Lecture 3 MBB

Catalyst

substance that lowers activation energy of a reaction

Enzyme

A biological catalyst that speeds up a reaction by lowering the activation energy; not consumed in the reaction and acts at the active site.

activation energy

energy for a molecule to undergo a reaction

does an enzyme change Gibbs FE?

No

Active site

The region of the enzyme where the substrate binds to form the enzyme-substrate complex.

Substrate

The molecule that binds to an enzyme and is converted to product during a reaction.

Enzyme-substrate complex

The transient pairing of enzyme and substrate during catalysis.

Vmax

The maximum velocity of an enzyme-catalyzed reaction when the substrate is saturated.

Michaelis constant (Km)

The substrate concentration at which the enzyme operates at half its Vmax

what does Km tell about an enzymatic reaction

• indicates enzyme affinity for the substrate

• measures change in reaction rate with substrate concentration

what influences reaction rates

substrates, products, and inhibitors

Substrate concentration

The amount of substrate available for enzyme binding, influencing reaction rate.

First law of thermodynamics and give example in cells

Energy in the universe is conserved; energy can be transformed from one form to another.

• cells convert EM energy to chemical bond energy

Second law of thermodynamics. Effect on cells?

Entropy tends to increase/systems become more disordered

• living cells release heat to their surroundings.

Entropy

A measure of the disorder or randomness of a system.

• heat is most disordered energy form

Metabolism

The sum of all chemical reactions that occur in a living organism.

Catabolic pathways

Metabolic pathway that breaks down molecules into smaller molecules to release energy and generate chemical building blocks.

Anabolic pathways

Metabolic pathway that synthesizes larger molecules using energy from catabolism

Equilibrium

A state where forward and reverse reaction rates are equal and ΔG = 0.

carbon cycle, describe energy change

connects photosynthesis with cell respiration

• photosynthesis (EM energy to chemical bond energy)

• cellular respiration (energy from organic molecules, producing CO2 and H2O)

oxidation

the removal of an electron from an atom

reduction

the addition of an electron to an atom

is a full transfer of electrons required during redox?

no, covalent interaction can occur

The energy yielding (catabolic) pathways of metabolism are ______ sequences (favourable in the physiological conditions of the cell)

oxidative reaction sequences

whats the result of redox reactions in the cell

transfer of electrons from fuel molecules through a series of electron carriers and finally to oxygen

Cells use enzymes to ____________ through a sequence of small steps that allows useful energy to be harvested

catalyze the oxidation of organic molecules

ΔG (Gibbs Free Energy)

Energy available to perform work; determines whether a reaction is thermodynamically possible.

Equilibrium constant (K)

Ratio of product to reactant concentrations at equilibrium; related to ΔG°.

ΔG° (Standard free energy)

ΔG under standard conditions (298 K, 1 M, pH 7); used to compare reactions.

Spontaneous reaction/ Energetically favorable

A process with negative ΔG that can occur given suitable conditions and mechanism. Free energy of Y is greater than X

how can an unfavorable reaction occur?

ATP is added to the reaction. Breakdown of ATP (hydrolysis) to ADP gives the energy needed for the reaction to be negative

ATP

Adenosine triphosphate; the cell’s activated carrier and primary energy currency.

Hydrolysis of ATP

ATP → ADP + Pi

• releases energy for work.

Dephosphorylation of glucose

Glucose-6-phosphate - Pi → glucose

• releases energy

factors the affect free energy

temp, pressure, pH, concentration

ΔG at equilibrium

0

Do our cells reach and maintain equilibrium?

Living cells are characterized by continuous reactions and maintain themselves in states far from equilibrium

relationship between K and G

K= products/reactants

K>1 → -G → spontaneous reaction

K<1 → +G → non-spontaneous reaction

thermal motion purpose

allows enzymes to find their substrates because they are VERY fast

describe movement of molecules through cytosol

Diffusion: molecules move randomly and rapidly through the cytosol, allowing for reactions and interactions like formation of enzyme-substrate complex

• cytosol is crowded → larger molecules diffuse slower

what do enzyme kinetics show

describes the quantitative aspects of enzyme catalysis and the rate of substrate conversion into products

process of enzyme reaction

• Enzyme must bind substrate

• Substrate undergoes a reaction to form product

• Product is released, enzyme is free to bind another molecule of substrate