Nerve activates contraction

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Chapter 7 Tour of the Cell
Cell first seen by Robert Hooke 1665!
Dendrtitic cell
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Cells are the basic unit of life.

• Cell Theory
• All organisms are made of cells
• All cells arise from other cells
• Therefore.Cells are the basic living unit of
  organization of all organisms.

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Microscopes

• First microscope was a magnifying lens
• Light microscope (LMs)
• Visible light passes through the specimen and
  then through glass lenses.
• -The lenses refract light such that the image
  is magnified into the eye or a video screen.

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• Smallest object visible w/ LM is bacterium
• 1000x magnification max.
• Limitations of LM
• 1) As mag. resolution
• 2) Only see small cross-section
• 3) Can see cell but not
• internal anatomy ie. organelles.

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Measurement scale

• 1 meter is 39 inches (3 longer than yard)
• One millimeter (mm) is 10-3m
• One micrometer (µm) is 10-6m
• .000001m
• One nanometer (nm) is 10-9 .000000001m

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• One of the key developments in microscopy of 20th
  century is the
• Electron microscope (EM).
• Uses a beam of electrons instead of light
• Theoretically, the resolution of a modern EM
  could reach 0.1 nanometer (nm).

2 types of EM TEM SEM
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• Transmission electron microscopes (TEM)
• Studies the internal ultra-structure of cells
  using electron beam as the light source.

L-Section of rabbit trachea
Virus
Fig. 7.2a
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• Scanning electron microscopes (SEM) study surface
  structures.
• The SEM gives image that seems 3-D

Fig. 7.2b
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Cell biologists can isolate organelles to study
their functions

• By cell fractionation
• separate the major organelles of the cells so
  that
• their individual functions can be studied.

Fig. 7.3
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Cell Fractionation

• Ultracentrifuge spins homogenate at high speeds
  (100,000 Gs)
• Separates the components of the cell
• Heavier pieces fall to bottom of tube
• Lighter particles remain in the supernatant.

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Components of the Eukaryotic Cell

• Eukaryotic cell
• - Membrane bound
• compartments
• (each w/ own function)
• - Membrane bound
• nucleus true nucleus
• Complex

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Plasma membrane

• Outermost layer of cell
• separates the internal environment from external
  environment
• Acts as selective barrier that allows passage of
  specific molecules into and out of the cell

Fig. 7.7
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• Cytoplasm soup
• Semifluid environment
• Contained by plasma membrane
• Composed of water and dissolved macro molecules
• Various organelles are suspended
• Function participates in catabolic and anabolic
  reactions of the cell

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Membrane bound compartments

• Internal environment of cell is
  compartmentalized.
• What is their purpose?
• Create local micro-environments that would
  facilitate specific metabolic functions.
• These compartments include
• Nucleus
• ribosomes
• Endomembrane system
• Membrane enclosed organelles

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Nucleus
Fig. 7.8
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• Nucleus is the control center of the cell
• It is the most prominent organelle under a light
  microscope

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Structures of Nucleus

• Nuclear membrane separates contents of nucleus
  from cytoplasm
• double membrane structure
• The regions where the double membranes fuse lead
  to formation of
• nuclear pores
• They allows large macromolecules and particles to
  pass through.

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Inside nucleus

• ChromatinDNA and proteins as fibrous structures
• Tightly packed chromatin is called chromosome
• Non-dividing cell see chromatin
• Dividing cell see chromosomes.

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Cytoplasm of the nucleus

• Nucleoplasm The nuclear membrane encloses
  cytoplasmic environment called nucleoplasm
• Contains enzymes necessary for
• chromosomal duplication
• Ribosome synthesis
• RNA synthesis

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• The nucleolus
• region of densely stained fibers and granules
  adjoining chromatin
• Ribosomal RNA is synthesized here.
• (This RNA combines with protein to form a
  ribosome.)

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Ribosomes

• Ribosomes are made of rRNA and protein.
• A ribosome is composed of two subunits
• as a unit they help in the protein synthesis

Fig. 7.10
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• Active cells have many ribosomes and prominent
  nucleoli.
• Depending on the type of the protein made,
  ribosomes can exist in two varieties
• free ribosomes suspended in the cytosol.
  Synthesize proteins that function within the
  cytosol.
• bound ribosomes attached to the outside of the
  endoplasmic reticulum.
• Synthesis of secretory proteins

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Endomembranous system

• The endomembrane system includes
• the nuclear envelope,
• endoplasmic reticulum,
• Golgi apparatus,
• lysosomes,
• vacuoles, and
• the plasma membrane.
• Each membrane is structurally and functionally
  different

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The Endoplasmic Reticulum (ER)

• Network of connected tubules and flattened sacs
  called cisternae.
• The ER membrane is contiguous with
• the nuclear envelope.
• Space inside sacs is the cisternal space.

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• 2 types ER
• Smooth ER looks smooth because it lacks
  ribosomes.
• Rough ER looks rough because ribosomes (bound
  ribosomes) are attached.

