Unit 3 - V. Lipoproteins

Question 1

Lipoprotein

Answer 1

• complexes of lipid and protein
• main function is to transport lipid through the bloodstream
• because lipid molecules are nonpolar/hydrophobic and the bloodstream is aqueous

Question 2

apolipoprotein

Answer 2

• the protein component of a lipoprotein
• amphipathic property allows it to surround lipid and be water soluble
• 3 major classes: Apo-A, -B, - C
• 2 minor classes: Apo-D, -E
• Major role = receptor recognition

Question 3

apo-A-I

Answer 3

• mostly found in HDL

- Function = major protein in HDL (75%); activates LCAT

Question 4

apo-A-II

Answer 4

• mostly found in HDL

- function - 20% of protein in HDL; enhances lipase activity in liver

Question 5

apo-B-100

Answer 5

• mostly found in LDL

- function: only protein component of LDL; binds to LDL receptor

Question 6

Apolipoproteins in HDL

Answer 6

Apo-A-I
Apo-A-II
Apo-D

Question 7

Apolipoproteins in LDL

Answer 7

Apo-B-100

Question 8

Apolipoproteins in VLDL

Answer 8

Apo-C-I
Apo-C-II
Apo-C-III

Question 9

Apolipoproteins in Chylomicron

Answer 9

Apo-A-IV
Apo-B-48
Apo-E

Question 10

Apolipoproteins in IDL

Answer 10

Apo-E

Question 11

Density of lipoprotein

Answer 11

- directly related to the percentage of protein in the molecule 
Highest Density - high protein, low fat
HDL
LDL
VLDL
Chylomicron
Lowest Density = High fat, low protein

Question 12

Chylomicrons (Chylo)

Answer 12

• 2% protein, 98% lipid
• predominant lipid = triglycerides
• assembled in endoplasmic reticulum of intestinal mucosal cells
• largest lipoprotein, lowest density
• function = transport dietary triglycerides, cholesterol, and cholesterol esters
• Lipoprotein lipase hydrolyzes triglyceride into glycerol + fatty acids. Fatty acids can attach to serum albumin to remain in circulation, stored in adipose tissue, or used as fuel by converting into ATP

Question 13

Chylomicron remnant

Answer 13

• “leftover”, lipid component mostly consitists of cholesterol and cholesterol esters
• taken up by liver, mediated by receptors specific for apo-E
• lysosomal acid lipase hydrolyzes remnant
• cholesterol can be converted into bile salts, neutral sterol, VLDL or HDL

Question 14

VLDL (Very low density lipoprotein)

Answer 14

• 10% protein, 90% lipid
• predominant lipid = triglycerides
• assembled in liver
• Function = transport triglycerides to adipose tissue for storage; transfer/exchange triglyceride with cholesterol esters in HDL to make LDL
• Remnant = IDL

Question 15

IDL (Intermediate Density Lipoprotein)

Answer 15

• 12% protein, 88% lipid
• predominant lipid = cholesterol
• formed when VLDL indergoes hydrolysis
• Function = taken up by liver, mediated by receptors specific for apo-B and apo-E, to convert IDL into LDL

Question 16

LDL (Low density lipoprotein)

Answer 16

• 25% protein, 75% lipid
• predominant lipid = half cholesterol
• majority synthesized in the liver
• protein component: 100% apo-B-100 one of the longest known polypeptide chains
• Function: Transport cholesterol to be incorporated into cell membranes of tissues or to synthesize various hormones

Question 17

LDL subcategories

Answer 17

• LDL I, IIa, IIb = large = penetrate vascular endothelium = not associated with CAD
• LDL IIIa, IIIb, IVa, IVb = small = can penetrate endothelial cells = cause CAD (coronary artery disease)

Question 18

LDL and Cardiovascular disease

Answer 18

• decrease in synthesis of LDL receptors due to saturated fatty acids or dysfunctional/absent LDL receptors
• genetic predispositions result in cholesterol not being removed from circulation or an increase in cholesterol synthesis by liver = raise LDL cholesterol
• accumulation of LDL cholesterol causes atherosclerosis (chronic inflammation of medium/large arteries)
• atherosclerosis is a common cause of coronary artery obstruction which leads to coronary artery disease (CAD), seen in Cardiovascular disease.

Question 19

Statins

Answer 19

• used to treat hypercholesterolemia
• hypolipidemic agents, competitive inhibitors of HMG-CoA reductase (an enzyme that catalyzes a rate-limiting step in liver’s synthesis of cholesterol)
• reduces synthesis of cholesterol => increase production of LDL receptors => remove LDL from blood

Question 20

Non modifiable risk factors of CAD

Answer 20

• advanced age
• male gender or women after menopause
• family history

Question 21

Modifiable risk factors of CAD

Answer 21

• dyslipidemia
• hypertension
• cigarette smoking
• type 2 diabetes and insulin resistance
• obesity (central)
• sedentary life style
• atherogenic diet

Question 22

HDL (high density lipoprotein)

Answer 22

• 55% protein, 45% lipid
• predominant lipid = phospholipid
• made in liver from chylomicrons and IDL
• function = cholesterol scavenger; LCAT helps esterify cholesterol into cholesterol esters

Question 23

2 Fates of Cholesterol in HDL

Answer 23

1. HDL taken up by liver where cholesterol is converted to bile acids/salts and secreted in bile to be removed from body (reduces risk of atherosclerosis)
2. Cholesterol transferred to VLDL or LDL in exchange for triglyceride; catalyzed by CETP

Question 24

Lipoprotein Lipase

Answer 24

• hydrolyzes triglycerides into glycerol and fatty acids

- used with chylomicrons, VLDL, and IDL

Question 25

Lecithin Cholesterol acyltransferase

Answer 25

• LCAT
• catalyzes the esterification of cholesterol with fatty acid to made cholesterol ester
• in HDL

Question 26

Cholesterol ester transfer protein

Answer 26

• CETP

- catalyzes the transfer of cholesterol from HDL to VLDL or LDL in exchange for triglyceride

Question 27

Metabolic syndrome

Answer 27

• diagnosed with the presence of 3 out of 5 factors.
• treatment = pharmacological and nutritional therapy
  Factors:
  1. Elevated triglycerides
  2. HDL cholesterol low
  3. Abdominal obesity
  4. Hypertension
  5. Elevated fasting glucose

Question 28

Determination of LDL

Answer 28

• can be measured (direct LDL) or calculated
  Friedwald equation: LDL = total cholesterol - HDL - TG/5
  *patient must be fasting
• TG must be < 400