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UNC-Chapel Hill BIOL 205 - Study Guide

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01.13.10Lecture 2: How to Study CellsLight microscopy led to the discovery of cellsThe microscope used by Robert Hook, the first person to discover cells in thin sections of cork Robert Hook(1635-1703)Schwann’s Cell Theory• All organisms are made of cells• Cells are the fundamental unit of life• Cells come from other cellsTheodor Schwann(1810-1882)Cellular Unity and Diversity• Delimiting membrane to separate inside from out• Metabolism to build complex molecules from food and energetic molecules from light (photosynthesis) or respiration• Capacity for reproduction:Genes ==> transcription ==> translation ==> structure & regulation DNA ==> mRNA ==> proteins ==> subunits & enzymesCellular Unity: all cells share a set of common characteristics• Common biochemistry: all cells use the same basic building blocks (e.g. DNA, RNA, amino acids, lipids, carbohydrates)• Common macromolecules and supramolecular structures and physiology (e.g. lipid bilayers, ribosomes, use ATP as energy)Cellular Diversity: cells may be categorized based on their complexityTwo major classes of cells based on complexity of intracellular organization:1. Prokaryotes (no nuclear envelope)2. Eukaryotes (nuclear envelope)A typical prokaryotic cellCapsule: Layer of polysaccharide (sugars) that protects the bacterial cell. Often associated with pathogenic bacteria as it serves as a barrier against phagocytosis by white blood cells.Cell wall: Composed of peptidoglycan (polysaccharides + protein). Maintains the overall shape and structure of the cell.Plasma membrane: The external membrane. Regulates selective transport into and out of the cell.A typical prokaryotic cellFlagella: Stiff helical structure rotated by a rotary engine embedded in the membrane. Produces motility.Pili: Hollow, hair-like structures that allow bacrterial conjugation.Nucleoid: DNA in the bacterial cell is generally confined to this region - not bounded by a membrane.Ribosomes: The sites of protein synthesis - smaller than the ribosomes in eukaryotic cells.A typical eukaryotic cellPlasma membrane: The external membrane. Regulates selective transport into and out of the cell. Has proteins that serve as receptors and cell-cell connectors.Nucleus: Houses most of the cell's genetic material as DNA packaged into chromatin. The site of DNA replication and gene transcription. Bound by a double membrane with access possible through nuclear pores.Mitochondria: Composed of a double membrane (like the nucleus). Cellular "power factory" - major site of ATP synthesis. Possesses its own DNA and ribisomes (beleived to be evolved from bacteria).A typical eukaryotic cellRibosomes: Molecular machines that read mRNAs and direct protein synthesis. Soluble in cytosol and bound to Rough Endoplasmic Reticulum (RER)Endoplasmic reticulum (ER): Site of lipid biosynthesis: Site of membrane protein synthesis (by RER-bound ribosomes) and of proteins destined for secretionGolgi apparatus: Stacks of membrane-bound discs. Proteins coming from the ER are modified with sugars (glycosylation)Lysosomes: Contain proteases and digestive enzymes. Fuse with endocytic vesicles to digest contentsA typical eukaryotic cellPeroxisomes: Contain oxidative enzymes for lipid and amino acid metabolism. Hydrogen peroxide (very toxic) generated and degraded here.Cytosol: A solution of large and small molecules - very dynamic.Cytoskeleton: 3 types of filamentous polymers that act as a scaffolding to give cells shape and mechanical strength. Tracks for transport of organelles and machinery for cell division.Centrosome: Organizes cytoskeleton. Pairs of centrioles + pericentriolar material (PCM).Prokaryotes vs. EukaryotesWhat kind of cells to study?Experimental organisms are valuable for the study of cell and developmental biologyCultured animal cells are an experimentally tractable system• Primary culture: cells are taken directly from the organism and grown. These cultures only divide for a certain number of time, then quit.• Cell lines: derived from undifferentiated embryonic cells or tumor cells. These cultures are immortal.• Cultured cells are grown in mediumPros and cons of cultured cells as a modelAdvantages:1. Most tissues consist of multiple cell types, whereas cells of a specific type with homogeneous properties can be grown in culture.2. Experimental conditions are easier to manipulate and observe with cultured cells than with organisms.A BIG disadvantage:1. Cells cultured in a dish are not in their normal environment and their behaviors are not regulated by other cells and tissues the way they are in an organismCells are (relatively) small. How do we study them?A modern light microscopeWhat microscopes do - designed for:1. Magnification: the relative enlargement of the specimen when viewed through the microscope2. Resolution: the ability to discern fine details. The resolution of a microscope is determined by the wavelength of light (or energy) used for illumination. For light microscopy,the limit is ~200 nm.3. Contrast: the difference in intensity between the image and the background. Contrast is produced in the specimen by staining with colored dyes that absorb light, by using special optical techniques, or 2 Pictures of a flea at same magnification. (a) was acquired using optics that provided higher resolution than (b)Contrast may be generated using colored stains or interference effectsHistological staining for thick specimens such as tissues1. Specimens must be preserved and “glued” together in a process called fixation.2. Thick specimens (such as intact tissues) are embedded in a solid matrix (paraffin or plastic) and cut in to thin sections.3. Sections may then be stained with dyes to highlight certain cells or parts of cells and viewed by light microscopy.Living cells can be visualized using techniques that generate contrast using interference effects•Most cells and tissues are transparent and colorless (low contrast•Cellular components differ from each other in refractive index•Optical techniques such as phase -contrast and differential interference contrast can be used to view living, unstained cellsPhase contrast DICLiving cells can be visualized using techniques that generate contrast using interference effects•Most cells and tissues are transparent and colorless (low contrast•Cellular components differ from each other in refractive index•Optical techniques such as phase


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UNC-Chapel Hill BIOL 205 - Study Guide

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