Fig. 7.11
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• Smooth ER (SER) Functions
• 1) Has enzymes to synthesize lipids oils,
  phospholipids, and steroids, ie. sex hormones)
• 2) Enzymes w/ role in carbohydrate metabolism.
• 3) Detoxification of drugs.

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• Rough ER Functions
• Has ribosomes bound to its membrane!
• Involved in producing secretory proteins.
• Many of these polypeptides are glycoproteins.
• These secretory proteins are packaged in
  transport vesicles that carry them to their next
  stage.

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• Golgi Apparatus membranous sacs cisternae
• filled with cytosolic environment looking like a
  sac of pita bread.
• Carry enzymes that modify the proteins brought
  from ER
• Also modify phospholipids.

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• Modification is unidirectional, 2 faces of Golgi
  have different function.
• The Golgi is a center or warehousing for sorting,
  and shipping

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Lysosomes

• The lysosome is a membrane-bounded sac of
  hydrolytic enzymes that digests macromolecules.

Fig. 7.13a
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• Lysosomes can fuse with food vacuoles, formed
  when a food item is taken in by the cell.
• Lysosome is also known as recycling center
• autophagy

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Lysosome

• Lysosomal enzymes can hydrolyze proteins, fats,
  polysaccharides, and nucleic acids.
• These enzymes work best at pH 5.

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Vacuoles

• vacuoles (larger than vessicles) are
  membrane-bound sacs with varied functions.
• Food vacuoles, formed by food surrounded by
  plasma membrane, fuse with lysosomes.
• Contractile vacuoles, found in freshwater
  protists, pump excess water out of the cell.
• Central vacuoles are found in many mature plant
  cells and store food.

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Vacuoles
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Mitochondria

• found in plants and animal cells
• Sites of cellular respiration
• They generate ATP by breaking down sugars
• The number of mitochondria is correlated with
  aerobic metabolic activity.

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• Structure
• 1) Outer mitochondrial membrane
• 2) Inner mitochondrial membrane that is folded
  called as cristae
• 3) Mitochondrial matrix
• 4) Has its own
• ribosmes DNA

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• Chloroplasts
• found in plants and eukaryotic algae
• - Site of photosynthesis.
• - They convert solar energy to chemical energy
• - Synthesize new organic compounds from CO2 and
  H2O.
• Chloroplasts are green in color because of the
  pigment chlorophyll.

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• Enclosed in membranes ( outer and inner
  membrane). It encloses pigments eg) chlorophyll
  and caroteniods.

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COMMON FEATURES SHARED BY CHLOROPLAST AND
MITOCHONDRIA

• Mitochondria and chloroplasts grow and reproduce
  as semi-autonomous organelles.
• Both organelles have their own DNA
• They have their own ribosomes which help in the
  synthesis of organelle specific proteins

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Peroxisomes

• -are bound by single bilipid membrane
• Contain enzymes to produce hydrogen peroxide.
• detoxify alcohol and other harmful compounds.
• Break down fatty acids

Peroxisome
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• H2O2 is further broken down into water and O2
• It uses an enzyme known as catalase or peroxidase
  
• Why is it good that the cell can break down
  peroxide?

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Cytoskeleton

• Network of fibers extending throughout the
  cytoplasm.
• 3 types, based on size
• 1) Microtubules
• 2) Microfilaments
• 3) Intermediate filaments

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Cytoskeleton
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• Microtubules (25nm),
• Microfilaments or actin filaments (7nm)
• Intermediate filaments(10-12nm)

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• Microtubules
• thickest fibers
• They are built from tubulin
• Functions
• They move chromosomes during cell division.
• Help organelles to move to their destination.

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Microtubules

• Central structural supports in cilia and
  flagella.
• Cilia usually occur in large numbers on the cell
  surface.
• For example, cilia sweep mucus carrying trapped
  debris from the lungs.

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• Flagella

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• Microfilaments
• Solid rods of the globular protein actin.
• network just beneath the plasma membrane.
• Functions
• Microfilaments resist tension and
• maintain shape of the cell.
• Movement of cell
• Eg) muscle!

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• Prominently found in muscle cells
• Help in muscle contraction

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• Intermediate filaments
• Made from keratins.
• Present beneath microfilaments
• are specialized for bearing tension.
• They reinforce cell shape and
• fix organelle location.

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• Cell wall
• In plants, bacteria and fungi
• is made of cellulose or chitin other assoc.
  proteins.

Fig. 7.28
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Cell Wall

• The thickness and chemical composition of cell
  walls differs from species to species and among
  cell types.
• Generally
• protects the cell
• maintains its shape
• prevents excessive uptake of water.
• Supports the plant against the force of gravity.

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Eukaryotes vs Prokaryotes
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Prokaryotic cells do not have nucleus

• Most primitive organisms evolved about three
  billion years ago.
• All cells are surrounded by a plasma membrane.
• The semifluid substance within the membrane is
  the cytosol, containing the organelles.

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• Have ribosomes, help in the synthesis of
  proteins.
• genetic material DNA is concentrated in the
  nucleoid without a membrane separating it from
  the rest of the cell.
• It has the blue print for the bacteria to grow
  survive and divide.

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