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CHAPTER 4 A Tour of the Cell By Dr. Par Mohammadian PowerPoint PPT Presentation

CHAPTER 4 A Tour of the Cell By Dr. Par Mohammadian Overview: Microscopes Cells Prokaryotes Eukaryotes Animal Cells Plants Cells Cell Junctions Microscopes INTRODUCTION TO THE WORLD OF THE CELL Using a microscope, Robert Hooke discovered cells in 1665

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CHAPTER 4 A Tour of the Cell By Dr. Par Mohammadian

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Chapter 4 a tour of the cell by dr par mohammadian l.jpg

CHAPTER 4A Tour of the Cell By Dr. Par Mohammadian

  • Overview:

  • Microscopes

  • Cells

  • Prokaryotes

  • Eukaryotes

  • Animal Cells

  • Plants Cells

  • Cell Junctions


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Microscopes


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INTRODUCTION TO THE WORLD OF THE CELL

  • Using a microscope, Robert Hooke discovered cells in 1665

  • Cells are the building blocks of all life

  • Organisms are either

  • Single-celled, such as most bacteria

  • Multicelled, such as plants, animals


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Microscopes provide windows to the world of the cell

The light microscope (LM) enables us to see the overall shape and structure of a cell


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  • Micrograph: A photograph taken through a microscope.

  • LM 109X: The image under the light microscope is 109 times the actual size of the organisms.

  • Magnification: Increase in the apparent size of an object.

  • Resolving power: Measure of the clarity of an image.


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  • Electron microscopes (EM) were invented in the 1950s

  • They use a beam of electrons instead of light

  • The greater resolving power of electron microscopes

    • allows greater magnification (0.2 nm vs. LM 0.2 µm)

    • reveals cellular details

  • LM remains the major tool to study living organisms because in EM specimen must be held in vacuum.


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  • Scanning electron microscope (SEM) used to study the detailed architecture of the surface of a cell


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  • Transmission electron microscope (TEM) is useful for exploring the internal structure of a cell


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Natural laws limit cell size

  • At minimum, a cell must be large enough to house the parts it needs to survive and reproduce

  • The maximum size of a cell is limited by the amount of surface needed to obtain nutrients from the environment and dispose of wastes


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CellsProkaryotic CellsEukaryotic CellsAnimal CellsPlant Cells


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The Two Major Categories of Cells

  • The countless cells on earth fall into two categories

  • Prokaryotic cells

  • Eukaryotic cells

  • Prokaryotic and eukaryotic cells differ in several respects


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  • Are smaller than eukaryotic cells and are simple

  • Lack internal structures surrounded by membranes

  • Lack a nucleus

  • Prokaryotic cells


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  • A prokaryotic cell is enclosed by a plasma membrane (protects & shape of the cell) and is usually encased in a rigid cell wall (further protection)

  • The cell wall may be covered by a sticky capsule (help glue prok. to surfaces)

  • Inside the cell are its DNA and other parts


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Eukaryotic cells are partitioned into functional compartments

  • All other life forms (such as animals, plants, protists, or fungi) are made up of one or more eukaryotic cells

  • These are larger and more complex than prokaryotic cells

  • Eukaryotes are distinguished by the presence of a true nucleus


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  • The plasma membrane controls the cell’s contact with the environment

  • The cytoplasm contains organelles

  • Many organelles have membranes as boundaries

    • These compartmentalize the interior of the cell

    • This allows the cell to carry out a variety of activities simultaneously


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  • A plant cell has some structures that an animal cell lacks:

  • Chloroplasts

  • A rigid cell wall

  • Central vacuole


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The nucleus is the cell’s genetic control center

  • The largest organelle is usually the nucleus

  • The nucleus is separated from the cytoplasm by the nuclear envelope

  • The nucleus is the cellular control center

    • It contains the DNA that directs the cell’s activities

  • Genes in the nucleus store information necessary to produce proteins


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MEMBRANE STRUCTURE AND FUNCTION

