Anaphy- Chapter 3 PDF

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Summary outline of chapter 3; from Fundamentals of Anatomy and Physiology by Dr. Ronald C. Rizzo...

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CHAPTER 3: Cell structure

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INTRODUCTION 

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The cell is the basic unit of biologic organization. It is composed of a fluid medium called protoplasm surrounded by a cell or plasma membrane. Structures within this protoplasm are called organelles. The protoplasm inside the nucleus is called nucleoplasm; the protoplasm outside the nucleus is called cytoplasm.

CYTOPLASM OF THE CELL 

 HISTORY OF THE CELL THEORY 

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Two Germans, Matthias Schleiden, a botanist, and Theodor Schwann, a zoologist, were the first biologists to propose the cell theory in the 1830s. The modern cell theory states that cells are the basic units of organization of all organisms; all organisms are composed of one or more cells; cells arise from only preexisting cells through cell division; and all existing cells are the descendants of the first cells formed early in the evolutionary history of life on earth.

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THE CELL MEMBRANE 

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The cell membrane or plasma membrane is made up of a double phospholipid layer with proteins embedded in the phospholipid layer. The phospholipid layer allows for the free passage of water molecules through the cell membrane via osmosis, while the proteins act as channels, active transport areas, receptor sites, and identity markers for the cell.

This molecular arrangement of the cell membrane is referred to as a fluid mosaic model and is responsible for the selective permeability of the membrane. It is through the membrane that materials enter and exit the cell.

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The main constituent of cytoplasm is water. Chemical compounds like the mineral salts are dissolved in solution in this water; chemical compounds with the C-H bond (organic molecules) are in colloidal suspension. In a solution, individual atoms or ions are distributed throughout the watery medium; in a colloid, clumps of atoms rather than individual atoms are distributed throughout the watery medium. The water molecule has unique properties, which determine whether molecules will go into solution or a colloidal suspension. The oxygen atom in H2O has a stronger attraction for the electrons in the H-O bond than the hydrogen atoms; thus, the oxygen atom is slightly negative, whereas the two hydrogen atoms are slightly positive. Polar compounds, such as the ionically bonded mineral salts, will dissolve in water and go into solution; nonpolar compounds, such as the covalently bonded molecules of proteins, carbohydrates, fats, and nucleic acids, will go into colloidal suspension The cytoplasm of the cell will also contain storage granules, fat droplets, and vacuoles.

THE NUCLEUS 

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The nucleus is the control center of the cell. It is surrounded by a double nuclear membrane. The inner nuclear membrane surrounds the fluid part of the nucleus, called nucleoplasm, whereas the outer nuclear membrane connects with the endoplasmic reticulum. The nuclear membrane is perforated with pores that allow materials like messenger RNA to leave the nucleus and go into the cytoplasm of the cell. The genetic material inside the nucleoplasm is darkly stained threads of nucleic acids called chromatin. This chromatin will duplicate, shorten, and thicken during cell division and will become visible as chromosomes. The nucleolus is a spherical particle within the nucleoplasm that does not have a covering membrane. It is the site where ribosomes are made.

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ENDOPLASMIC RETICULUM 

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THE MITOCHONDRIA 

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The mitochondria are the powerhouses of the cell. Each mitochondrion is composed of two membranes. The outer membrane forms its capsular shape, and the inner membrane folds on itself to increase surface area. The inner folds of the mitochondrion are called cristae. It is in the mitochondrion where the aerobic phase of cellular respiration occurs: CoH1206 + 602 → ATP (energy) + 6CO2 + 6H20 Cells with higher energy requirements, like muscle cells, will have mitochondria with many cristae; those with lower energy requirements will have fewer cristae.

LYSOSOMES

Lysosomes are small structures in the cytoplasm surrounded by a membrane and contain powerful digestive enzymes. Lysosomes function in three different ways in the cell: they function with food vacuoles to digest stored food; they function in the maintenance and repair of cellular organelles; and they act as suicide agents in old and weakened cells.

