Funbio 6 2024 Cell Structure Mitochondria PDF

Cell Structure: Mitochondria Class Foundation Year Course Fundamentals of Human Biology Code FUNBIO.6 Lecturer Dr Irene Oglesby Date 10th October 2024 Learning outcomes At the end of this lecture, the learner will be able to; ALO1 - Describe mitochondrial structure...

Cell Structure: Mitochondria Class Foundation Year Course Fundamentals of Human Biology Code FUNBIO.6 Lecturer Dr Irene Oglesby Date 10th October 2024 Learning outcomes At the end of this lecture, the learner will be able to; ALO1 - Describe mitochondrial structure and morphology. ALO2 - Discuss mitochondrial function and the role of the F1 particles in ATP production. ALO3 - Explain the significance of the extrachromosomal DNA in the mitochondrial matrix. ALO4 - Consider the various hypotheses for the origins of mitochondria in the cell and explain the serial symbiotic theory. 2  Cellular Structures The cytoplasm of cells contain structures called organelles Endoplasmic Reticulum Golgi Complex Vesicles – Lysosomes, Peroxisomes, Secretary vesicles Mitochondrion Mitochondrial Structure and Nature Reviews Molecular Cell Biology Morphology volume 11, pages872–884(2010) 4 Mitochondria Structure and morphology 2nd most prominent cellular organelle Visible with the light microscope Detailed structure requires an Electron Microscope (EM) Singular: mitochondrion From the Greek mitos (thread) Chondrios (granule) Found in all eukaryotic cells (plant and animal) Number varies from a few to >1000 per cell Mitochondria Structure and morphology Shape varies from rods to spheres Characteristic of a particular cell type Living mitochondria are not static Move around in cytoplasm Aggregate in areas of high metabolic activity Nature Reviews Molecular Cell Biology volume 11, pages872–884(2010)  Mitochondrial Structure Variable size: 0.5-1.0 µm diameter, 5-10 µm long Each mitochondrion is bound by two membranes: 1. A smooth outer membrane 2. An inner membrane, folded into thin plates/infolds called cristae Inner mitochondrial membrane Matrix Cristae Outer mitochondrial membrane Figure 4-20 p96 Mitochondrial Structure - Cristae Cristae – infolds of the inner plasma membrane May extend from wall to wall or only part of the way Cristae may be tubular or some other shape Cristae Function: Provide a large surface area for sequential chemical reactions to take place Direct correlation between number of cristae and the activity of the cell ATP Synthase  Mitochondrial Structure - Matrix The interior of the mitochondrion is called the matrix Contains mitochondrial ribosomes and non- chromosomal DNA 5 - 10 identical circular DNA molecules, 2-3nm in diameter Manufactures its own proteins. Matrix The number of proteins produced by mitochondrial DNA (mtDNA) is small Contains Kreb’s / Citric acid cycle enzymes which convert chemical energy in our food into ATP energy. Mitochondrial Function ATP Production via Oxidative Phosphorylation 10  Mitochondria - Function The Powerhouse of the Cell – ATP production They contain the enzymes used in oxidative phosphorylation The oxidative process uses O2 to convert Adenosine diphosphate (ADP) into Adenosine Triphosphate (ATP) ADP + Pi ATP + H2O ATP contains a high energy bond which is used to drive metabolic processes in the cell The central set of reactions involved in ATP production are collectively known as the Citric Acid Cycle / Krebs Cycle. (aerobic respiration) Aerobic respiration recap *not for examination* Glucose breakdown – ‘Glycolysis’ (take place in cytoplasm) generates pyruvate, ATP and NADH Krebs/Citric acid cycle in mitochondria - main role is to generate NADH for use in the Electron transport chain In mitochondria - NADH – coenzyme, carrier molecule, donates electrons and hydrogens ions to ‘Electron Transport Chain’ Cellular respiration; Ameoba Sisters https://www.youtube.com/watch?v=eJ9Zjc-jdys A simple summary of aerobic respiration geared towards Irish Leaving Cert Biology revision. https://www.youtube.com/watch?v=BuEPgnag0Sc IMPORTANT: Glycolysis and Krebs cycle not for examination – reminder only of where NADH comes from for the Electron Transport Chain IMPORTANT: Glycolysis and Krebs cycle not for examination – reminder only of where NADH comes from for the Electron Transport Chain  OXIDATIVE PHOSPHORYLATION (ELECTRON TRANSPORT AND CHEMIOSMOSIS) = ENERGY PRODUCTION Oxidative phosphorylation, the final stage of cellular respiration. made up of two closely connected components: the electron transport chain and chemiosmosis. 1. Electron transport chain, electrons are passed from one molecule to another, and energy released in these electron transfers is used to form an electrochemical gradient. 