Chapter 4 The Eukaryotic Cell The Nervous System.pdf

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Biology - Biological Sciences
BSC 3096

Chapter 4 The Eukaryotic Cell; The Nervous System Wednesday, July 03, 2013 1:04 AM 1. The nucleus a. Contains all of the DNA in an animal cell (except for small amounts in the mitochondria) b. Aqueous soup inside the nucleus is called the nucleoplasm c. Wrapped in a double phospholipid bilayer called the nuclear envelope/membrane i. Perforatedwith large holes called nuclear pores 1) RNA can exit through the pores but DNA cannot d. Within the nucleus there is an area called the nucleolus where rRNA is transcribed and the subunits of the ribosomes are assembled i. NOT separated from the nucleus by a membrane 2. The membrane a. Cells can acquire substances from the extracellular environment though transport and endocytosis b. i. Phagocytosis 1) Cell membrane protrudes outward to envelopeand engulf particulate matter 2) Only a few special cells are capable of phagocytosis, macrophages and neutrophils a) Antibodies or complementproteins bind to particles to be engulfed 3) Once the particulate matter has been engulfed, it is called a phagosome ii. Pinocytosis 1) Extracellular fluid is engulfed by small invaginations of the cell membrane a) Performedby most cells and in a random fashion (nonselective) iii. Receptor mediated endocytosis 1) Uptake of macromoleculessuch as hormones and nutrients 2) Ligand bands to a receptor protein on the cell membrane and then movedto a clathrin coated pit a) Clathrin is a protein that forms a polymer adding structure to the underside of the coated pit 3) The pit invaginates to form a coated vesicle 4) One way this process differs from phagocytosis is that its purpose is to absorb the ligands, whereas the ligands in phagocytosis exist only to act as signals to initiate phagocytosis of other particles c. Exocytosis is the reverse of endocytosis d. Phospholipid bilayer of eukaryotes is similar to prokaryotesexcept d. Phospholipid bilayer of eukaryotes is similar to prokaryotesexcept membrane invaginates and separates to form individual membrane bound organelles 3. Organelles a. ER i. ii. Network of interconnected membrane tubes that are a continuation of the outer membrane of the cell nucleus iii. Three major functions of both rough and smooth: 1) Synthesis 2) Storage 3) Transport of biomolecules iv. The lumen is contiguous in places with the space between the double bilayer of the nuclear envelope 1) v. ER near the nucleus have many ribosomesattached to it on the cytosolic surface 1) Translation on the rough er propels proteins into the ER lumen where they are created then tagged with a signal sequence and sometimes glycosylated 2) The newly synthesized proteins are movedthrough the lumen towards the Golgi apparatus via small transport vesicles that bud off the ER vi. Smooth ER have no ribosomes 1) Contain glucose-6-phosphatase,an enzyme used in the liver, intestinal epithelial, and renal tubule epithelial cells, to hydrolyze glucose from g-6-p 2) Triglycerides are produced in the smooth ER and stored in fat droplets 3) Plays a role in cholesterol formation and conversion to steroids to steroids 4) Synthesis of cell membrane phospholipids 5) Oxidized foreign substances, detoxifies drugs, pesticides, toxins and pollutants b. Golgi apparatus i. Series of flattened, membrane bound sacs ii. The Golgi organizes and concentrates proteins as they are shuttled by transport vehicles progressively outward from one compartment(called cisterna) to the next iii. Proteins are distinguished based upon their signal sequence and carb chains 1) Proteins that do not possess signal sequences are packaged into secretory vesicles and expelled from the cell in a process called bulk flow iv. The Golgi may change proteins by glycosylationor by removing AA v. Some polysaccharide formationalso takes place vi. The end product of the Golgi is a vesicle full of proteins 1) Proteins can either be expelled from the cell as secretory vesicles 2) Or released from the Golgi and mature into lysosomes 3) Or transported to other parts of the cell, such as the mitochondria or even back to the ER c. Secretory vesicles (zymogen granules) i. May contain enzymes, growth factors, or extracellular matrix components ii. Release contents via exocytosis,which incorporates the vesicle membrane into the cell membrane 1) In other words, they act as the vehicle to supply the cell membrane with its integral proteins and lipids and the method for membrane expansion 2) In the reverse process, endocytoticvesicles made of the cell membrane are recycled by the Golgi iii. Constitutive secretion 1) Secretory vesicles are continuously released 2) Used to maintain cell membrane 3) iv. Regulated Secretion 1) Some vesicles chill out in the cytoplasm waiting for a signal 2) Once the signal is received,the vesiclesfuse with the membrane v. Some proteins are activated once they are inside the secretory vesicles, such as proinsulin d. Lysosomes i. Small spherical storage vesicles that act as the digestive system of the cell ii. Use powerful enzymes to break down bacteria or old organelles iii. Enzymes inside are not always active 1) When lysosomesfirst pinch off the Golgi, the interior pH is about the same as the cytosoland the enzymes are inactive a) This acts as insurance. If the lysosome were to rupture, they will not harm the cell 2) As the lysosomesits in the cytoplasm,it accumulates H+, lowering the pH and activating the enzymes iv. The digestive enzymes are not always kept isolated inside iv. The digestive enzymes are not always kept isolated inside 1) They can release their enzymes outside the cell to dissolve extracellular support material, such as hard the hard calcium carbonate portion of bone 2) Can also release contents into cytosoland kill the cell, called autolysis e. Peroxisomes i. Grow by incorporating lipids and proteins from the cytosol ii. Self-replicate instead of budding off the Golgi iii. Main function is to degrade long chain fatty acids and potentially toxic