Cell Organelles Lecture (4) PDF

COURSE NAME : CELL BIOLOGY CODE: CPB1101 Lecture (4): Cell organelles Part : 2 Dr/ Asmaa Tarek Biochemistry Department Objectives: After going through this chapter, you should be able to : 1- Describe the structure of...

COURSE NAME : CELL BIOLOGY CODE: CPB1101 Lecture (4): Cell organelles Part : 2 Dr/ Asmaa Tarek Biochemistry Department Objectives: After going through this chapter, you should be able to : 1- Describe the structure of mitochondria and state its function. 2- Illustrate oxidative phosphorylation and electron transport chain. 3- Describe the structure of centrosome and state its function..4- Describe the structure of centriole and state its function 5- Describe the structure of cytoskeleton and state its function.6- Describe the structure of vacuole and state its function  Mitochondria Structure 1. Mitochondrion membranes: The mitochondrion contains an outer and an inner membrane separated by the intermembrane space. The outer membrane (double phospholipid bilayer membrane) contains special channels, making it freely PCM permeable to most ions and small molecules. Mitochondria PCM  Mitochondria 1. Mitochondrion membranes: The inner membrane is a specialized structure that is impermeable to most small ions, including protons and small molecules such as ATP, ADP, pyruvate, and other metabolites important to mitochondrial function. Specialized carriers or transport systems are required to move ions or molecules across this membrane. The inner mitochondrial membrane is unusually rich in protein, over half of which is directly involved in oxidative phosphorylation. It also is highly convoluted. The convolutions, called cristae, serve to greatly increase the surface area of the inner membrane and protrude into the  Mitochondria 2. Mitochondrion matrix: This gel-like solution in the interior of mitochondria is also rich in protein. These molecules include the enzymes responsible for the oxidation of pyruvate, amino acids, and fatty acids (by β-oxidation) as well as those of the tricarboxylic acid (TCA) cycle. The synthesis of glucose, urea, and heme occurs partially in the matrix of mitochondria. In addition, the matrix contains NAD and FAD (the oxidized forms of the two coenzymes that are required as hydrogen acceptors), and ADP and P, which are used to produce ATP. The matrix also contains mitochondrial DNA (mtDNA) and RNA (mtRNA) and ribosomes.  Mitochondria 1. Function in energy production Protons (H+) are pumped out of the mitochondrial matrix, creating an electrochemical gradient of protons. The flow of protons back into the matrix drives the formation of ATP from carbohydrates and lipids in the process of oxidative phosphorylation (The coupling of electron transport chain (ETC) with ATP synthesis). The presence of mitochondria within a cell enhances the amount of ATP produced from each glucose molecule that is broken down, as evidenced by human red blood cells that lack mitochondria. In red blood cells, only 2 ATP molecules are generated per glucose molecule. In contrast, in human cells Mitochondria PCM  Mitochondria 2. Role as independent units within the eukaryotic cells Mitochondria also contain DNA (mtDNA) and ribosomes for the production of RNA and some mitochondrial proteins. mtDNA is approximately 1% of total cellular DNA and exists in a circular arrangement within the mitochondrial matrix. Mutations or errors in some mitochondrial genes can result in disease. Most mitochondrial proteins, however, are encoded by the genomic DNA of the cell’s nucleus. Mitochondria self replicate or divide by fission, as do bacteria.  Mitochondria 3. Function in cell survival Survival of eukaryotic cells depends on intact mitochondria. During development, some cells must die to allow for proper tissue and organ formation. Death of abnormal cells, such as virally infected cells or cancerous cells, is also for the good of the organism. In all these cases, mitochondrial involvement is important to ensure cell survival when it is appropriate and also to facilitate programmed cell death when necessary.  