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Transcript
The Cellular Level of Organization –Part B 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 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 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 Proteasomes • Hollow cylinders which contain proteindigesting enzymes ( proteases) • Remove and recycle damaged or denatured proteins • Also play a role in the immune response 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 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 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 Vesicles • Membrane bound sacs • Formed during endocytosis or by golgi apparatus • Transport • Renew membrane – membrane flow 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 Peroxisomes • Smaller than lysosomes • Enzymes use molecular oxygen to oxidize substances • Reactions produce Hydrogen PeroxideH2O2 – Free radicals 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 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 Flagella and cilia • Cilia – “eyelashes” cilium • 9+2 array • Anchored to basal body Flagella 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 Inclusions Usually contain chemical substances produced by the cell, these are temporary structures that are not surrounded by a membrane. Melanin, glycogen, triglycerides ribosomes 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 The Cell Cycle • • • • Nuclear division (mitosis or meiosis) Cytoplasmic division – cytokinesis Mitosis is somatic (body) cell division Meiosis is reproductive cell division Mitosis Homologous chromosomes Cell cycle – from one cell division to the next Interphase – “resting phase” G1 – Gap1 – growth phase S – Synthesis – replication of DNA G2 – Gap 2 Nuclear division – mitosis or karyokinesis Prophase Metaphase Anaphase Telophase PMAT Cytokinesis • Contractile ring of actin microfilament • Cleavage furrow • Two new daughter cells GPCR GPCR Steroid receptors 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 Control – contd. • Cell size • External factors –hormones and growth factors • Contact inhibition 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