  • The plasma membrane separates the living cell from its nonliving surroundings

A Fluid Mosaic of Lipids and Proteins

  • The membranes of cells are composed of

  • Lipids

  • Proteins


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Cytoplasm

  • The endomembrane system is a collection of membranous organelles

    • These organelles manufacture and distribute cell products

    • The endomembrane system divides the cell into compartments

    • Endoplasmic reticulum (ER) is part of the endomembrane system


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Rough endoplasmic reticulum makes membrane and proteins

  • The rough ER manufactures membranes

  • Ribosomes on its surface produce proteins

  • The “roughness” of the rough ER is due to ribosomes that stud the outside of the ER membrane

  • Synthesized polypeptide is passed into ER

  • Sugars attach to polypeptides forming glycoprotein

  • ER packages it in tinny sacs called transport vesicles

  • It buds off from the ER & secretory vesicles travel to Golgi apparatus.


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  • Producing proteins

  • Producing new membrane

  • The functions of the rough ER include


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Smooth endoplasmic reticulum has a variety of functions

  • Smooth ER synthesizes lipids

  • In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs

  • Stores Ca ions


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The Golgi apparatus finishes, sorts, and ships cell products

  • The Golgi apparatus consists of stacks of membranous sacs

    • These receive and modify ER products, then send them on to other organelles or to the cell membrane


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Lysosomes digest the cell’s food and wastes

  • Lysosomes are sacs of digestive enzymes

  • Lysosomal enzymes

  • digest food

  • destroy bacteria

  • recycle damaged organelles

  • function in embryonic development in animals


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Vacuoles

  • Two types are the contractile vacuoles of protists and the central vacuoles of plants

  • Vacuoles are membranous sacs

  • The vacuole has lysosomal and storage functions


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CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION

  • Cells require a constant energy supply to do all the work of life


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CHLOROPLASTS

  • Chloroplasts are the sites of photosynthesis, the conversion of light energy to chemical energy


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Mitochondria

  • Mitochondria are the sites of cellular respiration, which involves the production of ATP from food molecules


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THE CYTOSKELETON AND RELATED STRUCTURES

The cell’s internal skeleton helps organize its structure and activities

  • A network of protein fibers makes up the cytoskeleton


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Maintaining Cell Shape

  • One function of the cytoskeleton

  • Provide mechanical support to the cell and maintain its shape


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  • This allows cells like amoebae to move

  • The cytoskeleton can change the shape of a cell


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  • Intermediate filaments reinforce the cell and anchor certain organelles

  • Microtubules

    • give the cell rigidity

    • provide anchors for organelles

    • act as tracks for organelle movement

  • Microfilaments of actin enable cells to change shape and move


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Cilia and flagella move when microtubules bend

  • Eukaryotic cilia and flagella are locomotor appendages that protrude from certain cells

  • A cilia or flagellum is composed of a core of microtubules wrapped in an extension of the plasma membrane


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  • Flagella propel the cell in a whiplike motion

  • Cilia move in a coordinated back-and-forth motion


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  • Some cilia or flagella extend from nonmoving cells

  • The human windpipe is lined with cilia


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Cell Junctions


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EUKARYOTIC CELL SURFACES AND JUNCTIONS

Cell surfaces protect, support, and join cells

  • Cells interact with their environments and each other via their surfaces

  • Plant cells are supported by rigid cell walls made largely of cellulose

    • They connect by plasmodesmata, channels that allow them to share water, food, and chemical messages


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Plant Cell Walls and Cell Junctions

  • These provide support for the plant cells

  • Plant cells are encased by cell walls


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Animal Cell Surfaces and Cell Junctions

  • Animal cells lack cell walls

  • They secrete a sticky covering called the extracellular matrix

  • This layer helps hold cells together

  • Animal cells connect by various types of junctions

  • Tight junctions

  • Adhering junctions

  • Communicating junctions


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  • Anchoring junctions link animal cells

  • Communicating junctions allow substances to flow from cell to cell

  • Tight junctions can bind cells together into leakproof sheets


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