Chapter 3 Anatomy of Cells

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Chapter 3 Anatomy of Cells
Department of Applied Science King Saud
University/ Community College By Murad Sawalha
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Introduction

• Cell is defined as the fundamental living unit of
  any organism.
• Cell is important to produce energy for
  metabolism (all chemical reactions within a cell)
• Cell can mutate (change genetically) as a result
  of accidental changes in its genetic material
  (DNA).
• Cytology the study of the structure and
  functions of cells.

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Functional Anatomy of Cells

• The typical cell
• Also called composite cell
• Varies in size all are microscopic
• Varies in structure and function

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Functional Anatomy of Cells

• Cell structures
• Plasma membraneseparates the cell from its
  surrounding environment
• Cytoplasmthick gel-like substance inside of the
  cell composed of numerous organelles suspended in
  watery cytosol each type of organelle is suited
  to perform particular functions
• Nucleuslarge membranous structure near the
  center of the cell

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Cell Membranes

• Each cell contains a variety of membranes
• Plasma membrane
• Membranous organellessacs and canals made of the
  same material as the plasma membrane

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Cell Membranes

• Fluid mosaic modeltheory explaining how cell
  membranes are constructed
• Molecules of the cell membrane are arranged in a
  sheet
• The mosaic of molecules is fluid that is, the
  molecules are able to float around slowly
• This model illustrates that the molecules of the
  cell membrane form a continuous sheet

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Cell Membranes

• Chemical attractions are the forces that hold
  membranes together
• Groupings of membrane molecules form rafts, each
  of which float as a unit in the membrane
• Rafts may pinch inward, bringing material into
  the cell or organelle

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Cell Membranes

• Primary structure of a cell membrane is a double
  layer of phospholipid molecules
• Heads are hydrophilic (water-loving)
• Tails are hydrophobic (water-fearing)
• Molecules arrange themselves in bilayers in water
• Cholesterol molecules are scattered among the
  phospholipids to allow the membrane to function
  properly at body temperature
• Most of the bilayer is hydrophobic therefore
  water or water-soluble molecules do not pass
  through easily

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Cell Membranes

• Membrane proteins
• A cell controls what moves through the membrane
  by means of membrane proteins embedded in the
  phospholipid bilayer
• Some membrane proteins have carbohydrates
  attached to them, forming glycoproteins that act
  as identification markers
• Some membrane proteins are receptors that react
  to specific chemicals, sometimes permitting a
  process called signal transduction

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Cell membrane

• Its composed of large molecules of protiens
  phospholipids (certain types of fats).
• The cell membrane is seperating the contents of
  the cell from the outside world.
• It has the property of selective permiability
  only certain substances may enter leave the cell

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Cell Membrane

• Phospholipid bi-layer that separates the cell
  from its environment.
• Selectively permeable to allow substances to pass
  into and out of the cell.

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Nucleus

• Double membrane-control, integrates the
  functions of the entire cell.
• Consider the command center of the cell.
• Separates the genetic material from the rest of
  the cell.

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Parts of the nucleus

• Chromatin - genetic material of cell in its
  non-dividing state.
• Nucleoplasm is the gelatenous matrix of the
  nucleus, like cytoplasm.
• Nucleolus - dark-staining structure in the
  nucleus that plays a role in making ribosomes.
• Nuclear envelope - double membrane structure that
  separates nucleus from cytoplasm.

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Cytoplasm

• Is a gel-like matrix of water, enzymes,
  nutrients, wastes, and gases and contains cell
  structures (organelles).
• Fluid around the organelles called cytosol.
• Most of the cells metabolic reactions occur in
  the cytoplasm.

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The Endoplasmic Reticulum

• The endoplasmic reticulum (ER)
• Accounts for more than half the total membranes
  in many eukaryotic cells
• The ER membrane is continuous with the nuclear
  envelope
• There are two distinct regions of ER
• Smooth ER, which lacks ribosomes
• Rough ER, which contains ribosomes

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Rough Endoplasmic Reticulum

• Network of continuous sacs, studded with
  ribosomes.
• Manufactures, pro-cesses, and transports proteins
  for export from cell (vesicles)
• Continuous with nuclear envelope.

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Smooth Endoplasmic Reticulum

• Similar in appearance to rough ER, but without
  the ribosomes.
• Involved in the production of lipids,
  carbohydrate metabolism, and detoxification of
  drugs and poisons.
• Stores calcium.

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Ribosomes

• Are the sites of protein synthesis.
• Found attached to the Rough endoplasmic reticulum
  or free in the cytoplasm.
• 60 RNA and 40 protein.
• Protein released from the ER are not mature, need
  further processing in Golgi complex before they
  are able to perform their function within or
  outside the cell.

