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Transcript
Chapter 3 Anatomy of Cells Cell Theory • • • All living things are composed of one or more cells. Cells are the basic units of structure and function in living things. New cells are produced from existing cells. In 1839 German Scientists Theodor Schwann and Matthias Schleiden suggested that cells were the basic unit of life and that all living things came from cells Functional Anatomy • Refers to study of structure as they relate to function The World of Microscopy Light Microscope • Also referred to as the optical microscope • Uses visible light and a system of lenses to magnify images of small samples. • Limit of 2000 times greater Skin cells Anton Van Leeuwenhoek • • • • • Dutchman Commonly known as "the Father of Microbiology“ Considered to be the first microbiologist. Didn’t invent but did improve the light microscope. He was first to observed single celled organisms which he called animalcules Robert Hooke • • • • Englishman Known as "the father of microscopy“ Coined the term "cell" due to the fact that what he was looking at reminded him of a monk’s cell in a monastery Published a book in 1665 titled Micrographia Electron Microscope • Uses a particle beam of electrons to illuminate a specimen and create a highly-magnified image. • Can obtain much higher magnifications of up to 2 million times. • First prototype built in 1931 Fly foot Transmission Electron Microscope TEM • Electrons are emitted by an electron gun • Images are called transmission electron micrographs Hair Scanning Electron Microscope SEM • Beam of electrons scan the surface and are reflected from the surface • Gives illusion of depth Dust mite Single hair cell from frog’s ear Principle of Complementarity of Structure and Function • An organ's structure cannot be studied without understanding how it functions in the living system • An organ's function cannot be studied without understanding it’s structure in the living system. Cell Types Nerve Cell • Surface sensitive to stimuli • Long extensions • Detects changes in internal or external environment • Transmit nerve impulses from one part of the body to another Muscle Cell • Elongated and threadlike • Has tiny fibers that slide together forcefully • Made to contract or shorten • Used in movement of body parts Red Blood Cells • Contains hemoglobin • Transports oxygen in the blood stream RBC with malaria Gland Cells • Contain sacs that release secretion to outside of the cells • Releases substances such as hormones, enzymes, mucous and sweat. Exocrine gland Immune Cells • Main function is to destroy “nonself” cells such as cancer or bacteria. • Some have outer membranes that can engulf other cells • Some can manufacture antibodies • Some can destroy other cells T cell Composite Cell • Typical cell • Cells have many similarities 3 Main Cell Structures • Plasma membrane • Cytoplasm • Nucleus Cell Structures • Plasma membrane surrounds the cell • Inside cell is composed gel-like substance called cytoplasm • Cytoplasm is made up of various organelles and a watery fluid called cytosol or intracellular fluid • Nucleus is in the center of cell and is not part of cytoplasm. Review 1. What important concept was purposed by Schleiden and Schwann? 2. Give example of how cell structure relates to its function. 3. Three main cell structures Cell Membranes and Organelles • Made of lipids, protein and other molecules • Each cell has various membranous organelles which are sacs and canals made from the same material as the plasma membrane (See Table 3-2 page 77) Membranous Structures • Plasma membrane • Endoplasmic Reticulum (ER) • Golgi Apparatus • Lysosomes • Peroxisomes • Mitochondria • Nucleus Nonmembranous Structures • • • • Ribosomes Cytoskeleton Cilia and flagella Nucleolus Fluid Mosaic Model • Model of cell membrane structure composed of a lipid bilayer with scattered proteins; often described as a sea of lipids with protein icebergs. Fluid and moves around with a flowing changing pattern of arrangement. Plasma Membrane Plasma Membrane/Cell Membrane • Bi-layer of phospholipids • Hydrophobic tails and Hydrophilic heads Cholesterol •Steroid lipid that mixes with the phospholipids. •Stays fluid enough to function at body temperature. •Without it cell membranes would break far too easily •Forms fence like material that allows lipid soluble molecules to pass through Membrane Proteins •Act like gates allowing water soluble molecules through membranes. •Glycoproteins are formed •Glycoproteins have carbohydrates attached to them acting like identification markers •Some are receptors that react to things such as hormones •Carry molecules across membrane in a process known as signal transduction See Table 3-3 page 80 Cytoplasm • Gel-like internal substance • Contains suspended structures • Highly differentiated into organelles and cytosol Organelles Endoplasmic Reticulum (ER) • Endoplasm means cytoplasm is located toward the center of the cell • Reticulum means network • ER however is located throughout the cell as seen by electron microscopes • ER walls are basically