A Brief History of Respiration How cells get their ATP. How cells get their ATP. There are three parts— glycolysis, the Krebs cycle, and the electron transport chain. There are three parts— glycolysis, the Krebs cycle, and the electron transport chain. Total ATP count from all of these parts is about 36. Total ATP count from all of these parts is about 36. This is what respiration looks like if you’re a chemist: C 6 H O 2 → 6CO 2 + 6H 2 O + ≈ 36 ATP This is what respiration looks like if you’re a chemist: C 6 H O 2 → 6CO 2 + 6H 2 O + ≈ 36 ATP

Glycolysis! Occurs in the cytoplasm and produces 2 net ATP (although it produces 4 ATP total) Occurs in the cytoplasm and produces 2 net ATP (although it produces 4 ATP total) Six-carbon glucose is converted into two three-carbon pyruvates. Six-carbon glucose is converted into two three-carbon pyruvates. Glucose Priming Glucose Priming Phosphates from 2 ATP are added to the glucose, but this makes it unstable, so it breaks into 2 G3P (a 3-carbon glucose/phosphate compound). Phosphates from 2 ATP are added to the glucose, but this makes it unstable, so it breaks into 2 G3P (a 3-carbon glucose/phosphate compound). Oxidation Oxidation G3P are converted into pyruvate. G3P lose 2 electrons and 1 proton each to NAD+, which become NADH. G3P are converted into pyruvate. G3P lose 2 electrons and 1 proton each to NAD+, which become NADH. G3P donate two phosphates to ADP, in a process called substrate level phosphorylation. G3P donate two phosphates to ADP, in a process called substrate level phosphorylation. ANIMATION! ANIMATION! ANIMATION!

IMPORTANT QUESTION: Do we have oxygen? If not, cells undergo fermentation. If not, cells undergo fermentation. The 2 pyruvate from glycolysis accept H from NADH. The 2 pyruvate from glycolysis accept H from NADH. In bacteria and yeast, this produces ethanol, and CO 2 is released. In bacteria and yeast, this produces ethanol, and CO 2 is released. In mammals, this produces lactic acid. Too much lactic acid = pain. In mammals, this produces lactic acid. Too much lactic acid = pain. If so, pyruvate is oxidized and the Krebs cycle begins. If so, pyruvate is oxidized and the Krebs cycle begins.

Pyruvate Oxidation and the Krebs Cycle! Pyruvate Oxidation Pyruvate Oxidation Occurs in the mitochondria. Occurs in the mitochondria. -1 C from pyruvate; produces CO 2 waste. New molecule is called acetyl, and another NAD+ becomes NADH. -1 C from pyruvate; produces CO 2 waste. New molecule is called acetyl, and another NAD+ becomes NADH. Acetyl + coenzyme A = Acetyl CoA. Acetyl + coenzyme A = Acetyl CoA. Krebs Cycle (citric acid cycle) Krebs Cycle (citric acid cycle) Occurs in the matrix. Occurs in the matrix. 6CO 2 waste, NADH and FADH2 electron carriers also produced. 6CO 2 waste, NADH and FADH2 electron carriers also produced. Happens twice per glucose molecule. Happens twice per glucose molecule. ANIMATION! ANIMATION! ANIMATION!

ETC! Also in the mitochondria, on the cristae. Also in the mitochondria, on the cristae. NADH and FADH 2 produced in the Krebs Cycle are oxidized. NADH and FADH 2 produced in the Krebs Cycle are oxidized. Complexes containing heme lie across the folded membrane (they are transmembrane proteins) and pass electrons down from one complex to another. Complexes containing heme lie across the folded membrane (they are transmembrane proteins) and pass electrons down from one complex to another. As the electrons travel down the chain this happens, the protons that had been connected to those electrons are pushed into the intermembrane space. The concentration there becomes great enough for chemiosmosis to occur. As the electrons travel down the chain this happens, the protons that had been connected to those electrons are pushed into the intermembrane space. The concentration there becomes great enough for chemiosmosis to occur.

ETC! The protons go back into the matrix to achieve concentration equilibrium, but must pass through ATP synthase first. (This is facilitated diffusion.) The protons go back into the matrix to achieve concentration equilibrium, but must pass through ATP synthase first. (This is facilitated diffusion.) Three protons are needed to create ATP. About 34 molecules of ATP are created per molecule of glucose. Three protons are needed to create ATP. About 34 molecules of ATP are created per molecule of glucose. The left over electrons join with oxygen and the protons to make H 2 O. The left over electrons join with oxygen and the protons to make H 2 O. Animation! Animation! Animation!