Cell Membrane Structure and Functions|CELL BIOLOGY

Cell Membrane Structure and Functions|CELL BIOLOGY


Hi! Welcome to our tutorial.This video is
of descriptive class on basics of cell biology, precisely cell membrane.
Structure cell membranes are crucial to the life of the cell we are going to
make series of tutorial videos on this chapter as playlist.If you are new in
this channel please explore our other videos if you like,then please subscribe
and hit the bell icon for further notifications. Let’s learn . The plasma
membrane encloses the cell defines its boundaries and maintains the essential
differences between the cytosol and the extracellular environment inside
eukaryotic cells.The membranes of the endoplasmic reticulum,Golgi apparatus,
mitochondria and other membrane-enclosed organelles maintain the characteristics
differences between the contents of each organelle and the cytosol. Ion
gradients across membranes established by the activities of specialised
membrane proteins can be used to synthesize ATP to drive the
transmembrane movement of selected solutes or as in nerve and muscle cells
to produce and transmit electrical signals.In all cells the plasma membrane
also contain proteins that act as sensors of external signals allowing the
cell to change its behavior in response to environmental cues including signals
from other cells these protein sensors or receptors transfer information rather
than molecules across the membrane all biological membranes have a common
general structure each is a very thin film of lipid and protein molecules held
together mainly by non covalent interactions cell membranes are dynamic
fluid structure and most of their molecules move about in the plane of the
membrane the lipid molecules are arranged as a continuous double layer
about 5 nanometer thick. This lipid bilayer provides the basic fluid
structure of the membrane and serves as a relatively impermeable barrier to the
passage of most water-soluble molecules. Protein molecules that span the lipid
bilayer mediate nearly all of the other functions of the membrane transporting
specific molecules across it for example or catalyzing membrane-associated
reactions such as ATP synthesis in the plasma membrane some transmembrane
proteins serve as structural links that connect the cytoskeleton through the
lipid bilayer to either the extracellular matrix or an adjacent cell
while other serve as receptor to detect and transduce chemical signals in the
cell’s environment as would be expected. It takes many different membrane
proteins to enable a cell to function and interact with its environment and it
is estimated that about 30% of the proteins encoded in an animal cells
genomes are membrane proteins. Lipid molecules constitute about 50% of a mass
of most animal cell membranes.All of the lipid molecules in cell membranes are
amphiphilic that is they have a hydrophilic or polar end and hydrophobic
or nonpolar end.The most abundant membrane lipids are the phospholipids.
These have a polar head group and two hydrophobic hydrocarbons tails in animal
plant and bacterial cells. The tails are usually fatty acids and
they can differ in length.One tail typically has one or more sis double
bonds that is it is unsaturated while the other tail does not that is it is
saturated.Each sis double bond creates a small kink in the tail differences in
the length and saturation of the fatty acid tails influence how phospholipid
molecules pack against one another, thereby affecting the fluidity of the
membrane the main phospholipids in most animal cell membranes are the
phosphoglycerate which have a three carbon glycerol backbone ,two long-chain
fatty acids are linked through ester bonds to adjacent carbon atoms of the
glycerol and the third carbon atom is attached to a phosphate group which in
turn is linked to one of several different types of head group by
combining several different fatty acids and head groups cells make many
different phosphoglycerates phosphatidyl ethanolamine
phosphatidylserine and phosphatidyl choline are the main ones in mammalian
cell membranes another important phospholipid called
sphingomyelin is built form sphingosine. Rather than glycerol sphingosine is a
long acyl chain with a minor group and two hydroxyl groups at one end of
the molecule in sphingomyelin,a fatty acid tail is attached to the amino group
and a phosphocholine group is attached to the terminal hydroxyl group leaving
one hydroxyl group free. The three hydroxyl group contributes to the polar
properties of the adjacent head group as it can form hydrogen bonds with the head
group of a neighboring lipid with the water molecule or with membrane protein.
Together the phospholipids phosphatidylcholine,phosphatidylethanolamine and phosphatidyl serine and sphingomyelin constitute more than half
the mass of lipid in most mammalian cell membranes. In addition to phospholipids
the lipid bilayers in many cell membranes contain cholesterol and
glycolipids. Eukaryotic plasma membranes contain a spatially large amount of
cholesterol up to one molecule for every phospholipid molecule. Cholesterol is a
sterile it contains a rigid ring structure to which is attached a single
polar hydroxyl group and a short nonpolar hydrocarbon chain.The
cholesterol molecules oriented themselves in the bilayer with their
hydroxyl group close to the polar head groups of adjacent phospholipid
molecules.The hydrophobic and hydrophilic regions of lipid molecules
behave in the same way thus lipid molecules spontaneously
aggregate to bury their hydrophobic hydrocarbon tails in the interior and
expose their hydrophilic heads to water depending on their shape they can do
this in either of two ways. They can form spherical Micelles with the tails
inward, or they can form double layered sheets or by layers with the hydrophobic
tails sandwiched between the hydrophilic head groups.Being cylindrical
phospholipid molecules spontaneously formed bIlayers in aqueous environments
in this energetically most favorable arrangement the hydrophilic heads face
the water at each surface of the bilayer and the hydrophobic tails are shielded
from the water in the interior.The same forces that drive phospholipids to form
by layers also provide a self-healing property. A small tear
in the bilayer creates a free edge with water because this is
energetically unfavorable.The lipids tend to rearrange spontaneously to
eliminate the free Edge the prohibition of free edge has a profound consequence
the only way for a bilayer to avoid having ages is by closing in on itself
and forming a shield compartment. Around 1970 researchers first recognized
that individual lipid molecules are able to diffuse freely within lipid bilayers
the initial demonstration came from studies of synthetic lipid bilayers two
types of preparations having very useful in such studies,the first one is by
layers made in the form of spherical vesicles called Liposomes and the next
one planar by layers called Black membranes formed across a hole in a
partition between two across compartments. That’s it for today’s class.
We’re not finished yet,for better understanding we will continue elaborated
tutorials regarding this chapter.We’ll be back soon,if you like this video
please put thumbs up and do not forget to comment regarding this chapter or
your any kind of suggestion for betterment of this channel.THANKS for
watching,stay with us.PAPERPENBIOLOGY

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