The endoplasmic reticulum or ER is a complex system of membranes that makes up a collection of membrane-bound cavities or channels. These channels are called cisternae. The ER connects with the outer nuclear membrane and with the cell membrane. There are two types of ER. All cells have a rough or granular ER whose membranes have attached ribosomes. The function of a rough ER is protein synthesis. Some cells also have a smooth or agranular ER, which does not have attached ribosomes. The function of a smooth ER can be the transportation of fats or the synthesis of the sex hormones.

THE GOLGI APPARATUS  

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The Golgi body or apparatus is a collection of flat sac-like cisternae that look like a stack of pancakes. They function as points within the cytoplasm where compounds to be secreted by the cell are concentrated and collected. They act like storage warehouses of the cell. If the cell is synthesizing carbohydrates and proteins, the carbohydrates will be synthesized in the Golgi apparatus.

RIBOSOMES 

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Ribosomes are small granules distributed throughout the cytoplasm and attached to the rough ER. They are not covered by a membrane. Ribosomes are the site of protein synthesis.

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Two centrioles are found at right angles to each other near the nuclear membrane. The pair is referred to as a centrosome. Each centriole is composed of nine sets of triplet fibers. The centrioles form the spindle fibers during cell division and guide the duplicated chromosomes to their daughter cells.

PROTEIN SYNTHESIS  

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Proteins function in major and essential ways for cellular function and survival. They are part of the structure of membranes; they act as enzymes or catalysts that make chemical reactions occur in the cell; and they function in our immune response. The code to make a particular protein is a gene on a DNA molecule. The DNA is found in the nucleus, whereas the protein is made at a ribosomal site in the cytoplasm. A special molecule called messenger RNA copies the code from the DNA molecule in a process called transcription. The mRNA then leaves the nucleus through a nuclear pore and takes the code to a ribosome or group of ribosomes. Other molecules called transfer RNAs go into the cytoplasm and pick up particular amino acids. Each tRNA molecule is coded for a particular amino acid by its anticodon loop at the end of the molecule. The anticodon loop will only match a particular site on the mRNA molecule called the codon. This process is called translation. The ribosomes will now link up the amino acids brought to the mRNA molecule by the tRNA molecules and will construct the protein with the assistance of enzymes.

CILIA AND FLAGELLA 

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PLASTIDS OF PLANT CELLS 

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CENTRIOLES

Cilia are short and flagella are long hair like protrusions from the cell membrane. Internally, they are composed of nine double fibrils arranged in a ring around two, single central fibrils. A cell with cilia will have row upon row of cilia. Cilia will move materials across the free surface of a cell, like respiratory tract cells, which move the mucus dust package to our throat. A cell with a flagellum, like the sperm cell, will propel the cell through a medium.

The most common plastid of plant cells is the chloroplast, which contains the green pigment chlorophyll that allows plant cells to perform photosynthesis. Photosynthesis is the conversion of light energy (the sun) into chemical energy (food like glucose). Chromoplasts are plastids that contain the carotenoid pigments, xanthophyll (yellow), and carotene (orange-red). Leucoplasts are plastids that store food (e.g., sugar and starch). They contain no pigment and are colorless.

13. List the functions of cilia and flagella. THE CELL WALL OF PLANT CELLS 

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The cell membrane of plant cells is surrounded by a semirigid covering called the cell wall. It is composed of cellulose, synthesized by the Golgi apparatus, and secreted through the cell membrane. Cellulose is the material in our diet that we call fiber

REVIEW QUESTIONS 1. Define a cell. 2. List the major points of the modern cell theory. 3. Why is the molecular structure of a cell membrane referred to as a fluid mosaic model? 4. Explain why some chemical compounds go into solution and others go into a colloidal suspension in the cytoplasm of a cell 5. Why is the nucleus considered the control center of the cell? 6. Based on their structure, why are mitochondria called the powerhouses of the cell? 7. List three functions of lysosomes. 8. What are the two types of endoplasmic reticula and what are their functions in the cell? 9. What is the function of a Golgi apparatus? 10. Why are ribosomes so numerous in the cytoplasm of a cell? 11. List three important functions of proteins in a cell. 12. What is a centrosome?

14. Name and define the three types of plastids found in plant cells. 15. Why should plant cells be studied in a human anatomy and physiology class?...