Cytology: the Study of the Structure and Function of Cells

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Cytology the Study of the Structure and Function
of Cells

• LO Covered B1

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A Bit of History

• Cell research began in the 17th century
• 3 researchers are credited with developing the
  cell theory
• SchleidenSchwann all living things are composed
  of cells
• Virchow all cells come from pre-existing cells

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Some Cell Terms Basic Info

• There are 2 basic types of cells
• Prokaryotic (no internal membranes?no nucleus or
  membrane-bound organelles)
• Eukaryotic (nucleus membrane-bound organelles)
• Organelle a distinct sub-cellular structure
  which carries out a specific function
• Ultrastructure the inner makeup of a cell

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Meet the Organelles..

• 4 groups
• cell membrane
• nucleus-related structures
• endomembrane system organelles
• energy-producing organelles

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The Cell Membrane

• Well focus on this later in the unit but why do
  all cells have a membrane? In our bodies cell
  membranes have 4 functions
• Act as a barrier to pathogens, toxins, etc.
• To mark the cell as self
• To act as a receptor for messages from other
  cells in the body
• To allow things to be transported in and out of
  cell (Big Marty Rips Tops)

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All of These Functions Allow the Cell to Maintain
Homeostasis

• Homeostasis is maintenance of a relatively
  constant internal environment
• its one of the BIG concepts this year!!

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Associated With the Cell Membrane are some
Vesicles and Vacuoles

• Secretory Vesicles carry things out of the cell
  by fusing with the membrane so that their
  contents are released outside the cell
  (exocytosis)
• Vesicles and Vacuoles are created by the cell
  membrane when it pinches in (endocytosis)

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The Nucleus-related Organelles Structures

• The Nucleus contains the cells chromosomes and
  therefore controls the cells ability to
• make proteins
• undergo cell division
• Related structures nuclear envelope, nucleolus,
  nucleoplasm, chromosomes, chromatin, and
  ribosomes (all but ribosomes are part of the
  nucleus)

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Proteins VIMs (Very Important Molecules!)

• Many of the cells important structures are made
  from proteins
• Enzymes which are needed for the cell to carry
  most cellular reactions necessary for life are
  also proteins
• The type of proteins that your cells make
  determine who you are

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Chromosomes, Chromatin, Chromatids...Confusion!

• When the cell is in its normal state (not
  dividing) the cells genetic information (encoded
  in DNA) is dispersed within the nucleus?chromatin
• When a cell is replicating (mitosis or meiosis)
  the chromatin condenses to form chromosomes
• Each chromosome consists of 2 sister chromatids

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The Nucleolus The Instructions for Making
Ribosomes

• Makes ribosomal RNA (rRNA) which is a building
  block of ribosomes
• There may be more than one present (nucleoli)
• Surrounded by semifluid medium nucleoplasm

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The Nuclear Envelope

• Surrounds the nucleus
• Continuous with the ER
• A double membrane
• Has openings nuclear pores to allow certain
  things in and out
• Function? Regulate entry/exit of materials

Nuclear pore
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The Connection Between the Nucleus and Ribosomes

• Nucleus is where the instructions for making
  proteins are located (genes)
• Ribosomes actually synthesize (make) proteins
• How do the instructions get from the nucleus to
  the ribosomes?
• mRNA

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An Analogy
ribosomes
nucleus
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There Are Two Types of Ribosomes

• Cytoplasmic
• Free-floating in the cytoplasm, make proteins
  (such as enzymes) needed within the cell

• Endoplasmic
• Attached to endoplasmic reticulum
• When attached to ER the ER is called Rough ER
  (RER)
• Proteins made here are often secreted (e.g. a
  peptide hormone)

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Cytoplasmic ribosomes
Endoplasmic ribosomes (RER)
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Ribosomes a connection between prokaryotes and
eukaryotes

• Ribosomes are the smallest and most numerous
  organelle in the average eukaryotic cell. They
  differ from other organelles because they lack
  membranes
• Bacteria also have ribosomes
• Eukaryotic cells also have ribosomes within their
  mitochondria and chloroplasts

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Endomembrane System Organelles

• There are 2 types of Endoplasmic Reticulum
• Rough (has ribosomes attached to it)
• Smooth (lacking ribosomes)
• Associated with the ER are
• Transition or transport vesicles
• the Golgi Apparatus (Bodies)
• Lysosomes
• All of these organelles compartmentalize the cell
  so that chemical rxns take place only in certain
  areas

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RER Vs. SER

• Smooth ER
• Continuous with the RER
• Lacks attached ribosomes
• There are various functions assoc .with the SER
• Synthesis of lipids(fats)
• membrane phospholipids
• steroid hormones (e.g.. Testosterone)
• Detoxification of drugs in liver
• Forms vesicles to transport ER products to GA or
  PM

• Rough ER
• Continuous with the nuclear envelope
• Studded with ribosomes
• Proteins that are made by these ribosomes are
  processed, modified and transported within the
  lumen of the RER
• Protein may pass on to the SER for packing into
  vesicles
• (See figure 3.5c p53)

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Golgi Apparatus processing, packaging, secretion

• A stack of curved saccules
• Receives protein or lipid-filled vesicles from ER
  
• GA modifies the contents of the vesicles (e.g.
  adds sugar groups or makes a proteins toxin
  active)
• Vesicles leave GA for plasma membrane (secretion)
  others become lysosomes

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Lysosomes Prepare to Die Mr. Bond

• The cells poison pill
• Contains digestive (hydrolytic) enzymes
• Involved in autodigestion
• Digest old organelles
• Allows cell to commit suicide if infected with a
  virus
• Programmed cell death (e.g.. tadpoles tale)
• Produced by the GA
• Digestion of food in single-celled organisms
  (intracellular digestion)
• Killing of bacteria by WBCs involves lysosomes

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http//www.cellsalive.com/mac.htm
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The Energy-related Organelles

• Mitochondria and chloroplasts are both related to
  obtaining energy
• Chloroplasts are only found in plant cells. They
  are the site of photosynthesis
• Mitochondria are found in both plant and animal
  cells and make ATPthe cells main energy
  currency (how energy requiring processes are
  paid for by the cell)

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Whats Left?

• Cytoplasm and Vacuoles
• The cytoplasm is the site of many of the cells
  key biochemical rxns
• It is semifluid?but cytoskeleton is located here
• Plant cells have one large vacuole whereas animal
  cells have smaller and more numerous vacuoles
• Vacuoles are storage areas for important
  substances (e.g.. In plants?water)

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Your Assignment

• Complete the Cell organelle chart and practice
  questions (all)
• Read pages 5657 and write a summary about the
  structure and functions of chloroplasts and
  mitochondria
• Your summary should be
• Brief
• Point form
• Contain what you consider to be the essential
  information about these organelles