NOTES: Ch 7 A Tour of the Cell

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NOTES Ch 7 A Tour of the Cell
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Overview The Importance of Cells

• ? All organisms are made of cells
• ? The cell is the simplest collection of matter
  that can live
• ? Cell structure is correlated to cellular
  function
• ? All cells are related by their descent from
  earlier cells

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10 m
Human height
1 m
Length of some nerve and muscle cells
Unaided eye
0.1 m
Chicken egg
1 cm
Frog egg
1 mm
Measurements 1 centimeter (cm) 102 meter (m)
0.4 inch 1 millimeter (mm) 103 m 1 micrometer
(µm) 103 mm 106 m 1 nanometer (nm) 103
µm 109 m
100 µm
Most plant and animal cells
Light microscope
10 µm
Nucleus
Most bacteria
Mitochondrion
1 µm
Electron microscope
Smallest bacteria
100 nm
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
Atoms
0.1 nm
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• Brightfield (unstained
• specimen)

50 µm

• Brightfield (stained
• specimen)

Phase-contrast
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MICROSCOPES

• 1) Light Microscope
• 2) Electron Microscope (1950s)
• ? Transmission Electron Microscope
• ? Scanning Electron Microscope

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Light Microscope

• ? works by passing visible light through a thin
  section of specimen and then through glass lenses
• ? resolving power 0.2 µm (size of small
  bacteria)
• ? magnification about 1000x

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Electron Microscope (1950s)

• ? uses electron beams which have shorter
  wavelengths of light
• ? resolving power 0.2 nm (most cell structures)
• ? magnification up to 40,000x

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Electron Microscope

• 1) Transmission Electron Microscope
• -electrons transmitted through specimen are
  focused and image is magnified using
  electromagnets
• -used to study internal cell structure
• 2) Scanning Electron Microscope
• -electron beam scans the surface of a spec.
• -useful for studying the surface of specimen in
  3-D.

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Disadvantages to EM

• ? can only view dead cells (elaborate
  preparation)
• ? very expensive!

zooxanthellae cells cultured from coral Aiptasia
pulchella in a Scanning Electron Microscope
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WE CAN ALSO STUDY CELLS BY...

• ? Cell Fractionation disrupting cells to
  separate out cell organelles
• ? Centrifugation spinning mixtures of cells and
  their parts at very high speeds separates the
  components

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Cell Components and Classification!
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Types of CELLS

• ? The basic structural and functional unit of
  every organism is one of two types of cells
  prokaryotic or eukaryotic
• ? Only organisms of the domains Bacteria and
  Archaea consist of prokaryotic cells
• ? Protists, fungi, animals, and plants all
  consist of eukaryotic cells

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ALL CELLS

• ? have a cell membrane
• ? have cytoplasm / cytosol
• ? have ribosomes (make proteins)
• ? can reproduce contain genetic material (DNA /
  chromatin / chromosomes)

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CELLS CAN BE CLASSIFIED AS

• 1) PROKARYOTES
• 2) EUKARYOTES

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LE 6-6
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• ? although eukaryotic cells are larger than
  prokaryotes, there is a limit on cell size due to
  the logistics of carrying out cellular metabolism

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LE 6-7
Surface area increases while Total volume remains
constant
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1
1
Total surface area (height x width x number of
sides x number of boxes)
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150
750
Total volume (height x width x length X number of
boxes)
125
125
1
Surface-to-volume ratio (surface area ? volume)
1.2
6
6
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PLASMA MEMBRANE the boundary of every cell

• ? The plasma membrane is a selective barrier that
  allows sufficient passage of oxygen, nutrients,
  and waste to service the volume of the cell
• ? The general structure of
• a biological membrane is
• a double layer of
• phospholipids

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LE 6-8
Outside of cell
Carbohydrate side chain
Hydrophilic region
Inside of cell
0.1 µm
Hydrophobic region
Hydrophilic region
Phospholipid
Proteins
Structure of the plasma membrane
TEM of a plasma membrane
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Cell Components!
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A Panoramic View of the Eukaryotic Cell

• ? A eukaryotic cell has internal membranes that
  partition the cell into organelles
• ? Plant and animal cells have most of the same
  organelles