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Golgi Apparatus

• Modifies proteins and lipids made by the ER and
  prepares them for export from the cell
  (exocytosis).
• Encloses digestive enyzymes into membranes to
  form lysosomes.
• Consists of flattened membranous sacs called
  cisternae

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Lysosome

• Single membrane bound structure.
• Contains digestive enzymes that break down
  cellular waste and debris and nutrients for use
  by the cell.
• Originate at the Golgi complex.

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Lysosome

• They contain lysozymes other digestive enzymes
  that breakdown foreign material taken into the
  cell by phagocytosis (e.g Amebas, and certain
  types of WBCs phagocyte).
• Also these enzymes may breakdown parts of the
  cell or destroy the entire cell by process called
  autolysis if the cell damaged or deteriorated.
• They contain up to 40 enzymes for digestion

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Proteasomes

• Hollow, protein cylinders found throughout the
  cytoplasm
• Break down abnormal/misfolded proteins and normal
  proteins no longer needed by the cell
• Break down protein molecules one at a time by
  tagging each one with a chain of ubiquitin
  molecules and unfolding it as it enters the
  proteasome, then breaking apart peptide bonds

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Peroxisomes

• They are similar to lysosome but smaller.
• Peroxisomes contain the enzyme catalase, which
  breakdown of hydrogen peroxide into water and
  oxygen.
• Found mainly in liver and kidney cells
• Main function is detoxification of toxic
  materials.

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Mitochondrion

• Membrane bound organelles that are the site of
  cellular respiration (ATP production)
• Mitochondrial enzymes catalyze series of
  oxidation reactions that provide about 95 of
  cells energy supply
• Each mitochondrion has a DNA molecule, allowing
  it to produce its own enzymes and replicate
  copies of itself
• Mitochondria are enclosed by two membranes
• A smooth outer membrane
• An inner membrane folded into cristae

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Cytoskeleton

• The cytoskeleton
• Is a network of fibers extending throughout the
  cytoplasm
• Fibers appear to support the endoplasmic
  reticulum, mitochondria, and free ribosomes

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Roles of the Cytoskeleton Support, Motility, and
Regulation

• The cytoskeleton
• Gives mechanical support to the cell
• Is involved in cell motility, which utilizes
  motor proteins
• rodlike pieces that provide support and allow
  movement and mechanisms that can move the cell or
  its parts

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Components of cytoskeleton 1) Microfilaments

• Solid rods of globular proteins.
• Important component of cytoskeleton which offers
  support to cell structure.
• Microfilaments can slide past each other, causing
  shortening of the cell

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Components of cytoskeleton 1) Intermediate
filaments

• Intermediate filaments are twisted protein
  strands slightly thicker than microfilaments
  they form much of the supporting framework in
  many types of cells

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Components of cytoskeleton 2) Microtubules

• Microtubules
• Shape the cell
• Guide movement of organelles (their function is
  to move things around in the cell)
• Help separate the chromosome copies in dividing
  cells

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Components of cytoskeleton 2) Microtubules

• Centrosomes and Centrioles
• The centrosome
• An area of the cytoplasm near the nucleus that
  coordinates the building and breaking of
  microtubules in the cell
• Its considered to be a microtubule-organizing
  center
• Plays an important role during cell division
• Contains a pair of centrioles

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Components of cytoskeleton 2) Microtubules
Centrioles

• Self-replicating
• Made of bundles of microtubules.
• Help in organizing cell division.

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Cytoskeleton

• Cell extensions
• Cytoskeleton forms projections that extend the
  plasma membrane outward to form tiny, fingerlike
  processes

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Cytoskeleton

• There are three types of these processes each
  has specific functions
• Microvillifound in epithelial cells that line
  the intestines and other areas where absorption
  is important they help to increase the surface
  area manyfold
• Cilia and flagellacell processes that have
  cylinders made of microtubules at their core
  cilia are shorter and more numerous than
  flagella flagella are found only on human sperm
  cells

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Cilia and Flagella

• External appendages from the cell membrane that
  aid in locomotion of the cell.
• Cilia also help to move substance past the
  membrane.

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Cell Connections

• Cells are held together by fibrous nets that
  surround groups of cells (e.g., muscle cells), or
  cells have direct connections to each other
• There are three types of direct cell connections

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Cell Connections

• Desmosome
• Fibers on the outer surface of each desmosome
  interlock with each other anchored internally by
  intermediate filaments of the cytoskeleton
• Spot desmosomes, connecting adjacent membranes,
  are like spot welds at various points
• Belt desmosomes encircle the entire cell like a
  collar

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Cell Connections

• Gap junctionsmembrane channels of adjacent
  plasma membranes adhere to each other have two
  effects
• Form gaps or tunnels that join the
  cytoplasm of two cells
• Fuse two plasma membranes into a single structure

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Cell Connections

• Tight junctions
• Occur in cells that are joined by collars of
  tightly fused material
• Molecules cannot permeate the cracks of tight
  junctions
• Occur in the lining of the intestines and other
  parts of the body, where it is important to
  control what gets through a sheet of cells