Lipoproteins

Question 1

Lipids synthesized in the liver and the intestine has to be transported to the various tissues to accomplish their metabolic functions. Because of their insolubility, they are transported in the plasma in macromolecular complexes called______.

Answer 1

lipoproteins

Question 2

______are spherical particles with______ (triglycerides and cholesterol esters) in their core and more______ (phospholipids and free cholesterol) oriented near the surface.

Answer 2

Lipoproteins

nonpolar lipids

polar lipids

Question 3

Lipoproteins also contain one or more specific proteins, called______, which are located on their surfaces.

Answer 3

apolipoproteins

Question 4

_________ are primarily located on the surface of lipoprotein particles.

They help maintain the structural integrity of lipoproteins and also serve as ligands for cell receptors and as activators and inhibitors of the various enzymes that modify lipoprotein particles.

Answer 4

Apolipoproteins

Question 5

Apolipoproteins contain a structural motif called an ______, which accounts for the ability of these proteins to bind to lipids.

Answer 5

amphipathic helix

Question 6

________ are protein segments arranged in coils so that the hydrophobic amino acids residues interact with lipids, whereas the part of the helix containing hydrophilic amino acids faces away from the lipids and toward the aqueous environment.

Answer 6

Amphipathic helices

Question 7

Each class of lipoprotein has a variety of apolipoproteins in differing proportions, with the exception of LDL, which contains only_____

Answer 7

apo B-100

Question 8

_____is the major protein in HDL.

Answer 8

Apo A-I

Question 9

_______________ are present in various proportions in all lipoproteins except LDL.

Answer 9

Apo C-I, C-11, C-111, and E

Question 10

Apolipoproteins collectively have three major physiological functions.

They are involved in:

Answer 10

1) activating important enzymes in the lipoprotein metabolic pathways;

2) maintaining the structural integrity of the lipoprotein complex; and

3) facilitating the uptake of lipoprotein into cells through their recognition by specific cell surface receptors.

Question 11

_______, the major protein on HDL, is frequently used as an index of the amount of the antiatherogenic HDL present in plasma.

Answer 11

Apolipoprotein A-1

Question 12

_____is a large protein with a molecular weight of approximately 500 kD and the principal protein on LDL. VLDL and chvlomicrons.

Answer 12

Apo B

Question 13

_____ is found on LDL and VLDL and is a ligand for the LDL receptor, and it is, therefore, critical in the uptake of LDL by cells.

Answer 13

Apo B-100

Question 14

________, exclusively found in chylomicrons, is essentially the first 48% or half of the apo B molecule and is produced by posttranscriptional editing of the apo B-100 mRNA.

Answer 14

Apo B-48

Question 15

______can also be found covalently linked to apo (a); a plasminogen-like protein that is found in a proatherogenic lipoprotein particle called lipoprotein (a) (Lp(al).

Answer 15

Apo B-100

Question 16

____, another important apolipoprotein found on many types of lipoproteins (LDL, VLDL, and HDL), also serves as a ligand for the LDL. receptor and the chylomicron remnant receptor.

Answer 16

Apo E

Question 17

There are three major isoforms of apo E: apo E2, E3, and E4.

The apo E isoforms affect_____ metabolism because they cliffer in their ability to interact with the LDL receptor.

Answer 17

lipoprotein metabolism

Question 18

______have different physical and chemical properties as they contain different proportions of lipids and proteins.

Historically, ______ have been categorized based on differences in their hydrated densities as determined by ___________.

Answer 18

Lipoproteins

ultracentrifugation

Question 19

Categories of lipoprotein

Answer 19

1) chylomicrons (CM),
2) very-low density lipoprotein (VLDL),
3) intermediate-density lipoprotein (IDL),
4) low-density lipoprotein (LDL),
5) high-density lipoprotein (HDL), and
6) lipoprotein (a) [Lp (a)l.

Question 20

are large particles produced by the intestine that transport lipids of dietary origin to the tissues of the body.

They are very rich in triglycerides, but relatively poor in free cholesterol, phospholipids, and protein.

Answer 20

Chylomicrons

Question 21

When present at high levels,_____ result in “milky” plasma and accumulate as a floating creamy layer when left undisturbed for several hours.

