Cell Structure

Category: Education

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Structures or Organism or Cell Type Process Procaryote Protozoa Algae Fungi Metazoan Membrane- Absent Present Present Present Present bound nucleus Histones Absent Present Present Present Present Mitochondria Absent Present Present Present Present Chloroplasts Absent Absent Present Absent Absent Phagocytosis Absent May occur Absent Absent May occur Pinocytosis Absent May occur Absent Absent May occur Protoplasmic Absent May occur Absent Absent Absent Streaming ER Absent Present Present Present Present Mesosomes Present Absent Absent Absent Absent Electron In cytoplasmic In mitochondria In mitochondria Transport membrane Rigid cell wall Present Absent Present Present Absent Ribosomes Cytoplasmic 70S Cytoplasmic 80S Cytoplasmic 80S Mitochondrion 70S Mitochondrion 70S Golgi Apparatus Absent Present Dictyosomes Present Present Some Critical Differences in the Structures and Processes of Procaryotic and Eucaryotic Cells

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These are proteins associated with the DNA of prokaryotes, consider the chromosomes of prokaryotes to be “naked” DNA

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It is a process in which a cell takes up water. Tiny pockets along the cell membrane, and then fill with liquid. Those tiny pockets then break off into the cell to form tiny vacuoles filled with water. It is a process in which cells take in large particles, clumps of food and even other cells! In phagocytosis, extensions of cytoplasm surround and engulf the object that it is trying to take in. A type of a single celled organism that uses this process to capture its food is the Ameba.

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Mesosomes - membrane invaginations

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Dictyosomes – golgi apparatus of plant cells

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Bacteria Archae Eukarya

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Structurally, a prokaryotic cell has three architectural regions: 1. Appendages (attachments to the cell surface) in the form of flagella and pili or fimbriae 2. A cell envelope consisting of a capsule, cell wall and plasma membrane 3. A cytoplasmic region that contains all the genome (DNA) and ribosomes and various sorts of inclusions

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Characteristics of Typical Bacterial Cell Structures

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Components External to the Cell Wall Gelatinous Surface Layers ciliate protozoa - pellicle (often proteinaceous) ameboid protozoa - polysaccharide slime algae and fungi - glycocalyx bacteria - slime layer or biofilm(morphologically discrete) - capsule (morphologically indiscrete)

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Functions of Cytoplasmic Membrane Osmotic or permeability barrier Location of transport systems for specific solutes (nutrients and ions) Energy generating functions involving respiratory and photosynthetic electron transport systems, establishment of proton motive force and transmembranous, ATP-synthesizing ATPase Synthesis of membrane lipids (including lipopolysaccharides in G- cells) Synthesis of murein (cell wall peptidoglycan) Assembly and secretion of extracytoplasmic proteins Coordination of DNA replication and segregation with septum formation and cell division Chemotaxis (both motility per se and sensing functions) Location of specialized enzyme system

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Proposed Physiological Functions for Capsules 1. Capsule is recognized, along with wall and flagellum, as one of the major antigenic sites of the cell 2. The capsule or extruded slimy material may inhibit the process of phagocytosis and thereby protect the organism from destruction 3. Production of capsular material is regarded as a mechanism for motility, helping organisms devoid of flagella to glide along surfaces 4. Serves as a vehicle for nutrient accumulation in nutritionally sparse environments 5. Serves as a “cellular garbage dump” 6. The capsule may protect the cell from physical injury and dehydration

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Chemical Composition of Some Bacterial Capsules

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Pili ( protein strands to the outside that are used for attachment; one type is used for prokaryotic 'sex'

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Some Properties of Pili and Fimbriae

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Flagellar Structure (diameter – 20 nm) Bacterial flagella – powered by pmf

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50 genes – flagellar synthesis (Innermost rings- motor apparatus) Outermost rings as bushings to support the rod

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Flagellar Movement Flagellin does not flex but moves by rotation Rotary motion is imparted through the motor which comes from proton motive force Do not rotate at a constant speed Increase/decrease rotational speed in relation to the strength of a proton motive force

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Individual flagellum grows not from its base but from the tip

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Different arrangements of bacterial flagella. Swimming motility, powered by flagella, occurs in half the bacilli and most of the spirilla.