C₆H₁₂O₆ + 6O₂ -----> 6CO₂ + 6H₂0 + energy (heat and ATP)

Adenosine triphosphate (ATP)

• Energy carrying molecule used by cells to fuel their cellular processes

• ATP is composed of an adenine base, ribose sugar, & 3 phosphate (PO₄) groups

• The PO₄ bonds are high-energy bonds that require energy to be made & release energy when broken

• ATP is made & used continuously by cells

• Every minute all of an organism's ATP is recycled

• Phosphorylation refers to the chemical reactions that make ATP by adding P_i to ADP

  ADP + P_i + energy «  ATP + H₂O

   

• Enzymes  (ATP synthetase& ATPase) help break & reform these high energy PO₄ bonds in a process called substrate-level phosphorylation

• When the high-energy phosphate bond is broken, it releases energy, a free phosphate group, & adenosine diphosphate (ADP)

Enzymes in Metabolic Pathways:

• Biological catalysts
• Speeds up chemical reactions
• Lowers the amount of activation energy needed by weakening existing bonds in substrates

• Highly specific protein molecules
• Have an area called the active site where substrates temporarily join

  

   

• Form an enzyme-substrate complex to stress bonds
• Enzyme usable

enzyme substrate complex
 

 

NADH: A second energy carrying molecule in the mitochondria; produces 3 ATP

FADH₂: A third energy carrying molecule in the mitochondria; produces 2 ATP

Mitochondria:

• Has outer smooth, outer membrane & folded inner membrane
• Folds are called cristae
• Space inside cristae is called the matrix & contains DNA & ribosomes
• Site of aerobic respiration
• Krebs cycle takes place in matrix
• Electron Transport Chain takes place in cristae 

Cellular Respiration Overview:

C₆H₁₂O₆ + 6O₂ -----> 6CO₂ + 6H₂0 + energy (heat and ATP)

• Controlled release of energy from organic molecules (most often glucose)
• Glucose is oxidized (loses e-) & oxygen is reduced (gains e-)
• The carbon atoms of glucose (C₆H₁₂O₆) are released as CO₂
• Generates ATP (adenosine triphosphate)

• The energy in one glucose molecule may be used to produce 36 ATP
• Involves a series of 3 reactions --- Glycolysis, Kreb's Cycle, & Electron Transport Chain

Glycolysis:

• Occurs in the cytoplasm
• Summary of the steps of Glycolysis:

  a. 2 ATP added to glucose (6C) to energize it.

  b. Glucose split to 2 PGAL (3C). (PGAL = phosphoglyceraldehyde)

  c. H+ and e- (e- = electron) taken from each PGAL & given to make 2 NADH.

  d. NADH is energy and e- carrier.

  e. Each PGAL rearranged into pyruvate (3C), with energy transferred to make 4 ATP (substrate phosphorylation).

  f. Although glycolysis makes 4 ATP, the net ATP production by this step is 2 ATP (because 2 ATP were used to start glycolysis). The 2 net ATP are available for cell use.

  g. If oxygen is available to the cell, the pyruvate will move into the mitochondria & aerobic respiration will begin.

  
  

   

  Net Yield from Glycolysis

  4 NADH2

  2 CO2

  4 ATP ( 2 used to start reaction)

h. If no oxygen is available to the cell (anaerobic), the pyruvate will be fermented by addition of 2 H from the NADH (to alcohol + CO2 in yeast or lactic acid in muscle cells). This changes NADH back to NAD+ so it is available for step c above. This keeps glycolysis going!

Alcoholic Fermentation

Aerobic Respiration:

• Occurs in the mitochondria

• Includes the Krebs Cycle & the Electron Transport Chain

• Pyruvic acid from glycolysis diffuses into matrix of mitochondria & reacts with coenzyme A to for acetyl-CoA (2-carbon compound)

• CO₂ and NADH are also produced

Kreb's Cycle:

• Named for biochemist Hans Krebs

• Metabolic pathway that indirectly requires O₂ 

• Kreb's Cycle is also known as the Citric acid Cycle

• Requires 2 cycles to metabolize glucose

• Acetyl Co-A (2C) enters the Kreb's Cycle & joins with Oxaloacetic Acid (4C) to make Citric Acid (6C)

• Citric acid is oxidized releasing CO₂ , free H⁺, & e^- and forming ketoglutaric acid (5C)

• Free e^- reduce the energy carriers NAD⁺ to NADH₂ and FAD⁺ to FADH₂

• Ketoglutaric acid is also oxidized releasing more CO₂ , free H⁺, & e^-

• The cycle continues oxidizing the carbon compounds formed (succinic acid, fumaric acid, malic acid, etc.) producing more CO_2, NADH_2, FADH_2, & ATP

• H₂O is added to supply more H⁺

• CO₂ is a waste product that diffuses out of cells

• Oxaloacetic acid is regenerated to start the cycle again

• NADH₂ and FADH₂ produced migrate to the Electron Transport Chain (ETC)

Electron Transport Chain:

• Found in the inner mitochondrial membrane or cristae

• Contains 4 protein-based complexes that work in sequence moving H+ from the matrix across the inner membrane (proton pumps)

• A concentration gradient of H⁺ between the inner & outer mitochondrial membrane occurs

• H⁺ concentration gradient causes the synthesis of ATP by chemiosmosis

• Energized e^- & H+ from the 10 NADH₂ and 2 FADH₂ (produced during glycolysis & Krebs cycle) are transferred to O₂ to produce H₂O (redox reaction)

O₂  +  4e^-  +  4H⁺  2H₂O

• Most cells produce 36- 38 molecules of ATP per glucose (66% efficient)

• Actual number of ATP's produced by aerobic respiration varies among cells