Chapter 7: Membranes Roles of Biological Membranes Roles of Biological Membranes The Lipid Bilayer...
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Chapter 7: Membranes Roles of Biological Membranes Roles of Biological Membranes The Lipid Bilayer and the Fluid Mosaic Model The Lipid Bilayer and the
. Chapter 7: Membranes Roles of Biological Membranes Roles of
Biological Membranes The Lipid Bilayer and the Fluid Mosaic Model
The Lipid Bilayer and the Fluid Mosaic Model Transport and Transfer
Across Cell Membranes Transport and Transfer Across Cell Membranes
Specialized contacts (junctions) between cells Specialized contacts
(junctions) between cells
Slide 2
. What are the major roles of biological membranes?
Slide 3
. Roles of Biological Membranes border: keeping in in and out
out border: keeping in in and out out membranes separate aqueous
environments, so that differences can be maintained membranes
separate aqueous environments, so that differences can be
maintained the plasma membrane surrounds the cell and separates the
interior of the cell from the external environment the plasma
membrane surrounds the cell and separates the interior of the cell
from the external environment membrane-bound organelles have their
interior region separated from the rest of the cell membrane-bound
organelles have their interior region separated from the rest of
the cell
Slide 4
. Roles of Biological Membranes border guarding: controlling
what gets in and out border guarding: controlling what gets in and
out passage of substances across membranes is generally regulated
passage of substances across membranes is generally regulated helps
to establish and maintain appropriate environments in the cell even
as the outside environment changes helps to establish and maintain
appropriate environments in the cell even as the outside
environment changes
Slide 5
. Roles of Biological Membranes surface for chemistry surface
for chemistry many enzymes are embedded in membranes many enzymes
are embedded in membranes helps make reactions easier to control
helps make reactions easier to control can help in getting
reactants together can help in getting reactants together can help
in getting catalysts and reaction chains together can help in
getting catalysts and reaction chains together sometimes, reactants
on one side of a membrane and products are released on the other
side, helping cells avoid equilibrium sometimes, reactants on one
side of a membrane and products are released on the other side,
helping cells avoid equilibrium
Slide 6
. Roles of Biological Membranes more surface chemistry: raising
flags and sending or receiving messages more surface chemistry:
raising flags and sending or receiving messages proteins and
glycoproteins embedded in membranes are used for chemical
recognition and signaling proteins and glycoproteins embedded in
membranes are used for chemical recognition and signaling
Slide 7
. What are the major roles of biological membranes?
Slide 8
. Chapter 7: Membranes Roles of Biological Membranes Roles of
Biological Membranes The Lipid Bilayer and the Fluid Mosaic Model
The Lipid Bilayer and the Fluid Mosaic Model Transport and Transfer
Across Cell Membranes Transport and Transfer Across Cell Membranes
Specialized contacts (junctions) between cells Specialized contacts
(junctions) between cells
Slide 9
. What about phospholipids makes a bilayer when mixed with
water? Use the term amphipathic, and contrast with what detergents
do.
