Lab  7
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Lab 7

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    Lab  7 Lab 7 Document Transcript

    • December 8, 2013 PRACTICAL CELL BIOLOGY LAB 7 Mitochondria Introduction Mitochondria called the “powerhouse” of the cell. While metaphorically correct, biochemical events occurring in this tiny organelle. For instance, it is now well known that these events are not only producing energy but also playing intriguing roles for immunity and cell death. The energy produced by mitochondria, is in the form of a molecule called adenosine triphosphate (ATP), which effectively stores energy in its chemical bonds between phosphate molecules. Making and breaking those bonds stores and releases energy, respectively. The ATP formed by mitochondria can be distributed throughout the cell to facilitate other chemical processes. Past and current mitochondrial research has been performed on mitochondria prepared from rat liver, rat heart, or beef heart. Toward the end of the 1980s, a new branch of human pathology began with the discovery of human disorders linked to mitochondrial dysfunction. Therefore, it became necessary to investigate and to study the status of mitochondria in human tissue. Actually we have to know that it is not always possible to obtain large amounts of human tissues for extracting mitochondria. The energy required to power living cells comes from the sun. Plants capture this energy and convert it to organic molecules. Animals in turn, can gain this energy by eating plants or other animals. The energy that powers our cells is obtained from the foods we eat. The most efficient way for cells to harvest energy stored in food is through cellular respiration, a catabolic pathway for the production of adenosine triphosphate (ATP). Glucose, derived from food, is broken down during cellular respiration to provide energy in the form of ATP and heat.
    • December 8, 2013 PRACTICAL CELL BIOLOGY LAB 7 Cellular respiration has three main stages: glycolysis, the citric acid cycle and electron transport chain. The Krebs cycle (citric acid cycle) and electron transport occur within mitochondria, so that the mitochondria are known as the powerhouses of the cell. In general, the number of mitochondria per cell and the number of cristae per mitochondrion are related to the energy requirement for the function carried out by that cell type. So the number of mitochondria in a cell depends on the cell's function. Cells with particularly heavy energy demands, such as muscle cells, have more mitochondria than other cells. That is mean a cell rich in mitochondria is likely to be a very energetic cell. A cell poor in mitochondria is less energetic such as adipose cell. Origin of mitochondria Mitochondria show many similarities to free-living procaryotic organisms, for example, they often resemble bacteria in size and shape, they contain DNA, they make protein, and they reproduce by dividing in into two. Structure of mitochondria The outer membrane of mitochondria is smooth and separates the mitochondrion from the cytoplasm. In contrast, the inner membrane has numerous invaginations called cristae, that is mean it forms septum-like folds (cristae), which extend to various lengths across the organelle. These membranes divides mitochondrion into two submitochondrial compartments: the intermembrane space between the outer membrane and the inner membrane with its cristae, which it is the narrow liquid part between the two membranes, separated by about 8nm, and the matrix,
    • December 8, 2013 PRACTICAL CELL BIOLOGY LAB 7 which it is the part enclosed by the innermost membrane. Several of the steps in cellular concentration of respiration occur enzymes, also deoxyribonucleic acid (mtDNA) in the matrix matrix and due to its high contains mitochondrial mitochondria reproduce independently of the cell by fission. Size and shape of the mitochondria Size and shapes of mitochondria can be very different. On average, they are 0. 25μm thick and 2–7μm long. There are also giant forms (giant mitochondria). The number of cristae mitochondriales also varies. As a result, the sizes of the inner and outer compartments are also different. The folds that originate at the inner membranes and extend into the inner centers of the mitochondria—the cristae mitochondriales—are different in length and form a series of incomplete transverse septa.
    • December 8, 2013 PRACTICAL CELL BIOLOGY LAB 7 The mitochondrion is composed of two layers of phospholipids making an outer smooth membrane that forms a characteristic ball- or bean-shaped structure and a highly folded inner membrane. The inner membrane marks the location for the biochemical events (the electron transport system), which will produce energy for the cell. By folding the inner membrane, the surface area is increased two to three times compared to the flat surface area, and there by more energy can be produced. Mitochondria and energy production Most eukaryotic cells contain many mitochondria, which occupy up to 25 percent of the volume of the cytoplasm. These complex organelles, the main sites of ATP production during aerobic metabolism. The two membranes that bound a mitochondrion differ in composition and function. The outer membrane, composed of about half lipid and half protein. The inner membrane, which is much less permeable, is about 20 percent lipid and 80 percent protein. In nonphotosynthetic cells, the principal fuels for ATP synthesis are fatty acids and glucose. The complete aerobic degradation of glucose to CO2 and H2O is coupled to the synthesis of as many molecules of ATP. In eukaryotic cells, the initial stages of glucose degradation take place in the cytosol, where 2 ATP molecules per glucose molecule are generated. The terminal stages of oxidation and the coupled synthesis of ATP are carried out by enzymes in the mitochondrial matrix and inner membrane. so many ATP molecules per glucose molecule are generated in mitochondria.
    • December 8, 2013 PRACTICAL CELL BIOLOGY LAB 7 The size, Coding Capacity and inheritance of mtDNA Mitochondrial DNA (mtDNA ) is the DNA located in organelles called mitochondria, surprisingly, the size of the mtDNA, the number and nature of the proteins it encodes, and even the mitochondrial genetic code itself varies greatly between different organisms. In humans, mitochondrial DNA can be assessed as the smallest chromosome coding for only 37 genes and containing only about 16,600 base pairs. Human mitochondrial DNA was the first significant part of the human genome to be sequenced. In most species, including humans, mtDNA is inherited solely from the mother. The mtDNA is organized as a circular, double-stranded DNA. In mammals, each double-stranded circular mtDNA molecule consists of 15,000-17,000 base pairs. The two strands of mtDNA encodes 37 genes, 13 are for proteins (polypeptides), 22 are for transfer RNA (tRNA) and two are for the small and large subunits of ribosomal RNA (rRNA). Mitochondria contain multiple copies of their own DNA genomes, which code for some of the mitochondrial proteins. Because each human inherits mitochondrial DNA only from his or her mother (it comes with the egg but not the sperm), the distinctive features of a particular mitochondrial DNA can be used to trace maternal history.
    • December 8, 2013 PRACTICAL CELL BIOLOGY LAB 7 Mitochondria and cell death In a healthy cell, the outer membranes of its mitochondria display the protein Bcl-2 on their surface. Bcl-2 inhibits apoptosis. Internal damage to the cell o causes a related protein, Bax, to migrate to the surface of the mitochondrion where it inhibits the protective effect of Bcl-2 and inserts itself into the outer mitochondrial membrane punching holes in it and causing o cytochrome c to leak out. The released cytochrome c binds to the protein Apaf-1 ("apoptotic protease activating factor-1"). Using the energy provided by ATP, These complexes aggregate to form apoptosomes. The apoptosomes bind to and activate caspase-9. Caspase-9 is one of a family of over a dozen caspases. Caspase-9 cleaves and, in so doing, activates other caspases (caspase-3 and 7). The activation of these "executioner" caspases creates an expanding cascade of proteolytic activity which leads to o digestion of structural proteins in the cytoplasm, o degradation of chromosomal DNA, and phagocytosis of the cell.