Post on 02-Jun-2018
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Cell Structure and Function
Chapter 4
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• Mid 1600s - Robert Hooke observed
and described cells in cork• Late 1600s - Antony van Leeuwenhoek
observed sperm, microorganisms
• 1820s - Robert Brown observed and
named nucleus in plant cells
Early Discoveries
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Developing Cell Theory
• Matthias Schleiden
• Theodor Schwann
• Rudolf Virchow
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Cell Theory
1) Every organism is composed of one or
more cells2) Cell is smallest unit having properties
of life
3) Continuity of life arises from growth
and division of single cells
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• Smallest unit of life
•
Can survive on its own or has potentialto do so
• Is highly organized for metabolism
• Senses and responds to environment
• Has potential to reproduce
Cell
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Structure of Cells
All start out life with:
– Plasma membrane
– Region where DNA
is stored
– Cytoplasm
Two types:
– Prokaryotic
– Eukaryotic
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• Main component of cell membranes
• Gives the membrane its fluid properties
• Two layers of phospholipids
Lipid Bilayer
one layer
of lipids
one layer
of lipids
Figure 4.3Page 56
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Membrane Proteins
Proteinpump across
bilayer
Proteinchannel
across bilayer
Protein pump
Recognitionprotein
Receptorprotein
extracellularenvironment
cytoplasm
lipid bilayer
Figure 4.4Page 57
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Why Are Cells So Small?
• Surface-to-volume ratio
• The bigger a cell is, the less surface
area there is per unit volume
•
Above a certain size, material cannot bemoved in or out of cell fast enough
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• Create detailed images of something
that is otherwise too small to see
• Light microscopes
– Simple or compound
• Electron microscopes
– Transmission EM or Scanning EM
Microscopes
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Limitations of Light
Microscopy• Wavelengths of light are 400-750 nm
• If a structure is less than one-half of a
wavelength long, it will not be visible
• Light microscopes can resolve objects
down to about 200 nm in size
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Electron Microscopy
• Uses streams of accelerated electrons
rather than light
• Electrons are focused by magnets
rather than glass lenses
• Can resolve structures down to 0.5 nm
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Eukaryotic Cells
• Have a nucleus and other
organelles
• Eukaryotic organisms
– Plants
– Animals
– Protistans
– Fungi
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Animal Cell Features
• Plasma membrane
• Nucleus
• Ribosomes• Endoplasmic
reticulum
•
Golgi body• Vesicles
• Mitochondria
•
Cytoskeleton Figure 4.10bPage 61
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Plant Cell Features
• Cell wall
• Central vacuole
• Chloroplast
• Plasma membrane
• Nucleus
• Ribosomes• Endoplasmic
reticulum
•
Golgi body• Vesicles
• Mitochondria
•
Cytoskeleton Figure 4.10aPage 61
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• Keeps the DNA molecules of eukaryotic
cells separated from metabolic
machinery of cytoplasm
• Makes it easier to organize DNA and to
copy it before parent cells divide intodaughter cells
Functions of Nucleus
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Components of Nucleus
nuclear envelope
nucleoplasm
nucleolus
chromatin
Figure 4.11b
Page 62
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Nuclear Envelope
• Two outer membranes (lipid bilayers)
• Innermost surface has DNA attachment sites
Nuclear pore bilayer facing cytoplasm Nuclear envelope
bilayer facingnucleoplasm
Figure 4.12bPage 63
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• Group of related organelles in which
lipids are assembled and new
polypeptide chains are modified
• Products are sorted and shipped to
various destinations
Cytomembrane System
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Components of
Cytomembrane System
Endoplasmic reticulum
Golgi bodies
Vesicles
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Golgi Body
• Puts finishing touches on proteins and
lipids that arrive from ER
•
Packages finished material for shipment tofinal destinations
• Material arrives and leaves in vesicles
buddingvesicle
Figure 4.15Page 65
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Vesicles
• Membranous sacs that
move through cytoplasm
• Lysosomes
• Peroxisomes
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• Plastids
• Central Vacuole
Specialized Plant Organelles
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Chloroplasts
Convert sunlight energy to ATP through
photosynthesis
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Other Plastids
• Chromoplasts
– No chlorophyll
– Abundance of carotenoids
– Color fruits and flowers red to yellow
• Amyloplasts
– No pigments
– Store starch
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Microtubules
• Largest elements
• Composed of tubulin
• Arise from microtubule
organizing centers (MTOCs)
• Involved in shape, motility,
cell division
Figure 4.21Page 71
tubulinsubunit
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Microfilaments
• Thinnest elements
• Composed of actin
• Take part in movement,
formation, and
maintenance of cell
shape
actinsubunit
Figure 4.21Page 71
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Intermediate Filaments
• Only in animal
cells of certain
tissues
• Most stable
cytoskeletal
elements
• Six known groups
onepolypeptidechain
Figure 4.21Page 71
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Motor Proteins
• Kinesins and dyneins move along
microtubules
• Myosins move along microfilaments
kinesin
microtubule
Figure 4.24b, Page 72
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Flagella and Cilia
• Structures for
cell motility
• 9 + 2 internal
structure
dynein
microtubule
Figure 4.25
Page 73
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Plant Cell Walls
Primary cell wall
Secondary cell wall
(3 layers)
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Plant Cuticle
• Cell secretions and waxes accumulate
at plant cell surface
• Semitransparent
• Restricts water loss
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Cell-to-Cell Junctions
• Plants
–
Plasmodesmata• Animals
–Tight junctions
– Adhering junctions
–Gap junctions
plasmodesma
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Animal Cell Junctions
tight
junctions
adhering
junction
gap junction
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• Archaebacteria and Eubacteria
• DNA is not enclosed in nucleus
• Generally the smallest, simplest cells
• No organelles
Prokaryotic Cells
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Prokaryotic Structure
DNA
pilus
flagellum
cytoplasm
with ribosomes
capsule
cell
wall
plasma
membrane