KEY STAGES OF AEROBIC CELLULAR RESPIRATION (after glycolysis)

oxidative decarboxylation

an oxidation reaction in which a carboxylate group is removed

oxidative decarboxylation (1)

pyruvate crosses the mitochondrion’s outer and inner membranes and then enters the matrix

oxidative decarboxylation (2)

pyruvate dehydrogenase complex aids the process of oxidative decarboxylation, removing the carboxyl group from pyruvate

oxidative decarboxylation (3)

NAD+ is reduced to become NADH

oxidative decarboxylation (4)

carbon dioxide is removed, leaving a two-carbon acetyl group that combines with coenzyme A to form acetyl-CoA

Krebs cycle

a series of enzymatic reactions that occurs in all aerobic organisms

Krebs cycle

Involves the oxidative metabolism of acetyl units and serves as the main source of cellular energy

Krebs cycle

also known as the citric acid cycle or the tricarboxylic acid cycle because of the presence of three carboxyl groups (COOH)

Krebs Cycle A

Condensation of acetyl-CoA with oxaloacetate catalyzed by citrate synthase, adding its 2 carbon fragments (acetyl group)

and forms a 6-C molecule

→ once oxaloacetate is joined with acetyl-CoA, a water molecule attacks the acetyl leading to the release of coenzyme

A from the complex

Krebs Cycle B

citrate is converted to its isomer (isocitrate) via the removal and addition of water molecule using the enzyme aconitase

→ the overall effect of this conversion is that the –OH group is moved from the 3′ to the 4′ position on the molecule

Krebs Cycle C

isocitrate dehydrogenase catalyzes oxidative decarboxylation of isocitrate to form α-ketoglutarate, releasing CO2 molecule

which results to a 5-C compound that is oxidized, reducing NAD+

to NADH

Krebs Cycle D

α-ketoglutarate is oxidized using the enzyme alpha-ketoglutarate dehydrogenase, resulting to the removal of a CO2, a

coenzyme A is added to form the 4-carbon compound, succinyl-CoA

• during this oxidation, NAD+ is reduced to NADH

Krebs Cycle E

CoA is displaced from succinyl-CoA by a phosphate group which is then transferred to GDP to form Guanosine Triphosphate

(GTP), which can then be used to make ATP

* the reaction is catalyzed by the enzyme succinyl-CoA synthase which stimulates the hydrolysis of succinyl CoA into

succinate and ATP

Krebs Cycle F

succinate is oxidized to fumarate using the enzyme succinate dehydrogenase which catalyzes the removal of two hydrogen

atoms from succinate which are then transferred to FAD to form FADH2

Krebs Cycle G

The enzyme fumarase catalyzes the hydration of fumarate, turning it into malate, by rearranging the bond through the

addition of hydrogen and oxygen

Krebs Cycle H

malate is oxidized to produce oxaloacetate, the starting compound of the citric acid cycle using the enzyme malate

dehydrogenase, causing NAD+

to be reduced to NADH + H+

electron transport chain

- a series of proteins and organic molecules found in the inner membrane of the mitochondria where electrons are

passed from one member of the transport chain to another in a series of redox reactions

- it is the first stage in the process of oxidative phosphorylation

1

as the electron travels through the chain, they go from higher to lower energy level because energy is released from this

electron transfers

2

several of the protein complexes use the released energy to pump protons from the mitochondrial matrix to the

intermembrane space, forming a proton gradient

3

NADH is very good at donating electrons in REDOX reactions and transfers its electrons directly to complex I (NADH

dehydrogenase complex), turning back into NAD+

4

the complex uses this energy to pump protons from the matrix into the intermembrane space

5

FADH2 is not as good at donating electrons as NADH and cannot transfer its electrons to complex I, instead, it feeds them

into the transport chain through complex II (Cytochrome b-c1), which does not pump protons across the membrane

6

electrons from NADH and FADH2 travel the same route as they are released by both complexes to a small, mobile electron

carrier called ubiquinone (Q)

7

Q travels through the membrane, delivering the electrons to complex III, which pumps more H+ across as electrons move

through this complex

7

electrons are ultimately delivered to another mobile carrier called cytochrome C (cyt C) which carries the electrons to

complex IV (Cytochrome oxidase complex), where a final batch of H+

is pumped across the membrane

8

complex IV passes the electrons to O2, which splits into two oxygen atoms and accepts protons from the matrix to form

water; 4 electrons are required to reduce each molecule of O2, and 2 H2O molecules are formed in the process

chemiosmosis

The diffusion of ions (usually H+, also known as protons) across a selectively permeable membrane

chemiosmosis 1

protons from the intermembrane space can't pass directly through the phospholipid bilayer of the membrane because its

core is too hydrophobic, instead, H+

can move down their concentration gradient only with the help of channel proteins that form hydrophilic tunnels

across the membrane

chemiosmosis 2

in the inner mitochondrial membrane, H+ have just one channel available: a membrane-spanning protein known as ATP

synthase

chemiosmosis 3

ATP synthase is a lot like a turbine in a hydroelectric power plant, instead of being turned by water, it’s turned by the flow

of H+ moving down their electrochemical gradient

chemiosmosis 4

as ATP synthase turns, it catalyzes the addition of a phosphate to ADP, capturing energy from the proton gradient as ATP

glycolysis

* reactants: glucose and 2 ATP

* products: 2 ATP, 2 NADH, 2 pyruvate

Oxidative decarboxylation (Link Reaction)

• reactants: 2 pyruvate, (2 NAD+), and 2 CoA

• products: 2 acetyl CoA, 2 CO2, and 2 NADH

Krebs Cycle

* reactants: 2 acetyl CoA, (6 NAD+), (2 FAD), (2 ADP) and (2 Pi)

* products: 2 ATP, 6 NADH, 2 FADH2, 4 CO2, and 2 CoA

Electron transport chain

* reactants: 10 NADH, 2 FADH2, and 6 O2

* products: 12 H2O (minus the 6 H2O used during the processes of hydrolysis and hydration), H+

Chemiosmosis

* reactants: H+, (ADP and Pi)

* products: H+ of NADH = 3 ATP H+ of FADH2 = 2 ATP