Aerobic Respiration & Energy Production

Aerobic Respiration & Energy

ProductionDr. Michael P. Gillespie11

Mitochondria

• Mitochondria are football-shaped organelles that are roughly the size of a bacterial cell.

• They are bound by an outer mitochondrial membrane and an inner mitochondrial membrane.

• The space between these membranes is the intermembrane space and the space inside the inner membrane is the matrix space.

Dr. Michael P. Gillespie 2

Mitochondria


Mitochondria

• The mitochondria has it’s own genetic information and is able to make some of its own proteins.

• Mitochondria grow and multiply in a way that is very similar to simple bacteria.

• Mitochondria are most likely the descendants of bacteria that were captured by eukaryotic cells millions of years ago. Approximately 1.5 X 109 years ago.


Outer Mitochondrial

Membrane• The outer mitochondrial membrane

has small pores through which small molecules can pass.

• The molecules that are oxidized for the production of ATP are small enough to easily enter the mitochondrial membrane.


Inner Mitochondrial Membrane

• The inner membrane is highly folded to create a large surface area.

• The folded membranes are known as cristae.

• The inner membrane is almost completely impermeable.


Inner Mitochondrial Membrane

• Transport proteins bring specific food molecules into the matrix space.

• The protein electron carriers of the electron transport system are embedded within the inner membrane.

• ATP synthase is embedded in the membrane.


Origin Of Mitochondria

• Mitochondria are roughly the size of bacteria.

• Mitochondria have their own genetic information (DNA).

• They make their own ribosomes that are very similar to those of bacteria.

• The DNA and ribosomes allow the mitochondria to synthesize their own proteins.

• Mitochondria are self-replicating. They grow in size and divide to produce new mitochondria.


Glucose Utilization

• Under anaerobic conditions, glucose is broken down into two pyruvate molecules.

• Very little of the stored potential energy in glucose is released from this limited degradation of glucose.

• Under aerobic conditions the cells can use oxygen and completely oxidize glucose to CO2 in a metabolic pathway called the citric acid cycle.


Citric Acid Cycle

• Often referred to as the Krebs cycle in honor of Sir Hans Krebs who elucidated the steps of this cyclic pathway.

• Also called the tricarboxylic acid (TCA) cycle because several of the early intermediates in the pathway have three carboxyl groups.


Pyruvate Conversion To Acetyle CoA

• When pyruvate enters the mitochondria, it must be converted to a two-carbon acetyl group.

• The acetyl group must be activated to enter into Krebs cycle.

• It is activated when it is bonded to coenzyme A.

• Acetyle CoA is the “activated” form of the acetyl group.


Pyruvate Conversion To Acetyle CoA

• Four coenzymes from four different vitamins are necessary for this reaction to occur.• Thiamine pyrophosphate from thiamine

(Vitamin B1)• FAD derived from riboflavin (Vitamin B2)• NAD+ derived from niacin• Coenzyme A derived from pantothenic

acid


Aerobic Respiration

• Aerobic respiration is the oxygen-requiring breakdown of food molecules and production of ATP.


Compartments of Mitochondria

• Different steps of aerobic respiration occur in different compartments of the mitochondria.

• The enzymes for the citric acid cycle are found in the mitochondrial matrix.



• Electrons from NADH and FADH2 are passed through the electron transport system located in the inner mitochondrial membrane.

• This transfer of electrons causes protons to be pumped out of the mitochondrial matrix into the intermembrane compartment (resulting in a high energy H+ reservoir.



• The high energy H+ reservoir is used to make ATP. The enzyme ATP synthase facilitates this step.

• The protons flow back into the mitochondrial matrix through a pore in the ATP synthase complex and ATP is generated.


The Citric Acid Cycle

• The citric acid cycle is the final stage of the breakdown of carbohydrates, fats, and amino acids.

• The following steps will follow the acetyl group of an acetyle CoA as it passes through the citric acid cycle.

• Pyruvate was converted to acetyl CoA when it entered the mitochodria, thus preparing it for entry into Krebs cycle.


Krebs Cycle


Reaction 1

• 4-Carbon Oxaloacetate combines with Acetyle CoA to yield 5-carbon Citrate and Coenzyme A.

• Citrate Synthase catalyzes this reaction.


Reaction 2

• Citrate is isomerized to Isocitrate.

• Aconitase catalyzes this reaction in two steps.


Reaction 3

• Isocitrate is oxidated to α-ketoglutarate.

• CO2 is released.

• NAD+ is reduced to NADH.

• Isocitrate dehydrogenase catalyzes this reaction.


Reaction 4

• 5-carbon α-ketoglutarate is converted to 4-carbon Succinyl CoA.

• A carboxylate group is lost in the form of CO2.


• The enzyme α-ketoglutarate dehydrogenase catalyzes this reaction.

• Coenzyme A assists.


Reaction 5

• Succinyl CoA is converted to Succinate.

• An inorganic phosphate is added to GDP to create GTP.

• The enzyme Succinyl CoA synthase catalyzes this reaction.

• Coenzyme A is restored.

• Dinucleotide diphosphokinase transfers a phosphoryl group from GTP to ADP to make ATP.


Reaction 6

• Succinate is converted into Fumarate.

• FAD is reduced to FADH2.

• Succinate dehydrogenase catalyzes this reaction.


Reaction 7

• Fumarate is converted into Malate.

• The enzyme Fumarase catalyzes this reaction.


Reaction 8

• Malate is converted back into Oxaloacetate.

• The citric acid cycle began with this product so we have come full circle.


• Malate dehydrogenase catalyzes this reaction.



Point to Remember

• Recall that for every glucose molecule that was degraded in glycolysis, two molecules of pyruvate were created.

• Therefore, two turns of the TCA cycle happen for every molecule of glucose.


Important Products From The TCA Cycle

• Per turn of the TCA cycle• 1 ATP• 3 NADH

• 1 FADH2

• Per glucose molecule• 2 ATP• 6 NADH

• 2 FADH2


Important Products From The TCA Cycle


Krebs Cycle Products


Krebs Mnemonic


Oxidative Phosphorylation

• Electrons carried by NADH can be used to produce three ATP molecules.

• Electrons carried by FADH2 can be used to produce two ATP molecules.



• Electron transport systems are embedded within the mitochondrial inner membrane.

• These electron carriers pass electrons from one carrier in the membrane to the next.

• Protons (H+) can be pumped from the mitochondrial matrix to the intermembrane space at three sites in the electron transport system.



• At each site, enough H+ are pumped into the H+ reservoir to produce one ATP molecule.

• A multiprotein complex called ATP synthase catalyzes the phosphorylation of ADP to produce ATP.

• There is a channel in the ATP synthase through which H+ pass. The energy of the flow of H+ is harvested to make ATP.


ATP Yield From Aerobic Respiration

• 2 ATP / glucose from glycolysis

• 34 ATP / glucose from aerobic respiration

• 26 ATP / glucose


ATP Yield From Aerobic Respiration

• Glycolysis• Substrate level phosphorylation – 2 ATP• 2 NADH X 2 ATP / cytoplasmic NADH – 4 ATP

• Conversion of 2 pyruvate molecules to 2 acetyl CoA molecules• 2 NADH X 3 ATP / NADH – 6 ATP

• Citric Acid Cycle (2 Turns)• 2 GTP X 1 ATP / GTP – 2 ATP• 6 NADH X 3 ATP / NADH – 18 ATP• 2 FADH2 X 2 ATP / FADH2 – 4 ATP

• 36 ATP Total


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Aerobic Respiration & Energy Production