Biology Poster

Cellular Respiration

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Link Reaction

1) Glycolysis: Produces ATP and NADH. Glucose is split apart and oxidized, resulting in a three carbon molecule called pyruvate, that still has lots of potential energy

What is "Link Reaction"- The link reaction refers to a stage in cellular respiration that “links” two other stages. The link reaction takes the products of the first stage, glycolysis, and converts them into reactants that will enter the Krebs cycle The Process - Pyruvate is transported from the cytoplasm into the mitochondrial matrix by carrier proteins on the mitochondrial membrane. - The pyruvate loses a carbon atom (decarboxylation), which forms a carbon dioxide molecule - The 2C compound then forms an acetyl group when it loses hydrogen atoms via oxidation (NAD+ is reduced to NADH + H+) - The acetyl compound then combines with coenzyme A to form acetyl CoA - As glycolysis splits glucose into two pyruvate molecules, the link reaction occurs twice per molecule of glucose. - Per glucose molecule, the link reaction produces acetyl CoA (×2), NADH + H+ (×2) and CO2 (×2)

2) Link Reaction: Pyruvate diffuses into the mitochondrial matrix and gets oxidized to produce more NADH. In this process a carboxyl group is removed, leaving a two carbon molecule called acetyl Co-A.

3) Krebs Cycle: This two-carbon acetyl Co-A still has plenty of potential energy. In the Krebs Cycle, this energy is harvested to generate ATP, NADH, and FADH2.

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4) ETC (Electron Transport Chain): In the ETC, the cell harvests the electon energy it stored away in the reduced mobile electron carriers NADH and FADH2. The majority of the ATP generated during cellular respiration is synthesised in this final step.

Krebs Cycle

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What is Krebs Cycle?The Krebs Cycle is a series of chemical reactions that produce ATP as part of the metabolism of aerobic organisms. The Process - In the Krebs cycle, acetyl CoA transfers its acetyl group to a 4C compound (oxaloacetate) to make a 6C compound (citrate) - Coenzyme A is released and can return to the link reaction to form another molecule of acetyl CoA - Over a series of reactions, the 6C compound is broken down to reform the original 4C compound (hence, a cycle) - Two carbon atoms are released via decarboxylation to form two molecules of carbon dioxide (CO2) - Multiple oxidation reactions result in the reduction of hydrogen carriers (3 × NADH + H+ ; 1 × FADH2) - One molecule of ATP is produced directly via substrate level phosphorylation - As the link reaction produces two molecules of acetyl CoA (one per each pyruvate), the Krebs cycle occurs twice - Per glucose molecule, the Krebs cycle produces: 4 × CO2 ; 2 × ATP ; 6 × NADH + H+ ; 2 × FADH2 Key Takeaway In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide.

Glycolysis

Phases of Glycolysis

1) Phosphorylation: - Glucose phosphorylated by 2 ATP molecules. - Unstable + reactive hexose triphosphate formed 2) Lysis: - Hexose triphosphate is split into two triose phosphates.

3) Oxidation: - Hydrogen atoms are removed from each 3C (oxidation) to reduce NAD+ into NADH. - Two molecules of NADH produced in total 4) ATP Formation: - Energy from sugar intermediate directly synthesises ATP. - Substrate level phosphorylation takes place. 2 ATP per 3C sugar produced

What is Glycolysis: A process in which glucose is partially broken down by cells in enzyme reactions that do not need oxygen. Glycolysis is one method that cells use to produce energy. Purpose: Glycolysis gives a small net gain of ATP without the use of oxygen and occurs in the cytoplasm.

Depending on oxygen availability, the product, pyruvate, may be either subjected to aerobic or anaerobic respiration Aerobic Respiration If oxygen is present, the pyruvate is transported to the mitochondria for further breakdown (complete oxidation) - This further oxidation generates large numbers of reduced hydrogen carriers (NADH + H+ and FADH2) - In the presence of oxygen, the reduced hydrogen carriers can release their stored energy to synthesise more ATP Anaerobic Respiration - If oxygen is not present, pyruvate is not broken down further and no more ATP is produced (incomplete oxidation) - The pyruvate remains in the cytoplasm and is converted into lactic acid or ethanol and CO2 - Glycolysis involves oxidation reactions that cause hydrogen carriers (NAD+) to be reduced (becomes NADH + H+) - In the absence of oxygen, glycolysis will quickly deplete available stocks of NAD+, preventing further glycolysis. - Fermentation of pyruvate involves a reduction reaction that oxidises NADH (releasing NAD+ to restore available stocks) - Hence, anaerobic respiration allows small amounts of ATP to be produced (via glycolysis) in the absence of oxygen

The Electron Transfer Channel

Oxidative phosphorylation occurs over a number of distinct steps: - Proton pumps create an electrochemical gradient (proton motive force) - ATP synthase uses the subsequent diffusion of protons (chemiosmosis) to synthesise ATP - Oxygen accepts electrons and protons to form water

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- The final stage of aerobic respiration is the electron transport chain, which is located on the inner mitochondrial membrane - The inner membrane is arranged into folds (cristae), which increases the surface area available for the transport chain. - The electron transport chain releases the energy stored within the reduced hydrogen carriers in order to synthesise ATP. - This is called oxidative phosphorylation, as the energy to synthesise ATP is derived from the oxidation of hydrogen carriers