Slide 10
. Physical properties of cell membranes: the lipid bilayer and
the fluid mosaic model biological membranes are lipid bilayers with
associated proteins and glycoproteins biological membranes are
lipid bilayers with associated proteins and glycoproteins most of
the lipids involved are phospholipids, although others like
cholesterol and various glycolipids are also present most of the
lipids involved are phospholipids, although others like cholesterol
and various glycolipids are also present
Slide 11
. Physical properties of cell membranes: the lipid bilayer and
the fluid mosaic model phospholipids molecules spontaneously form
bilayers in aqueous environments phospholipids molecules
spontaneously form bilayers in aqueous environments means no energy
required from cells to get this to happen means no energy required
from cells to get this to happen two reasons two reasons
amphipathic nature (distinct hydrophobic and hydrophilic regions)
amphipathic nature (distinct hydrophobic and hydrophilic regions)
overall cylindrical structure overall cylindrical structure
Slide 12
. Physical properties of cell membranes: the lipid bilayer and
the fluid mosaic model recall the hydrophilic head and hydrophobic
tails of phospholipids recall the hydrophilic head and hydrophobic
tails of phospholipids tails come from two chains of fatty acids
linked to glycerol tails come from two chains of fatty acids linked
to glycerol head comes from a polar organic molecule linked via a
phosphate group to the glycerol backbone head comes from a polar
organic molecule linked via a phosphate group to the glycerol
backbone
Slide 13
. Physical properties of cell membranes: the lipid bilayer and
the fluid mosaic model roughly cylindrical shape to the
phospholipid molecule roughly cylindrical shape to the phospholipid
molecule favors the formation of lipid bilayers over lipid spheres
favors the formation of lipid bilayers over lipid spheres there are
other amphipathic molecules, such as detergents (soaps, etc.), that
come to a point at their single hydrophobic tail, thus tending to
form spheres instead of bilayers there are other amphipathic
molecules, such as detergents (soaps, etc.), that come to a point
at their single hydrophobic tail, thus tending to form spheres
instead of bilayers
Slide 14
. Physical properties of cell membranes: the lipid bilayer and
the fluid mosaic model detergents can solubilize lipids to varying
degrees; high enough concentrations of detergents will disrupt cell
membranes detergents can solubilize lipids to varying degrees; high
enough concentrations of detergents will disrupt cell
membranes
Slide 15
. What about phospholipids makes a bilayer when mixed with
water? Use the term amphipathic, and contrast with what detergents
do.
Slide 16
. Describe the fluid mosaic model: what does it mean to have a
2-dimensional fluid and not a 3-dimensional one, and what does the
mosaic term mean here? Discuss membrane fluidity: why it is
important and the ways it can be adjusted. Contrast integral and
peripheral membrane proteins.
Slide 17
. fluid mosaic model the fluid mosaic model describes the
structure and properties of cell membranes the fluid mosaic model
describes the structure and properties of cell membranes From the
1930s: the sandwich model From the 1930s: the sandwich model EM
data after the 1950s ruled out the sandwich model EM data after the
1950s ruled out the sandwich model membrane bilayers are uniformly
about 8 nm thick, too thin for the sandwich model membrane bilayers
are uniformly about 8 nm thick, too thin for the sandwich model
isolated membrane proteins were often found to have a globular
nature isolated membrane proteins were often found to have a
globular nature
Slide 18
. fluid mosaic model the fluid mosaic model was proposed in
1972 the fluid mosaic model was proposed in 1972 model has some
proteins imbedded in lipid bilayers that act as two-dimensional
fluids model has some proteins imbedded in lipid bilayers that act
as two-dimensional fluids
Slide 19
. fluid mosaic model biological membranes act as
two-dimensional fluids, or liquid crystals biological membranes act
as two-dimensional fluids, or liquid crystals free to move in two
dimensions, but not in the third, the molecules of the membrane can
rotate or move laterally free to move in two dimensions, but not in
the third, the molecules of the membrane can rotate or move
laterally molecules rarely flip from one side of the membrane to
the other (that would be movement in the third dimension) molecules
rarely flip from one side of the membrane to the other (that would
be movement in the third dimension)
Slide 20
. fluid mosaic model this model explained the existing data and
made two key predications that have been verified: this model
explained the existing data and made two key predications that have
been verified: materials, including embedded proteins, can be moved
along the membrane due to its fluid properties materials, including
embedded proteins, can be moved along the membrane due to its fluid
properties digestion of certain transmembrane proteins applied to
