Chapter 8 - Energy and Enzymes: An Introduction to Metabolism

• The total energy in a molecule (heat)

• Heat energy is absorbed; ΔH is positive; products have higher potential energy 

• Heat energy is released; ΔH is negative; products have lower potential energy than reactants 

• Amount of disorder (randomness) 

• More ordered = less entropy, less ordered = more entropy 

• ΔS = change in entrop

• Spontaneous - no energy required for reaction 

• Non-spontaneous - energy input is required for reaction 

• Gibbs free energy (G)

• ΔG = ΔH - TΔS

  •  ΔG = change in free energy 

  • ΔH = change in enthalpy 

  • ΔS = change in entropy 

  • T = temperature in kelvin 

• Exergonic 

• Endergonic 

• Reaction is at equilibrium 

• Gibbs free energy is absorbed 

• Gibbs free energy is released 

• Higher concentration → more collisions 

• Higher temperature → higher reaction rate 

• Concluded:

  • Reaction rate increased when the temperature of the reaction mixture was higher

  • Reaction rates higher when reaction concentrations are higher

• Between endergonic and exergonic reactions; when the release of chemical energy from an exergonic reaction powers an endergonic reaction 

• Energy can be transferred through electrons or transfer of a phosphate group

• Oxidation is loss of electrons, so exergonic 

• Reduction is gaining electrons, so endergonic

• Change in number of electrons in valence shell

• Electrons are transferred as new covalent bonds form with other atoms - atom is either reduced or oxidized 

• Electron donor → electron acceptor 

  • Acceptors gain potential energy as they are reduced (bc reduction is gaining electrons)

  • Electrons are accompanied by a proton, so add H’s

• FADH2: Flavin adenine dinucleotide (FAD) accepts two electrons + two protons to form FADH2 → has reducing power

• NADH: Nicotinamide adenine dinucleotide (NAD+) accepts two electrons plus one proton to form NADH

  • They readily donate electrons to other molecules 

• Energy currency for cells:

  • Provides fuel for cellular activities 

  • Ribonucleotide used for RNA synthesis 

  • Has a lot of potential (stored) energy - bond between 3 negatively charged phosphate groups 

    • The negative charges repel each other, but are forced together

• Bond between the outermost P group and its neighbor is broken --> becomes ADP (now only 2 phosphate groups)

• Highly exergonic reaction (bc losing a P group releases energy)

  • Raises the temperature of water, 1 kg per 1 degree Celsius

• 7.3 kilocalories of energy per mole of ATP released during the reaction 

  • A kilocalorie raises 1kg of water by 1 degree Celsius 

• Provide energy for cellular activity

ATP reacts w/ H20 & breaks down into ADP & 1 P group -> free energy & H2O

• Phosphate Transfer: P group transferred from 1 molecule to another, changing receiving molecule & helps drive energy-requiring rxn.

• Electron transfer: e- are transferred from 1 molecule to another-redox rxn.

• The process of adding a P group to a molecule.

  • Potential E: Adding a P group can increase a molecule’s potential energy, making it more reactive.

  • Energetic coupling: Cells use energy released from ATP hydrolysis to transfer a P group to another molecule. This helps drive reactions that need energy.

• Activation energy: The minimum energy needed to start a chemical reaction.

• Transition state: The unstable, high-free-energy state that molecules pass through as bonds are breaking and forming during a reaction

• Must collide in a PRECISE orientation

• Have enough kinetic energy to overcome activation energy barrier & achieve transition state

• Catalysts that bring reactants together in more precise orientations

• By decreasing activation energy required for reaction to proceed

• Substrate

• Active site

• A change in a protein’s shape that affects how it works.

• An enzyme changes shape when a substrate binds to it, helping the enzyme carry out a reaction.

  • Called an “induced fit”

• Hydrogen bonding 

• Weak amino acid residue interactions 

• Initiation - substrates precisely oriented as they bind to active site 

• Transition state facilitation - interaction between substrate and active site R-groups lowers activation energy 

• Termination - reaction products are released from enzyme 

• Decrease with high concentrations of substrate - “saturation kinetics” 

• Increase at low substrate concentrations

• Cofactors - inorganic ions that help enzymes work by reversibly reacting with it - Zn+2, Fe+2

• Coenzymes - organic molecules that carry e- or chemical grps to the enzyme - NADH, FADH2

• Prosthetic grps - non-amino acid atoms or molecules permanently attached to proteins

  • Ex - prosthetic leg

• Temperature 

• pH 

• Interactions with other molecules 

• Modification of primary structure

• Molecules that regulate cells' enzymatic activity

  • Can change enzyme structure, change ability to bind to its substrate, or activate/inactivate the enzyme

• Molecule competes with the substrate for the active site

• Molecule binds at a location other than the active site → causes a change in the shape of the enzyme, deactivating or activating it

• Break down molecules into sources of energy and carbon building blocks 

• Use energy and carbon building blocks to synthesize molecules

The cell attaches a small chemical grp to an enzyme via covalent bond, altering its primary structure--either irreversible (peptide bond cleavage) or reversible

• Phosphorylation = the most common reversible. The phosphate's charges shift a loop, changing the enzyme's shape & flipping it ON or OFF

When the link between two amino acids gets cut, splitting the protein chain — and it can't be undone on its own.