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ENDOPLASMIC RETICULUM (ER
Nuclear envelope
Flagellum
Rough ER
Smooth ER
NUCLEUS
Nucleolus
Chromatin
Centrosome
Plasma membrane
CYTOSKELETON
Microfilaments
Intermediate filaments
Microtubules
Ribosomes
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
In animal cells but not plant cells
Lysosomes Centrioles Flagella (in some plant
sperm)
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Nuclear envelope
Rough endoplasmic reticulum
NUCLEUS
Nucleolus
Chromatin
Smooth endoplasmic reticulum
Centrosome
Ribosomes (small brown dots)
Central vacuole
Golgi apparatus
Microfilaments
Intermediate filaments
CYTOSKELETON
Microtubules
Mitochondrion
Peroxisome
Chloroplast
Plasma membrane
Cell wall
Plasmodesmata
Wall of adjacent cell
In plant cells but not animal cells
Chloroplasts Central vacuole and tonoplast Cell
wall Plasmodesmata
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The eukaryotic cells genetic instructions are
housed in the NUCLEUS and carried out by the
ribosomes

• ? the nucleus contains most of the DNA in a
  eukaryotic cell
• ? ribosomes use the information from the DNA to
  make proteins

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The Nucleus Genetic Library of the Cell

• ? the nucleus contains most of the cells genes
  and is usually the most conspicuous organelle
• ? the nuclear envelope encloses the nucleus,
  separating it from the cytoplasm
• ? houses the information / instructions for cell
  functioning and maintenance the control center
  of the cell
• ? averages 5 µm in diameter

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LE 6-10
Nucleus
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope Inner membrane
Outer membrane
Nuclear pore
Pore complex
Rough ER
Surface of nuclear envelope
Ribosome
1 µm
0.25 µm
Close-up of nuclear envelope
Pore complexes (TEM)
Nuclear lamina (TEM)
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NUCLEAR ENVELOPE

• ? double membrane which encloses the nucleus
• -each of the 2 membranes is a phospholipid
  bilayer w/specific proteins
• -is perforated by pores which regulate molecular
  traffic into and out of the nucleus
• -RNA and proteins enter or leave the nucleus
  through these pores
• -breaks down prior to cell division

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CHROMATIN

• ? fibrous, threadlike complex of DNA and histone
  proteins which make up chromosomes in eukaryotic
  cells

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CHROMOSOMES

• ? compacted, coiled up chromatin
• ? visible under microscope
• ? form just prior to cell division
• ? human cells have 46 chromosomes (23 pairs)

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NUCLEOLUS

• ? dense, spherical region in the nucleus
• -visible in a nondividing cell
• -may be 2 or more per cell
• -packages ribosomal subunits from
• 1) rRNA transcribed in nucleolus
• 2) RNA produced elsewhere in nucleus
• -ribosomal subunits pass through nuclear pores
  to the cytoplasm where assembly into ribosomes is
  completed

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RIBOSOMES

• ? cytoplasmic organelle site of protein
  synthesis
• -made of RNA and protein
• -made in the nucleolus
• -cells with high rates of protein synthesis have
  large numbers of nucleoli ribosomes (e.g. human
  liver cells have millions)

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RIBOSOMES

• ? Ribosomes carry out protein synthesis in two
  locations
• -in the cytosol (free ribosomes)
• -attached to the outside of the endoplasmic
  reticulum (ER) or the nuclear envelope (bound
  ribosomes)

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LE 6-11
Ribosomes
ER
Cytosol
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large subunit
Small subunit
0.5 µm
TEM showing ER and ribosomes
Diagram of a ribosome
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Cell Organelles (continued)
YES! There are MORE!!
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The Endomembrane System

• all structures are essentially compartments,
  closed off by their membranes from the cytoplasm

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The endomembrane system regulates protein traffic
and performs metabolic functions in the cell

• ? Components of the endomembrane system
• Nuclear envelope
• Endoplasmic reticulum
• Golgi apparatus
• Lysosomes
• Vacuoles
• Plasma membrane
• ? These components are either continuous or
  connected via transfer vesicles

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The Endoplasmic Reticulum Biosynthetic Factory

• ? The endoplasmic reticulum (ER) accounts for
  more than half of the total membrane in many
  eukaryotic cells
• ? The ER membrane is continuous with the nuclear
  envelope

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ENDOPLASMIC RETICULUM (ER)

• ? extensive network of tubules and sacs
• ? used for transport and/or modification of
  proteins
• ? can be ROUGH (ribosomes) or SMOOTH (no
  ribosomes)

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Rough ER

• ? manufactures secretory
• proteins and membranes
• ? proteins made here may
• be modified
• (i.e. folded into their
• tertiary structure)
• ? usually closer in to nucleus
• than smooth ER

