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Cell Structures
Cell Theory
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All organisms are composed of one or more
cells.
Cells are the smallest living units of all living
organisms.
Cells arise only by division of a previously
existing cell.
Generalized Eukaryotic Cell
Cell Size
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Most cells are relatively small because as
size increases, volume increases much
more rapidly (this increases diffusion time).
Visualizing Cells
Prokaryotic Cells
Eukaryotic Cells
Characterized by
compartmentalization by an
endomembrane system, and the
presence of membrane-bound
organelles.
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Nucleus
Repository for genetic material
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Directs activities of the cell
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Surface of nucleus bound by two phospholipid
bilayer membranes
 nuclear membrane
 Nuclear pores
Nucleus
Chromosomes
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DNA of eukaryotes is divided into linear
chromosomes.
Endomembrane
System
Endoplasmic reticulum
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Largest internal membrane
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Composed of Lipid bilayer
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Serves as system of channels outward from the nucleus
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Functions in storage and secretion
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Rough ER is “rough” because of associated ribosomes
(sites of protein synthesis
Smooth ER – has no ribosomes – contained embedded
enzymes (for synthesis of carbohydrate and lipid
molecules)
Ribosomes
Ribosomes are RNA-protein complexes
composed of two subunits that join and
attach to messenger RNA.
– site of protein synthesis
– assembled in nucleoli
Golgi Apparatus
Collects, packages, and distributes molecules
synthesized at one location in the cell and
utilized at another location.
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cis face
Proteins
trans face
Transport
vesicle
Golgi
apparatus
LYSOSOMES
Membrane-bound vesicles containing
digestive enzymes (broken off from Golgi
Bodies)
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Cytoplasm
Endoplasmic
reticulum
Phagocytosis
Food
vesicle
Golgi
apparatus
Lysosomes
Plasma
membrane
Extracellular
fluid
Digestion of
phagocytized
food particles
or cells
Transport
vesicle
Old or damaged
organelle
Breakdown
of old
organelle
Organelles With DNA
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Mitochondria
– bounded by exterior and interior
membranes
– interior partitioned by cristae
Chloroplasts
– have enclosed internal compartments of
stacked grana, containing thylakoids
– found in photosynthetic organisms
Mitochondria
A. "Powerhouse of the cell" - cellular
metabolism
B. Structure- outer and inner membranes,
cristae
C. Have their own DNA
Chloroplasts
•Chloroplasts are larger and more complex than
mitochondria
•Grana – closed compartments of stacked membranes
•Thylakoids – disc shaped structure – light capturing
pigment
•Stroma – fluid matrix
Endosymbiosis
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Endosymbiotic theory suggests engulfed
prokaryotes provided hosts with advantages
associated with specialized metabolic
activities.
Theory of Endosymbiosis
Evidence for the endosymbiont theory is that
mitochondria and chloroplasts:
- Are appropriate size to be descendants of eubacteria.
- Have inner membranes similar to those on prokaryotic
plasma membranes.
- Replicate by splitting, as in prokaryotes.
- DNA is circular and different from the DNA of the cell's
nucleus.
- Contain their own components for DNA transcription and
translation into proteins .
- Have ribosomes similar to prokaryotic ribosomes.
- Molecular systematics lend evidence to support this
theory.
- Many extant organisms are involved in endosymbiotic
relationships.
Cytoskeleton
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Network of protein fibers supporting cell shape and
anchoring organelles
– Actin filaments
Microtubules
 cell movement
– Microtubules
Intermediate
filaments
 Hollow tubes
 Facilitate cell movement
 Centrioles – barrel shaped
 organelles occur in pairs –
 help assemble animal cell’s microtubules
Actin
– Intermediate filaments
 Stable - don’t break down
Cytoskeleton
Plant Cells
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Central vacuole
– often found in the center of a plant, and
serves as a storage facility for water and
other materials
Cell wall
– primary walls – laid down while cell is
growing
– middle lamella – glues cells together
– secondary walls – inside the primary cell
walls after growth
Plant Cell
Animal Cells
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Animal cells lack cell walls.
– form extracellular matrix
 provides support, strength, and resilience