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PHOTOSYNTHESIS AND CELLULAR RESPIRATION by ASAK

CELLULAR RESPIRATION: GLYCOLYSIS, FERMENTATION, AND AEROBIC RESPIRATION

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Cellular Respiration

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 Glycolysis & Fermentation
 
     Glycolysis is one of the stages of cellular respiration. It is a biochemical pathway where 2 three-carbon moecules of pyruvic acid are produced as a result of the oxidation of 1 six-carbon molecule of glucose. During glycolysis, 2 phosphate groups attach to 1 glucose molecule and form a new 6-carbon compound with 2 phosphate groups. The compound is split into 2 three-carbon molecules of G3P. These molecules are oxidized and recieve a phosphate group. Two molecules of a new three-carbon compound are produced. The added phosphate groups are removed from the last compouds produced and 2 molecules of pyruvic acid are produced. Each phosphate group combines with a molecule of ADP to make 4 molecules of ATP.
      Fermentation is the combination of glycolysis and the additional pathways that occur in the cytosol. With this, NAD+ is regenerated. There are many different fermentation pathways that differ in terms of the compounds that are made from pyruvic acid and the enzymes that are used. There are 2 common fermentation pathways. They result in the production of lactid acid and ethyl alcohol.

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Fermentation of yeast is used to make alcoholic beverages and bread.

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Aerobic respiration takes place in the mitochondria of cells.

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Aerobic Respiration
 
Aerobic Respiration is the second part of cellular respiration. Aerobic respiration is the release of energy from glucose or another organic substrate in the presence of Oxygen. Aerobic means in air, but it is the Oxygen in the air which is necessary for aerobic respiration. This is the part of cellular respiration that most of the ATP is produced. After glycolysis, if oxygen is present in the cells environment, pyruvic acid is broken down and NADH is used to make a large amount of ATP through this process. Oxygen is important to aerobic respiration because oxygen allows additional electrons to pass along the chain and if they didn't ATP synthesis would stop. In aerobic respiration pyruvic acid is converted into Carbon Dioxide and water, producing a large amount of ATP. Aerobic respiration has two major stages known as the Krebs Cycle (named after a German biochemist, Hans Krebs), and the elctron transport chain. In the Krebs Cycle the oxidation of glucose is complete. The Krebs cycle takes 2 full turns during cellular respiration. In a prokaryote Aerobic respiration takes place in the cytosol, but in a eukaryote aerobic respiration takes place in the mitochondria.(The Krebs cycle in the mitochondrial matrix and the electron transport chain in the inner membrane.) Most of the ATP molecules are produced during the Krebs Cycle. It may make up to 34 molecules of ATP.
Krebs Cycle
1.Acetyl combines with Oxaloactic acid to produce citric acid.
2.The citric acid releases a carbon dioxide and a hydrogen atom.
3.The carbon compound formed in step 2 also releases a carbon dioxide and hydrogen atom. 
4.The new 4-carbon compound forms another 4-carbon compound by releasing a hydrogen atom.
5. Now, the new 4-carbon compound produced in step 4 releases a hydrogen atom to regenerate oxaloacetic acid, which keeps the Kreb cycle going.
 
 
The Electron Transport Chain
1.NADH and FADH2 give up electrons to the electron transport chain.
2.The molecules are passed down the chain. As they move through each molecule they lose more and more energy.
3.The energy lost from the electrons is used to pump protons from the matrix.
4.The concentration and electrical gradients of protons drive the synthesis of ATP by chemiosmosis (the same process that generates ATP in photosynthesis).As protons move through ATP synthase and down their concentrational and electrical gradients, ATP is made from ADP and phosphate.
5.Oxygen is the final acceptor of electrons that have been passed down the chain. The protons, electrons, and oxygen all combine to make water.     
 
      

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