MULTICELLULARITY
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Multicellular
Single organism composed of more than one
cell
Main benefit from the division of labor
Larger genomes = larger proteomes
Additional proteins for
Cell communication
Arrangement and attachment of cells
Cell specialization
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Extracellular matrix (ECM)
Network of material secreted from the cells
forming a complex meshwork outside of
cells
Major component of certain parts of plants
and animals
Bone
and cartilage of animals
Woody parts of plants
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Extracellular matrix (ECM)
Major macromolecules of ECM are
proteins and polysaccharides
Proteins form large fibers
Polysaccharides give a gel-like character
Important roles such as strength, structural
support, organization, and cell signaling
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Proteins of ECM
Adhesive
Fibronectin
and laminin
Help cells adhere to ECM
Structural
Collagen
Main protein found in bone, cartilage, tendon, skin
Elastin
provides tensile strength
provides elasticity
Needed in areas that expand and return to original
shape
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Collagens are a family of proteins that give
animal cells a variety of ECM properties
At least 27 different types of collagens in
humans
Collagens all have a common triple helix
structure
Similar yet distinct amino acid sequence affects
structure and function of collagen fibers
Differential gene regulation controls which types
of collagens are made
Wrinkling a symptom of decreasing collagen
synthesis with age
Polysaccharides in animal ECM
In vertebrates, the most abundant are
glycosaminoglycans (GAGs)
Long,
unbranched polysaccharides with a
repeating disaccharide unit
Highly negatively charge attracts ions and
water
Majority linked to core proteins to form
proteoglycans
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GAGs and proteoglycans resist
compression
Abundant
in joints
Chitin important ECM in invertebrates
Exoskeleton
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Plant cell walls
Protective ECM outside the plasma
membrane
Usually stronger, thicker and more rigid
than animal ECM
Primary
cell wall
Develops between newly made cells
Flexible and allows for size increase
Main macromolecule is cellulose
Secondary
cell wall
Layers of cellulose and other components
More variable structure than primary cell wall
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Cell junctions
Adhere cells to each other and to the ECM
Animals cells have a more varied group of
junctions
In plants, cellular organization is different
because of the rigid cell wall
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Anchoring junctions
Attach cells to each other and to the ECM
Rely on cell adhesion molecules (CAM)
Cadherin and integrin
4 main categories
1.
2.
3.
4.
Adherins junctions
Desmosomes
Local adhesions
Hemidesmosomes
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Cadherins: Major CAMs of
Vertebrates
CAMs that create cell-to-cell junctions
Dimer of identical subunits
Extracellular domain of two cadherin dimers,
each in adjacent cells, bind to each other to
promote cell-to-cell adhesion
Inside the cell, linker proteins connect cadherins
to the cytoskeleton
By expressing only certain types of cadherins,
each cell will only bind to other expressing same
type
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Integrins
Group of cell-surface receptor proteins
Extracellular domain for binding cell to
ECM
Intracellular domain for binding to
cytoskeleton
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CAMs and cell signaling
CAMs originally thought to be only
mechanical
Recent evidence points to role in cell
signaling
When junctions are formed or broken,
signaling pathways are affected
Signaling pathways can also affect CAM
Integrins are capable of both outside-in
and inside-out signaling
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Tight junctions (Occluding
Junctions)
Forms tight seal between adjacent cells
Prevents ECM from leaking between cells
Tight junctions
Made
by occludin and claudin
Bind to each to form tight seal
Not mechanically strong, not bound to
cytoskeleton
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Gap junctions
Small gap between plasma membranes of cells
at junction
Six connexin proteins in one cell align with six
connexin proteins in an adjacent cell to form a
connexon
Connexon allows passage of ions and small
molecules
Allow adjacent cell to share metabolites and
directly signal each other
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Loewenstein and colleagues followed the transfer of
fluorescent dyes to determine the size of gapjunction channels
Gap junctions allow passage of small molecules
up to about 1,000 Daltons
Determined by experiments using fluorescent
dyes
Monolayer of rat liver cells injected with
fluorescent dyes of different masses
Dyes up to 901 Daltons moved from cell to cell
HYPOTHESIS: Gap-junction channels allow the passage of ions & molecules,
but there is a limit to how large the molecules can be.
STARTING MATERIALS: Rat liver cells grown in laboratory
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Middle lamella
Plants don’t form cell-to-cell connections
The middle lamella is an additional
component of ECM
First layer to form when cells dividing
Cement cell walls of adjacent cells
together
Middle lamella rich in pectins
Ripening fruit secrete pectinases such that
ripe fruit is less firm than unripe fruit
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Plasmodesmata
Functionally similar to gap junctions
Allow passage of ions, water, signaling
molecules between cells
Different in that they are open channels
where the cell membrane of one cell is
continuous with adjacent cell membrane
Desmotubule connects ER membrane of
adjacent cells
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Tissues and organs
Tissue
Group
of cells having a similar structure or
function
Organ
Collection
of two or more tissues that perform
a specific function or set of functions
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6 basic cell processes
1.
2.
3.
4.
5.
6.
Cell division
Cell growth
Differentiation
Migration
Apoptosis
Cell connections
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4 general types of animal tissue
1.
Epithelial tissue
2.
Connective tissue
3.
Support body or connect tissues
Muscle tissue
4.
Cells joined together forming continuous
sheets to cover and line body surfaces
Facilitates movement
Nervous tissue
Receives, generates and conducts electrical
signals
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3 types of plant tissue
1.
Dermal tissue
2.
Ground tissue
3.
Covering on various plant parts
Most of plant’s body with variety of functions
Parenchyma, collenchyma, sclerenchyma
Vascular tissue
From interconnected conducting vessels for
water and nutrients
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