one side of a membrane will produce protein fragments that differ
from those found if digestion is done only on the other side
digestion of certain transmembrane proteins applied to one side of
a membrane will produce protein fragments that differ from those
found if digestion is done only on the other side
Slide 21
. fluid mosaic model the fluidity of a membrane is a function
of both temperature and the molecules in the membrane the fluidity
of a membrane is a function of both temperature and the molecules
in the membrane cells need membranes to be within a reasonable
range of fluidity too fluid and they are too weak, too viscous and
they are more like solid gels cells need membranes to be within a
reasonable range of fluidity too fluid and they are too weak, too
viscous and they are more like solid gels at a given temperature,
phospholipids with saturated fats are less fluid than those with
unsaturated fats at a given temperature, phospholipids with
saturated fats are less fluid than those with unsaturated fats
Slide 22
. fluid mosaic model in an unsaturated fat, a carbon-carbon
double bond produces a bend that causes the phospholipids to be
spaced further away from its neighbors, thus retaining more freedom
of motion in an unsaturated fat, a carbon-carbon double bond
produces a bend that causes the phospholipids to be spaced further
away from its neighbors, thus retaining more freedom of motion
Slide 23
. fluid mosaic model the upshot is: the upshot is: at colder
temperatures, unsaturated fats are preferred in cell membranes
(makes them more fluid) at colder temperatures, unsaturated fats
are preferred in cell membranes (makes them more fluid) at higher
temperatures, saturated fats are preferred (make them less fluid)
at higher temperatures, saturated fats are preferred (make them
less fluid) other lipids, such as cholesterol, can stabilize
membrane fluidity other lipids, such as cholesterol, can stabilize
membrane fluidity
Slide 24
. fluid mosaic model organisms control membrane fluidity by
several means organisms control membrane fluidity by several means
by regulating their temperature (fastest method) by regulating
their temperature (fastest method) by changing the fatty acid
profile of their membranes (slow process) by changing the fatty
acid profile of their membranes (slow process) by adding fluidity
modifiers or stabilizers like cholesterol (fluidity buffer usually
always present) by adding fluidity modifiers or stabilizers like
cholesterol (fluidity buffer usually always present)
Slide 25
. fluid mosaic model biological membranes resist having open
ends biological membranes resist having open ends a lipid bilayer
will spontaneously self-seal a lipid bilayer will spontaneously
self-seal usually, this results in nearly spherical vesicles with
an internal, aqueous lumen usually, this results in nearly
spherical vesicles with an internal, aqueous lumen
Slide 26
. fluid mosaic model the spherical tendency can be modified
with structural elements, such as structural proteins the spherical
tendency can be modified with structural elements, such as
structural proteins winding membrane surfaces must be kept far
enough apart and structurally supported to prevent them from
self-sealing winding membrane surfaces must be kept far enough
apart and structurally supported to prevent them from self-sealing
vesicle formation takes advantage of self-sealing as regions of
membrane are pinched off by protein contractile rings vesicle
formation takes advantage of self-sealing as regions of membrane
are pinched off by protein contractile rings
Slide 27
. fluid mosaic model fusion of membrane surfaces can occur when
they are in close proximity (spontaneously; no energy cost) fusion
of membrane surfaces can occur when they are in close proximity
(spontaneously; no energy cost) fusion is common between vesicles
and various organelles fusion is common between vesicles and
various organelles contents of two separate membrane-bound lumens
are mixed when fusion occurs contents of two separate
membrane-bound lumens are mixed when fusion occurs fusion of
vesicles with the plasma membrane delivers the material in the
vesicle lumen to the outside of the cell fusion of vesicles with
the plasma membrane delivers the material in the vesicle lumen to
the outside of the cell
Slide 28
. Membrane-Associated Proteins membrane proteins are classified
as either integral or peripheral membrane proteins are classified
as either integral or peripheral
Slide 29
. Membrane-Associated Proteins integral proteins are
amphipathic proteins that are firmly bound to the membrane, and can
only be released from the membrane by detergents integral proteins
are amphipathic proteins that are firmly bound to the membrane, and
can only be released from the membrane by detergents some integral
proteins are transmembrane proteins, extending completely across
the membranesome integral proteins are transmembrane proteins,
extending completely across the membrane hydrophobic -helices are
common in the membrane spanning domains of transmembrane
