Energy Transfers: Coupled reactions and Redox

First Law of Thermodynamics

Energy cannot be created or destroyed, only change forms. One material gains energy --> another loses

Second Law of Thermodynamics

Every energy transfer causes some usable energy to be lost. Increases the entropy of the universe.

Living things increase their own complexity/decrease their randomness

Increase randomness of their surroundings/They expel wastes from breakdown of more complex molecules and expel thermal energy (heat)

How do chemical reactions in living things proceed?

Energy stored in the form of chemical energy in chemical bonds are released by breaking those bonds.

endothermic reaction

Energy is absorbed. Products have MORE potential energy than the reactants.

Exothermic Reaction

Energy is released. Products have LESS potential energy than reactants

Free Energy (G)

Energy that can do useful work - not lost during energy transfer

(T/F) All energy released in an exothermic reaction can do useful energy

FALSE

(T/F) Exothermic reactions require energy to proceed

TRUE - all chemical reactions require some energy INPUT to proceed

endergonic reaction

have a positive △G value

Products have more FREE ENERGY than reactants (absorbs)

endergonic reactions

Reaction DOESNT proceed spontaneously

endergonic reactions

exergonic reaction

have a negative △G value

Products have less FREE ENERGY than the reactants (release)

exergonic reactions

How do cells harness released energy from broken bonds + put it to work for a chemical reaction?

Coupled reactions

Energy coupling

To facilitate desired reaction in cell --> exothermic reaction is coupled with desired reaction to overcome activation energy barrier

ATP (energy currency of cell)

Nucleoside triphosphate - energy input for endergonic reactions

How does ATP power cellular reactions?

Releasing energy when one of its phosphates is cleaved

Why do living things use ATP for cellular processes (used directly by cells)?

Cells can readily regenerate ATP using free energy from exergonic reactions (readily reversible - can make more when used up)

Why dont cells use energy from hydrolysis of food molecules directly?

Amount of energy released from food is too fast/too much to be managed efficiently by cells in one step. ATP can be readily coupled and universally used. Predictable amount of energy stored in it

Phosphorylation

Transfer of inorganic phosphate to another molecule

How to make ATP?

Add Pi to ADP: ADP + Pi + energy --> ATP + H2O

Phosphorylation of ADP occurs by these two kinds of reactions:

1. Substrate-level phosphorylation and 2. Oxidative phosphorylation/chemiosmosis

substrate-level phosphorylation

When ATP is synthesized in the cytosol/fluid of organelle it's S.L.P. Enzyme-mediated process where energy from high-energy substrate is used to transfer a phosphate group directly to ADP to form ATP.

oxidative phosphorylation/chemiosmotic phosphorylation

Process that forms ATP using energy transferred indirectly via series of REDOX reactions

Outline process of oxidative phosphorylation/chemiosmotic phosphorylation

Energy from redox reactions used to create an electrochemical gradient (source of potential energy) by pumping H+ ions into a specific compartment within organelle. ATP is produced as H+ ions move back by diffusion through ATP synthase. Potential energy is transferred + used to add Pi to ADP

Redox Reactions - Oxidation

LE(H atoms)O - release energy

Redox Reactions - Reduction

GE(hydrogen atoms)R - gain of energy.

(T/F) Oxidation and reduction occur together

TRUE - when a molecule is oxidized, another must be reduced

When carbon is bound to oxygen, electrons:

are shifted away from carbon + toward oxygen. Akin to losing electrons - oxidation

When carbon is bound to hydrogen, electrons:

are shared evenly with carbon, hence move toward carbon. Akin to gaining electrons - reduction

How do you extract energy from food like glucose?

Must go through a process of controlled oxidation. As food becomes oxidized --> releases energy that can be stored or used

Controlled oxidation vs Combustion

NAD+ (oxidized - low energy, dead battery) becomes reduced to NADH (charged battery)

High energy electron carrier molecules

NADH and FADH2

CONTROLLED oxidation (aerobic cellular respiration) uses what?

High energy electron carrier molecules (NADH and FADH2)

NAD+

Functions in cellular respiration by carrying 2 electrons from one reaction site --> another

NADH

Can transfer 2 electrons (1 is a hydrogen atom) to another molecule

Equation for NAD+ and NADH

NAD+ + 2H --> NADH + H+

FAD

Reduced to FADH2. Then transfers 2 electrons to another molecule. Equation: FAD + 2H --> FADH2

How are electrons brought to the electron transport system in cellular respiration?

NADH and FADH2 bring electrons to the electron transport system in cellular respiration.