Lipoprotein Synthesis, Transport And Metabolism

Front 1

۞ -----Classification of Lipoproteins

Back 1

Purpose of the lipoproteins is to transport lipids

The lipoproteins vary in the amount of Cholesterol, TG, phospholipid and protein they contain.

Lipoproteins can be separated by ultracentrifugation or electrophoresis based on their density or electrophoretic migration.

Front 2

۞ -----Density least to greatest density

Back 2

• Chylomicron – high after a meal
• VLDL – high TG
• IDL
• LDL – major cholesterol carrier
• HDL – high in cholesterol but removes LDL from circulation and returns it to liver

Front 3

۞ -----
Lipoproteins separated by electrophoresis related to charge to mass ratio

Back 3

• Alpha migrating further (HDL)
• Beta (LDL) or pre-beta (VLDL)
• Chylomicrons migrating less

Front 4

۞ -----Apolipoprotein – protein only portion

Back 4

• Provide water solubility
• Specificity
• Stimulate enzymatic reactions which regulate the lipoprotein metabolic functions
• Named A-E with sub classes

Front 5

۞ -----Major circulating lipoproteins

Back 5

are HDL and LDL

Front 6

۞ -----
Synthesis and Secretion of Plasma Lipoproteins

Back 6

• Short and medium chain fatty acids are absorbed directly to the portal vein and are transported by albumin to liver

• Long chain un-esterified fatty acids are absorbed by the mucosal cells
• Re-esterified in the enterocyte
• A transport protein(from ER) adds the TG to the chylomicron
• TG resembles that of the dietary lipids
• Enter lymphatics via the lacteals
• To the venous compartment via the left thoracic lymph duct
o Chylomicrons enter the lymphatics slowly from ½ to 3 hours after a meal
o Fat may continue to enter the blood stream for up to 14 hours after a high fat meal

Front 7

۞ -----Clearance of TG from Chylomicrons and VLDL

Back 7

• Most of the lipoprotein lipase is in the muscle and adipose tissue
o ffa in the muscle are oxidized for energy
o ffa in adipose resynthesized to TG for storage

Front 8

۞ -----facts

Back 8

Following a meal CHO is channeled to glycogen until stores are replenished
Excess CHO will be converted to acetyl Co-A and converted to fat
Excess amino acids can also be converted to fat

Diets high in simple sugars can lead to elevated TG levels (problem with very low fat diets)

Front 9

۞ -----Fed state favors TG storage; insulin ↑

Back 9

• increases conversion of glucose to TG
• accelerates the entrance of glucose to the fat cell
• stimulates lipoprotein lipase
• inhibits intracellular lipase responsible for hydrolyzing TG

Front 10

۞ -----Fasting

Back 10

as glucose level decreases, insulin level decreases
• reduces the inhibitory effect on the hydrolyzing enzymes so lipolytic activity increases
• ffa’s enter the blood stream and are transported via albumin to the liver where they can be oxidized for energy – acetyl CoA to ATP production

Front 11

۞ -----Primary lipoproteins in the fasting state

Back 11

are LDL and HDL (no chylomicrons without a meal)

Front 12

۞ -----LDL:

Back 12

• major cholesterol carrier

Front 13

۞ -----HDL:

Back 13

• Function is to remove LDL from circulation and return it to the liver for excretion in the bile

Front 14

۞ -----
LCAT: Lecithin cholesterol acyltransferase

Back 14

• Removes cholesterol from cell membranes or other lipoproteins and transports them back to the liver

Front 15

۞ -----Cholesterol:

Back 15

• Is the primary focus in heart disease because it is the primary component in plaque
• Dietary cholesterol has little impact on serum cholesterol
• About 2/3 of serum cholesterol produced body (about 1 gram of cholesterol per day)
• Lower diet intake, increase production of cholesterol by body