proteinshydrophobic -helices are common in the membrane spanning
domains of transmembrane proteins some wind back-and-forth across
the membranesome wind back-and-forth across the membrane
Slide 30
. Fig. 6.11
Slide 31
. Membrane-Associated Proteins peripheral proteins are not
embedded in the membrane peripheral proteins are not embedded in
the membrane usually bound ionically or by hydrogen bonds to a
hydrophilic portion of an integral protein usually bound ionically
or by hydrogen bonds to a hydrophilic portion of an integral
protein
Slide 32
. Membrane-Associated Proteins the protein profile of one
membrane side typically differs from that of the other side the
protein profile of one membrane side typically differs from that of
the other side many more proteins are on the cytoplasmic side of
the plasma membrane, as revealed by freeze-fracturing plasma
membranes many more proteins are on the cytoplasmic side of the
plasma membrane, as revealed by freeze-fracturing plasma membranes
the types of processing that a protein receives differs depending
on the target side, or if it is integral the types of processing
that a protein receives differs depending on the target side, or if
it is integral
Slide 33
.
Slide 34
. Describe the fluid mosaic model: what does it mean to have a
2-dimensional fluid and not a 3-dimensional one, and what does the
mosaic term mean here? Discuss membrane fluidity: why it is
important and the ways it can be adjusted. Contrast integral and
peripheral membrane proteins.
Slide 35
. Chapter 7: Membranes Roles of Biological Membranes Roles of
Biological Membranes The Lipid Bilayer and the Fluid Mosaic Model
The Lipid Bilayer and the Fluid Mosaic Model Transport and Transfer
Across Cell Membranes Transport and Transfer Across Cell Membranes
Specialized contacts (junctions) between cells Specialized contacts
(junctions) between cells
Slide 36
. Define and discuss these terms related to transport/transfer
across cell membranes: selectively permeable diffusion
concentration gradient osmosis tonics isotonic hypertonic hypotonic
turgor pressure
Slide 37
. Transport and transfer across cell membranes cell membranes
are selectively permeable cell membranes are selectively permeable
some substances readily pass through, others do not some substances
readily pass through, others do not most permeable to small
molecules and lipid- soluble substances most permeable to small
molecules and lipid- soluble substances water(!) and other small
molecules like CO 2 and O 2 can pass through easily water(!) and
other small molecules like CO 2 and O 2 can pass through easily
some examples of molecules that do not pass through easily: amino
acids, sugars, ions some examples of molecules that do not pass
through easily: amino acids, sugars, ions
Slide 38
. Transport and transfer across cell membranes cell membranes
are selectively permeable cell membranes are selectively permeable
some passage across the membrane is assisted with special channels
to allow or speed up the passage some passage across the membrane
is assisted with special channels to allow or speed up the passage
the specific selectivity can vary depending on the membrane the
specific selectivity can vary depending on the membrane
Slide 39
. Transport and transfer across cell membranes diffusion across
membranes is based on random motion of particles diffusion across
membranes is based on random motion of particles particles move by
random motion (kinetic energy); over time, the concentration across
a membrane will tend to equalize particles move by random motion
(kinetic energy); over time, the concentration across a membrane
will tend to equalize diffusion is the net movement of particles
from an area with a high (initial) concentration to an area with a
low (initial) concentration diffusion is the net movement of
particles from an area with a high (initial) concentration to an
area with a low (initial) concentration
Slide 40
. Transport and transfer across cell membranes a difference in
concentrations establishes a concentration gradient, which provides
the energy for diffusion a difference in concentrations establishes
a concentration gradient, which provides the energy for diffusion
given enough time, equilibrium will be reached (the concentrations
on both sides of the membrane will be equal) given enough time,
equilibrium will be reached (the concentrations on both sides of
the membrane will be equal) often equilibrium is never reached due
to continual removal and/or continual production of a substance
often equilibrium is never reached due to continual removal and/or
continual production of a substance rate of diffusion is a function
temperature and of the size, shape, and charge nature of the
substance rate of diffusion is a function temperature and of the
size, shape, and charge nature of the substance
Slide 41
. Transport and transfer across cell membranes osmosis is
diffusion of a solvent across a membrane osmosis is diffusion of a
solvent across a membrane in biology, the solvent is typically
water in biology, the solvent is typically water solutes do not
