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A Tour of the Cell.docx

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Biology 1201A
Richard Gardiner

A Tour of the Cell Early microscope: Dutch republic started making microscopes Anthony Van Leeuwenhoele (1673) is known for the best microscope for his time.  Made people such as the Dutch royalty interested in “looking at things” Robert Hooke coined the word “cell” as the tiniest living system  Called it a cell because it looked like a cell in a bee hive. Types of Microscopes Stero-scanning microscopes used to look at surface of specimen. Light microscopes and Electron microscopes are used to look inside specimen Light microscopes has resolution limit of about 0.2 microns  Magnification limit of about 1000 times In 1950 electron microscope was introduced  Allowed to view protons, viruses etc. Cell Fraction Take cells apart to study their components  Done by use of centrifuge with spins the specimen.  The spinning causes certain elements of the cell to fall to bottom depending on density of organelle and speed of centrifuge The cell: A cell is the simplest collection of matter, which has all components of life. 1. Lowest Hierarchical level which is alive 2. Cell is the basic unit of life 3. Cells preform all functions necessary to live and reproduce Virus: Occurs in virtually every kind of organism Some wreck havoc others cause no disease or outwards sign of their presence  Often highly specific to host Can only reproduce when they enter a host cell  Cant reproduce by themselves There are two types of cells: Prokaryotes and Eukaryotes. Prokaryotic Cells: Derives from words Pro=before and Karyote=nucleus An example of a prokaryotic cell is bacteria, cyanobacteria, mycoplasmas etc. No nucleus (genetic information is located in nucleioud) Visible components:  Plasma membrane, ribosomes, nucleoid, cytoplasm, cell wall, pilli, flagella, mesosomes, photosynthetic membrane. Early form of life Eukaryotic cells: Derived from the words Eu=true and karyote=nucleus Found in 4 kingdoms:  Animals  Plants  Fungi  Protist Characteristics: True nucleus  Surrounded with nuclear membrane  Contains DNA Visual Components:  Plasma membrane, cytoplasm. Nucleus, ribosomes, organelles, endomembrane etc. Nucleus: Most genes in nucleus  Some in mitochondria and chloroplast Average size about 5 microns in diameter Separated from the cytoplasm by a double membrane  Separated by 20-40nm Where the double membranes are fuses, a pore allows large macromolecules and particles to pass through The nuclear side of the envelope is lined by the nuclear lamina, a network of intermediate filaments that maintain the shape of the nucleus Within the nucleus, DNA and associated proteins are organized into fibrous material, chromatin  Appears as diffuse mass When the cell prepares to divide, the chromatin fibers coil up to be seen as separate structures, chromosomes Each eukaryotic species has a characteristic number of chromosomes In the nucleus is a region of density stained fibers and granules adjoining chromatic, the nucleolus.  In the nucleolus, ribosomal RNA is synthesized and assembled with proteins from the cytoplasm to form ribosomal subunits. The nucleus directs protein synthesis by synthesizing messengers RNA. Cytoplasm: Material between the plasma membrane and the nuclear envelop. Has a variable viscosity Main chemical constituents are water (approx. 80%) nucleic acids, proteins, lipids, carbohydrates, pigments, etc. Ribosomes Build: Ribosomes contain rRNA and proteins. Ribosomes are composed of two subunits that combine to carry out protein synthesis. Cell types that synthesize large quantities of proteins (e.g. the pancreas) have large numbers of ribosomes and prominent nuclei. Free ribosomes, are suspended in the cytosol and synthesize proteins that function within the cytosol. Bound ribosomes, are attached to the outside of the endoplasmic reticulum. Ribosomes can shift between roles. Endomembrane System: Many of the internal membranes in a eukaryotic cell are part of the endomembrane system. These membranes are either in direct contact or connected via transfer of vesicles, sacs of membrane. The endomembrane system includes:  Nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and the plasma membrane. There are two regions of ER that differ in structure and functions: 1. Smooth ER looks smooth because is lacks ribosomes 2. Rough ER look rough because ribosomes are attached to the outside including the outside of the nuclear envelope. Smooth ER: Smooth ER is rich in enzymes and plays a role in a variety of metabolic processes Synthesize lips, including oils, phospholipids and steroids Smooth ER also catalyzes a key step in the mobilization of glucose from stored glycogen in the liver. Other enzymes in the smooth ER of the liver help detoxify drugs and poisons  These include alcohol and barbiturates  Frequent exposure leads to proliferation of smooth ER, increasing tolerance to the target and other drugs Muscle cells are rich in enzymes that pump calcium ions from the cytosol to the cisternae. Rough ER: Rough ER is especially abundant in those cells that secrete proteins  As a polypeptide is synthesized by the ribosome, it is threaded into the cisternal space through a pore formed by a protein in the ER membrane. Secretory proteins are packaged in transport vesicles that carry them to their next stage. Rough ER is also a membrane factory.  Membrane bound proteins are synthesized directly into the membrane  Enzymes in the Rough ER also synthesize phospholipids from precursors in the cytosol.  As the ER membrane expands, parts can be transferred as transport vesicles to other components of the endomembrane system. Golgi Apparatus: Transports vesicle from the ER for modification of their contents It is the center of manufacturing, sorting and shipping
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