2. Chemiosmosis, the energy stored in the gradient is used to make ATP. Involves the pumping of hydrogen ions through special channels in the membranes of mitochondria from the inner to the outer compartment. Mitochondrial Structure/Function – F1FO Particles Mitochondrial inner membrane is studded with round particles Called F1 particles – protruding from membrane F0 Base embedded in membrane  ATP Synthase - F1FO Particles Schematic diagram of ATP Synthase showing the F1 head and FO base a head 9nm diameter Acts as an enzyme: an ATPase ATP Synthase (F-type ATPase) Part of a respiratory assembly Electron Transport Chain Forms a transmembrane complex of 9 different polypeptides on the inner membrane The ATP synthase F1 portion synthesizes ATP from ADP + Pi. The F1 subunit squeezes ADP + Pi until they form ATP, then releases the ATP together. Respiratory Assembly (Electron Transport Chain) Energy obtained through the transfer of electrons (black arrows) Protons (red arrows) pumped from the mitochondrial matrix into the intermembrane space Allows ATP synthase to use the flow of H+ through the enzyme back into the matrix to generate ATP from ADP and inorganic phosphate (Pi). Electrons come from the Krebs cycle (NADH) and are passed along the carrier process Complex IV uses the electrons and hydrogen ions to reduce molecular oxygen to water  4 electron transport complexes Outer mitochondrial membrane Intermembrane space Comple Comple Complex I Complex x III x IV Inner mitochondrial Outer mitochondrial II membrane membrane Complex V: ATP synthase Matrix of mitochondrion 3 proton pumps Figure 8-11a p179 Solomon ! The energy released during electron transport is used to transport protons (H+) from the mitochondrial matrix to the intermembrane space ! The flow of the protons through ATP synthase provides the energy for generating ATP from ADP and inorganic phosphate (Pi) https://www.youtube.com/watch?v=zJNx1DDqIVo  Reproduction similar to Fisson Mitochondria: Reproduction and Theory of Origin A mitochondrion in a cell from the liver of a rat prepares to divide. Photo credits: Daniel Friend. 19  Mitochondria - Reproduction When a cell divides mitochondria are distributed equally to the two daughter cells Thereafter mitochondria increase in numbers to bring them up to the levels required for efficient cell function How do these new mitochondria arise? Fawcett, A Textbook of Histology, Chapman and Hall, 12th edition, 1994 The accepted theory is that they arise from pre- existing mitochondria by division They replicate by dividing in two, using a process similar to the simple, asexual form of cell division employed by bacteria - Fission https://cytochemistry.net/cell-biology/mitochondria_lifecycle.htm  Mitochondria - Origin Original prokaryotic host cell Serial Endosymbiotic Theory (SET) DNA Symbionts of prokaryotic origin take up Multiple invaginations of the Aerobic bacteria residence in the anaerobic cell and provide plasma membrane energy The more likely theory to mitochondrial evolution Endoplasmic reticulum and nuclear envelope form from Aerobic bacteria become the plasma membrane mitochondria invaginations (not part of Photosynthetic bacteria serial endosymbiosis) become chloroplasts Background/Extra Reading on SET: https://undsci.berkeley.edu/cells-within- cells-an-extraordinary-claim-with- Eukaryotic cells: extraordinary-evidence/a-world-under-the- microscope/ animals, fungi, some protists plants, some protists Biology Solomon, Fig. 21-8 p. 450  Mitochondria - Serial Endosymbiotic Theory (SET) Original prokaryotic host cell Supporting Evidence; DNA 1. Mitochondria and chloroplasts have their own circular DNA – mtDNA – Multiple invaginations of the Aerobic bacteria ALO3 plasma membrane 2. Produce their own proteins 3. They can replicate independently in Endoplasmic reticulum and the cell Aerobic bacteria become nuclear envelope form from mitochondria the plasma membrane 4. Their ribosomes are more like invaginations (not part of Photosynthetic bacteria serial endosymbiosis) bacterial ribosomes become chloroplasts 5. Bacterial antibiotics, which do not Eukaryotic cells: affect eukaryotic cells can poison mitochondria and chloroplasts Biology Solomon animals, Fig. fungi, 21-8 p. some 450 protists plants, some protists Figure 21-8 p450 Mitochondria - Serial Endosymbiotic Theory (SET) MAD DR mtDNA - 37 genes, essential for normal mitochondrial function. 13 of these genes provide instructions for making enzymes involved in oxidative phosphorylation Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA N T Irene Oglesby EMAIL: [email protected]