always travel across membranes with water, but they affect movement
by affecting the concentration of water solutes do not always
travel across membranes with water, but they affect movement by
affecting the concentration of water osmotic pressure is determined
by the amount of dissolved substances in a solution; it is the
tendency of water to move into the solution osmotic pressure is
determined by the amount of dissolved substances in a solution; it
is the tendency of water to move into the solution
Slide 42
. Transport and transfer across cell membranes comparing two
solutions: isotonic - both have the same osmotic pressure isotonic
- both have the same osmotic pressure if they have different
osmotic pressures, then: if they have different osmotic pressures,
then: water will tend to flow out of one solution and into the
other water will tend to flow out of one solution and into the
other hypertonic solution hypertonic solution more tonics, thus:
more tonics, thus: higher osmotic pressure higher osmotic pressure
water will tend to flow into it water will tend to flow into it
hypotonic solution hypotonic solution less tonics, thus: less
tonics, thus: lower osmotic pressure lower osmotic pressure water
will tend to flow out of it water will tend to flow out of itflow
out of itflow out of it
Slide 43
. Transport and transfer across cell membranes comparing two
solutions: isotonic isotonic hypertonic hypertonic hypotonic
hypotonic
Slide 44
. Transport and transfer across cell membranes turgor pressure
is hydrostatic pressure in cells with a cell wall turgor pressure
is hydrostatic pressure in cells with a cell wall a cell wall
enables cells to take in extra amounts of water without bursting a
cell wall enables cells to take in extra amounts of water without
bursting the cells take in water and push against the cell wall,
which pushes back the cells take in water and push against the cell
wall, which pushes back many cells use turgor pressure as part of
maintaining structure; thus, if they lose turgor pressure, plants
wilt many cells use turgor pressure as part of maintaining
structure; thus, if they lose turgor pressure, plants wilt
Slide 45
. Define and discuss these terms related to transport/transfer
across cell membranes: selectively permeable diffusion
concentration gradient osmosis tonics isotonic hypertonic hypotonic
turgor pressure
Slide 46
. What is carrier-mediated transport? Differentiate between
facilitated diffusion and active transport. Describe how the
sodium-potassium pump works. Explain linked cotransport.
Slide 47
. Transport and transfer across cell membranes special integral
membrane proteins assist in transport across membranes
(carrier-mediated transport) facilitated diffusion when net
transport follows a concentration gradient, but proteins are needed
to assist in transport facilitated diffusion when net transport
follows a concentration gradient, but proteins are needed to assist
in transport the carrier protein often provides a regulated channel
or pore through the membrane the carrier protein often provides a
regulated channel or pore through the membrane typically used to
transport ions and large molecules like glucose, although water
channels also exist typically used to transport ions and large
molecules like glucose, although water channels also exist added
energy is not required (concentration gradient provides the
energy), and in some cases is harvested during transport added
energy is not required (concentration gradient provides the
energy), and in some cases is harvested during transport
Slide 48
. Transport and transfer across cell membranes carrier-mediated
active transport requires energy to work against a concentration
gradient carrier-mediated active transport requires energy to work
against a concentration gradient energy is often supplied by ATP
powering a protein pump that moves a substance against a gradient
energy is often supplied by ATP powering a protein pump that moves
a substance against a gradient against a gradient against a
gradient example: sodium-potassium pump in nearly all animal cells
(moves 3 Na + out, 2 K + in) example: sodium-potassium pump in
nearly all animal cells (moves 3 Na + out, 2 K + in)
Slide 49
. Transport and transfer across cell membranes more
carrier-mediated active transport linked cotransport can also
provide the energy for active transport linked cotransport can also
provide the energy for active transport Na +, K +, or H + is
transported down its gradient, providing energy Na +, K +, or H +
is transported down its gradient, providing energy another
substance is transported at the same time against its gradient,
using the energy another substance is transported at the same time
against its gradient, using the energy the Na +, K +, or H +
gradient is often produced by active transport via a pump that uses
ATP the Na +, K +, or H + gradient is often produced by active
transport via a pump that uses ATP
Slide 50
. What is carrier-mediated transport? Differentiate between
facilitated diffusion and active transport. Describe how the
sodium-potassium pump works. Explain linked cotransport.