Mitochondria 3. Function in cell survival When the process of programmed cell death or apoptosis is stimulated in a cell, proapoptotic proteins insert into the mitochondrial membrane, forming pores. A protein known as cytochrome c can then leave the intermembrane space of the mitochondria through the pores, entering the cytosol. Cytochrome c in the cytosol stimulates a cascade of  Mitochondria Mitochondrial diseases Mitochondrial cytopathies: are disorders that result in an inability of mitochondria to properly produce ATP. These disorders may result from mutations in mtDNA or from mutations in genomic genes that encode mitochondrial proteins and enzymes. Because mitochondria from sperm cells do not enter a fertilized egg, mitochondria are inherited exclusively from the mother. Therefore, disorders of mtDNA are also inherited from the mother only. The different mitochondrial disorders share the common feature of a reduced ability of mitochondria to completely oxidize or breakdown fuel sources such as carbohydrates. The buildup of intermediates can further damage mitochondria and  Mitochondria Mitochondrial diseases Mitochondrial cytopathies Mitochondrial diseases are categorized by the organ that is affected. Defects in oxidative phosphorylation will affect tissues with the greatest need for ATP. Brain, heart, liver, skeletal muscles, and eyes are examples of organs often affected in some mitochondrial cytopathies. Developmental delays, poor growth, loss of muscle coordination, and loss of vision are various signs of these  Mitochondria Examples of mitochondrial disorders Kearns-Sayre syndrome is caused by defective mtDNA (single large deletion of mtDNA). It is rare and results in paralysis of eye muscles and degeneration of the retina. Leber hereditary optic neuropathy is caused by single change (point mutation) in mtDNA that results in blindness, primarily in young men. Cures are not presently available for mitochondrial cytopathies and treatments are designed to reduce symptoms or to prevent progression of disease.  Centrosomes 15 Centrosomes are composed of two arranged centrioles surrounded by a shapeless mass of protein termed pericentriolar material (PCM). The PCM contains proteins responsible for microtubule nucleation. PCM  Centrosomes 16 Function: In mitosis the nuclear membrane breaks down and the centrosome nucleated microtubules can interact with the chromosomes to build the mitotic spindle.  Centrioles 17 A centriole is a cylindrical cell structure composed mainly of a protein called tubulin that is found in animal cells. Most centrioles are made up of nine sets of microtubule triplets, arranged in a cylinder. Centrioles are involved in the organization of the mitotic spindle and in the completion of cytokinesis.  Centrioles 18 Before DNA repication, cells contain two centrioles. The older of the two centrioles is termed the mother centriole, the other the daughter. During the cell division cycle, a new centriole grows at the proximal end of both mother and daughter centrioles. After duplication, the two centriole pairs (freshly assembled centriole is now a daughter centriole in each pair) will remain attached to each other orthogonally until mitosis. At that point, the mother and daughter centrioles separate dependently on  Cytoskeleton 19 Organelles do not float freely within the cytosol but are interconnected and joined by the framework established by proteins of the cytoskeleton.  Cytoskeleton 20 The cytoskeleton is a complex network of protein filaments found throughout the interior of cells. The three principal types of protein filaments of the cytoskeleton are actin filaments, microtubules, and intermediate filaments. Organelles reside within the framework established by the cytoskeleton. The cytoskeleton is not simply a passive internal skeleton but is a dynamic regulatory feature of the cell. Microtubules are one type of cytoskeletal protein. They organize the cytoplasm and interact with organelles to induce their movement. In addition to microtubules, actin filaments and intermediate filaments constitute the cytoskeleton. These components of the cytoskeleton work together as an  Cytoskeleton 21  Cytoskeleton 22 Each type of cytoskeletal filament is formed from a specific association of protein monomer subunits. Actin filaments and microtubules formed from globular protein subunits (more compact), while intermediate filaments contain fibrous protein subunits (more extended).  Vacuole 23 Vacuole is a membrane-bound organelle which is present in all Plant and fungal cells , animal and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these. Vacuole has no basic shape or size; its structure varies according to the needs of the cell. Vacuoles are more important to the survival of plant cells than they are to animal cells.  Vacuole 24 The functions of the vacuole include:  Isolating materials that might be harmful or a threat to the cell.  Containing waste products.  Containing water in plant cells.  Maintaining internal hydrostatic pressure or turgor within the cell.  Allows plants to support structures such as leaves and flowers due to the pressure of the central vacuole.