Cellular Respiration

Cellular Respiration Glycolysis, Kreb’s, and ETC

Cellular Respiration • How our body turns food and oxygen into ENERGY called ATP • Glycolysis • Kreb’s Cycle • ETC (Electron Transport Chain)

Redox Reactions • Chemistry review: • Oxidation = losing an electron • Reduction = gaining an electron • A redox reaction is a chemical reaction in which one molecule gains electrons and one loses them • Example of cellular respiration: glucose is oxidized into carbon dioxide, oxygen is reduced to water

Glycolysis • Glycolysis is the first step of cellular respiration • It means “splitting sugar” • One molecule of glucose is split in half into 2 molecules of pyruvic acid (pyruvate) • C6H12O6 2 C3H6O6

Glycolysis • Occurs in the cytoplasm of cells • It is a 10 step process that occurs in 2 phases • It can occur whether or not oxygen is present

Glycolysis • Input: glucose • Output: 2 molecules of pyruvate, 2 ATP, and 2 NADH • NADH is a molecule that carries electrons from glycolysis and the Kreb’s Cycle to the ETS (it gains electrons = reduced) • Once there, it releases the electrons to make ATP (it is oxidized to NAD+)

Kreb’s Cycle • Step 2 of Cellular Respiration is called the Kreb’s Cycle, and is also known as the Citric Acid Cycle • It ONLY occurs in the presence of oxygen • It takes place in the mitochondrial matrix, the space between the inner folded membranes of the mitochondria

Kreb’s Cycle • The 2 pyruvates from glycolysis are converted to 2 molecules of acetyl coenzyme A (acetyl coA) • This enters the Kreb’s Cycle one at a time. • For each original glucose molecule, the Kreb’s Cycle will spin twice, one for each acetyl coA

Kreb’s Cycle • Figure 9.6 Homework

Kreb’s Cycle • Acetyl coA undergoes a series of redox reactions in the Kreb’s cycle, rearranging its formula and transferring electrons • The net output for 2 TURNS of Kreb’s is: 6 NADH, 2 FADH2 (another electron carrier), and 2 ATP • A byproduct, carbon dioxide, is released

Electron Transport Chain • The last step is called the electron transport chain (ETC) or system (ETS), or oxidative phosphorylation (means losing electrons and adding a phosphate group to ADP to make ATP) • It occurs in the cristae of the mitochondria, on the membranes on the inside

ETC • The NADH and FADH2 molecules made in glycolysis and Kreb’s are what are used by the ETC to make ATP

ETC • The ETC is a series of proteins embedded in the cristae like a waterfall • NADH and FADH2 enter the highest protein, and as they “fall” down the waterfall, they pass their electrons down to more electronegative carriers • As this occurs, hydrogen ions (H+), which have lost their electrons, are pumped to the outside of the membrane

ETC • At the end of the chain, there is a big protein enzyme called ATP Synthase • The H+ ions flow down their concentration gradient through ATP synthase • ATP synthase spins around each time and generates enough energy to add a P to ADP, making ATP

ETC • As ADP is getting phosphorylized (called chemiosmosis), the electrons have reached the bottom of the waterfall • The electrons are attracted to a super electronegative atom, oxygen • Oxygen is the final electron acceptor. It gains electrons (is reduced) and joins with the H+ ions coming through ATP synthase to make water • We breathe out the water (along with the CO2 from Kreb’s)

ETC • At the end of the ETC, approximately 34 ATP are generated through the processes of Oxidative Phosphorylation (the electrons moving down the waterfall) and chemiosmosis (the diffusion of H+ ions through ATP synthase)

Summary • Oxygen we breathe in becomes water • Glucose we eat is used to make ATP and CO2 (waste) • A total of approximately 38 ATP are made per glucose molecule

Cellular Respiration