Slide 51
. Define the processes of exocytosis and endocytosis (include
different forms of endocytosis).
Slide 52
. Transport and transfer across cell membranes large particles
are transported across membranes via exocytosis and
endocytosis
Slide 53
. Transport and transfer across cell membranes exocytosis -
fusion of vesicles or vacuoles with the plasma membrane that
results in secretion outside the cell or discarding waste outside
the cell exocytosis - fusion of vesicles or vacuoles with the
plasma membrane that results in secretion outside the cell or
discarding waste outside the cell
Slide 54
. Transport and transfer across cell membranes endocytosis
vesicles or vacuoles bud into the cell from the plasma membrane,
bringing materials into the cell; several types endocytosis
vesicles or vacuoles bud into the cell from the plasma membrane,
bringing materials into the cell; several types
Slide 55
.endocytosis phagocytosis large solid particles are ingested
(including whole cells in some cases) phagocytosis large solid
particles are ingested (including whole cells in some cases)
Slide 56
.endocytosis pinocytosis smaller regions of dissolved materials
are ingested pinocytosis smaller regions of dissolved materials are
ingested
Slide 57
.endocytosis receptor-mediated endocytosis receptor proteins in
the plasma membrane bind to specific molecules, causing protein
conformational (shape) changes that lead to the formation of a
coated vesicle receptor-mediated endocytosis receptor proteins in
the plasma membrane bind to specific molecules, causing protein
conformational (shape) changes that lead to the formation of a
coated vesicle typically, lysosomes bind with the vesicles or
vacuoles formed via phagocytosis or receptor-mediated endocytosis
typically, lysosomes bind with the vesicles or vacuoles formed via
phagocytosis or receptor-mediated endocytosis
Slide 58
. Define the processes of exocytosis and endocytosis (include
different forms of endocytosis).
Slide 59
. Where does exocytosis fit? Where does endocytosis fit (all
forms)?
Slide 60
. Summarize processes for transport of materials across
membranes; include information about which ones are active
(energy-requiring).
. Discuss information transfer across a membrane (signal
transduction); why is it needed, what are some concepts that you
should associate with it?
Slide 63
. Cell Signaling signal transduction is the transfer of
information across the cell membrane two aspects: signal reception
signal reception signal transmission* signal transmission**
Slide 64
. signal transduction signal reception - special protein
receptors in the cell membrane bind to signaling molecules outside
the cell signal reception - special protein receptors in the cell
membrane bind to signaling molecules outside the cell
Slide 65
. signal transduction signal transmission signal transmission
the receptor, now activated, changes shape in some way the
receptor, now activated, changes shape in some way then it
transfers information to the interior of the cell then it transfers
information to the interior of the cell often done using a series
of protein activations and eventual formation of a second messenger
such as cAMP on the cytosolic side of the cell membrane often done
using a series of protein activations and eventual formation of a
second messenger such as cAMP on the cytosolic side of the cell
membrane
Slide 66
. Fig. 7.5 (TEArt) Chemically gated ion channel Signal G
protein Activated G protein Enzyme or ion channel Activated enzyme
or ion channel Ions Enzymic receptor G-protein-linked receptor
Signal Inactive catalytic domain Active catalytic domain
Slide 67
. signal transduction
Slide 68
. signals often wind up greatly amplified amplified
Slide 69
. Discuss information transfer across a membrane (signal
transduction); why is it needed, what are some concepts that you
should associate with it?
