Mid 2: Lec 12

Question 1

4 types lipoproteins

Answer 1

VLDL, LDL, IDL, HDL

Question 2

lipoprotein shell

Answer 2

composed
of a single-layer of phospholipids, free
cholesterol and proteins

Question 3

Lipoprotein exogenous protein general what does it do with fat and cholesterol

Answer 3

absorption and transport of fat (TAGs) and cholesterol from diet.

also, reabsorption of recycled cholesterol

Question 4

formation secondary bile salts (what conjugated to and what combined with)

Answer 4

Primary bile acids conjugated to glycine and taurine
in the liver will be combined to sodium and
potassium salts to form bile salts.

Secondary bile salts are the result of the
transformation of primary bile salts by the bacteria
found in the colon.

Question 5

Lipoprotein exo pathway after bile salt formation before absorption

Answer 5

bile salts creates emulsion with dietary lipids and forms micelles

dietary cholesterol and TAGs are absorbed by micelles

The hydrophilic side of the bile salts will allow the recruitment of Pancreatic lipases and colipases.

lipase and colipase will release fatty acids from the TAGs producing a mixture of
glycerol, free fatty acids, monoacyl-glycerols and
diacylglycerols

Question 6

Lipoprotein exo pathway >= absorption

Answer 6

Free fatty acids, monoacylglycerols and cholesterol will be
absorbed by enterocytes lining the small intestine lumen

they will then be reassembled into TAGs

A portion of cholesterol will be converted to cholesterol ester.

Within the enterocytes, more precisely in the golgi apparatus,
TAGs, cholesterol and cholesterol esters will be combined
with apolipoproteins to form chylomicrons.

Chylomicrons will be released into the lymphatic system and
then, the bloodstream

Question 7

cholesterol esters and created by

Answer 7

less polar than free cholesterol

used for transport in plasma as well
as a way to store cholesterol in a biological inert form

created by ACAT

Question 8

Apolipoproteins and categories

Answer 8

proteins associated with lipoproteins.

1. Exchangeable apolipoproteins
2. Non-exchangeable apolipoproteins

Question 9

Exchangeable apolipoproteins

Answer 9

tethered to the lipoprotein surface;
they can dissociate from one
lipoprotein particle and become
associated with another lipoprotein
particle.

Question 10

Non-exchangeable apolipoprotein

Answer 10

tightly bound to a
lipoprotein particle and do not dissociate from it

Question 11

lipoprotein exo path: dist of TAGs

Answer 11

After being secreted into bloodstream, chylomicron-
carried TAGs are hydrolyzed by lipoprotein lipase; the released FAs are delivered to adipose tissue, and other organs.

resulting chylomicron remnants are taken up by the liver
through endocytosis.

Question 12

Lipoprotein endogenous path for VLDL

Answer 12

LDL are synthesized in the liver (hepatocytes) via assembly of synthesized lipids (mostly TAGs) and
apolipoproteins

After being secreted into bloodstream, TAGs contained in
the VLDL are hydrolyzed by lipoprotein lipase and the released FAs are delivered to adipose tissue (for storage)
and other cells (for energy)

Question 13

IDL and fate

Answer 13

remnants of VLDL after TAGs are hydrolyzed

may be cleared from the bloodstream by endocytosis in the
liver.

may go for a second round of
bloodstream circulation.

may also exchange
apolipoproteins and lipids with HDL
to become LDL.

Question 14

lipoprotein endog path for LDL

Answer 14

primary function of LDL is to deliver cholesterol to
extrahepatic tissues

Uptake of plasma LDL is achieved by the LDL receptor-
dependent endocytosis

Question 15

lipoprotein endog path for HDL general

Answer 15

HDL removes cholesterol from tissues and brings it back to the liver.

Question 16

HDL cycle

Answer 16

1. Free ApoA-I is secreted from the liver
2. It will interact with the ABCA1 transporter located at
   the cell surface of peripheral cells. free
   cholesterol and phospholipids will be released and
   combine with ApoA-I to form Nascent HDL
3. Free cholesterol will be esterified by the action of LCAT leading to the transformation of the disk-shaped HDL into spherical mature HDL called HDL3
4. interaction of HDL3 with CETP leads to a transfer of cholesterol ester to apoB containing lipoproteins (VLDL, IDL and LDL)
5. HDL will acquire new exchangeable
   apolipoprotein apoC-I, C-II and C-III as well as TAGs. This HDL is called HDL2
6. Fate of HDL2: Selective uptake of CEs
   Liver and steroidogenic tissues (adrenal, testis, ovary)
   uptake of CE from HDL is mediated by SR-B1.