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Nucleus, ribosomes and endoplasmic reticulum 5/25/12 Cellular Uptake • • • • • • • • • • • • • • • • • • • • Major ways that cells acquire large samples from environment Phagocytosis-”cell-eating” or engulfment – – Amoebae or macrophages Cell produces pseudopod to surround large object Pinocytosis-”cell drinking” – Vesicle forms and brings in liquid Endocytosis-receptor mediated – – A specific receptor-target interaction triggers Forms coated pit and vesicle Vesicle Nomenclature Vesicles have specific names that are linked to their origin – – – Phagocytosis=phagosome Pinocytosis=pinosome or uncoated vesicle Endocytosis=endocytic vesicle or coated vesicle Nucleus Command center of cell Where DNA as chromosomes is located Membrane bound Site of transcription and RNA modification and maturation Normally only one per cell unless cell is actively dividing Nuclear membrane Double membrane with perinuclear space in between Very important for cell function – Allow separation of mRNA from translational machinery • Allows modification and maturation of mRNA before it is translated into proteins Membrane is covered with octameric pores that allow mRNA out and nuclear proteins in Ribosomes cover outer membrane and translate mRNA into proteins Nucleolus Very dense core of nucleus Easy to see on EM Responsible for synthesis of ribosomes Essential for cell function DNA Structure In the nucleus, DNA exists as highly compact structures known as chromosomes Many levels of compaction – – – DNA is wound around Histone proteins like rope around a barrel Histones associate and bring the complexes closer together Looping and supercoiling compact DNA even further • • • • • DNA would be larger than cell if not compacted Ribosomes Synthesize protein via translation – Use mRNA as template Comprises two subunits-60S and 40S Very complex structures made up of many small proteins and rRNA molecules Ribosome Location Ribosomes perform one function but are found at several locations – – – On outer surface of nuclear membrane On Rough Endoplasmic Reticulum Free in cytosol Endoplasmic Reticulm • • • Complex mass of membranes with cytoplasm of cell • Complex structure with: – Tubules-thin tubes of membrane – Cisternae-large holding vats Extension of nuclear membranes and perinuclear space Two varieties – Rough-coated with ribosomes – Smooth-no ribosomes Roles of ER • • Rough Ribosomes synthesize excreted proteins – Stored in cisternae or vesicle • Modify proteins – Glycosylation of proteins • • Delivery of membrane associated proteins Often interacts with the Golgi • • • • • Smooth Tissue-specific uses Storage of carbohydrates Detoxification reactions in liver Synthesizes much of the new membrane material • Modification of existing molecules