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Prokaryotic and Eukaryotic Cellular Structure Prokaryotic & Eukaryotic Cells: an Overview

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Prokaryotic and Eukaryotic Cellular Structure Prokaryotic & Eukaryotic Cells: an Overview Prokaryotic and Eukaryotic Cellular Structure Prokaryotic & Eukaryotic Cells: An Overview Prokaryotes Do not have membrane surrounding their DNA lack a nucleus Lack various internal structures bound with phospholipid membranes Are small, ~1.0 µm in diameter Have a simple structure Composed of bacteria and archaea Prokaryotic & Eukaryotic Cells: An Overview Eukaryotes Have membrane surrounding their DNA Have a nucleus Have internal membrane-bound organelles Are larger, 10-100 µm in diameter Have more complex structure Composed of algae, protozoa, fungi, animals, and plants Prokaryotic & Eukaryotic Cells: An Overview [INSERT FIGURE 3.1] Prokaryotic Cell Membrane • Structure – Referred to as phospholipid bilayer; composed of lipids and associated proteins – Approximately half composed of proteins that act as recognition proteins, enzymes, receptors, carriers, or channels • Integral proteins • Peripheral proteins • Glycoproteins – Fluid mosaic model describes current understanding of membrane structure Cell Membrane Membranes contain a hydrophilic and hydrophobic side Composed of many different types of proteins Proteins in the lipid bilayer move freely within the membrane Thin pliable lipid and protein envelope that defines a cell. Cell Membrane Phospholipid bilayer Functions: • Regulates nutrient and water intake • Regulates waste removal • Site of prokaryotic respiration • Site of prokaryotic flagella attachment • Involved in the distribution of genetic material during binary fission Flagella Bacterial Appendages Structures of locomotion Originate in the plasma membrane In bacteria rotate like a propellar Many different arrangements External Structures of Prokaryotic Cells • Flagella – Are responsible for movement – Have long structures that extend beyond cell surface – Are not present on all prokaryotes External Structures of Prokaryotic Cells Flagella Structure Composed of filament, hook, and basal body Flagellin protein (filament) deposited in a helix at the lengthening tip Base of filament inserts into hook Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings of integral proteins Filament capable of rotating 360º Bacterial Appendages Arrangements of Flagella A. Monotrichous B. Lophotrichous C. Amphitrichous D. Peritrichous 5. Mesosome Mesosomes - invagination of the plasma membrane that increases the surfaces area of the plasma membrane during binary fission. The mesosome also serves as a site for the attachment and distribution of genetic material during binary fission. Inclusion Bodies 6. gas vacuoles - storage of metabolic gases such as methane or hydrogen gas. The gas vacuoles help in the buoyancy of the cell and aids in it motility. 7. ribosomes - responsible for the synthesis of proteins. 8. nucleoid material - the genetic material of bacteria, which usually is balled up in the cell. During binary fission the nucleoid material unravels within the cell in order to be copied and distributed to the daughter cells. 9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for the resistance to antibiotics or for the productions of a specific metabolite, i.e. toxins, pigments. These plasmids may be transferred from one bacterial cell to another by the F-pili. Inclusion Bodies 9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for the resistance to antibiotics or for the productions of a specific metabolite, i.e. toxins, pigments. These plasmids may be transferred from one bacterial cell to another by the F-pili. Intracellular Structures of Eukaryotic Organisms (organelles) Membranous Organelles Nucleus Often largest organelle in cell Contains most of the cell’s DNA Semi-liquid portion called nucleoplasm One or more nucleoli present in nucleoplasm; RNA synthesized in nucleoli Nucleoplasm contains chromatin – masses of DNA associated with histones Surrounded by nuclear envelope – double membrane composed of two phospholipid bilayers Nuclear envelope contains nuclear pores Intracellular Structures of Eukaryotic Organisms (organelles) Nucleus - double membraned organelle that houses the genetic material of cell. Nuclear membrane contains numerous pores through which proteins and RNA can move. Intracellular Structures of Eukaryotic Organisms (organelles) Membranous Organelles Endoplasmic reticulum Netlike arrangement of flattened, hollow tubules continuous with nuclear envelope Functions as transport system Two forms Smooth endoplasmic reticulum (SER) – plays role in lipid synthesis Rough endoplasmic reticulum (RER) – ribosomes attached to its outer surface; transports proteins produced by ribosomes Intracellular Structures of Eukaryotic Organisms (organelles) Endoplasmic reticulum - network of cytoplasmic membranes where lipids and proteins are produced. Smooth ER - synthesis of lipids Rough ER - associated with ribosomes and is responsible for the synthesis of proteins. Intracellular Structures of Eukaryotic Organisms (organelles) Membranous Organelles Golgi body Receives, processes, and packages large molecules for export from cell Packages molecules in secretory vesicles that fuse with cytoplasmic membrane Composed of flattened hollow sacs surrounded by phospholipid bilayer Not in all eukaryotic cells Intracellular Structures of Eukaryotic Organisms (organelles) Golgi apparatus (dictyosome) is associated with the ER. It modifies and packages the lipids and proteins manufactured by the ER and places them in vesicles for cellular use. Intracellular Structures of Eukaryotic Organisms (organelles) • Membranous Organelles – Lysosomes, peroxisomes,vacuoles, and vesicles • Store and transfer chemicals within cells • May store nutrients in cell • Lysosomes contain catabolic enzymes • Peroxisomes contain enzymes that degrade poisonous wastes Intracellular Structures of Eukaryotic Organisms (organelles) • Membranous Organelles – Mitochondria • Have two membranes composed of phospholipid bilayer • Produce most of cell’s ATP • Interior matrix contains 70S ribosomes and circular molecule of DNA Intracellular Structures of Eukaryotic Organisms (organelles) mitochondria - involved in the production of chemical energy in the form of ATP. Consist of convoluted inner membrane and outer membrane. Invaginations are called cristae and contain enzymes used to synthesis ATP. All respiratory enzymes are located in the inner membrane of the mitochondria. Cytoplasm of Eukaryotes • Membranous Organelles – Chloroplasts • Light-harvesting structures found in photosynthetic eukaryotes • Have two phospholipid bilayer membranes and DNA • Have 70S ribosomes Cytoplasm of Eukaryotes • Endosymbiotic Theory – Eukaryotes formed from union of small aerobic prokaryotes with larger anaerobic prokaryotes – smaller prokaryotes became internal parasites • Parasites lost ability to exist independently; retained portion of DNA, ribosomes, and cytoplasmic membranes • Larger cell became dependent on parasites for aerobic ATP production • Aerobic prokaryotes evolved into mitochondria • Similar scenario for origin of chloroplasts – Not universally accepted Cytoplasm of Eukaryotes [INSERT TABLE 3.5] Cytoplasm of Eukaryotes [INSERT TABLE 3.4] .
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