foreign material iv. Reactions inside generate hydrogen peroxide, which is toxic to the cell 1) The enzymes inside the peroxisomescovert h202 into oxygen and water 4. Cellular filaments a. Structure and motility of a cell determined by cytoskeleton b. Cytoskeleton i. Anchors some membrane proteins and other cellular components,moves components within the cell, and moves the cell itself ii. Made from microtubules and microfilaments 1) Tubules are larger than filaments c. Microtubules i. Rigid hollow tubes made from tubulin 1) Tubulin is a globular protein, but under certain cellular conditions it will polymerize into long straight filaments 2) There are tubulin types α and β 3) Thirteen of these filaments lie alongside each other to form the tube 4) The mitotic spindle is made from microtubules 5) d. Microfilaments i. Smaller than microtubules i. Smaller than microtubules ii. Actin forms a major component iii. Produce the contracting force in muscle iv. Responsible for Cytoplasmic streaming 1) Directed flow of cytosoland organelles around fungal and plant cells using actin v. Responsible for phagocytosis and microvillimovement e. Flagella and cilia i. ii. Made from microtubules iii. Membrane bound cylinders consisting of an inner core called the axoneme iv. Axoneme 1) Contains nine pairs of microtubules forming a circle around two lone microtubules 2) Arrangement is known as 9+2 3) Cross bridges made from the protein dynein connect each pair to each other a) These cross bridges cause the microtubule pairs to slide along their neighbors creating a whip action in cilia or wiggle action in flagella b) v. Microtubules have a + and - end 1) The - end attaches to the microtubule organizing center in the cell (the centrosome in animal cells) vi. Centrioles function in the production of flagella and cilia, but are not necessary for microtubule production 5. Cellular Junctions a. Consists of multiprotein complexes that provide contact between neighboring cells b. Tight Junctions i. Forms a watertight seal from cell to cell that can black water, ions, and other molecules from moving around and past the cells cells ii. Acts as a complete fluid barrier iii. Epithelial tissue in various organs contain tight junctions to stop waste materials from seeping around cells iv. c. Desmosomes i. Join two cells at a single point ii. Attach directly to the cytoskeletonof each cell iii. Usually found in tissues that normally experience a lot of stress, such as the skin or intestinal epithelium iv. Often accompany tight junctions v. Not water tight vi. d. Gap Junctions i. Small tunnels connecting cells ii. Allow small molecules and ions to move between cells iii. In cardiac muscle, allow for the spread of the action potential from cell to cell 6. Mitochondria a. b. Powerhouse of the cell c. Endosymbiont theory i. Mitochondria evolvedfrom a symbioticrelationship between ancient prokaryotes and eukaryotes ii. Like prokaryotes,mitochondria have their own circular DNA that replicates independently from the eukaryoticcell 1) Contains no histones or nucleosomes iii. The genes in the mDNA code for mRNA that is distinct from the RNA in the rest of the cell 1) Thus, mitochondria have their own ribosomes 2) Still, most proteins used by the mitochondria are made in the nucleus, not the mitochondria iv. Antibiotics that black translation by prokaryoticribosomes also block mitochondrialribosomes d. Mitochondrial DNA is passed maternally e. Surrounded by two phospholipid bilayers f. The inner membrane invaginates to form cristae i. The inner membrane holds the ETC g. Between the inner membrane and outer membrane is the inner membrane space 7. Extracellular Matrix a. Tissue- a group of biological cells that perform a similar function i. Muscle tissue, connective tissue, nervous tissue, epithelial tissue b. ECM is extracellular material that issynthesized and secreted by cells of a tissue i. Compositionof ECM varies from tissue to tissue ii. Two basic components are proteoglycansand insoluble protein fibers 1) Proteoglycansare proteins with a polysaccharide chain 2) Insoluble protein fibers (collagen, fibronectin, laminin) provide strength and anchor cells to the matrix) iii. The amount of ECM depends on the tissue that it is around 1) Nerve and muscle tissue have very little matrix iv. Consistency can be watery(blood) or rigid (bone) 1) Blood cells are the tissue (scattered throughout the ECM like other connective tissue) and the plasma is the ECM c. Basal lamina is ECM secreted by epithelia cells that separates the epithelial cells from the connective tissue below epithelial cells from the connective tissue below i. d. e. Glycocalyx i. Separates the cell membrane from the ECM ii. Consists of the glycoproteinsand glycolipids of the cell membrane iii. An identifier the body uses to distinguish between its own healthy cells and transplanted tissue, diseased cells, or invading organisms 8. Intercellular communication a. Communication can be accomplished chemically by either neurotransmitters (nervous system), local mediators (paracrine system), or hormones (endocrine system) 9. Paracrine system a. Local mediators are released from a variety of cells into the interstitial fluid b. Local mediators can be proteins, other AA derivatives, fatty acids i. Prostaglandins are fatty acid derivatives 10. Nervous System a. Allows for rapid and direct communication between specific parts of the body b. Includes sense organs (eye, ears…) c. Neuron i. Highly specialized cell capable of transmitting an electrical signal from one cell to another ii. Cannot divide iii. Depends almost entirely upon glucose for its chemical energy 1) Unlike most other cells which depend on insulin for glucose uptake, the neuron depends heavily on aerobic glucose uptake, the neuron depends heavily on aerobic respiration iv. Have many shapes, but all have cell bodies, dendrites, and axons (can have multiple of each) v. Classified either structurally or functionally 1) Structural classifications: a) Unipolar (Sensory)
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