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Lecture 2: Membranes

The water molecules have an attraction to each other
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) Surface tension: at the top of water, if there is an object placed on the surface, if it is not
enough to break the surface tension of the water the object will remain on top of the water
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) Phase transition: water becomes shaped in very structured lattices
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If heat is
added it becomes liquid
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The amount of energy that is needed to break the attraction of the
water molecules is responsible for the transition into the gas phase
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If you look at a kind of receptor, even if isolated from different animals, it is likely that these
receptors will appear
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Another example
is the channel protein
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The amino acids that make up this channel you will find
them to be as a motif
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Sugars are very important in many different ways
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Sugars have a ring structures
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So through the process of condensation (removal of water) they
attach and the two hydroxyl groups will be joined together
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There are other hydroxyl groups so the joining is not restricted
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This happens all the time because a
polysaccharide when our body uses them is broken up
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Galactose is something that we will also see, and also another monosccharide that is important is
mannose and galactose that have precise functions in the cell
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Well
maltose is the major form of canned sugar, I mention it because our body once it takes it in needs to be
able to deal with it
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There you
have a specific enzyme called maltase that will break up this disaccharide
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Another example of a disaccharide is
sucrose
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Sucrose is mainly
found in sugar cane, it is the main form that we use to sweeten our food
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There are two forms of glucose the D glucose and the
L glucose that are optical isomers of each other
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We make D- glucose, our body is not able
to use L glucose
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It will taste sweet and when you eat it your body cannot digest
it, so you will stay nice and slim
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Well it is very important that we are able to break it up with lactase
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Polyscharides are not only linear they can
branch off
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It is
actually two polymers
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Fortunaltely we have the enzyme that can break this kind of polymer and derive nutrition from it
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Cellulose, we cannot digest it, we don’t have the enzyme
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A lot of the biofuels is built on breaking down the cellulose and
converting the glucose to energy
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Kitin is made up of monomer of nacytlglucosamine
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This is a lot and arthropods
constitute 90% of the animal species in this world
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Nucleic acids have four bases
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Adenine and ribose and then three phosphate
groups that carry a tremendous amount of energy
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Besides ATP there are other molecules that are very important for
providing energy for all kinds of processes in the cell (Check on slides)
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NADPH is used in biosynthetic reactions
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If you break it you will release a lot of energy
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Carboxylated Biotin is the vitamin B6—the carboxyl group joined to the vitamin in a high energy group
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Adenosine methionine is a molecules that
transfers a methyl group to another molecule and Uridine diphosphate the bond that joins the glucose is
again high energy it is a way of transferring sugar
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Well where do we find lipids,
well they form the boundary of the cell within the plasma membrane
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This membrane is just the same as the ER, Golgi but there is one thing that is important to
note is that it is continuous with the ER
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It is very
difficult to make a distinction between their boundaries
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It is responsible of transporting molecules inside and outside of the cell
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Transport has a lot of specificity
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This process is called signal
transduction and membranes are very important in generating this kind of signal
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This is for cells that line up next to each other
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Usually only part of the
membrane adhere together and then you have space in between
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This area is
the side is called basolateral
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They do not function in the same way they are very
very different and also the last point about the function of a membrane is in protein trafficking
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In the membrane you have protein in there
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These
types traverse the whole membrane and it has an intracellular side, a part in the transmembrane part
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The protein
moves very rapidly along the plasma membrane
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There are four classes of important lipids that are associated with the membrane:
1
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What does it
involve? First you have a glycerol molecule (3 carbon alcohol) and two of the carbons of the
glycerol molecule is joined to two fatty acids and the bond of the fatty acid joining the glycerol
molecule are acyl bonds
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The third carbon of the glycerol molecule is bound to choline and
choline to phosphate
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We also have phosphotidylethanolamine
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) sphingomyelin which is very important but the structure is a little different
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Sphingomyolein has a precursor, the body does not produce it
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Myelin is highly charge so that electrical activity can move across very, very
quickly
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) Sphingosine is the precursor of shingomyelin
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) Cholesterol: very important
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Our body is capable of
total synthesis of cholesterol starting from two carbon units all the way to the heterocyclic
structure
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So how do
arthropods synthesize cholesterol, they do it through their diet
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Cholesterol has four rings, in ring one there is a very distinct
hydroxyl group
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This molecule
has a polar end and a hydrophobic end
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There are actually different shapes of lipid molecules
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I will continue this line on how these lipids account for the
properties of the membrane in the next lecture

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