Cellular Respiration
Energy Conversion
Why?
• Convert energy to forms usable by cells
– Chemical bond energy  ATP energy
– ATP via chemiosmosis; NADH via redox reaction
– Electron transport
– Electrochemical proton concentration gradient
• Have store of ATP & NADH molecules available
• Drive cellular processes
– Transportation of metabolites, organelles, etc…
– Locomotion of cell
– Synthesizing complex molecules
ATP = adenosine triphosphate
• Adenosine
– Adenine = nitrogenous purine base
– Ribose = a cyclic 5-carbon sugar
• Triphosphate
– Phosphate is negatively charged polyatomic ion
– Placing phosphates near each other requires work
– Energy of electrostatic repulsion is stored in bond
– Broken bond releases energy for doing work
Who?
• Aerobic bacteria
• All aerobic eukaryotic organisms
– 1000 to 2000 mitochondria in each liver cell
– Mitochondria associated with microtubules
– May move in cytoplasm or be fixed in location
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Concentrated in areas of high energy demands
Form long chains with each other
Wrapped around flagellum
Packed between cardiac myofibrils
Where?
• Mitochondrion is site of oxidative respiration
• Mitochondria have double membranes
– Inner vs. outer membrane
• Outer membrane has transport proteins & large pores
• Inner membrane is selectively permeable; forms cristae
• Membranes create 2 internal compartments
– Matrix is inside organelle
• Enzyme-rich mixture, mDNA, ribosomes, tRNA, etc…
– Intermembrane space is between membranes.
• Site of ATP synthesis
When?
• Begins when large amounts of acetyl
coenzyme A (acetyl CoA)are produced in the
matrix space
• Major fuel is acetyl CoA from pyruvate usually
• Stores of fatty acids & glycogen fuel process
– Fats are stored in adipose tissue (fuel for 1 month)
– Glycogen/ glucose is stored in liver (fuel for 1 day)
– Glucose via glycolysis yields pyruvate
When else?
• Fats can be broken down into fatty acids and
glycerol
– Glycerol broken down in glycolysis to pyruvate
– Fatty acids broken down into 2-C fragment
• Proteins can be broken down into amino acids
– Certain amino acids can lose NH3 to form pyruvate
– Some amino acids minus NH3 form 2-C fragment
• Pyruvate/2-C fragment (acetyl CoA) enters
mitochondria for citric acid cycle
How?
• Glycolysis
– Sugar is broken down into pyruvic acid + 2 ATP
• Citric acid cycle (Kreb’s cycle)
– Acetyl CoA from pyruvate enters cycle
– H2O supplies extra O2 & H+
– 2 CO2 + 2 NADH + FADH2 + 2 GTP exit
• Electron transport chain
– Electrons from NADH move down chain
– 26 ATP formed via ATP synthase
Anaerobic: Step 1
• Glycolysis
C6H12O6  2 C3H3O3- + 2 ATP + 2 NADH (net)
Glucose via 9 steps is broken down into 2 pyruvates
• 3-C Pyruvate  2-C acetyl CoA + CO2
Citric Acid Cycle: Step 2
• Citric acid cycle (Kreb’s cycle) in matrix
Pyruvate  Acetyl CoA + CO2 + NADH
Acetyl CoA enters Kreb’s cycle
Kreb’s has 8 enzymatic reactions that harvest electrons
NAD+ accepts electrons  NADH carries electrons
CO2 + electrons (NADH + FADH2) + 2 ATP & H+
movement are end products
Electron Transport Chain
• Oxidative phosphorylation
– In inner mitochondrial membrane
– Electrons are delivered by NADH
– Electrons move down chain of proteins
– H+ build up in mitochondrial intermembrane space
due to movement of electrons
ATP synthase is powered by H+ movement across
membrane
 26 ATP are produced
½ O2 + 2 H+  H2O {oxygen is final electron acceptor)
Final Count
• Glucose + oxygen  carbon dioxide + water +
38 ATP