Abstract Cells “breathe” by a process known as cellular respiration. This can be aerobic or anaerobic. To test how anaerobic respiration works, yeast was used for fermentation, a form of anaerobic respiration. To test cellular respiration with the presence of oxygen, mitochondria from lima beans were evaluated.
Cellular Respiration Just like humans break down food into energy, cells break down molecules to generate energy called adenosine triphosphate (ATP). These broken down molecules are organic, composed of stored energy that break down and release energy to eventually create ATP. ATP fuels the cells of the bodies, which cannot survive without it. This process of breaking down organic molecules to create ATP is called cellular respiration. Cellular respiration sometimes occurs in the cytoplasm, although mostly takes place in the mitochondrial matrix (Figure 1). The stages of cellular respiration include, glycolysis, pyruvate oxidation, the citric acid cycle (known as the kreb’s cycle) and oxidation phosphorylation (which includes the electron transport chain and ATP synthase).
Figure 1: Metabolism in a eukaryotic cell: Glycolysis, the citric acid cycle, and oxidative phosphorylation: Glycolysis takes place in the cytoplasm. Within the mitochondrion, the citric acid cycle occurs in the mitochondrial matrix, and oxidative metabolism occurs at the internal folded mitochondrial membranes (cristae).
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Glycolysis is the first process of cellular respiration and is the only process that occurs in the cytoplasm. The end product of glycolysis is pyruvate. Pyruvate oxidation, the citric acid cycle, and oxidation phosphorylation take place in the mitochondrial matrix. Pyruvate oxidation creates acetyl CoA, the molecule needed for the citric acid cylce to begin (“Cell Energy and Cell Functions.”).
The citric acid cycle generates the energy for oxidative phosphorylation. Oxidative phosphorylation requires oxygen to function, whereas the other three processes of cellular respiration do not. The basic molecular break down of cellular respiration is (Upadhyaya, 68):
C6H12O6 + 6O2 → 6CO2 6H2O + Energy (ATP)
Oxygen is added to a carbohydrate, signified by the molecular formula for glucose, which in turn forms carbon dioxide, water and releases energy that will be used to make ATP. Eukaryotic cells and many types of prokaryotic cells perform cellular respiration. Eukaryotic cells may perform fermentation, although most cannot live long without oxygen. Some types of prokaryotic organisms, called facultative anaerobes, can survive in aerobic and anaerobic environments. Obligate anaerobes cannot live in the presence of oxygen and live only by anaerobic respiration or fermentation (Reece, 179).
Fermentation is similar to glycolysis, breaking down glucose molecules, although the end products are alcohol, or lactic acid, and CO2 (Goddard, 352).
The molecular formula is represented (Upadhyaya, 68):
C6H12O6 → 2C2H5OH + 2CO2 + Energy (ATP)
The first step of fermentation converts glucose into pyruvate. Pyruvate can be further transformed into two different senarios-CO2 and acetylaldehyde, known as alcohol fermentation, or lactic acid, which is called lactic acid fermentation. The fermentation experiment evaluated was focused on alcohol fermentation from yeast. Fermentation is similar to glycolysis although after pyruvate is made, oxygen is not present and therefore does not continue on to cellular respiration. In both cellular respiration and fermentation, understanding the pathways is importance in order to understand how cells are able to survive.
Goals of Experiment 1 Monosaccharides, composed of one sugar molecule, disaccharides, composed of 2 sugars molecules, and polysaccharides,