Cellular Respiration

What is Cellular Respiration? The process of converting food energy into ATP energy C 6 H 12 O O 2 → 6 CO H 2 O + 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 –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 C 6 H 12 O O 2 → 6 CO H 2 O 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. (Oxidation) (Reduction)

Loss of hydrogen atoms Glucose Gain of hydrogen atoms Energy Reduction and Oxidation OILRIG Oxidation is losing electrons Reduction is gaining electrons Glucose gives off energy as is is oxidized

Reduction and Oxidation OILRIG Gain or loss of electrons is often in the form of hydrogen. The hydrogen is then passed to a coenzyme such as NAD+

Reduction and Oxidation What are some common co-enzymes? NAD+ and FAD NAD+ + 2 H  NADH + H+ FAD + 2 H  FADH 2 Remember that H = 2 electrons and 2H+

Reduction and Oxidation These co-enzymes are very important for cell respiration because they transfer high-energy electrons to electron transport systems (ETS).

Reduction and Oxidation As the electrons move from carrier to carrier, energy is released in small quantities. Electron transport system (ETS)

Generation of ATP There are two ways to generate ATP Chemiosmosis Substrate-Level Phosphorylation

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.

Carbohydrates Monosaccharides (CH 2 O) –Major cell nutrient, produced during PSN, raw material for other molecules. –6 Carbon sugars [Hexoses] Glucose, Fructose, Galactose –5 Carbon sugars [Pentose] Deoxyribose, Ribose

Fatty Acids Carbon backbone (4 – 24 carbon atoms) Carboxyl group (- COOH) Unsaturated –One or more double bonds in backbone Saturated –All single bonds in backbone

Dehydrogenases They are enzymes that remove a pair of hydrogen atoms (2 protons + 2 electrons) from the substrate (glucose) oxidizing it. The enzyme delivers the 2 electrons along with one proton to its coenzyme NAD+. The other proton is released as a hydrogen ion to the surrounding solution. H-C-OH+NAD + C=O+NADH+ H +

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 Chemiosmotic Phosphorylation

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

Parts of the Mitochondria

Anaerobic Respiration (no oxygen required, cytoplasm) 1.Glycolysis (substrate level) Glucose  2 Pyruvate 2 ATP4 ATP (Net 2 ATP) 2 NADH Aerobic Respiration (oxygen required, mitochondria) 2. Oxidation of Pyruvate 2 Pyruvate  2 CO 2 2 NADH 2 Acetyl CoA 3.Krebs Cycle (substrate level) 2 Acetyl CoA  4 CO 2 2 ATP 6 NADH 2 FADH 2 4.Electron Transport Chain (chemiosmotic) 10 NADH  32 ATP 2 FADH 2 H 2 O Oxygen 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 (C 6 ) is split to make 2 Pyruvates (C 3 ) –1 st : ATP energy used to phosphorylate glucose (stored energy) –2 nd : phosphorylated glucose broken down into two C 3 sugar phosphates –3 rd : 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) –4 th : 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. Glucose  2 Pyruvate 2 ATP4 ATP (Net 2 ATP) 2 NADH

Pyruvate Dehydrogenase catalyzes oxidative decarboxylation of pyruvate, to form acetyl-CoA. The overall reaction is shown at right.

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

The Krebs Cycle / Citric Acid Cycle 8 Enzymatic Steps in Matrix of Mitochondria: Break down and Oxidize each Acetyl CoA (2-C’s) to release 2 CO 2 and yield electrons and H + ions to 3 NAD FAD → 3 NADH + FADH 2. 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 FADH 2 which then go on to the Electron Transport Chain. 2 Acetyl CoA  4 CO 2 2 ATP 6 NADH 2 FADH 2

NAD vs FAD FAD (Flavin Adenine Dinucleotide) is a derivative of the B-vitamin riboflavin (dimethylisoalloxazine- ribitol). The flavin ring system undergoes oxidation/reduction. Whereas NAD+ is a coenzyme that reversibly binds to enzymes, FAD is a prosthetic group, that is permanently part of the complex. FAD (Flavin Adenine Dinucleotide) is a derivative of the B-vitamin riboflavin (dimethylisoalloxazine- ribitol). The flavin ring system undergoes oxidation/reduction. Whereas NAD+ is a coenzyme that reversibly binds to enzymes, FAD is a prosthetic group, that is permanently part of the complex.

The Electron Transport Chain NADH and FADH 2 produced earlier, go to the Electron Transport Chain. NADH and FADH 2 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 O electrons + 2 H + (from NADH and FADH 2 ) → H 2 O. 10 NADH  32 ATP 2 FADH 2 H 2 O Oxygen

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.

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 FADH 2 produces 2 ATP so 2 FADH 2 → 4 ATP Total = 36 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.

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 + CO 2 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)