose:

  • Red = oxygen

  • White = hydrogen

  • Grey = carbon

• Bonds with High Potential Energy in Glucose:

  • O-H

  • C-C

  • C-H

  • C-O

Energy Transformations

• Energy can be converted into different forms; total amount remains constant:

  • Forms of Energy:

  • Potential (Ep)

  • Kinetic (Ek)

  • Diagram Overview:

  • Ep (top) to Ek (sunlight) to Heat/Ek (mechanical energy/sound)

    • Ep (bottom): Example includes chlorophyll molecule in excited state, photosynthesis leading to high-energy electrons and chemical bond energy.

    • Input of electromagnetic (light) energy.

Gibb's Free Energy (G)

• Gibb's Free Energy: Energy within a molecule available for work.

  • Within a molecule, multiple sources of energy exist, but only a portion is available for work. Examples:

  • Vibrations

  • Rotations

  • Energy stored within bonds (chemical potential energy)

Gibb’s Free Energy & Disorder

• Relationship Between Gibb's Free Energy and Disorder (Entropy):

  • More disorder (higher entropy) results in less energy available for work.

SLO 2: Endergonic vs. Exergonic Reactions

• Define and contrast endergonic and exergonic reactions with respect to changes in Gibb’s free energy.

• SLO 3: Define and contrast anabolic and catabolic reactions (examples provided).

• SLO 4: Correlate terms:

  • Endergonic / Exergonic

  • Anabolic / Catabolic

  • Condensation / Hydrolysis

• SLO 5: Identify whether reactions are endergonic or exergonic using free energy change graphs.

Free Energy Changes in Reactions

• Free Energy Changes Over Course of Reactions (ΔG):

  • If ΔG increases:

  • Endergonic (+ΔG)

  • Requires continual input of energy

  • Energetically unfavorable (non-spontaneous)

  • Decrease in entropy

  • Anabolic (building) reactions

  • If ΔG decreases:

  • Exergonic (-ΔG)

  • Energy is released during the reaction

  • Energetically favorable (spontaneous)

  • Increase in entropy

  • Catabolic (breaking) reactions

Reaction Graphs

• Free Energy vs. Reaction Progress - Labeling:

  • Graphical representation required for identifying endergonic or exergonic reactions.

SLO 6: Activation Energy

• Identify activation energy, free energy change (ΔG), and transition state on a graph of free energy change.

Biological Reaction Overview

• Biological Reaction:

  • Determine if the reaction is exergonic or endergonic.

  • Describe changes in free energy through the reaction.

Energy Profile of a Biological Reaction

• Activation Energy:

  • Energy required for reactants to reach the high-energy transition state; relatively high due to biological molecules' stability.

  • Often heat is absorbed from surroundings.

  • Inquiry: Activation energy included in overall ΔG?

Reaction Rates & Activation Energy

• Is the reaction anabolic or catabolic? Determine if it is endergonic or exergonic.

  • Glucose reaction is important but must be sped up for cellular utility.

  • Mechanism: Addition of a protein catalyst = Enzyme.

Enzyme Function

Action of Enzymes

• What does an enzyme alter?

  • How does it speed up reactions?

  • Does it affect overall free energy change (ΔG)?

SLO 7: Role of Active Site

• Identify the location of the active site on the enzyme and explain its role:

  • Reactants (substrates) bind to the active site, which is highly specific.

  • Binding transforms enzyme shape facilitating transition state achievement.

  • Products are released, and the enzyme is recyclable.

SLO 8: Inhibition Types

• Contrast allosteric inhibition vs. competitive inhibition:

  • Allosteric Regulation:

  • Majority of biological reactions need enzymes.

  • Cells regulate reactions by controlling the enzymes.

  • Most regulated via allosteric regulation:

    • Regulatory molecules bind outside the active site, altering enzyme shape for activation or inhibition.

Competitive Inhibition of Enzymes

• Many drugs/medications mimic substrate shape, binding to the enzyme's active site, blocking the natural substrate.

SLO 9: Negative Feedback Inhibition

• Describe the negative feedback inhibition process:

  • Many reactions are multi-step pathways.

  • Product interacts with early enzyme: Assess if it is competitive or allosteric inhibitor.

  • Importance of feedback inhibition.

SLO 10: Cofactors and Coenzymes

• Describe the role of cofactors and coenzymes in enzyme function; contrast their structures:

  • Role of Cofactors:

  • Inorganic ions (e.g., $Mg^{2+}, Zn^{2+}$) that may bind anywhere on the enzyme to function.

  • Role of Coenzymes:

  • Organic molecules that bind to the active site and improve substrate binding (e.g., Vitamin C binding to enzyme).

SLO 11: Enzyme Consequences

• Predict potential consequences of a nonfunctional enzyme for a cell:

  • Discussion on the role of enzyme regulation determining reactions occurring within a cell.

  • Explore how alterations in enzyme shape can affect enzyme function.