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The Cellular Level of Organization –Part B
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Cytoplasm Cytosol –Semifluid, mostly water –Protein, carbohydrates, lipids, and inorganic substances (ions) –Many important metabolic reactions take place here –Cytoplasm is the cytosol plus the organelles
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Organelles “little organs” – have characteristic appearance and have specialized functions in cell growth, maintenance, repair and control. Number and types of organelle vary with cell. Two basic types: nonmembranous membranous
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Ribosomes Made of ribosomal RNA and protein –Free and associated with the endoplasmic reticulum ( fixed ribosomes) –Site of protein synthesis –Nonmembranous, Temporary structures made of large and small subunits
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Proteasomes Hollow cylinders which contain protein- digesting enzymes ( proteases) Remove and recycle damaged or denatured proteins Also play a role in the immune response
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Endoplasmic reticulum (ER) Endo – within Plasm – cytoplasm Reticulum - network Can be rough or smooth Rough ER has ribosomes, makes proteins for export outside of cell
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Smooth Endoplasmic Reticulum Synthesis of phospholipids and cholesterol Synthesis of steroid hormones Synthesis and storage of triglycerides Synthesis and storage of glycogen Storage of ions ( e.g. Ca++ in muscle) Detoxification and inactivation of drugs
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Gogli apparatus (body, complex) Made of flattened sacs called cisternae cis, medial, trans -Process, sort and deliver proteins and lipids to the plasma membrane -forms vesicles and lysosomes. -forms new plasma membrane The “UPS” of the cell
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Vesicles Membrane bound sacs Formed during endocytosis or by golgi apparatus Transport Renew membrane – membrane flow
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Lysosomes The cell’s “stomach” – vesicles that contain digestive enzymes. Primary lysosomes contain inactive enzymes work at low pH Found in large numbers in white blood cells Intracellular digestion ( phagocytosis etc.) worn-out organelles ( autophagy) digestion of cell contents (autolysis) Tay-Sachs disease
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Peroxisomes Smaller than lysosomes Enzymes use molecular oxygen to oxidize substances Reactions produce Hydrogen Peroxide- H 2 O 2 –Free radicals
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Mitochondria Mitochondrion – singular Two membranes – inner folds called cristae. Main function is the use of oxygen to produce ATP – cellular (aerobic) respiration These are the “power plants” of the cell. Have their own DNA and RNA
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Centrosomes and Centrioles Centrioles are 2 cylinders of tubules arranged at right angles. 9 + 0 array Form the microtubules of the mitotic spindle during cell division, and also make up a part of cilia and flagella Heart of the cytoskeleton
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Flagella and cilia Cilia – “eyelashes” cilium 9+2 array Anchored to basal body
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Flagella
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Cytoskeleton Microfilaments, intermediate filaments and microtubules Give the cell shape, and allow it to move – the Musculoskeletal system of the cell. Myofilaments are made of the protein actin Myotubules are made of the protein tubulin
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Inclusions Usually contain chemical substances produced by the cell, these are temporary structures that are not surrounded by a membrane. Melanin, glycogen, triglycerides ribosomes
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Nucleus Double membrane called the nuclear envelope Nucleoplasm Chromatin granules – unwound DNA Nucleoli – puts RNA and protein together to make ribosomes Nucleus is essential for cell survival
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The Cell Cycle Nuclear division (mitosis or meiosis) Cytoplasmic division – cytokinesis Mitosis is somatic (body) cell division Meiosis is reproductive cell division
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Mitosis Homologous chromosomes Cell cycle – from one cell division to the next Interphase – “resting phase” G 1 – Gap1 – growth phase S – Synthesis – replication of DNA G 2 – Gap 2
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Nuclear division – mitosis or karyokinesis Prophase Metaphase Anaphase Telophase PMAT
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Cytokinesis Contractile ring of actin microfilament Cleavage furrow Two new daughter cells
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GPCR
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Steroid receptors
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Control of cell division How many times a cell divides depends on the type of cell Stem cells retain the ability to divide and differentiate Cell senescence Telomeres Levels of proteins called kinases and cyclins
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Control – contd. Cell size External factors –hormones and growth factors Contact inhibition
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Loss of control over division Neoplasm or tumor Benign tumors remain in a single location Malignant tumors (cancer) can spread or metastasize Oncogenes – want these turned “off” Tumor suppressor genes – want these turned “on” Apoptosis
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