Cellular Respiration: Harvesting Chemical Energy

Cellular Respiration

1. Glycolysis2. The Kreb Cycle (Citric Cycle)3. Electron Transport Chain

(Chemiosmosis and oxidative phosphorylation)

Cellular Respiration Cells harvest chemical energy stored in

molecules and use this to generate ATP.

Organic compounds store energy in their arrangements of atoms.

Catabolic (releases energy) Exergonic (- G, products store less

energy than reactants) Occurs mostly in the mitochondria (but

first step is in cytosol) C6H12O6 + 6O2 6CO2 + 6H2O + energy

(ATP and heat)

General Points Phosphorylation: the transfer of a

phosphate moleculethe production of ATP (adenosine triphosphate)ADP + P i ATP

Oxygen is very electronegative (i.e. it wants electrons ...think of its Bohr

model)

Redox Reaction Recap Involves the transfer of electrons

LEO (loss of electrons) oxidation (less -)

GER (gain of electrons) reduction (more -)

Electron donor (reducing agent) the atom that becomes less negative (positive)

Electron acceptor (oxidizing agent) the atom that becomes more negative

Sodium and Chlorine (think of the Bohr Models) Which atom is the electron donor?

Acceptor/ Which atom is the reducing agent?

Oxidizing agent?

Overview of Cellular Respiration

Step by step process that releases energy along the way (does not release all energy at once)

Hydrogen atoms are stripped away from glucose

Hydrogen atoms ultimate destination is the oxygen molecule

First they are transferred to a coenzyme NAD+

• NAD + wants to gain electrons (to be neutral)

NAD + traps electrons from glucose using dehydrogenase (enzyme) which removes a pair of hydrogen atoms from glucose

STOP and THINK of a Bohr model for hydrogen: How many electrons? How many protons?

So if we removed two hydrogen atoms, that means we remove two electrons and two protons

C6H12O6

Enzyme gives two electrons and one proton to its coenzyme NAD + forming NADH

The other proton (left over) is released into the surrounding environment

Is NAD+ an electron acceptor or donor? Is NAD+ an oxidizing agent or a

reducing agent?**NAD+ is the most versatile electron

acceptor in cell resp.

Little potential energy is lost when e- are transferred from glucose (food) to NAD+

NADH molecules represent stored energy that can be used to make ATP when e- complete their “fall” to oxygen

An electron transport chain is used to break the fall of electrons to oxygen Produces several energy releasing steps

NOT one big explosion of energy

Pathway of Electrons Electrons (from glucose in the form

of hydrogen atoms) move to NAD+ NADH oxygen (final electron acceptor)

Glycolysis(“splitting of sugar”) Glucose is split into two, three carbon sugars

called pyruvate

Catabolic pathway (breakdown) Occurs in the cytosol Two major phases

Energy investment (puts in 2 ATP) Energy payoff (creates 4 ATP)

Produces a net result of 2 molecules of usable ATP

Produces 2 molecules of NADH Can occur without the presence of oxygen

glycolysis

Oxidizing Glucose The oxidation of glucose allows

energy to be taken out of storage and make energy available to make ATP.

Glucose is broken down gradually in a series of steps catalyzed by an enzyme: dehydrogenase

Hydrogen atoms are stripped from glucose and passed to a coenzyme: NAD + (oxidizing agent)

The dehydrogenase removes two hydrogen atoms from the glucose (2 p+ and 2e-)

NAD+ traps 2e- and 1p+ from glucose break down = NADH

NADH-stored energy ready to make ATP when e- complete their journey to oxygen.