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Smooth ER

• ? synthesizes lipids, phospholipids, steroids
• ? participates in carbohydrate metabolism
• ? detoxifies drugs and poisons
• ? stores calcium ions (for muscle contraction)

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Smooth ER
Nuclear envelope
Rough ER
ER lumen
Cisternae
Ribosomes
Transitional ER
Transport vesicle
200 nm
Smooth ER
Rough ER
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The Golgi Apparatus Shipping and Receiving
Center

• ? The Golgi apparatus consists of flattened
  membranous sacs called cisternae
• ? Functions of the Golgi apparatus
• Modifies products of the ER
• Manufactures certain macromolecules
• Sorts and packages materials into transport
  vesicles

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GOLGI APPARATUS

• ? cis face (forming face faces the rough ER)
  receives products by accepting transport vesicles
  from the rough ER
• ? trans face (maturing face faces the
• cell membrane) pinches off vesicles
• from the Golgi and transports
• molecules to other sites

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Golgi apparatus
cis face (receiving side of Golgi apparatus)
Vesicles coalesce to form new cis Golgi
cisternae
Vesicles move from ER to Golgi
0.1 µm
Vesicles also transport certain proteins
back to ER
Cisternae
Cisternal maturation Golgi cisternae move
in a cis- to-trans direction
Vesicles form and leave Golgi,
carrying specific proteins to other locations or
to the plasma mem- brane for secretion
Vesicles transport specific proteins
backward to newer Golgi cisternae
trans face (shipping side of Golgi apparatus)
TEM of Golgi apparatus
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Lysosomes Digestive Compartments

• ? A lysosome is a membranous sac of hydrolytic
  enzymes
• ? Lysosomal enzymes can hydrolyze proteins, fats,
  polysaccharides, and nucleic acids
• ? Lysosomes also use enzymes to recycle
  organelles and macromolecules, a process called
  autophagy

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LE 6-14a
1 µm
Nucleus
Lysosome
Lysosome contains active hydrolytic enzymes
Hydrolytic enzymes digest food particles
Food vacuole fuses with lysosome
Digestive enzymes
Plasma membrane
Lysosome
Digestion
Food vacuole
Phagocytosis lysosome digesting food
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LE 6-14b
Lysosome containing two damaged organelles
1 µm
Mitochondrion fragment
Peroxisome fragment
Hydrolytic enzymes digest organelle components
Lysosome fuses with vesicle containing damaged
organelle
Lysosome
Digestion
Vesicle containing damaged mitochondrion
Autophagy lysosome breaking down damaged
organelle
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LYSOSOMES

• ? probably pinch off from the trans face of
  Golgi
• ? are responsible for intracellular digestion
• ? recycle the cells own organic material
• ? destroy cells

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Other Membrane-Bound Organelles

• 1) Vacuoles
• 2) Peroxisomes

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VESICLES / VACUOLES

• ? membrane-enclosed sac used for storage and/or
  transport animal cells, vacuoles are small and
  look like vesicles
• Vacuoles in plants have special
  characteristics
• -plant cells have a LARGE central vacuole that
  stores water and water-soluble organic compounds
  and inorganic ions (K and Cl-)

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• PLANT VACUOLES
• ? contain soluble pigments in some cells (red and
  blue pigments in flowers)
• ? play a role in plant growth by absorbing water
  and elongating the cell

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• PLANT VACUOLES
• ? help protect from predators by storing waste
  products that may also be poisonous compounds
• ? Are surrounded by a membrane called the
  TONOPLAST
• ? some fresh-water protists
• have a contractile vacuole
• that pumps excess water
• from the cell

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LE 6-15
Central vacuole
Cytosol
Tonoplast
Central vacuole
Nucleus
Cell wall
Chloroplast
5 µm
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The Endomembrane System A Review

• ? The endomembrane system is a complex and
  dynamic player in the cells compartmental
  organization

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LE 6-16-1
Nucleus
Rough ER
Smooth ER
Nuclear envelope
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LE 6-16-2
Nucleus
Rough ER
Smooth ER
Nuclear envelope
cis Golgi
Transport vesicle
trans Golgi
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LE 6-16-3
Nucleus
Rough ER
Smooth ER
Nuclear envelope
cis Golgi
Transport vesicle
Plasma membrane
trans Golgi
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MORE ORGANELLESMitochondria and chloroplasts
change energy from one form to another

• ? Mitochondria are the sites of cellular
  respiration
• ? Chloroplasts, found only in plants and algae,
  are the sites of photosynthesis
• ? Mitochondria and chloroplasts are not part of
  the endomembrane system
• ? Peroxisomes are oxidative organelles