Slide 70
. Chapter 7: Membranes Roles of Biological Membranes Roles of
Biological Membranes The Lipid Bilayer and the Fluid Mosaic Model
The Lipid Bilayer and the Fluid Mosaic Model Transport and Transfer
Across Cell Membranes Transport and Transfer Across Cell Membranes
Specialized contacts (junctions) between cells Specialized contacts
(junctions) between cells
Slide 71
. Differentiate between the following in terms of structure and
function: anchoring junctions (such as desmosomes) tight junctions
gap juntions plasmodesmata
Slide 72
. Specialized Contacts (junctions) Between Cells Cell Contacts
(junctions) typically connect cells and can allow special transport
between connected cells Cell Contacts (junctions) typically connect
cells and can allow special transport between connected cells
Anchoring Junctions Anchoring Junctions Tight Junctions Tight
Junctions Gap Junctions Gap Junctions Plasmodesmata
Plasmodesmata
Slide 73
. Specialized Contacts (junctions) Between Cells anchoring
junctions hold cells tightly together; one common type in animals
is the desmosome anchoring junctions hold cells tightly together;
one common type in animals is the desmosome desmosomes form strong
bonds, including merging of cytoskeletons, making it hard to
separate the cells from each other desmosomes form strong bonds,
including merging of cytoskeletons, making it hard to separate the
cells from each other materials can still pass in the space between
cells with anchoring junctions materials can still pass in the
space between cells with anchoring junctions NOT involved in the
transport of materials between cells NOT involved in the transport
of materials between cells
Slide 74
. Specialized Contacts (junctions) Between Cells tight
junctions between some animal cells are used to seal off body
cavities tight junctions between some animal cells are used to seal
off body cavities cell plasma membranes are adjacent to each other
and held together by a tight seal cell plasma membranes are
adjacent to each other and held together by a tight seal materials
cannot pass between cells held together by tight junctions
materials cannot pass between cells held together by tight
junctionstight junctionstight junctions NOT involved in the
transport of materials between cells NOT involved in the transport
of materials between cells
Slide 75
. Specialized Contacts (junctions) Between Cells gap junctions
between animal cells act as selective pores gap junctions between
animal cells act as selective pores proteins connect the cells
proteins connect the cells those proteins are grouped in cylinders
of 6 subunits those proteins are grouped in cylinders of 6 subunits
the cylinder can be opened to form a small pore (less than 2 nm),
through which small molecules can pass the cylinder can be opened
to form a small pore (less than 2 nm), through which small
molecules can pass
Slide 76
. Specialized Contacts (junctions) Between Cells plasmodesmata
act as selective pores between plant cells plasmodesmata act as
selective pores between plant cells plant cell walls perform the
functions of tight junctions and desmosomes plant cell walls
perform the functions of tight junctions and desmosomes plant cell
walls form a barrier to cell-to-cell communication that must be
breached by the functional equivalent of a gap junction plant cell
walls form a barrier to cell-to-cell communication that must be
breached by the functional equivalent of a gap junction
plasmodesmata are relatively wide channels (20-45 nm) across the
cell wall between adjacent cells plasmodesmata are relatively wide
channels (20-45 nm) across the cell wall between adjacent cells
actually connect the plasma membranes of the two cells actually
connect the plasma membranes of the two cells allow exchange of
some materials between the cells allow exchange of some materials
between the cells
Slide 77
. Differentiate between the following in terms of structure and
function: anchoring junctions (such as desmosomes) tight junctions
gap juntions plasmodesmata