Topic 6 CELLS STRUCTURE FUNCTIONAL COMPONENTS lecture 8 OBJECTIVES 1 Be able to differentiate prokaryotic vs eukaryotic cells 2 Know the classes of major chemical components in the cytosol 3 Know the general structures properties and general function of the major organelles nucleus ER both rough and smooth Golgi apparatus lysosomes and perxisomes 4 Be able to compare and contrast the structure and functions of mitochondria vs chloroplasts 5 Be able to differentiate between the various types of cell junctions Cell the ultimate functional unit of life self replicating energy transducing etc however viruses viroids and prions potentially infectious proteins push this definition further more later Fig 7 1 cells vary in terms of their size from microscopic to macroscopic large Prokaryotic vs eukaryotic cells 1 prokaryotic fig 7 4 no distinct nucleus genetic material is not present in a nucleus but rather is aggregated in a nucleoid lack membrane enclosed internal structures organelles characteristically have a capsule which may be the target of antibiotics BACTERIA 2 eukaryotic distinct nucleus and membrane bound organelles yeast animal and plant cells Typical animal cell fig 7 7 Typical pant cell fig 7 8 unique structures are chloroplast presence of rigid cell wall central vacuole surrounded by a tonoblast plasma membrane is penetrated with plasmadesmata Cytoplasm the material within the area bounded by the plasma membrane excluding the nucleus includes organelles and the semi fluid material referred to as cytosol Cytosol is actually a term which refers to an experimental product of cell isolation If you gently break open cells and then centrifuge the material the cytosol is the semifluid material that does not sediment Cytosol consists mostly of the following 1 2 3 4 water inorganic ions mostly K Cl some Na PO42 and Mg2 trace amounts of Ca2 low molecular weight organic compounds glucose free amino acids nucleotides macromolecules proteins enzymes complex carbohydrates Note the cytosol differs radically in chemical composition form the fluid that bathes the cells the so called extracellular or interstitial fluid we ll talk about this later 1 There is considerable controversy as to the exact nature of the cytoplasm The traditional view is that it is simply a random mixture of the above components which passively diffuse throughout the intracellular space Others view the cytoplasm as a structured and organized space in which the above components may associate with various regions of the cell In other words distinct compartments may exist even in the absence of membrane barriers Scientific opinion is beginning to move towards this latter point of view Membrane bound compartments Organelles Nucleus contains the bulk of genes note mitochondria and chloroplasts have their own genome fig 7 9 nuclear envelope double membrane perforated by pores inner region is supported by the nuclear lamina which consists of a dense network of protein fibers chromatin DNA protein complexes chromosomes condensed chromatin structures prior to cell division nucleolus organizing center Endoplasmic reticulum ER extensive double membrane system spread throughout the cell according to your text it represents 50 of total membrane in the cell This structure is extensively involved in protein synthesis and packaging as well as other processes including membrane biosynthesis detoxification and storing of certain materials There are two basic types of ER 1 smooth ER and 2 rough ER see fig 7 11 1 smooth ER diverse array of functions biosynthesis of various lipids including steroids fatty acids phospholipids conversion of glucose 6 phosphate to glucose G6Pase glucose 6 phophatase detoxification of foreign substances converts them into more polar and easily excretable compounds by action of enzymes known as mixed function oxidases sarcoplasmic reticulum SR in muscle stores and releases calcium more later 2 rough ER studded with ribosomes ribosomes macromolecular complexes consisting of RNA and protein site of translation of genetic message into protein primary site of synthesis of proteins bound for the cell and those that will be secreted to the outside usually are glycoproteins and are wrapped in membrane vesicles Membrane fragments are also made here Golgi Apparatus fig 7 12 packages vesicles of protein for transport to the exterior Two sides to the structure 1 cis side or face receives materials from the ER reassembles them into laminar type structure and 2 trans side or face new vesicles pinch off form Golgi for transport elsewhere Chemical constituents of membranes are altered during residence in this structure 2 Lysosomes figs 7 13 7 14 membrane bound structures that contain degradative enzymes that hydrolyze the major classes of organic compounds engulf and digest materials acquired from the outside by phagocytosis and internal fragments autophagy Formed by the Golgi apparatus Vacuoles membrane bound structures that have a diverse array of functions particles engulfed during phagocytosis become food vacuoles plants have central vacuoles fig 7 15 which are used to create storage sites for materials such as citric acid Peroxisomes specialized organelles which have enzyme catalyzed reactions that ultimately produce hydrogen peroxide H 2O2 as a product H2O2 is highly reactive but there is an enzyme peroxidase that detoxifies H 2O2 Mitochondria and Chloroplasts extremely specialized organelles very likely derived in an evolutionary sense from early prokaryotic symbionts of other larger prokaryotic cells Endosymbiontic theory of origin of eukaryotic cells 1 both mitochondria and chloroplasts have their own genetic info and protein synthetic machinery 2 however a large fraction of proteins in mitochondria and chloroplasts are coded for by genes in the nucleus they are syhthesized on ribosomes in the cytoplasm Mitochondria fig 7 17 1 10 m long except for giant mitochondria from insect flight muscle cells two double membrane systems outer double membrane penetrated by pores which are very selective inner double membrane which is folded to form cristae inner membrane has a large number of peripheral and integral proteins membrane is extremely selective in terms of permeability between the two membranes is the intermembrane space the interior of the organelle is known as the matrix functional role is energy conversion Chloroplasts fig 7 18 also have two double membrane systems outer double membrane internal double membrane
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