Lecture #18 Cellular Respiration AP Biology Lecture #18 Cellular Respiration

Carbon dioxide, water are required Oxygen is released 1) Water is split by light energy. Oxygen escapes. Coenzymes pick up electrons, H+. 2)  ATP energy drives synthesis of glucose from hydrogen and electrons, plus carbon and oxygen (from CO2). Carbon dioxide, water are required Oxygen is released Carbon dioxide, water are released 1) Glucose is degraded to CO2 and water. Coenzymes pick up electrons, hydrogen. 2)  Coenzymes give up electrons, hydrogen to oxygen-requiring transfer chains that release energy to drive ATP formation. Oxygen is required Figure 7.2 Page 112 ATP is available to drive cellular tasks

Linked Processes Photosynthesis Aerobic Respiration Anabolic Pathway Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Catabolic Pathway Energy-releasing pathway Requires oxygen Releases carbon dioxide

What is Cellular Respiration? The process of converting food energy into ATP energy C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP

Why are both Photosynthesis and Cell Respiration important to Ecosystems? Light is the ultimate source of energy for all ecosystems Chemicals cycle and Energy flows Photosynthesis and cellular respiration are opposite reactions

Why do plants need both chloroplasts and mitochondria? Chloroplasts use energy from the sun to make glucose Mitochondria convert glucose to ATP—the energy currency of the cell

What is ATP? Adenosine Triphosphate Energy currency of the cell 5-Carbon sugar (Ribose) Nitrogenous base (Adenine) 3 Phosphate groups Energy currency of the cell The chemical bonds that link the phosphate groups together are high energy bonds When a phosphate group is removed to form ADP and P, small packets of energy are released

How is ATP used? As ATP is broken down, it gives off usable energy to power chemical work and gives off some nonusable energy as heat. Synthesizing molecules for growth and reproduction Transport work – active transport, endocytosis, and exocytosis Mechanical work – muscle contraction, cilia and flagella movement, organelle movement

Why use ATP energy and not energy from glucose? Breaking down glucose yields too much energy for cellular reactions and most of the energy would be wasted as heat. 1 Glucose = 686 kcal 1 ATP = 7.3 kcal 1 Glucose → 36 ATP How efficient are cells at converting glucose into ATP? 38% of the energy from glucose yields ATP, therefore 62% wasted as heat.

Cellular Respiration is a Redox Reaction (Oxidation) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O Oxidation is the loss of electrons or H+ Reduction is the gain of electrons or H+ Glucose is oxidized when electrons and H+ are passed to coenzymes NAD+ and FAD before reducing or passing them to oxygen. Glucose is oxidized by a series of smaller steps so that smaller packets of energy are released to make ATP, rather than one large explosion of energy. (Reduction)

Cell Respiration can be divided into 4 Parts: 1) Glycolysis 2) Oxidation of Pyruvate / Transition Reaction 3) The Krebs Cycle 4) The Electron Transport Chain and Chemiosmotic Phosphorylation

Where do the 4 parts of Cellular Respiration take place? Glycolysis: Cytosol Oxidation of Pyruvate: Matrix The Krebs Cycled: Electron Transport Chain and Cheimiosmotic Phosphorylation: Cristae

Parts of the Mitochondria

Anaerobic Respiration (no oxygen required, cytoplasm) Glycolysis (substrate level) Glucose  4 ATP (Net 2 ATP) 2 ATP 2 NADH 2 Pyruvate Aerobic Respiration (oxygen required, mitochondria) 2. Oxidation of Pyruvate 2 Pyruvate  2 CO2 2 NADH 2 Acetyl CoA Krebs Cycle (substrate level) 2 Acetyl CoA  4 CO2 2 ATP 6 NADH 2 FADH2 Electron Transport Chain (chemiosmotic) 10 NADH  32 ATP 2 FADH2 6 H2O 6 O2 Total: 36 ATP produced

ATP is made in two ways: 1) Substrate Level Phosphorylation (glycolysis & Krebs cycle) 2) Chemiosmotic Phosphorylation (electron transport chain) Substrate-Level Phosphorylation: Energy and phosphate are transferred to ADP using an enzyme, to form ATP. Phosphate comes from one of the intermediate molecules produced from the breakdown of glucose.

Glycolysis Glucose  2 Pyruvate 2 ATP 4 ATP (Net 2 ATP) 2 NADH Glucose (C6) is split to make 2 Pyruvates (C3) 1st: ATP energy used to phosphorylate glucose (stored energy) 2nd: phosphorylated glucose broken down into two C3 sugar phosphates 3rd: the sugar phosphates are oxidized to yield electrons and H+ ions which are donated to 2 NAD+ → 2 NADH (stored electron and hydrogen for the Electron Transport Chain) 4th: The energy from oxidation is used to make 4 ATP molecules (net 2 ATP) This is substrate level phosphorylation because an enzyme transfers phosphate to ADP making ATP Glycolysis produces very little ATP energy, most energy is still stored in Pyruvate molecules.

