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U-M BIOLOGY 172 - Cell Structure and Communication

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BIO 172 1st Edition Lecture 12Outline of Last Lecture I. Cell StructureII. Endomembrane SystemOutline of Current Lecture I. Cell StructureII. Extracellular MembraneIII. Cell Communication (begin)Current LectureLysosomes: Recycle organelles, and repurpose the materials for use by the cell.Autophagy is an important process for eukaryotes, where damaged organelles or unnecessary components are broken down by a lysosome.Phagocytosis is also important, because it is the lysosome digesting food.Receptor Mediated Endocytosis:Receptors found within the membrane. Receptors bind to whatever is specific for them.Materials brought into cell, early endosome engulfs it. Then the cell must recycle the receptors so the receptors can continue to bring in materials. Receptors are recognized and shuttled back to membrane.An Endosome moves stuff from outside to inside the cell.Mitochondria:Mitochondria are energy processing chemical reactions. Cell respiration happens in the mitochondria, and for plant cells, Photosynthesis happens in the chloroplasts.Mitochondria have two membranes. Outer membrane is a boundary to help the mitochondria keep its shape. The inner membrane is where energy reactions take place.Mitochondrial matrix contains the organelles.Mitochondria have some of their own DNA, and some of their own Ribosomes. They alsocode some of their own proteins.Mitochondria are the organelle that generates energy for the cell!Question: Are all mitochondrial proteins coded for by Mitochondrial DNA? Answer: NO: many genes in the nucleus encode for proteins that are sent to the mitochondria. So mitochondria do have genes for themselves, but they still use the nucleus and its longer DNA sequence that encode proteins.Plants and Algae have Chloroplasts . . .Chloroplasts carry out photosynthesis. They possess their own DNA and Ribosomes, similar to mitochondria of animal cells.Chloroplasts are composed of THREE membranes, part of two systems.Chloroplasts have an Inner and outer membranes, then Granum is a full stack of Thylakoids (which are the site of photosynthesis).REVIEW of endoplasmic reticulum: Question: what does the Rough E.R. do?Answer: it makes proteins that will be exported/secreted! It does NOT: degrade organelles (lysosomes do that), nor carboxylate proteins, nor synthesize steroids.A protein needs a signal peptidesequence to move to aRibosome. Without one, it staysin the Cytosol.<>Nuclear genes provide the endterminal amino acid signals inproteins. These direct theprotein to either theChloroplast or Mitochondria.DNA polymerase gamma has hesignal so the mitochondria cangive energy to the cell.An Internal Signal is used to say the protein needs to be sent back and imported back into the nucleus.<> Airport Signal Peptide analogy: if you lose your luggage, the tag on it must have been broken. Thus, your luggage stays at the airport. SIMIARLY, if the amino protein (your “luggage”) loses its end terminal (its “tag”), it would just stay in the cytosol (the “airport”).Cytoskeleton: a network of proteins provides structure, organization, and movement to cells.Microfilaments: made of ACTIN. Involved in muscle contraction, and cytoplasm streaming. Directs the flow of cytosol around and throughout the cell, and in this way, helps the cell change shape.Microtubules: made of TUBULIN, involved in chromosome distribution, and cell motility (cilia). Alpha and Beta monomers come together to form a dimer (which is a quaternary protein structure!). This allows chromosome to move during mitosis.Intermediate Filaments: made of various components (keratin, lamin, etc.). Provides structural support. Allow specific proteins to be made/anchored where they are supposed to be.Cytoskeleton is especially prominent in Animal Cells, because they lack a cell wall!A Motor Protein moves Vesicles along microtubules.Tail of a motor protein binds to vesicle. The stalk is between the head and tail of the motor protein. The HEAD binds to the microtubule.The head on the microtubule pulls the stalk, tail, and transport vesicle behind it! Thus, the head moves along the microtubule and around the cell, allowing the vesicle to follow it.Kinesin is a common stalk/motor protein!Actin and Myosin interact to cause movement . . .Myosin head connects to actin. This helps CYTOKINESIS in animal cells, because this interaction pinches the membrane in two, finally separating the cells.Properties of Eukaryotes: Extracellular Matrix. (Animal cells!!)The Extracellular Matrix, or ECM, is composed of: Collagen, Fibronectin, and Integrins.Collagen: the main structural protein of the ECM. Forms a flexible extracellular layer.Fibronectin: a glycoprotein dimer that binds integrins to collagen. IMPORTANT for cell adhesion and wound healing. Having been glycosylated is what gets the fibronectin to the ECM.Integrins: transmembrane receptors pass information about the ECM. Integrins help a cell deal with its environment, as they integrate between the intra and extra cell environments.Integrins transmit from outside to inside. Many of the proteins it sends are glycosylated.ECM of animals: Animal cells secrete an ECM that consists of a gelatinous polysaccharide as ground substance and protein fibers instead of polysaccharide filaments.Collagen, the most common ECM protein fiber, is more elastic than cellulose and forms a flexible extracellular layer. The collagen fibers are made up of thousands of smaller, stiff subunits of 150 nm in length.Cellulose in plant cell walls, is very tough. There are many H-bonds between adjacent polymers. This provides stability!H-Bonds between O-H groups on adjacent chains (like starch hydrogen bonded to glycogen) forms microfibers that toughen the cell wall!*Animals cannot digest cellulose (we have a bacteria in our gut that helps us).Extracellular Membrane of Plants: The extracellular material secreted by plant cells first builds a primary cell wall of long strands of cellulose bundled into microfibril filaments that form a crisscrossed network. This network becomes filled with a gelatinous polysaccharide such as pectin, which is hydrophilic and keeps the cell wall moist.Cells Communicate with their Surroundings:Unicellular organisms live together and communicate with one another, but cell-cell physical connections are the basis of multicellularity. In multicellular organisms, cells can form tissues, which may combine to form an organ specialized for one biological function.Tight


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