Lesson 1: Cell Structures Involved in Cell
Transport
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Describe the structure and function of the plasma
membrane in relation to cell transport.
Identify the types of membrane proteins involved
in cell transport.
Identify the roles of the cytoplasm and
cytoskeleton in cell transport.
Identify the role of the endomembrane system in
eukaryotic organisms in cell transport.
Discuss special transport structure of plant cells.
Outline the role of cell transport in homeostasis.
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Barrier between cytoplasm inside
and environment outside the cell
Protects, supports the cell
Controls what goes in and what goes out
◦ Selective permeability allows only certain substances
to pass through
 Water most important substance; most essential molecules
for life are soluble
 Inorganic ions: sodium (Na+), potassium (K+), calcium (Ca2+),
and chlorine (Cl-)
 Gases: oxygen helps release energy that powers cellular
reactions
 Hormones: transmit messages
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Consists of two layers of phospholipids
◦ hydrophobic, or water-hating, interior (tails)
◦ hydrophilic, or water-loving, exterior (heads)
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Proteins embedded within have a variety of
functions
Hydrophobic molecules are nonpolar, easily
cross; if small enough
Hydrophilic molecules are polar, need help to
cross; usually through embedded proteins
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NOT INVOLVED IN TRANSPORT
◦ Peripheral proteins loosely bound to membrane
surface or to part of a integral protein
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INVOLVED IN TRANSPORT
◦ Integral proteins transmembrane protein; extend
into and usually span interior of membrane
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Transport proteins ions, polar molecules
Types of transport proteins:
◦ Channel proteins hydrophilic channel
 Water passes through aquaporin channel proteins
 Ions pass through ion channels
 Other ions pass through gated channels; open and close
in response to a stimulus
◦ Carrier proteins hold molecules and change shape
as they pass them through
 Sodium-potassium pump
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Contains enzymes, salts, organelles, and a
variety of organic molecules
◦ Enzymes help dissolve cellular waste for export
◦ Salts are conductors of electricity
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Movement generated through churning of
cytoplasmic streaming speeds up
distribution of nutrients, proteins, and
organelles within cell
http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter4/animation__cytoplasmic_streaming.html
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Consists of three different threadlike structures:
microfilaments, intermediate filaments,
microtubules
◦ Microfilaments and microtubules both components of
intracellular transport
 Microfilaments composed of protein called actin; act like
tracks within cells for myosin molecules
 Microtubules tracks for vesicle intracellular transport
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Separates and compartmentalizes interrelated
functions of variety of organelles
◦ Equates to a division of labor
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Organelles involved:
◦ Nuclear envelope, smooth endoplasmic reticulum,
rough ER, Golgi, lysosomes, endosomes, vesicles,
vacuoles, and plasma membrane
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Some through direct connection; others
through vesicular transport
◦ Vesicles bud off of sending organelles; fuse with
receiving organelles
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Helps make and transport proteins and lipids
Connected to the pores of the nuclear envelope
Two types of endoplasmic reticulum:
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Rough Endoplasmic Reticulum (RER)
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Smooth Endoplasmic Reticulum (SER)
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◦ Rough endoplasmic reticulum (RER)
◦ Smooth endoplasmic reticulum (SER).
◦ Studded with ribosomes; involved in protein synthesis, the production and
transport of new membrane, and the modification and transport of newly
formed proteins within the cell
◦ Proteins synthesized on the RER are transported to other locations through
vesicles formed in the SER.
◦ Not studded with ribosomes
◦ Contains enzymes for lipid biosynthesis (change to phospholipids and
steroids)
◦ Forms transition vesicles that travel along microtubular tracks in the
cytoplasm
 Transport molecules made in the RER to the Golgi apparatus
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Processes proteins and prepares them for use
both inside and outside the cell
Receives proteins from the ER that have been
transported in vesicles, packages and labels
them
Sends them on to their next destinations in
another set of vesicles
Also involved in the transport of lipids around
the cell
http://www.johnkyrk.com/golgiAlone.html
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Sac-like organelles
Store and transport large molecules
Pinch off ER and Golgi
◦ Transport to plasma membrane; fuse with it
◦ Going out = exocytosis
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Pinch inward at plasma membrane
◦ Transport to destinations inside the cell
◦ Going in = endocytosis
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Lysosomes bud off of the Golgi apparatus; infused with
hydrolytic enzymes
◦ Digestive vesicles of the cell; contain enzymes called hydrolases
 Digest proteins, nucleic acids, lipids, and complex sugars.
◦ Vesicles enter the cell through endocytosis; sent to lysosomes contents
processed
 Break down and disarm many potentially pathogenic and foreign materials;
expel them outside the cell through exocytosis
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Endosomes formed during endocytosis allow materials from
outside the cell to enter the cell
◦ Formed when the cell’s plasma membrane folds inward to surround
macromolecules, encircles them, brings them into the cell by pinching
off the membrane at their point of entry
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Vesicles larger than 100 nanometers in size are referred to as
vacuoles.
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Structure not found in animal cells, cell wall
◦ Rigid layer that surrounds the plasma membrane
◦ Supports and protects the cell
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Tiny holes, or pores, in the cell wall called
plasmodesmata (singular, plasmodesma)
◦ Form open channels through which strands of cytosol
connect between adjacent cells
◦ Allow water, nutrients, and other substances to move
into and out of the cells
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Cell to function normally=> stable state must be
maintained inside the cell
◦ Example: concentration of salts, nutrients, and other substances
must be kept within a certain range
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Process of maintaining stable conditions inside a cell (or
an entire organism) is homeostasis
◦ Homeostasis requires constant adjustments, because conditions
are always changing both inside and outside the cell
◦ Structures and processes described in this lesson and the next
lesson play important roles in homeostasis and are consider
homeostatic mechanisms
◦ By moving substances into and out of cells, they keep conditions
within normal ranges and maintain homeostatic regulation inside
the cells and the organism as a whole
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If homeostatic mechanisms fail to maintain homeostatic
regulation disease or death of a cell or organism may
follow.
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A major role of the plasma membrane is transporting
substances into and out of the cell.
The plasma membrane is selectively permeable, allowing
only certain substances to pass through.
Proteins embedded within the plasma membrane help to
move hydrophilic, polar molecules into the cell.
The cytoplasm is the internal medium for cell transport.
Vesicle aids in the import and export of macromolecules.
Plant cells have a special transport structures that are not
found in animal cells, called plasmodesmata.
Cell transport helps cells maintain homeostasis by keeping
conditions within normal ranges inside all of an
organism’s cells.
If homeostatic mechanisms fail, homeostatic regulation
may fluctuate and disease or death of a cell or organism
can follow.