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MITOCHONDRIA

• ? sites of cellular respiration
• ? found in nearly all eukaryotic cells
• ? the in cells varies and is related to the
  cells metabolic activity

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• ? inner membrane is convoluted and contains
  proteins/enzymes involved in cellular respiration
• ? inner membranes many infoldings are called
  CRISTAE they increase the surface area for
  cellular respiration reactions to occur
• ? region within inner membrane is the
  MITOCHONDRIAL MATRIX

Mitochondria in a human liver cell
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LE 6-17
Mitochondrion
Intermembrane space
Outer membrane
Free ribosomes in the mitochondrial matrix
Inner membrane
Cristae
Matrix
Mitochondrial DNA
100 nm
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CHLOROPLASTS (the organelles that feed the
world)

• ? contain chlorophyll
• ? site of photosynthesis (convert light energy
  into chemical energy
• ? found in eukaryotic algae, leaves and other
  green plant organs
• ? can change shape, move and divide

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Chloroplasts Capture of Light Energy

• ? Chloroplast structure includes
• -Thylakoids, membranous sacs
• -Stroma, the internal fluid

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Chloroplast
Ribosomes
Stroma
Chloroplast DNA
Inner and outer membranes
Granum
1 µm
Thylakoid
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PEROXISOMES

• ? contain special enzymes for specific metabolic
  pathways
• ? found in nearly all eukaryotic cells

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• ? contain peroxide-producing enzymes that
  transfer hydrogen ions to oxygen producing
  hydrogen peroxide
• ? contain catalase enzyme which converts /
  detoxifies hydrogen peroxide to water

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LE 6-19
Chloroplast
Peroxisome
Mitochondrion
1 µm
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CYTOSKELETON

• ? The cytoskeleton is a network of fibers
  extending throughout the cytoplasm
• ? It organizes the cells structures and
  activities, anchoring many organelles
• ? It is composed of three types of molecular
  structures
• Microtubules
• Microfilaments
• Intermediate filaments

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LE 6-20
Microtubule
Microfilaments
0.25 µm
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Components of the Cytoskeleton

• ? Microtubules are the thickest of the three
  components of the cytoskeleton
• ? Microfilaments, also called actin filaments,
  are the thinnest components
• ? Intermediate filaments are fibers with
  diameters in a middle range

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Cytoskeleton
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Roles of the Cytoskeleton Support, Motility, and
Regulation

• ? the cytoskeleton helps to support the cell and
  maintain its shape
• ? it interacts with motor proteins to produce
  motility (movement)
• ? inside the cell, vesicles can travel along
  monorails provided by the cytoskeleton
• ? recent evidence suggests that the cytoskeleton
  may help regulate biochemical activities

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LE 6-21a
Vesicle
ATP
Receptor for motor protein
Motor protein (ATP powered)
Microtubule of cytoskeleton
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LE 6-21b
Microtubule
Vesicles
0.25 µm
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Microtubules

• ? straight, hollow rods made of protein called
  TUBULIN
• ? can serve as tracks to
• guide organelle movement
• ? involved in separation of chromosomes in cell
  division make up CENTRIOLES

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Cilia and Flagella

• ? Microtubules control the beating of cilia and
  flagella, locomotor appendages of some cells
• ? Cilia and flagella differ in their beating
  patterns

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FLAGELLA and CILIA

• ? FLAGELLA longer than cilia usually found
  singly or in pairs used to propel a cell
• ? CILIA shorter than flagella usually present
  in great numbers wavelike motion used to sweep
  extracellular material over/away from cell

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Direction of swimming
Motion of flagella
5 µm
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Direction of organisms movement
Direction of active stroke
Direction of recovery stroke
Motion of cilia
15 µm
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• ? Cilia and flagella share a common
  ultrastructure
• -A core of microtubules sheathed by the plasma
  membrane
• -A basal body that anchors the cilium or
  flagellum
• -A motor protein called DYNEIN, which drives the
  bending movements of a cilium or flagellum

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Outer microtubule doublet
Plasma membrane
0.1 µm
Dynein arms
Central microtubule
Cross-linking proteins inside outer doublets
Microtubules
Plasma membrane
Radial spoke
Basal body
0.5 µm
0.1 µm
Triplet
Cross section of basal body
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Microtubule doublets
ATP
Dynein arm
Dynein walking
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Cross-linking proteins inside outer doublets
ATP
Anchorage in cell
Effect of cross-linking proteins
Wavelike motion
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Microfilaments

• ? can exist as single filaments or in bundles
• ? formed from the protein ACTIN
• ? help the cell (or parts of the cell) to
  contract
• ? they stabilize cell shape
• ? Involved in pinching contractions during cell
  division
• ? Involved in forming pseudopodia that enable
  some cells to move.

