Mitochondria: Structure, Function & Origin - PDF

Cell Biology, Biochemistry 10.1. Lecture Mitochondria Edited by: Veronika Vincze  Mitochondria The mitochondrion (plural mitochondria) is a double membrane-bound organelle found in most eukaryotic cells. These structures are described as "the...

Cell Biology, Biochemistry 10.1. Lecture Mitochondria Edited by: Veronika Vincze  Mitochondria The mitochondrion (plural mitochondria) is a double membrane-bound organelle found in most eukaryotic cells. These structures are described as "the powerhouse of the cell" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy In addition to supplying cellular energy, mitochondria are involved in other tasks, such as signaling, cellular differentiation, and cell death, as well as maintaining control of the cell cycle and cell growth. Mitochondria have been implicated in several human diseases, including mitochondrial disorders, cardiac dysfunction, and heart failure  Origin of Mitochondria There are two hypotheses about the origin of mitochondria: endosymbiotic and autogenous. The endosymbiotic hypothesis suggests that mitochondria were originally prokaryotic cells, capable of implementing oxidative mechanisms that were not possible for eukaryotic cells; they became endosymbionts living inside the eukaryote.  Structure of Mitochondria A mitochondrion contains outer and inner membranes composed of phospholipid bilayers and proteins. The two membranes have different properties.  Structure of Mitochondria Because of this double-membraned organization, there are five distinct parts to a mitochondrion. They are: the outer mitochondrial membrane the intermembrane space (the space between the outer and inner membranes), the inner mitochondrial membrane, the cristae space (formed by infoldings of the inner membrane), and the matrix (space within the inner membrane). Fig.1 (A)cross section, as seen in the electron microscope. (B) A drawing of a mitochondrion with part of it cut away to show the three-dimensional structure. (C) A schematic eukaryotic cell, with the interior space of a mitochondrion.  Structure of Mitochondria Outer Membrane encloses the entire organelle contains large numbers of integral membrane proteins called porins porins form channels that allow molecules of 5000 daltons or less in molecular weight to freely diffuse contains enzymes the mitochondrial outer membrane can associate with the endoplasmic reticulum (ER) membrane, in a structure called MAM (mitochondria-associated ER-membrane disruption of the outer membrane permits proteins in the intermembrane space to leak into the cytosol, leading to certain cell death  Structure of Mitochondria Intermembrane space the intermembrane space is the space between the outer membrane and the inner membrane because the outer membrane is freely permeable to small molecules, the concentrations of small molecules, such as ions and sugars, in the intermembrane space is the same as the cytosol protein composition of this space is different from the protein composition of the cytosol. One protein that is localized to the intermembrane space in this way is cytochrome c  Structure of Mitochondria Inner membrane The inner mitochondrial membrane contains proteins with five types of functions: 1. Those that perform the redox reactions of oxidative phosphorylation 2. ATP synthase, which generates ATP in the matrix 3. Specific transport proteins that regulate metabolite passage into and out of the matrix 4. Protein import machinery 5. Mitochondrial fusion and fission protein  Structure of Mitochondria Christae The inner mitochondrial membrane is compartmentalized into numerous cristae, which expand the surface area of the inner mitochondrial membrane, enhancing its ability to produce ATP.  Structure of Mitochondria Matrix The matrix is the space enclosed by the inner membrane. It contains about 2/3 of the total protein in a mitochondrion. The matrix is important in the production of ATP with the aid of the ATP synthase contained in the inner membrane. The matrix contains a highly concentrated mixture of hundreds of enzymes, special mitochondrial ribosomes, tRNA, and several copies of the mitochondrial DNA genome. Of the enzymes, the major functions include oxidation of pyruvate and fatty acids, and the citric acid cycle.  Function of Mitochondria The most prominent roles of mitochondria are to produce the energy currency of the cell, ATP (i.e., phosphorylation of ADP), through respiration, and to regulate cellular metabolism. The central set of reactions involved in ATP production are collectively known as the citric acid cycle, or the Krebs cycle. The citric acid cycle oxidizes the acetyl-CoA to carbon dioxide, and, in the process, produces reduced cofactors (three molecules of NADH and one molecule of FADH2) that are a source of electrons for the electron transport chain, and a molecule of GTP (that is readily converted to an ATP)  Genetic System of Mitochondria Mitochondria contain their own genetic system which is separate and distinct from the nuclear genome of the cell. The existence of a separate mitochondrial genome is explained by the widely accepted endosymbiotic theory Mitochondrial genomes are circular, double stranded DNA molecules which is about 16,600 bp in humans and are present in multiple copies per organelle. Mitochondrial genome is maternally inherited. mtDNA is continuously turned over and replicated throughout the entire cell cycle with no distinct phase specificity. the evolution rate of mtDNA is much faster than that of the nuclear genome.  Literature David L. Nelson and Michael M. Cox: LEHNINGER PRINCIPLES OF BIOCHEMISTRY, Sixth Edition Lodish et al., Molecular Cell Biology, Fifth Edition 16  Obligatory readings David L. Nelson and Michael M. Cox: LEHNINGER PRINCIPLES OF BIOCHEMISTRY, Sixth Edition Lodish et al., Molecular Cell Biology, Fifth Edition 17  List of topics 1. Introduction to cell biology. The structure of pro-and eukaryote cell. 2. Biomolecules of the cell: Saccharides. Mono- and disaccharides. Polysaccharides. 3. The structure of amino acids and proteins. Function of Proteins. Peptides with biological properties. The structure and function of enzymes. Regulation of enzyme activity. 4. Biomembranes: lipid composition and structural organization. Overview of membrane transport. 5. ATP-powered pumps and the intracellular ionic environment. Nongated ion channels and the resting membrane potential. 6. Integrating cells into tissues. Cell adhesion molecules and junctions. 7. The cytoplasma. The cell skeleton. Microfilaments and microtubules. 8. Rough and smooth endoplasmatic reticulum. 9. Lysosomes. Golgi body. Reactive oxygen species and antioxidant molecules. 10. Mitocondria. Principles of Bioenergetics. Glycolysis. Gycogen breakdown. 11. The structure and properties of nucleus. Nuclear transport processes. Chromosomes and DNA structure. mRNA, t RNA, rRNA structure 12. Cell cycle. Mitosis and meiosis. 13. DNA replication, transcription and translation. 18