Answer 21

chylomicrons

Question 22

The apolipoproteins in chylomicrons include

Answer 22

apoB-48
apo A-I
apo A-IV
apo C-1
apo C-II
apo C-Ill
apo E

Question 23

particles are produced by the liver and supply the tissues of the body with triglycerides of endogenous, primarily hepatic, origin and cholesterol.

Answer 23

Very Low-Density Lipoproteins

Question 24

As compared with chylornicrons,_____ particles are smaller and produce turbid plasma when present in excessive amounts.

Answer 24

VLDL

Question 25

By mass,_____ particles contain approximately 50% triglyceride, 40% cholesterol and phospholipid, and 10% protein, mostly apo B-100 and apo C-I, apo C-II, and apo C-IlI, but also apo E.

Answer 25

VLDL

Question 26

______ hydrolyzes VLDL, and this produces highly atherogenic, smaller triglyceride and surface material–depleted particles called VLDL remnants and IDL.

These particles can be removed from plasma by LDL receptors or further metabolized to LDL.

Answer 26

Lipoprotein lipase

Question 27

is produced through the metabolism of VLDL in circulation and constitutes about 50% of the total lipoprotein mass in human plasma.

Answer 27

Low-Density Lipoproteins

Question 28

do not scatter light or alter the clarity of plasma even at greatly increased concentrations.

Answer 28

LDL

Question 29

consists of approximately 50% cholesterol

mostly esterified

25% protein

mostly apoB-100 with traces of apo C

20% phospholipid

some triglycerides

Answer 29

LDL

Question 30

The_____ takes up most of the LDL in circulation (approximately 75%), with apo B-100 serving as a ligand for the hepatic receptor.

The remaining LDL is delivered to other_____.

Some LDL is modified and is removed from the circulation by _____such as those found in atheromatous plaque.

Answer 30

liver

tissues

scavenger cells

Question 31

is a small particle, consisting mostly of protein, cholesterol, and phospholipids, with only traces of triglycerides.

Answer 31

High-Density Lipoprotein

Question 32

Produced by the liver and intestine,_____ is involved in reverse cholesterol transport.

In vitro studies suggest that ____ is involved in anti-inflammatory, antioxiclant, antithrombotic, and nitric oxide-inducing mechanisms.

Answer 32

HDL

Question 33

The major site for the clearance of HDL cholesterol is the_____, and the best understood mechanism is the selective uptake of cholesterol esters from HDL by the SR-BI receptor expressed in the liver.

Answer 33

liver

Question 34

The__________ is considered to be an alternative pathway for HDL metabolism.

Answer 34

cholesterol ester transfer protein (CETP) pathway

Question 35

______transfers triglycerides from apo B lipoproteins in exchange for cholesterol esters in HDL.

The result is an HDL particle depleted of cholesterol esters but enriched with triglycerides.

Cholesterol transferred to apo B-lipoproteins is then cleared by LDL receptors.

Answer 35

CETP

Question 36

Formed through the metabolism of VLDL in circulation, ____ can be removed from circulation quickly through interaction with the LDL receptor, or can be further metabolized to LDL.

As expected, the lipid content, size, and density of ____ is intermediate between VLDL and LDL.

Answer 36

Intermediate-Density Lipoprotein

Question 37

_______is similar to LDL in terms of density and overall composition, and can be thought of as an LDL particle to which apo(a) has been added, linked to apoB-10C via a disulfide bond.

The electrophoretic mobility of _____ is usually pre-B but can vary between that of LDL (P) and albumin (pre-a).

Answer 37

Lipoprotein (a). Lp(a)

Question 38

Lipoproteins are classified on the basis of buoyant density or electrophoretic mobility.

Separation of lipoproteins based on_______ depends on the ratio between lipids and proteins present in them.

Lipoproteins that contain higher amounts of lipids have lower buoyant density and are collected on top of the centrifuge tube.

Answer 38

buoyant density

Question 39

Separations based on_______ are based on the number of charges present on lipoproteins and are independent of their size and buoyant density.

Answer 39

electrophoretic mobility