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NIU BIOS 208 - Cell Structure, Nucleus Structure, and Cell Fractionation

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Bios 208 1st Edition Lecture 15Outline of Last Lecture I. Cell theoryII. MicroscopyIII. A prokaryotic cellIV. Cell SizeOutline of Current Lecture I. The plasma membraneII. Cell Structure (Eukaryotes) common to both animals and plantsIII. Cell FractionationIV. Endomembrane SystemV. Nucleus StructureVI. RibosomesVII. Endoplasmic reticulumVIII. Smooth Endoplasmic reticulumIX. Golgi apparatusX. LysosomesCurrent LectureI. The plasma membraneA. Plasma membrane (PM)B. Lipid bilayer with embedded proteins.C. Encloses the cytoplasmD. Interfaces with the environment.Controls what enters and leaves the cellII. Cell Structure (Eukaryotes) common to both animals and plantsA. Animal and plant cells:a) Nucleusb) Ribosomec) Plasma membraned) EndoplasmicThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.e) Reticulumf) Golgi apparatusg) MitochondrionB. Animals onlya) Lysosomeb) Flagellumc) CentrioleC. Plants onlya) Chloroplastb) Cell wallc) Central vacuoled) PlasmodesmataIII. Cell FractionationA. Homogenize: Cells are disrupted (e.g., with a blender)B. Centrifuge: Spin faster higher centrifugal force (g = force ofgravity). At any given g-force, largest particles will be pelleted, and smaller particles will be in the supernatant.C. Differential centrifugation yields “fractions” enriched in various organelles or structuresa) P1 (1k x g): nuclei, cell debrisb) P20 (20k x g): mitochondria, chloroplasts, lysosomesc) P80 (80k x g): microsomal membranes (ER, Golgi Apparatus, Plasma Membrane, etc.)d) P150 (150k x g): ribosomese) S150 (150k x g supernatant):cytosol; proteins, amino acids, ions, etc.IV. Endomembrane SystemA. Endomembrane system consists of:a) Nuclear envelopeb) Endoplasmic reticulumc) Golgi apparatusd) LysosomesB. Endomembrane system is interconnected by transport vesicles.V. Nucleus StructureA. Nucleus- Chromatin = DNA + protein (~ 50% of each by mass)a) Linear chromosomes; condensed (mitosis) vs. decondensed(interphase)b) Pairs of homologous chromosomesB. Nuclear envelope (NE)- Double membrane;connected to Rough ERC. Nuclear pore complexes regulate movement into and out of nucleusD. Nucleolus - rRNA (ribosomal RNA) transcription and ribosome assemblyVI. RibosomesA. Ribosomes carry out protein synthesis (translation): seq. of nucleotides in mRNA is translated to the seq. of AA’s in a polypeptide.B. Ribosomes are large and complex: The large subunit has ~ 50 proteins and 2 rRNA’s. The small subunit has ~ 30 proteins and 1 rRNA. Translating ribosomes consist of 1 large and 1 small subunit.VII. Endoplasmic reticulumA. Rough endoplasmic reticulum (RER): parallel sheets of interconnected cisternae. RER serves as a membrane factory for the cell. Also distributes transport vesicles, proteins surrounded by membranesB. Translation always starts on free ribosomes; if they remain free cytosolic proteinsC. Some ribosomes attach to ER:a) Luminal proteins pass through the ER.b) Integral membrane proteins remain in the ER.D. Proteins may be glycosylated (have sugars attached).E. This process begins in the RoughF. Endoplasmic Reticulum, and continues in the Golgi Apparatus.VIII. Smooth Endoplasmic reticulumA. Smooth ER (SER) Membrane tubules are interconnected with Rough ER, but no ribosomes are attached.B. Functions of Smooth ER in various cell typesa) Lipid synthesis. (most cells)b) Steroid synthesis. (adrenal glands, testes, ovaries)c) Breakdown of toxins (liver) and drugs like sedatives and barbiturates.d) Store ions (Ca++ in sarcoplasmic reticulum of muscle)…Ca++ stored inside Smooth ER, nerve impulse leaks Ca++ and muscle contracts.IX. Golgi apparatusA. Group of stacked cisternae; not interconnected.B. 2 sides:a) cis or forming faceb) trans or maturing faceC. Proteins from Rough ER are delivered in vesicles to the cis face; proteins go through each cisterna sequentially; proteins (and attached sugars) are modified sequentially.D. Assembly line modification of proteins. e.g. addition of sugar chains which act as “sorting codes” for delivery to different parts of cell, or secretion.E. Mature proteins are: a) Sortedb) Packaged into vesicles c) Delivered to other parts of the cell.X. LysosomesA. Lysosomes are organelles that are travelling “bags of destruction”.B. Hydrolytic (digestive) enzymes degrade macromolecules (protease, nuclease, lipase, glycosidase).C. Maximum enzyme activity is at pH 5…acidic conditions. (cytoplasmic pH ~ 7)D. Degrade food ingested by phagocytosis; amino acids, etc., are released and used by the cell. A lysosome fuses with the food vacuole and digests the molecules. e.g. macrophage white blood cells destroy bacteria…use lysosomes for defense.E. Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy.F. Lysosome membranes are special and have a 3D conformation which resists digestion by hydrolytic enzymes


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NIU BIOS 208 - Cell Structure, Nucleus Structure, and Cell Fractionation

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