Cell and Molecular biology ppt

applications of molecular biology ppt and genetics and molecular biology ppt and molecular biology lecture notes ppt
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Published Date:19-07-2017
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Alberts • Johnson • Lewis • Raff • Roberts • Walter Molecular Biology of the Cell Fifth Edition Chapter 14 1. The Genetic System of Mitochondria and Plastids 2. The Evolution of Electron-Transport Chains Copyright © Garland Science 2008 Mitos, gr. Faden; Chondros, gr. Korn Figure 14-8 (part 2 of 2) Molecular Biology of the Cell (© Garland Science 2008) Apart from the oxidation of pyruvate and fatty acids Figure 14-32 Molecular Biology of the Cell (© Garland Science 2008) Figure 14-35b Molecular Biology of the Cell (© Garland Science 2008) Figure 14-37 Molecular Biology of the Cell (© Garland Science 2008) 1. The Genetic Systems of Mitochondria and Plastids •  These two organelles are never made de novo, but are inherited by growth and division •  Even in non-dividing cells, these organelles need to be replenished •  Plastids and mitochondria contain genetic information: Organelle Genome: rRNAs - ribosomes tRNAs mRNA - proteins (always….cytochrome oxidase) Genome needs to be replicated, inherited Euglenia gracilis stained with a mitotracker dye (green) and a DNA stain red Note the reticular mitochondrial network with its nucleoids Figure 14-52 Molecular Biology of the Cell (© Garland Science 2008) 1.1. Mitochondria and Chloroplasts contain complete genetic systems •  Biogenesis of these two organelles requires contribution of nuclear genes and organelle genome •  Unidirectional import of nuclear encoded proteins (99% ) •  Organelle protein synthesis resembles that of bacteria i.e., chloroplast ribosomes are very similar to that of E. coli sensitive to chloramphenicol etc. protein synthesis starts with N-formyl methionine Figure 14-53 Molecular Biology of the Cell (© Garland Science 2008) 1.2. Organelle growth and division determine the number of mitochondria and plastids in a cell •  In mammalian cells mitochondrial DNA makes up 1% of the total cellular DNA, but proportion higher in some plants or amphibian eggs (99%) •  Live cell images of mitochondria (mitotracker, membrane potential sensitive dyes how does this work?) = dynamic organelles: fuse and divide (fission) constantly •  Thus, number and shape of mitochondria vary dramatically •  In different cell types •  Under different physiological conditions •  Controlled by rates of fusion and fission •  Large mass increase (5-10fold) upon exercise in skeletal muscle Table 14-2 Molecular Biology of the Cell (© Garland Science 2008) Figure 14-55 Molecular Biology of the Cell (© Garland Science 2008) 1.2. Organelle growth and division determine the number of mitochondria and plastids in a cell •  = Number of genome per organelle varies •  DNA organized in clusters, nucleosids •  Replication is random, generally not coordinated with the cell cycle •  Genome can be circular or linear Figure 14-56a Molecular Biology of the Cell (© Garland Science 2008) Topological complex fusion and fission involves a double membrane Figure 14-56b Molecular Biology of the Cell (© Garland Science 2008) Figure 14-54 Molecular Biology of the Cell (© Garland Science 2008) 1.3. Mitochondria and chloroplasts have divers genomes •  Mitochondrial genome size similar to that of viruses: Range 6kb – 300kb •  Chloroplasts: 70-200kb •  Size of genome does not correlate with number of encoded proteins: •  Human, 16kb, 13 proteins •  Arabidopsis 22x larger, 32 proteins (2.5-fold) •  Reclinomonas americana, 98 proteins (max.) •  Rickettsia prowazekii, small pathogenic bacterium, genome most closely resembles that of present-day mitochondria Various sizes of mitochondrial genomes Figure 14-57 Molecular Biology of the Cell (© Garland Science 2008) 1.4. Mitochondria and chloroplasts probably both evolved from endosymbiotic bacteria •  Prokaryotic character of organellar genetic systems suggests origin from bacteria •  Endosymbiotic hypothesis: •  1 Mia years ago •  Firs eukaryotic cells were anaerobic •  Established stable endosymbiotic relation with bacteria to employ their oxidative phosphorylation •  Occurred while oxygen entered the atmosphere (due to photosynthesis by cyanobacteria) •  Gene-transfer from organelle to nuclear DNA •  Complex, different structures •  May still continue today