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Cell Structure 1. Cell Membrane cell is basic unit of all life; structural and functional anything that is alive must contain at least a single cell the function of an organism is the summation of functions of its individual cells phospholipids tend to arrange into a double layered film in human body single fertilized egg ! 75–100 trillion cells (adult) proteins “float” in this bilayer fluid mosaic (1972 Singer & Nicholson) [>10x’s more bacterial cells in body] ! proteins randomly arranged in lipid bilayer not fixed There are about 200 different kinds of cells in the human body with a variety of sizes and shapes some protein functions: receptors (ie. docking sites) for specific substances junctions between cells channel proteins: have pore, act as pumps and gates to selectively move specific substances through c.m. enzymes: energy transforming enzymes anchoring: bound to cytoskeleton human cells range in size from: human egg barely visible to naked eye to cells over 3 ft long diversity in size and shape !less diversity in function the cell membrane is selectively permeable some things enter freely 2. Cytoplasm (=Cytosol) Basic Components of Most Cell: a. cell membrane - boundary b. cytoplasm (=cytosol) c. nucleus d. organelles and internal structures – includes everything except cell membrane -genetic material contains mostly water, ions, organic molecules etc variety of enzymes eg. glycolysis - highly organized, specialized structures Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 defines boundary highly ordered !phospholipids, proteins, cholesterol 3. Nucleus 1 Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 contain enzymes for respiration and produces most of cells ATP (=energy) largest of internal cell structures number varies: one to many !use 02 in energy reactions in humans most cells have one nucleus RBC’s have none a few cells are multinucleate (2-50 nuclei) typical cell has dozens to 100,000’s !number related to cells activity eg: muscle cells liver cells sperm cells eg. liver, skeletal muscle cells and certain osteoblasts and ‘thromboblasts’ 100,000’s/cell 1000’s/cell ~25/cell 6. Ribosomes contains genetic material: replication and reproduction daily metabolism workbenches for protein synthesis !protein factories genetic material =chromosomes 100’s times length of cell humans ~3’ of DNA/cell = DNA with chromatin =highly organized histones up to 1000’s per cell ># ribosomes = > amount of protein synthesis 7. Endoplasmic Reticulum 4. Nucleolus (= “little network within the cytoplasm”) densely packed chromosome region within nucleus a single highly branched membranous tube, with sacs and channels site of RNA synthesis two types: most cells contain both types 5. Mitochondria (in different proportions) Rough ER: power plants of cells: Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 2 3 Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 4 lots of ribosomes attached to surface synthesizes carbohydrates and complex organic molecules protein synthesis and transport esp those that are secreted or those found in lysosomes encloses chemicals in vesicles and takes them to the cell membrane for secretion especially in protein exporting cells usually 1 to several 100 golgi bodies eg. liver and pancreas but can have up to 25,000/cell Smooth ER: !highest in secretory cells no ribosomes 9. Lysosomes lipid metabolism membrane bound package of digestive enzymes transports lipids throughout cell several 100/cell most cells have only a small amt of smooth ER contains at least 50 different enzymes !capable of breaking almost every kind of large organic molecule most common in lipid synthesizing cells esp liver cells adrenal cortex (steroid hormones) testes – steroid hormone synthesis digestive system for cell: destroys unwanted materials, cellular debris, worn out organelles, eg. mitochondria 8. Golgi Bodies (Golgi Apparatus) stack of membranes (flattened sacs) used to destroy invading pathogens eg WBC’s, neuroglial cells packing and shipping gets rid of worn out cells = suicide bags Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 5 Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 6 helps move things around in the cell = apoptosis (programmed cell death) 12. Centrioles eg. uterus at full term weighs ~900g, shrinks to 60 g within 5 or 6 weeks after delivery each cell has one pair – at right angles to each other 10. Peroxisomes functions in cell division: mitosis & meiosis ! helps form spindle resemble lysosomes but with a different set of enzymes ! contains oxidases Structures found on the surfaces of some cells: detoxification =removes poisons 13. Microvilli eg. alcohol and other drugs extensions of cell membrane that greatly increase its surface area eg. free radicals several 100 per cell best developed in cells specialized for absorption ! intestinal lining ! nephric tubules (PCT) ! esp in liver and kidney cells 11. Cytoskeleton 1000’s/cell in intestine ! give cells 15 – 40 times more surface area microfilaments and microtubules responsible for the overall shape & rigidity of each kind of cell 14. Membrane Junctions used in: cell movement phagocytosis holds organelles in place Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 formed by various proteins associated with the cell membrane a. tight junctions 7 Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 8 eg. mainly in respiratory tract and uterine tubes form impermeable barriers 16. Flagella eg: keeps digestive enzymes in intestine from leaking into blood similar to cilia but much longer and only 1/cell eg. prevents intestinal bacteria from invading tissues eg. flagella are found only on sperm cells 17. Membrane Surface Receptors b. desmosomes “guy wires” throughout sheet of cells diverse molecular sites at which cells chemically recognize and bind extracellular substances especially in tissues subjected to stretching proteins, glycoproteins, lipoproteins !prevents sheets of cells from tearing binding often causes metabolic changes => “activates” cell to do something eg. skin, neck of uterus, heart muscle also important in cell-to-cell identity eg. surface markers !defense against foreign cells and tissues c. gap junctions create pores between cells allows direct passage of small molecules and ions between cells eg. intercalated discs in cardiac muscle cells 15. Cilia cilia are hairlike processes found in some cells ! some are able to move = motile cilia beat in waves moving mucus or egg cells along tubes Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 9 Microscopy , Cells, Tissues: Cell Structure – Animals/Humans; Ziser Lecture Notes, 2005 10