the same molecular structure as the plasma membrane • Function in protein synthesis Endoplasmic Reticulum (ER) • Allows intracellular transport of molecules • Proteins move through canals toward the golgi apparatus • Two types: Rough and Smooth Rough ER • Ribosomes on the surface of the membrane make it rough • Proteins are synthesized, enter the canal and move toward the Golgi apparatus and eventually leave cell. Smooth ER • No ribosomes on walls • Smooth ER believed to synthesize lipids and carbohydrates Ribosomes • • • • Protein factories: Protein synthesis Many are attached to rough ER Can not be seen with a light microscope Made of two subunits. A large one and a small one (figure 3-6 page 82) Ribosomes • Each subunit contains a ribonucleic acid (RNA) bonded to a protein (rRNA, mRNA, tRNA) • Working ribosomes function in groups called polyribosomes. • Polyribosomes look like a string of beads under the electron microscope. Golgi Apparatus • It is a membranous organelle • Has several canals called cisternae • Process and packages protein molecules for export out of cell • Proteins are packaged into membranous bubbles called vesicles Golgi Apparatus Lysosomes • Lysosomes have membranous walls. • Vesicles that have been pinched off from the Golgi apparatus • Filled with enzymes capable of breaking down cell components • Lysosomes destroy cells by digesting them • They are the cellular garbage disposal of the cell • White blood cells Peroxisomes • Membranous organelle • Detoxify the cell • Contain peroxidase and catalase Mitochondria • • • • • • • Membranous organelle Called “the power house” of the cell Produce ATP for cell energy use Have 2 membrane walls Inner wall folded into cisternae Outer membrane has enzymes in it Number of mitochondria in a cell has been linked to the cell’s activity Mitochondria Other Organelles • • • • • Box 3-2 Page 81 Originally just listed as inclusions Barrel Compartment for Peptide Loading (CPL) Caveola Review • List 3 functions of the plasma membrane • Identify 3 organelle and give functions • Distinguish between membranous and nonmembranous structures Cytoskeleton Cytoskeleton • Cell’s internal supporting framework • Made up of rod-like pieces that support and allow movement • Has muscle-like groups of fibers that move the cell or cell parts Cell Fibers • Form 3D irregularly shaped lattice or scaffolding • Appear to support ER, mitochondria and free floating ribosomes • They have microfilaments, intermediate filaments and microtubules • See page 85 Microfilaments • Smallest cell fibers • Often serve as “cellular muscle” • Made of thin twisted strands of protein molecules • Some can slide past one another causing shortening of the cell, such as in muscle fibers Intermediate Filaments • Twisted protein strands • Thicker than microfilaments • Form much of the supporting framework Microtubules • Thickest fibers • Hallow tubes • Protein subunits arranged in spiral fashion • Engine of the cell, due to aid in movement of cell parts or even the cell itself Centrosomes • Near nucleus • Coordinates the building and breaking of microtubules • Moves chromosomes around in cell during cell division Cell Extensions • Microvilli, cilia and flagella • Projections that extend the plasma membrane outward • Assist in movement and absorption • Increases cell surface area Microvilli • Found in epithelial cells found in intestines and other areas • Used where maximum absorption is required Cilia and Flagella • Have cylinders made of microtubules at their core • Each cylinder is composed of 9 double microtubules arranged around 2 single microtubules in the center • Aids in movement • • • • • Nucleus Occupies the central portion of the cell Nuclear substance is known as nucleoplasm Nuclear membrane is called nuclear envelope Cell membrane seems to be extension of the ER The non-membranous nucleolus is in the nucleus, it contains the nucleic acid RNA instead of DNA • Functions in control and regulation of the cell Nucleolus • Membraneless body • Inside nucleus • “programs” the formation of ribosomes thus playing essential role in their formation DNA and Chromosomes • • Chromosomes are tightly coiled DNA molecules. Humans have 46 chromosomes Cell Connections Desmosomes • Small spot welds that hold adjacent cells together • Skin cells are held together this way • Holds together like hook and loop of velcro • Anchored internally by intermediate filaments of cytoskeleton. Gap Junction • Membrane channels of adjacent plasma membrane adhere to each other. • They form gaps or tunnels connecting 2 cells • They fuse 2 plasma membranes into a single structure • Advantages are certain molecules can pass directly from one cell to another and • Heart muscles cells are joined by Gap junctions Gap Junction • Electrical impulses can travel over many cell membranes in a row without stopping. • Heart muscle cells are joined by gap junctions. Tight Junction • Joined by collars of tightly fused membrane • Entire sheet of cells can be held together like a six pack of soda (only tighter) • Molecules can not permeate • Found in intestines