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Cytology - Coggle Diagram
Cytology
Microscopy
Light microscope: light is passed through specimen & glass lenses. The lenses refract (bend) the light so the image of the specimen is magnified as when viewed
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Scanning electron microscope (SEM): electron beam scans the surface of the sample, usually coated with a thin film of gold. The beam excites electrons on the surface, and secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal sent to a video screen. The result is 3D image of specimen's surface.
Transmission electron microscope: aims an electron beam through a thin section of the specimen. the specimen has been stained with atoms of heavy metals, which attach to certain cellular structures, thus enhancing the electron density of some parts of the cell more than others. The electrons passing through the specimen are scattered more in the denser regions, so fewer are transmitted. The image displays the pattern of transmitted electrons. SEM & TEM use electromagnets as lenses to bend paths of the electrons, ultimately focusing the image onto a monitor for viewing.
super-resolution microscopy: allowed researchers to break the resolution barrier & distinguish subcellular structures as small as 10–20 nm across.
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Cytoskeleton (euk.)
cytoskeleton: a bunch of fibers in the cytoplasm
- Supports & maintain cell shape
- important for animal cells, which lack walls
Cell motility: cell movement
- cell uses motor proteins to move (look like little legs)
Microtubules:
- hollow rods made from globular proteins called tubulins (each tubulin protein is a dimer)
- grow longer by adding tubulin dimers
- involved in separation of chromosomes during cell division
- guide vesicles from ER to Golgi & from Golgi to the cell membrane
- grow out from a centrosome (area sometimes near the nucleus)
- flagella & cilia (singular, cilium) r extensions that have microtubules
Cilia
- act as “antenna” for cell
- dyneins: help move cilia & flagella (& has walking feet)
Microfilaments (Actin Filaments)
- are thin solid rods
- built from molecules of actin
- helps cytoskeleton to to bear tension
- crawls on a surface by extending cellular extensions; pseudopodia (fake feet)
- In plant cells, actin-protein interactions contribute to cytoplasmic streaming: circular flow of cytoplasm
- Intermediate filaments: larger than the diameter of microfilaments but smaller than that of microtubules | more permanent fixtures | reinforce shape of a cell and fix the position of certain organelles
Cell Walls:
- protects plant cell
- maintains its shape
- prevents excessive take of water
- thicker than plasma membrane
- primary cell wall: thin & flexible layer that surrounds the plasma membrane of a young cell
- middle lamella layer of adhesive material found between the primary walls of adjacent young cells.
- secondary cell wall: durable; often deposited in several layers around plasma membrane; provides protection and support.
- plasmodesmata: channels that connect cell | filled with cytosol |
Animal Cell ECM (Extracellular Matrix)
- mainly glycoproteins and other carbohydrate-containing molecules
- collagen: which forms strong fibers outside cell
- fibronectin: glycoprotein
- integrins: surface receptor proteins (transmit signals between the ECM and the cytoskeleton)
Cell Junctions (animals)
- tight junctions: pressed together tightly, held by proteins prevent leakage of extracellular fluid
- desmosomes: Turn cells into strong sheets. attach muscle cells to each other
- gap junctions: like the plasmodesmata of plants
plasmodesmata: only in plants
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Cell structure
All cells have:
- Plasma/cell membrane: selective barrier
- Cytosol: semifluid portion of cytoplasm
- Chromosomes
- Ribosomes
Eukaryotic cell:
- DNA is in nucleus, which is bounded by a double membrane
- cytoplasm: region between the nucleus & plasma membrane. Within the cytoplasm of a eukaryotic cell, suspended in cytosol, are a variety of organelles of specialized form and funct
microvilli: thin projections from surface of some cells that increases surface area w/o increase in volume.
Nucleus:
- contains most DNA (Some in mitochondria & chloroplasts)
- nuclear envelope: encloses the nucleus & other layer is connected to ER. Both are phospholipid bilayers.
- Pore complex (protein) lines nuclear pores
- Inner nuclear membrane is lined by the nuclear lamina
- Chromosomes have: DNA, small basic proteins called histones (help coil DNA)
- Nucleolus: Site of r(ibosomal)RNA synthesis, contains RNA
Ribosomes:
- made of rRNAs & proteins
- carry out protein synthesis
- Not membrane bounded so not considered organelles.
- Cells with high rates of protein synthesis have large #'s of ribosomes & nucleoli
- free ribosomes -> in the cytosol
- bound ribosomes attached to the outside of the ER or nuclear envelope
ER (smooth)
- No ribosomes attached
- functions vary with cell type
- Produce steroids
- Enzymes of smooth ER detoxify drugs & poisons (usually by adding hydroxyl groups to drug molecules, making them more water-soluble and easier to flush out)
- stores C ions
ER (rough)
- Secrete proteins e.g glycoproteins(proteins with C's covalently bonded to them
- grows in place by adding membrane proteins and phospholipids to its own membrane
- Make Hydrolytic enzymes and lysosomal membrane
Golgi Apparatus
- products of ER, are modified & stored & sent elsewhere
- cis face: receiving dept. (usually located near ER)
- trans face: shipping dept.
- manufactures some macromolecules e.g polysaccharides
Lysosome
- Membranous organelle
- sac of hydrolytic enzymes that r used to digest (hydrolyze) macros
- Lysosomal enzymes work best in the acidic environment found in lysosomes
- excessive leakage from a large number of lysosomes can destroy a cell by self-digestion (found in death x - x )
- Carry out cell digestion aka phagocytosis
- Carry out autophagy (damaged organelle or small amt of cytosol becomes surrounded by a double membrane (of unknown origin), & a lysosome fuses with the outer membrane of this vesicle & the lysosomal enzymes dismantle it resulting in small organic compounds released to cytosol for reuse)
Vacuoles
- large vesicles from the ER & Golgi
- Food vacuoles: formed by phagocytosis
- contractile vacuoles: pump water out of cell; maintain suitable concentration of ions & molecules
- help protect plants by storing poisonous compouds
- contain pigments
- central vacuole: plays major role in the growth of plant cells, which enlarge as it absorbs water, enabling cell to become larger with a minimal investment in new cytoplasm
Prokaryotic cell:
- DNA is in nucleoid; not membrane bound
- cytoplasm: some prokaryotes contain regions surrounded by proteins (not membranes)