Yellow nucleus Green microfilaments throughout
cytoplasm
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Cortex (outer cytoplasm) gel with actin network
Inner cytoplasm sol with actin subunits
Extending pseudopodium
Amoeboid movement
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Muscle cell
Actin filament
Myosin filament
Myosin arm
Myosin motors in muscle cell contraction
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Nonmoving cytoplasm (gel)
Chloroplast
Streaming cytoplasm (sol)
Vacuole
Parallel actin filaments
Cell wall
Cytoplasmic streaming in plant cells
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Intermediate Filaments

• ? Intermediate filaments range in diameter from
  812 nanometers, larger than microfilaments but
  smaller than microtubules
• ? They support cell shape and fix organelles in
  place
• ? Intermediate filaments are more permanent
  cytoskeleton fixtures than the other two classes

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Extracellular components and connections between
cells help coordinate cellular activities

• ? Most cells synthesize and secrete materials
  that are external to the plasma membrane
• ? These extracellular structures include
• Cell walls of plants
• The extracellular matrix (ECM) of animal cells
• Intercellular junctions

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Extracellular Structures

• ? CELL WALL
• -semirigid structure
• outside of cell membrane
• of PLANT CELLS
• -consists of CELLULOSE
• fibers complex
• polysaccharides
• proteins
• -provides support, limits cells volume, and
  protects against fungi and/or microorganism
  infection.

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Cell Walls of Plants

• ? Plant cell walls may have multiple layers
• Primary cell wall relatively thin and flexible
• Middle lamella thin layer between primary walls
  of adjacent cells
• Secondary cell wall (in some cells) added
  between the plasma membrane and the primary cell
  wall
• ? Plasmodesmata are channels between adjacent
  plant cells

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Central vacuole of cell
Plasma membrane
Secondary cell wall
Primary cell wall
Central vacuole of cell
Middle lamella
1 µm
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Plasmodesmata
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The Extracellular Matrix (ECM) of Animal Cells

• ? Animal cells lack cell walls but are covered by
  an elaborate extracellular matrix (ECM)
• ? Functions of the ECM
• Support
• Adhesion
• Movement
• Regulation

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Extracellular Structures

• ? EXTRACELLULAR MATRIX
• fibrous proteins such as COLLAGEN and
  glycoproteins are secreted by and surround cells
• it holds cells together in tissues
• helps filter materials passing between different
  tissues
• orients cell movement during
• development
• involved in cell-cell signalling.

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Proteoglycan complex
EXTRACELLULAR FLUID
Collagen fiber
Fibronectin
Plasma membrane
CYTOPLASM
Integrin
Micro- filaments
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Proteoglycan complex
Polysaccharide molecule
Carbo- hydrates
Core protein
Proteoglycan molecule
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Intercellular Junctions

• ? Neighboring cells in tissues, organs, or organ
  systems often adhere, interact, and communicate
  through direct physical contact
• ? Intercellular junctions facilitate this contact

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Plants Plasmodesmata

• ? Plasmodesmata are channels that perforate plant
  cell walls
• ? Through plasmodesmata, water and small solutes
  (and sometimes proteins and RNA) can pass from
  cell to cell

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LE 6-30
Cell walls
Interior of cell
Interior of cell
Plasmodesmata
Plasma membranes
0.5 µm
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Animals Tight Junctions, Desmosomes, and Gap
Junctions

• ? At tight junctions, membranes of neighboring
  cells are pressed together, preventing leakage of
  extracellular fluid
• ? Desmosomes (anchoring junctions) fasten cells
  together into strong sheets
• ? Gap junctions (communicating junctions) provide
  cytoplasmic channels between adjacent cells

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Tight junction
Tight junctions prevent fluid from moving across
a layer of cells
0.5 µm
Tight junction
Intermediate filaments
Desmosome
1 µm
Gap junctions
Space between cells
Plasma membranes of adjacent cells
Gap junction
Extracellular matrix
0.1 µm
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The Cell A Living Unit Greater Than the Sum of
Its Parts

• ? Cells rely on the integration of structures and
  organelles in order to function
• ? For example, a macrophages ability to destroy
  bacteria involves the whole cell, coordinating
  components such as the cytoskeleton, lysosomes,
  and plasma membrane

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LE 6-32
5 µm