KCells - Basic Cell Structure The Cell Theory “Cell...

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Unformatted text preview: Basic Cell Structure The Cell Theory “Cell Doctrine” Into the Cell All organisms are constructed of one or more cells. The cell is the basic unit of life. 1. 2. ¸ Minimum level of complexity that exhibits all characteristics of life. All cells derive from previous cells. 3. What does a cell need? Isolated activity compartments Selective isolation from environment (plasma membrane) n Energy (ATP) n Instructions (DNA) n Machinery to carry out instructions and regulate processes (proteins) n Compartmentalization of incompatible or specialized activities (organelles) n Cell & Organelle Membranes: More than just a phospholipid bilayer • Cell membrane •Plasmalemma • Organelle membranes Cell Size Varies with Function n n n n n n n Heyer Human nerve cell: > 1 meter Frog egg: 2 mm Average animal cell: 50 µm Human red blood cell: ~8 um Bacteria: 1–2 µm Organelle: 1 µm Virus: 50 nm 1 Basic Cell Structure Why Must Cells Be Small? Smaller cells have more total surface area n Increased surface area makes it easier for gasses, nutrients, etc. to enter a cell ‹ Same volume fi Why Must Cells Be Small? So, Why Can’t Cells Be Even Smaller? Upper limits on cell size are set by diffusion distance. Molecules must diffuse through cell. v They must be big enough to hold all their parts! v Macromolecules cannot be shrunk. v Volume controlled by nucleus. Early views of cells n n n Plasma membrane “Nucleus” ( “center”) – filled with “chromatin” (“colored stuff”) “Cytoplasm” (“cell fluid”) Modern v iews o f c ells n Better microscopes and stains n “Cytoplasm” and “chromatin” much more complicated, structured, and dynamic than previously appreciated. unstained human cheek cell – Electron microscope. 50µ m stained 5 µm Heyer 2 Basic Cell Structure Two major types of cells EUKARYOTIC CELL Membrane Cell-Type Systematics PROKARYOTIC CELL Five-Kingdom Model DNA (no nucleus) Membrane Cytoplasm Contrasting eukaryotic and prokaryotic cells in size and complexity I. Prokaryotic — Bacteria • No membranous organelles II. Eukaryotic — Protists • Single celled or simple colonial III. Eukaryotic / multicellular — Plant • Organelles present, including chloroplasts • Cellulose cell wall around plasma membrane IV. Eukaryotic / multicellular —Fungi • No chloroplasts • Chitinous cell wall V. Eukaryotic / multicellular — Animal • No chloroplasts nor cell wall • Varied cell morphology Organelles Nucleus (contains DNA) 1 µm Prokaryotes lack a true endomembrane system Prokaryotic Cell Structure n n n n n Single-celled organisms No nucleus nor other membranous organelles No cytoskeleton Most with cell wall outside plasma membrane Some with capsule outside cell wall v The plasma membrane is the only membrane. Photosynthetic prokaryote Eukaryotic Cell Structure Cytoplasm —organelles & cytoskeleton n Fills cell; contains – cytosol • fluids and more • gel & sol state – membrane-bound organelles • concentrate specific enzymatic activities • isolate incompatible reactions or toxic products – cytoskeleton • maintain and alter cell shape • hold and move organelles, etc. Heyer 3 Basic Cell Structure Organelles & Cytosol Cellular Organelles n Nucleus – Nuclear envelope – Nucleolus • Nucleus of nucleus • Transcribes rRNA for ribosomes – Chromatin/ chromosomes – Nuclear lamina n • Protein scaffolding underlying the envelope and supporting the chromatin Cytosol : Dense, semisolid aqueous gel containing a tremendous variety of solutes and macromolecular machines Nuclear envelope: 2 membranes Nucleus n n n Nuclear envelope surface Double-membrane with pores Contains DNA of chromosomes Controls cell Pore complexes – structure – function n Blueprints for new cells Nuclear lamina Nuclear envelope: 2 membranes Cellular Organelles n Endoplasmic Reticulum Smooth E.R. – New membrane synthesis – Lipid synthesis & processing – Steroid synthesis – Lipophilic detoxification – Intra-cellular Ca ++ store – Usually tubular appearance Heyer 4 Basic Cell Structure Cellular Organelles n Endoplasmic Reticulum Cellular Organelles n Ribosomes – Free and RER-bound Rough E.R. – Ribosome attachment sites – Synthesis of membrane proteins – Synthesis of proteins for secretion or intra-organelle storage – Flattened beaded stacks; Membrane often continuous with nuclear envelope RER to Golgi Cellular Organelles n Golgi Complex Transporting proteins in vesicles – Further processing and trafficking of proteins from RER – Receives vesicles from ER; buds off vesicles to plasma membrane for export Progression of membrane & proteins Cellular Organelles n Vesicles – Shuttle between organelles and plasma membrane Heyer 5 Basic Cell Structure Cellular Organelles n Lysosomes are digestive compartments Lysosome – Contains hydrolytic enzymes – Digest food, bacteria, old cell parts – Apoptosis (cellular self-destruct)? Vacuoles Lysosomes are digestive compartments Lysosomes Central vacuole in a plant cell Large storage vessels 150 µ m Fat vacuoles in adipose cells Contractile vacuole Endomembrane System n Continuous exchange of membrane and membranous contents Paramecium lives in fresh water — takes on water by osmosis. Pumps out water with the contractile vacuole. Heyer 6 Basic Cell Structure Endomembrane System Peroxisomes n n May form from ER or autonomously Both produces and removes hydrogen peroxide – Detoxifies organic compounds, e.g. ethanol – Destroy bacteria w Nuclear envelope w Endoplasmic reticulum n w Golgi apparatus n w Lysosomes ß-oxidation of fatty acids Phospholipid synthesis — esp. myelin Chloroplast Peroxisome Mitochondrion w Vacuoles & vesicles Figure 6.19 Cellular Organelles: bioenergetics n Mitochondria 1 µm Cellular Organelles: bioenergetics n Chloroplast – Triple-membrane – Photosynthesis – Double-membrane – Aerobic respiration • uses sunlight to construct organic molecules (CO 2Æ sugar) • Powerhouse of cell • Converts chemical energy from catabolism into ATP – Also have some of their own DNA – Plants & some protists – Have some of own DNA to maintain activity when nucleus is unavailable Cytoskeleton Cytoskeleton protein framework that extends throughout the cytoplasm Organizing the organelles Heyer 7 Basic Cell Structure Cell Support Structures n Cytoskeletal structures Cytoskeleton microtubules structural protein motor protein Cytoskeleton microfilaments intermediate filaments Tubulin (dimer ) Actin Keratin (and others) Dynein (and others) Myosin ∅ Cytoskeleton Tensegrity: A balance of tension & compression Cytoskeleton Cellular Structure: Centrioles Microtubule organizing centers Heyer 8 Basic Cell Structure The nucleus & the cytoskeleton Vesicle transport along microtubule “rails” ATP energy is used to pull vesicles along microtubules. n Intermediate filaments penetrate envelope to connect with nuclear lamina n Microtubule organizing center adjacent to nucleus Cell Mobility Structures flagella & cilia Eukaryotic versions n Flagella n Cilia HOW DO CILIA AND FLAGELLA MOVE ? HOW DO CILIA AND FLAGELLA MOVE ? CILIA FLAGELLA n Dynein arms cause microtubules to bend Molecular motors: structure of cilia & flagella Fig. 4.19 Heyer 9 Basic Cell Structure Myosin cross-bridges pull actin filaments along Cytoskeletal support of cell membrane Crowded network of cross-linked microfilaments (red) underlying the plasma membrane (blue) . “cytoplasmic cortex ” Cytoskeleton and pseudopodia Cytoplasmic Streaming n n Motor proteins pull cytoplasmic macromolecular complexes and organelles along the microfilament meshwork Many Variations in Theme 5 µm The Cell: A Living Unit greater than the sum of Its parts n Cells rely on the integration of structures and organelles in order to function Selective growth of the microfilament meshwork produces a bulge (pseudopodium) in cell membrane for amoeboid movement or phagocytosis. Figure 6.32 Heyer 10 ...
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