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Ch 6: A Tour of the Cell - Coggle Diagram

- - - - Scanning electron microscopes (SEMs) focus a beam of electrons ONTO the surface of a specimen, providing images that look 3-D
      - Transmission electron microscopes (TEMs) focus a beam of electrons THROUGH a specimen. TEMs are used mainly to study the internal structure of cells.
      - Cryo-electron microscopy (cryo-EM) allows preservation of specimens at very low temperatures. This allows visualization of structures in their cellular environment, with no need for preservatives. This method is used to complement X-ray crystallography in revealing protein complexes and subcellular structures
- - - - Characteristics
        
        DNA in a nucleus that is bounded by a double membrane
        
        Membrane-bound organelles
        
        Cytoplasm in the region between the plasma membrane and nucleus
        
        Larger than prokaryotic
        
        Nucleus: contains most of the cell’s genes and is usually the most conspicuous organelle
        
        Nuclear envelope: encloses the nucleus, separating it from the cytoplasm. The nuclear envelope is a double membrane; each membrane consists of a lipid bilayer
        
        The nuclear side of the envelope is lined by the NUCLEAR LAMINA, which is composed of proteins and maintains the shape of the nucleus
        
        nucleolus: located within the nucleus, is the site of ribosomal RNA (rRNA) synthesis
        
        Endomembrane system: (consists of: nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, plasma membrane)
        
        Vacuoles: large vesicles derived from the ER and Golgi apparatus
        Vacuoles perform a variety of functions in different kinds of cells
        
        Subcategories
        
        Food vacuoles are formed by phagocytosis (temporary stomachs)
        
        Contractile vacuoles, found in many freshwater protists, pump excess water out of cells
        
        Central vacuoles, found in many mature plant cells, contain a solution called sap
        
        Endoplasmic Reticulum: accounts for more than half of the total membrane in many eukaryotic cells
        
        Smooth ER: lacks ribosomes
        
        Rough ER: whose surface is studded with ribosomes
        
        Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates)
        
        Distributes transport vesicles, secretory proteins surrounded by membranes
        
        Is a membrane factory for the cell
    - - Nucleoid region: an irregularly shaped, membrane-less area within prokaryotic cells (bacteria and archaea) that contains the cell's genetic material, primarily a single, circular chromosome
      - No nucleus
      - No membrane-bound organelles
      - Cytoplasm: the entire content within a cell's membrane. It is a thick, gel-like solution primarily composed of water, salts, and proteins, and it is where most cellular activities, including metabolic reactions like glycolysis and protein synthesis, take place. The cytoplasm provides structural support to the cell and facilitates the transport of materials between organelles
    - - Plasma membrane : flexible, semi-permeable lipid bilayer that surrounds all living cells, separating their internal contents from the external environment
      - Cytosol: the jelly-like, aqueous component of the cytoplasm (roughly 70% water) surrounding organelles, comprising over 70% of cell volume. It enables metabolism (glycolysis), protein synthesis, signal transduction, and metabolite transport. It acts as a crucial medium for maintaining homeostasis via ion regulation
      - Chomosomes: thread-like structures in the cell nucleus made of DNA tightly coiled around proteins (histones), which package genetic material for stability and proper division
        
        Chromatin: a complex of DNA, RNA, and proteins (mainly histones) found in the eukaryotic nucleus that packages long DNA molecules into compact structures to fit inside the cell’a nucleus. It regulates gene expression, facilitates DNA replication and repair, and condenses into chromosomes during cell division.
      - Ribosomes: essential molecular machines, found in all living cells, that synthesize proteins by translating messenger RNA (mRNA) into polypeptide chains
      - Mitochondria are the sites of cellular respiration, the metabolic process that uses oxygen to
        generate ATP
        
        They have a smooth outer membrane and an inner membrane folded into cristae
        
        Cristae present a large surface area for enzymes that synthesize ATP
        
        The inner membrane creates two compartments: intermembrane space and mitochondrial matrix
        
        Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix
      - Chloroplasts, found in plants and algae, are the sites of photosynthesis (they are considered a group of plant organelles called PLASTIDS)
        
        THYLAKOIDS (primary site for the light-dependent reactions of photosynthesis, converting light energy into chemical energy (ATP and NADPH)), stacked to form a GRANUM (containing chlorophyll and photosystems essential for the light-dependent reactions of photosynthesis. Each granum consists of 2–100 thylakoids, significantly increasing surface area for maximum light absorption and efficient sugar production)
        
        STROMA: the internal fluid
      - Peroxisomes are oxidative organelles (specialized metabolic compartments bounded by a single membrane, containing enzymes that remove hydrogen atoms from various substances and transfer them to oxygen which forms hydrogen peroxide. These reactions have many different functions).
      - Cytoskeleton: helps support the cell and maintain its shape
        
        INTERACTS WITH motor proteins (the cell’s “feet” used for moving) to produce CELL MOTILITY
        
        Fibers of the cytoskeleton
        
        Fibers
        
        Microtubules are the thickest of the three components of the cytoskeleton (shapes cell, guides movement of organelles, and helps separate chromosomes during cell division)
        
        In animal cells, microtubules grow out from a centrosome near the nucleus
        
        In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring (Other eukaryotic cells organize microtubules in the absence of centrosomes with centrioles)
        
        Microtubules control the beating of flagella and cilia, microtubule-containing extensions that
        project from some cells (They differ in their beating patterns)
        
        They have a basal body anchors the cilium or flagellum
        
        They have a motor protein called dynein drives the bending movements of a cilium or flagellum
        
        They have a group of microtubules sheathed in an extension of the plasma membrane
        
        They have nine doublets of microtubules are arranged in a ring with two single microtubules in the center
        
        Microfilaments, also called actin filaments, are the thinnest components (built as a twisted double chain of actin subunits. A network of these help support the cell shape)
        
        Form a CORTEX to help further support the cell shape
        
        Bundles of these make up the core of the microvilli of intestinal cells
        
        Contain the protein MYOSIN which converts chemical energy into mechanical force
        
        Form PSEUDOPODIA: Cells crawl along a surface by extending pseudopodia (cellular extensions) and moving toward them
        
        Intermediate filaments are fibers with diameters in a middle range (support cell shape and fix organelles in place)
      - Cell walls (plant cells only): protects the plant cell, maintains its shape, and prevents excessive uptake of water
        
        Layers
        
        Primary cell wall: Relatively thin and flexible, secreted first
        
        Middle lamella: Thin layer between primary walls, containing polysaccharides called pectins
        
        Secondary cell wall (in some cells): Added between the plasma membrane and the primary cell wall
      - Extracellular Matrix (ECM) (animal cells): can regulate cell behavior by communicating with a cell through integrins, influence the activity of genes in the nucleus, and mechanical signaling MAY occur through cytoskeleton changes that trigger chemical signals in the cell) (made of glycoproteins and proteoglycans)
      - Organelles: any of a number of organized or specialized structures within a living cell.
- - - - At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid
      - Desmosomes (anchoring junctions) fasten cells together into strong sheets
      - Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells