Respiration

A metabolic pathway is a series of chemical reactions occurring within a cell. Each step is catalyzed by a specific enzyme and involves small changes in the energy and form of the substrate. The product of one enzyme will become the substrate for the next in the chain B C D Enzyme Substrate Product Enzyme Substrate Product Enzyme Substrate Product A Enzyme Substrate Product Metabolism Anabolic pathway e.g. Photosynthesis building up breaking down Catabolic pathway e.g. Respiration Metabolic Pathways

Respiration ii. Aerobic respiration which requires oxygen, is much more efficient than anaerobic and produces carbon dioxide and water as end products Respiration: The process by which organisms oxidise organic matter to release energy. There are two types: i. Anaerobic respiration: which does not require oxygen, is less efficient and which usually produces ethanol and carbon dioxide or lactic acid as end products.

ATP

ATP is a nucleotide made from: 1. The nitrogenous base Adenine 2. A pentose sugar Ribose 3. Phosphate groups ATP Structure

2. It is the major energy currency of cells entrapping or releasing energy in most metabolic pathways. 1. It is a coenzyme involved in many enzyme reactions in cells. 5. It is one of the monomers used in the synthesis of RNA and, after conversion to deoxyATP (dATP), DNA. ATP: Function 4. It is a small molecule so will diffuse rapidly around the cell to where it is needed. 3. The energy is released from ATP in a single step and in a small manageable amount.

* Hydrolysis: Decomposition of a substance by the insertion of water molecules between certain of its bonds. Food is digested by hydrolysis) * Free energy: The energy that can be harnessed to do work. When the third phosphate group of ATP is removed by hydrolysis, a substantial amount of free energy is released, the exact amount depends on the conditions. For this reason, this bond is known as a "high-energy" bond. The bond between the first and second phosphates is also "high-energy". But note that the term is not being used in the same sense as the term "bond energy". In fact, these bonds are actually weak bonds with low bond energies. ATP + H 2 O -> ADP + Pi ADP is adenosine diphosphate. Pi is inorganic phosphate. ATP: and energy

Although ATP is always formed in a cell from ADP and P, the energy needed for the conversion may be supplied in 3 possible ways: Triose Phosphate Pyruvate ATPADP + P Substrate level phosphorylation does not need oxygen - it is always anaerobic. ADP to ATP 1. Substrate level phosphorylation Here energy comes from an exergonic reaction such as the conversion of triose phosphate to pyruvate in glycolysis, or the conversion of α Ketoglutarate to Succinate in Krebs cycle. Exergonic reaction *Exergonic

ADP to ATP 2. Oxidative phosphorylation Here ATP is formed from ADP and P in oxidative phosphorylation on the mitochondrial cristae. Energy is supplied by the oxidation of hydrogen and so this process is aerobic. 3. Photophosphorylation Here ATP is formed from ADP and P on the granal lamellae within the chloroplast. Energy is supplied by sunlight. This process is anaerobic.

NAD

Nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP) are two important cofactors found in cells. NADH is the reduced form of NAD +, and NAD + is the oxidized form of NADH. It forms NADP with the addition of a phosphate group to the 2' position of the adenosyl nucleotide through an ester linkage. NAD is used extensively in glycolysis and the citric acid cycle of cellular respiration. The reducing potential stored in NADH can be converted to ATP through the electron transport chain or used for anabolic metabolism. ATP "energy" is necessary for an organism to live. Green plants obtain ATP through photosynthesis, while other organisms obtain it by cellular respiration. NAD Function

Cell respiration has 4 main stages 1. Glycolysis 3. Krebs cycle 4. Oxidative Phosphorylation 2. The Link Reaction Respiration

1. Glycolysis = carbohydrate-splitting 2. It occurs in the cytoplasm 3. It converts 6c, hexose sugar glucose into 3c pyruvate 4. It is an anaerobic process Glycolysis IB

P P GLYCOLYSIS 2. The glucose is given activation energy by being phosphorylated twice by ATP. 3. The phosphorylated hexose sugar now has enough energy to split into two triose sugars. CCCCCC CCCCCC Glucose ATP ADP ATP P P CCCCCC 1. Glycolysis starts in the cytoplasm with the 6 carbon (hexose) sugar Glucose. Triose phosphate Triose phosphate

P GLYCOLYSIS P CCC P CCC 4. One triose sugar (Dihydroxyacetone phosphate) is converted into the other triose sugar GP, (Glycerate phosphate). 5. Each of the two triose sugars are then phosphorylated again by inorganic phosphates. P CCC x 2 NAD Reduced NAD At the same time the triose sugar is oxidised, losing hydrogen; the hydrogen reducing the coenzyme NAD. CCC x 2 6. The triose sugars are then converted to Pyruvate in the process two ADPs for each triose are phosphorylated to ATP. This is called substrate level phosphorylation ADP ATP ADP ATP Gross ATP = 4, Net = 2 Oxidoreductase

