Cellular Respiration Glycolysis Krebs and ETC Cellular Respiration

Cellular Respiration Glycolysis, Kreb’s, and ETC

Cellular Respiration The process used by heterotrophs to turn food (glucose) into energy (ATP) used to do work, and heat released to the environment. C 6 H 12 O 6 + 6 O 2 6 H 2 O + 6 CO 2 1 mole glucose = -686 kcal, and about 38 ATP per molecule

Redox Reactions 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

Step 1: Glycolysis Occurs in the cytoplasm of cells: even bacteria do it! It is a 10 step process that occurs in 2 phases It can occur whether or not oxygen is present: ANAEROBIC Evolved 3. 5 byo

Step 1: Glycolysis Input: One molecule of glucose Output: 2 molecules of pyruvate, 2 ATP, and 2 NADH C 6 H 12 O 6 2 C 3 H 6 O 3

Glycolysis: 2 NADH NAD+ is a molecule that accepts 2 electrons and 1 Hydrogen ion from glucose (it gains electrons = reduced) to become NADH Eventually, it releases the electrons to make ATP (it is oxidized back to NAD+)

Glycolysis: ATP is made through substrate level phosphorylation: an enzyme transfers a phosphate group from an organic substance to ADP

Transition step: Before the Kreb’s Cycle Input: The 2 pyruvates from glycolysis are oxidized to form 2 molecules of acetyl coenzyme A (acetyl co. A) These enter the Kreb’s Cycle one at a time.

Step 2: Kreb’s or Citric Acid Cycle It ONLY occurs in the presence of oxygen: AEROBIC It takes place in the mitochondrial matrix, the space between the inner folded membranes of the mitochondria

Kreb’s Cycle Acetyl co. A undergoes a series of redox reactions in the Kreb’s cycle, rearranging its formula and transferring electrons Output: for 2 TURNS of Kreb’s: 6 NADH, 2 FADH 2 (another electron carrier), and 2 ATP, and CO 2

Step 3: Electron Transport Chain It occurs in the cristae of the mitochondria, on the membranes on the inside Input: NADH and FADH 2 made in the first 2 steps (the H+ and the electrons are removed)

ETC The ETC is a series of increasingly electronegative proteins embedded in the cristae like a waterfall NADH and FADH 2 enter the first protein, and electrons “fall” down the chain As this occurs, hydrogen ions (H+), which have lost their electrons, are pumped to the outside of

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

ETC At the same time, the electrons from NADH and FADH 2 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 Output: water and 34 ATP, oxidized NAD+ and FAD molecules

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)

Fermentation and anaerobic respiration When oxygen is not present, cells still need ATP and go through fermentation instead. Pyruvate is still oxidized, but it produces much less ATP Bacteria and yeast: alcohol fermentation Fungi and bacteria, muscle cells: lactic acid fermentation Anaerobic respiration: bacteria can do oxidative phosphorylation in membrane pieces floating in the cytoplasm Note: Glycolysis was the first energy pathway to evolve (in bacteria 3. 5 byo, oxygen from