Biology: Cellular Metabolism Cheat Sheet

Glycolysis
• Inside cytoplasm
• Anaerobic
• Glucose converted into pyruvate -> Breaks one glucose molcule (six carbons) into two pyruvate molecules (3 carbons).
• NAD⁺ reduced -> NADH
• 2 ATP produced to start the process
• NADH are used by electron transport chain to produce a lot more ATP molecules

Pyruvate Oxidation
• Electrons and hydrogen ions moving from pyruvate to the electron acceptor NAD⁺ to produce more NADH molecules
• A carbon atom is removed from each pyruvate, leaving a 2 carbon molecule to combine with coenzyme A.
• The final product is acetyl­-Co­enzyme A (acety­l-CoA)
• The removed Carbon merges with oxygen making CO2

Krebs Cycle - Citric Acid Cycle
• Occurs in matrix of mitoch­ondria
• Aerobic - In this case, does not use up oxygen
• Acetyl-CoA (2 carbons) -> Oxaloa­cetic acid (4 carbons) = Citric acid (6 carbons)
• During the cycle carbon is removed to produce CO2, electrons and hydrogen ions are transf­erred to NAD+ and FAD forming NADH and FADH2.
• This leaves overall 6 NADH, 2 ATP, 2 FADH2

• NAD+ and FAD are coenzymes that, when changed into NADH and FADH2, supply the electrons and hydrogen ions needed for the electron transport chain.
• Proton pumps are proteins in the membrane that transport hydrogen ions across it.
• These proton pumps are found in the cristae, the inner part of the mitoch­ondrial membrane. They move hydrogen ions from inside the mitoch­ondria to the space between the inner and outer membranes, creating a concen­tration gradient.
• The high concen­tration of hydrogen ions in this space is vital because it stores energy that is used to produce ATP.
• Due to the tendency of molecules to reach equili­brium, the hydrogen ions in the interm­embrane space naturally want to move back into the matrix of the mitoch­ondria. ATP synthase is the protein that allows this movement to occur.
• Chemio­smosis is the process where a chemical gradient (H+ ions) is used to generate ATP molecules by passing through ATP synthase, which converts ADP into ATP.

• As NADH and FADH2 release their hydrogen ions (H+) into the interm­embrane space, their electrons pass through membrane proteins.
• The transfer of H+ ions into the interm­embrane space is powered by active transport, with the energy sourced from the movement of electrons through the electron transport proteins.

• Once carried by the membrane proteins, hydrogen ions and electrons must unite with oxygen.
• Without this union, they would accumulate in the mitoch­ond­ria­'s matrix, causing electrons to react with other molecules and protons to create acidity.
• Oxygen serves as the ultimate electron acceptor in our cells. The electrons and protons (H+) that traverse the ETC and ATP synthase join with oxygen to create water molecules.

• Occurs in the cytoplasm
• Anaerobic - in the absence of oxygen organisms rely exclus­ively on • glycolysis to produce ATP
• NADH that is made during glycolysis must get rid of electrons to regenerate NAD⁺
• With the recycling of NAD⁺ glycolysis is allowed to continue