Hexose x2 TRIOSE-P 2 PYRUVATE Energy Level 4 ATP 4 ADP + 2P i Energy used to split molecule GLYCOLYSIS ATP Hexose P Hexose x2P

Glycolysis Anaerobic Respiration Glycolysis is the first step in aerobic respiration. However on its own it is also the first part of Anaerobic respiration. Reduced NAD x2 Glucose GP x2 Pyruvate x2 x 2 ATP x 2 ADP x 4 ADP x 4 ATP Ethanol + CO 2 NAD x2 In yeast in the absence of oxygen the pyruvate is converted into ethanol and CO 2. This step regenerates the NAD from the reduced NAD. Without this there would be no NAD to allow the conversion of the GP to Pyruvate. Lactic acid Animals generally produce lactic acid instead of ethanol and CO 2. Gross ATP = 4, Net = 2

Mitochondria Outer Membrane Inner Membrane Matrix Cristae

The Link Reaction CCC Cytoplasm Mitochondria 7. The Pyruvate leaves the cytoplasm and enters the matrix of the mitochodria CCC CO 2 8. The three carbon pyruvate losses a carbon as carbon dioxide. (It is decarboxylated) Pyruvate CCC NAD Reduced NAD CC Coenzyme A At the same time the coenzyme NAD removes hydrogen from the pyruvate, the pyruvate is oxidised and the NAD reduced. The reaction is catalysed by an Oxidoreductase enzyme. Oxidoreductase 9. The two carbons from the pyruvate join with Coenzyme A to form Acetyl Coenzyme A. Excretion

Cytoplasm Mitochondria CC Coenzyme A The Link Reaction 10. The link reaction is a major crossroads in metabolism and Acetyl CoA can be formed from fatty acids as well as carbohydrates. CarbohydratesFatty acids

The Krebs Cycle 1. The Krebs Cycle occurs in the matrix of the mitochondria 2. Two carbon dioxide molecules are produced 3. One ADP is phosphorylated to ATP 4. Four coenzymes are reduced

Cytoplasm Mitochondrial matrix CC Coenzyme A CC 4C compound 6C compound NAD CO 2 x 2 Reduced NAD ATP ADP FAD x 3 Reduced FAD Krebs Cycle The Krebs Cycle 2. In a series of reactions the 6C compound is converted back to the 4C. In the process 3 NADs are reduced. In addition the coenzyme FAD is also reduced, both reductions are catalysed by oxidoreductase enzymes 1. Two carbons from Acetyl Coenzyme A pass to a 4 carbon (oxaloacetate) compound making a 6 carbon compound (citrate). 3. One ADP is phosphorylated to ATP 4. Two carbons are released as carbon dioxide

The Krebs Cycle x2 Reduced NAD Glucose GP Pyruvate x 2 ATP x 2 ADP x2 NAD x 4 ADP x 4 ATP Acetyl Coenzyme A x2 Reduced NAD x2 NAD 4C compound 6C compound CO 2 x2 F AD x2 Reduced FAD x6 Reduced NAD x6 NAD Respiration Summary Glycolysis produces a nett gain of x2 ATPs and two reduced NADs per glucose molecule. ATP Reduced NAD Reduced FAD The Link reaction produces 2 reduced NADs per glucose. The Krebs cycle produces 6 reduced NADs 2 reduced FADs and 2 ATPs per glucose. Six molecules of carbon dioxide are produced from the Link reaction and the Krebs cycle combined CO 2 ATP ADP x2

Oxidative Phosphorylation Reduced NAD NAD H+H+ The reduced NAD’s and reduced FAD in the mitochondria pass their hydrogen's and electrons to a chain of cytochrome carriers found in the cristae of the mitochondria. The cytochromes are alternately reduced and oxidised as they gain and lose electrons. This process separates the H+ from the electrons creating a proton gradient across the cristae. Cytochrome chain electrons H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Matrix

The H+ pass back through the membrane to the matrix through the stalked particles which are ATPase enzymes. So ultimately the energy contained in the reduced coenzymes is used to phosphorylate ADP to ATP. The final acceptor for the Hydrogen is Oxygen combining to producing water. The whole process is called oxidative phosphorylation. Oxidative phosphorylation in combination with the Krebs cycle and glycolysis form the pathways of aerobic respiration. This is much more efficient than anaerobic producing about 38 ATP as opposed to the net gain of 2 produced by anaerobic respiration. Reduced NAD NAD H+H+ Cytochrome chain electrons H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ADP ATP Hydrogens + Oxygen = Water Matrix Oxidative Phosphorylation

End

Glycolysis Glycolysis is the first step in aerobic respiration. In the first steps two ATP coenzymes donate energy to the glucose Reduced NAD Glucose 6C GP 3C (x2) Pyruvate 3C (x2) x 2 ATP x 2 ADP x 4 ADP x 4 ATP NAD This provides the activation energy to allow the glucose to split into two 3 carbon molecules which are then converted to pyruvate. In the process four molecules of ATP are produced, a net gain of two. Gross ATP = 4, Net = 2 IB