SBI 4U: Metablic Processes MITOCHONDRIA Oval shaped organelles; randomly scattered around the cytoplasm. Energy factories of the cell; produce the majority of the cell's ATP These ATP producing reactions cannot take place without oxygen, therefore the steps of cellular respiration that occur in the mitochondria are said to be aerobic. Pyruvate Oxidation (Link reaction), Krebs Cycle and the Electron Transport Chain (ETC) are all aerobic. Eukaryotes use mitochondria to produce cellular energy. Prokaryotes do these reactions in the cytoplasm and with much less energy being produced. Section 1.3

SBI 4U: Metablic Processes MITOCHONDRIA The mitochondria are double-membraned organelles. The folded inner membrane is known as cristae. The cristae has many proteins and other molecules embedded in it to help with the process of cellular respiration. The matrix is the protein rich fluid inside the cristae. The fluid-filled space between the two membranes is known as the intermembrane (-ous) space. Mitochondria have their own DNA, mtDNA, and can therefore reproduce on their own. This mtDNA is very similar to prokaryotic DNA and has lead to the creation of the endosymbiosis hypothesis which states that mitochondria are descendants of early prokaryotic cells who developed a symbiotic relationship with early eukaryotic cells. Section 1.3

PYRUVATE OXIDATION (LINK REACTION)‏ SBI 4U: Metablic Processes PYRUVATE OXIDATION (LINK REACTION)‏ The two pyruvates formed at the end of glycolysis are transported into the matrix In the matrix, under the control of a multi-enyzme, three changes occur. The carboxyl end is removed as carbon dioxide. This is known as a decarboxylation reaction and is catalyzed by pyruvate decarboxylase. Pyruvate becomes oxidized into acetate and NAD+ is reduced to NADH + H+ A sulfur-containing compound (coenzyme-A) is attached to the acetate, forming acetyl-coA. Section 1.3

SBI 4U: Metablic Processes PYRUVATE OXIDATION Co-A comes from vitamin B5 (pantothenic acid). The overall reaction: 2 pyruvate + 2NAD+ + 2 CoA --> 2 acetyl-CoA + 2NADH + 2H+ + 2CO2 Acetyl-coA enters the Kreb cycle, NADH go to the electron transport chain to produce ATP by oxidative phosphorylation Carbon dioxide diffuses out of the cell as a waste produt The protons (2H+) stay in the matrix. Acetyl-coA is the central molecule in energy metabolism. The majority of macromolecules that we use for catabolism are changed into acetyl-coA. Acetyl-coA can produce ATP or lipids. If you need energy you get it as acetyl-coA enters the Krebs Cycle. If you do not need energy then acetyl-coA is used to produce fat for energy storage. Section 1.3

SBI 4U: Metablic Processes KREBS CYCLE Founded by Hans Krebs (biochemist at the Univ. of Sheffield) in 1937. He won the Nobel Prize in 1953 along with Fritz Albert Lipmann who discovered the importance of coenzyme-A. An 8-step process with each step catalyzed by a specific enzyme. It is a cycle because the product of step 8 is the reactant in step 1 (oxaloacetate). Section 1.3

SBI 4U: Metablic Processes KREBS CYCLE The overall chemical equation is: Oxaloacetate + acetyl-coA + ADP + P + 3NAD+ + FAD --> CoA + ATP + 3NADH + 3H+ + FADH2 + 2CO2 + oxaloacetate By the end of the Krebs Cycle, the original glucose molecule is consumed. The six carbon atoms have left as carbon dioxide molecules. All that is preserved are 4ATP (two from glycolysis and two from the Krebs Cycle) and 12 reduced coenzymes: 2 NADH from glycolysis 2 NADH from pyruvate oxidation 6 NADH from the Krebs Cycle and 2 FADH2 from the Krebs Cycle Most of the energy from glucose will be produced in the next stage (ETC) Notice in the figure on page 103 that all the carbons in the original glucose molecule are transformed into carbon dioxide. Section 1.3