CHARACTERISTICS OF LIPOPROTEINS:
So, Lipoproteins we have talked about them in the last lecture and their
main functions are to:
1. Solubilize and carry plasma lipids: as we all know
that lipids are hydrophobic, so they tend to
cluster in the blood unless they have a carrier
protein, for ex: albumin, so the lipoproteins they
solubilize the lipids in the hydrophilic blood
2. Transport lipids from one tissue to another
These lipoproteins vary in size, so you have
chylomicrons being the largest and HDL being the
smallest
Also they differ in density (which is the ratio of
proteins to lipids), so chylomicrons have the
lightest density cuz they have a lot of lipids
compare to proteins, HDLs on the other hand have
the highest density cuz they have higher amount
of proteins comparing with lipids
They differ in lipid content, so chylomicron have a
lot of TAGs relative to cholesterol, same thing
with VLDL. HDLs and LDLs on the other hand carry
a lot of cholesterol esters
They differ in function as well, Chylomicrons carry
dietary lipids from intestinal cells to the liver,
while HDLs carry esters from peripheral tissues
back to liver. PAY ATTENTION TO THESE
DIFFRENCES PLEAS!!
, COMPOSITION OF LIPOPROTEINS:
• Now, these lipoproteins also differ in the type of proteins they carry these
proteins are known as APOLIPOPROTEINS and they are AMPHIPATHIC. They
exist on the surface of these lipoproteins, the hydrophilic part is on the outer
surface, while the hydrophobic is on the core
• Some lipids are amphipathic such as cholesterol which contains hydroxyl group
(these amphipathic lipids will have their hydrophilic regions on the surface
while other hydrophobic regions will be hidden inside) and
there are other lipids that are completely hydrophobic such
as cholesterol esters & TAG
• A neutral lipid core (containing TAG and CHOLESTEROL
ESTERS) surrounded by a shell of amphipathic
apolipoproteins, phospholipids, and non-esterified (free)
cholesterol. Cholesterol If it is not esterified the (OH) group
which is the hydrophilic part is exposed to the outside.
• They also differ in the sources of lipids, either they have a
dietary lipids which are known as EXOGENOUS SOURCE in which the lipids are
taken from intestinal cells to liver, and we have ENDOGENOUS lipids which are
synthesized de novo (by itself) from liver to peripheral tissues or back from
tissues like adipose tissues to liver
• Well, the three major cholesterol carriers are HDL, LDL and VLDL to some
extent, except that the VLDL carries five times more TAGs verses CHOLESTEROL
• So, in order to calculate how much CHOLESTEROL is there in the blood, we find
the summation of the amount of cholesterol that is present in LDL, HDL and
VLDL. *
o NOTE: VLDL -C is calculated by dividing VLDL- TAG by 5 because the
TAG/cholesterol ration is 5/1 in VLDL.
The goal value for total cholesterol is <200 mg/dl.
, APOLIPOPROTEINS:
FUNCTIONS: (notice the functions of these lipoproteins please)
I. Allow us to distinguish between the different lipoproteins
II. They recognize certain receptors on the cell surfaces, on the liver, tissue
receptors and so on.
III. They also act as activators or coenzymes for enzymes involved in
lipoprotein metabolism, so they interact with enzymes for ex: lipases on
the surface of endothelial cells and these enzymes get activated.
• Now, some of them are essential, so without them there would be no lipoprotein
like; Apo- B 48, Apo -B 100 and Apo A 1 , they are structural molecules that are
necessary for the formation of lipoproteins.(Can’t be removed)
• Some of the can be transferred freely from one lipoprotein to the another one
• Classes of lipoproteins are denoted by letters, and subclasses are designated by
ROMAN numbers.
Ex: Apolipoprotein [apo] C-l, apo C-ll and apo C-lll, so there us a variance
even with the same lipoprotein.
Don’t memorize this table, just focus on the mentioned in this sheet
So, Lipoproteins we have talked about them in the last lecture and their
main functions are to:
1. Solubilize and carry plasma lipids: as we all know
that lipids are hydrophobic, so they tend to
cluster in the blood unless they have a carrier
protein, for ex: albumin, so the lipoproteins they
solubilize the lipids in the hydrophilic blood
2. Transport lipids from one tissue to another
These lipoproteins vary in size, so you have
chylomicrons being the largest and HDL being the
smallest
Also they differ in density (which is the ratio of
proteins to lipids), so chylomicrons have the
lightest density cuz they have a lot of lipids
compare to proteins, HDLs on the other hand have
the highest density cuz they have higher amount
of proteins comparing with lipids
They differ in lipid content, so chylomicron have a
lot of TAGs relative to cholesterol, same thing
with VLDL. HDLs and LDLs on the other hand carry
a lot of cholesterol esters
They differ in function as well, Chylomicrons carry
dietary lipids from intestinal cells to the liver,
while HDLs carry esters from peripheral tissues
back to liver. PAY ATTENTION TO THESE
DIFFRENCES PLEAS!!
, COMPOSITION OF LIPOPROTEINS:
• Now, these lipoproteins also differ in the type of proteins they carry these
proteins are known as APOLIPOPROTEINS and they are AMPHIPATHIC. They
exist on the surface of these lipoproteins, the hydrophilic part is on the outer
surface, while the hydrophobic is on the core
• Some lipids are amphipathic such as cholesterol which contains hydroxyl group
(these amphipathic lipids will have their hydrophilic regions on the surface
while other hydrophobic regions will be hidden inside) and
there are other lipids that are completely hydrophobic such
as cholesterol esters & TAG
• A neutral lipid core (containing TAG and CHOLESTEROL
ESTERS) surrounded by a shell of amphipathic
apolipoproteins, phospholipids, and non-esterified (free)
cholesterol. Cholesterol If it is not esterified the (OH) group
which is the hydrophilic part is exposed to the outside.
• They also differ in the sources of lipids, either they have a
dietary lipids which are known as EXOGENOUS SOURCE in which the lipids are
taken from intestinal cells to liver, and we have ENDOGENOUS lipids which are
synthesized de novo (by itself) from liver to peripheral tissues or back from
tissues like adipose tissues to liver
• Well, the three major cholesterol carriers are HDL, LDL and VLDL to some
extent, except that the VLDL carries five times more TAGs verses CHOLESTEROL
• So, in order to calculate how much CHOLESTEROL is there in the blood, we find
the summation of the amount of cholesterol that is present in LDL, HDL and
VLDL. *
o NOTE: VLDL -C is calculated by dividing VLDL- TAG by 5 because the
TAG/cholesterol ration is 5/1 in VLDL.
The goal value for total cholesterol is <200 mg/dl.
, APOLIPOPROTEINS:
FUNCTIONS: (notice the functions of these lipoproteins please)
I. Allow us to distinguish between the different lipoproteins
II. They recognize certain receptors on the cell surfaces, on the liver, tissue
receptors and so on.
III. They also act as activators or coenzymes for enzymes involved in
lipoprotein metabolism, so they interact with enzymes for ex: lipases on
the surface of endothelial cells and these enzymes get activated.
• Now, some of them are essential, so without them there would be no lipoprotein
like; Apo- B 48, Apo -B 100 and Apo A 1 , they are structural molecules that are
necessary for the formation of lipoproteins.(Can’t be removed)
• Some of the can be transferred freely from one lipoprotein to the another one
• Classes of lipoproteins are denoted by letters, and subclasses are designated by
ROMAN numbers.
Ex: Apolipoprotein [apo] C-l, apo C-ll and apo C-lll, so there us a variance
even with the same lipoprotein.
Don’t memorize this table, just focus on the mentioned in this sheet