Oxidation of Pyruvate /Transition Reaction 2 Pyruvate  2 CO2 2 NADH 2 Acetyl CoA When Oxygen is present, 2 Pyruvates go to the matrix where they are converted into 2 Acetyl CoA (C2). Multienzyme complex: 1st: each Pyruvate releases CO2 to form Acetate. 2nd: Acetate is oxidized and gives electrons and H+ ions to 2 NAD+ → 2 NADH. 3rd Acetate is combined with Coenzyme A to produce 2 Acetyl CoA molecules. 2 NADH’s carry electrons and hydrogens to the Electron Transport Chain.

The Krebs Cycle / Citric Acid Cycle 2 Acetyl CoA  4 CO2 2 ATP 6 NADH 2 FADH2 8 Enzymatic Steps in Matrix of Mitochondria: Break down and Oxidize each Acetyl CoA (2-C’s) to release 2 CO2 and yield electrons and H+ ions to 3 NAD+ + 1 FAD → 3 NADH + FADH2. This yields energy to produce ATP by substrate level phosphorylation. The first step of the Krebs cycle combines Oxaloacetate (4 C’s) with Acetyl CoA to form Citric Acid, then the remaining 7 steps ultimately recycle oxalacetate. Two Turns of the Krebs Cycle are required to break down both Acetyl Coenzyme A molecules. The Krebs cycle produces some chemical energy in the form of ATP but most of the chemical energy is in the form of NADH and FADH2 which then go on to the Electron Transport Chain.

The Electron Transport Chain 10 NADH  32 ATP 2 FADH2 H2O Oxygen NADH and FADH2 produced earlier, go to the Electron Transport Chain. NADH and FADH2 release electrons to carriers/proteins embedded in the membrane of the cristae. As the electrons are transferred, H+ ions are pumped from the matrix to the intermembrane space up the concentration gradient. Electrons are passed along a series of 9 carriers until they are ultimately donated to an Oxygen molecule. ½ O2 + 2 electrons + 2 H+ (from NADH and FADH2) → H2O. http://vcell.ndsu.nodak.edu/animations/etc/movie.htm

Chemiosmotic Phosphorylation Hydrogen ions travel down their concentration gradient through a channel protein coupled with an enzyme called ATP Synthase. As H+ ions move into the matrix, energy is released and used to combine ADP + P → ATP. Hydrogens are recycled and pumped back across the cristae using the Electron Transport Chain. ATP diffuses out of the mitochondria through channel proteins to be used by the cell. http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

ATP Synthase Multisubunit complex with 4 parts: Rotor – spins as H+ ions flow Stator – holds the rotor and knob complex together in the cristae Internal Rod – extends between rotor and knob, spins when rotor spins which then turns the knob Knob – contains 3 catalytic sites that when turned change shape and activate the enzyme used to make ATP

Review ATP Production: 1) Glycolysis → 2 ATP 2) Oxidation of Pyruvate → No ATP 3) The Krebs Cycle → 2 ATP 4) The Electron Transport Chain and Chemiosmotic Phosphorylation: Each NADH produces 2-3 ATP so 10 NADH → 28 ATP Each FADH2 produces 2 ATP so 2 FADH2 → 4 ATP Total = 36 ATP 1 Glucose = 686 kcal 1 ATP = 7.3 kcal 1 Glucose → 36 ATP How efficient are cells at converting glucose into ATP? 38% of the energy from glucose yields ATP, therefore 62% wasted as heat (used to maintain body temperature or is dissipated) Ex. Most efficient Cars: only 25% of the energy from gasoline is used to move the car, 75% heat.

All Types of Molecules can be used to form ATP by Cell Respiration: Proteins, Carbohydrates, and Lipids must first be broken down into their monomers and absorbed in the small intestine. Monomers may be further broken down into intermediate molecules before entering different parts of Cell respiration to ultimately form ATP.

Anaerobic Respiration: Fermentation If there is NO oxygen, then cells can make ATP by Fermentation Without oxygen, Oxidation of Pyruvate and the Electron Transport Chain do not operate. Glucose → Pyruvate → Lactate NAD+ Glycolysis 2 NADH Reduction Rxn or 2 ATP Alcohol + CO2 Fermentation yields a net gain of 2 ATP by substrate level phosphorylation for every 1 Glucose. (Inefficient) Two Forms of Fermentation: Lactic Acid Fermentation (animals) Alcohol Fermentation (yeast)