Lecture 3 - Cell membrane and Signalling Flashcards
What are some major functions of membranes
Selective barrier to the passage of molecules
Detecting chemical signals from other cells
Anchoring cells to adjacent cells and to the extracellular matrix of connective-tissue proteins
What are the two classes of membrane proteins
Integral and peripheral
What are integral membrane proteins
closely associated with the membrane lipids, cannot be
extracted from the membrane without disrupting the lipid bilayer, and are amphipathic. Most
span the entire membrane and are referred to as transmembrane proteins.
What are peripheral membrane proteins
re not
amphipathic and do not associate with the
nonpolar regions of the lipids in the interior of
the membrane. They are located at the
membrane surface where they are bound to the
polar regions of the integral membrane proteins
How are cells joined
Desmosomes
Tight Junctions
Gap junctions
What are integrins
transmembrane
proteins in the plasma membrane
which bind to specific proteins in
the extracellular matrix and link
them to membrane proteins on
adjacent cells (e.g. CD11a)
What fills the gaps between cells
Interstitial fluid
What are desmosomes
Characterised by accumulations of
protein known as dense plaques along
the cytoplasmic surface of the plasma
membrane.
These proteins serve as anchoring points
for cadherins.
What is the function of a desmosome
hold adjacent cells firmly
together in areas that are subject to
considerable stretching, such as the skin.
What are cadherins
Cadherins are proteins that extend
from the cell into the extracellular
space, where they link up and bind
with cadherins from an adjacent cell.
What are tight junctions
Form when the extracellular surfaces of
two adjacent plasma membranes join
together so that no extracellular space
remains between them.
Unlike the desmosome, which is limited
to a disk-shaped area of the membrane,
the tight junction occurs in a band around
the entire circumference of the cell.
What are gap junctions
Consist of protein channels linking
the cytosols of adjacent cells.
Connexins from the two membranes
join, forming small, protein-lined
channels linking the two cells
What is diffusion
the movement of molecules from one location to another as a
result of their random “thermal motion
What is net flux
reflects the movement of material
from one compartment to another
How does temperature affect the magnitude of flux
higher = greater speed of molecular movement and greater net flux
How does the mass of a molecule affect the magnitude of a flux
molecules with a greater mass have a lower speed and smaller net flux
How does surface area affect magnitude of flux
the greater the surface area between the two regions the greater the space for
diffusion and the larger the net flux
how does the medium of which particles are moving through affect the magnitude of flux
molecules move quicker through air for example
What is the major factor limiting diffusion across a membrane
The hydrophobic interior
of its lipid bilayer
What are some properties of non polar molecules and examples
Oxygen, carbon dioxide, fatty acids, and steroid hormones
molecules that diffuse rapidly through the lipid portions of membranes
What are lipophilic molecules
Lipid-loving or hydrophobic substances that move through membranes easily
What are some properties of polar molecules
Hydrophilic, hence do not diffuse readily through the membrane
What are protein channels
integral membrane
proteins that span the lipid bilayer
A single protein may have a conformation
that looks like a doughnut, with the hole
in the middle providing the channel for
ion movement.
More often, several proteins
aggregate, each forming a subunit of
the walls of a channel.
for eg. Na+, K+, Cl-, Ca2+
What is channel specificity determined by
Pore size
Charge
Binding sites
