25. Lipids and Lipoproteins

Question 1

TAGs (triacylglycerides) contain almost 7 times as much energy as do? about 100,000kCal in TAGs in fat/muscle

Answer 1

carbohydrates/glucose

Question 2

The major source for TAG synthesis in intestinal cells are?

Answer 2

Dietary triacylglycerides

Question 3

Dietary TAGs are broken down into FA and MAGs in the intestinal lumen, and then intestinal cells remake TAGs using the MAG back bone. What is the product after TAGs synthesis in the intestinal cells?

Answer 3

Chylomicron which is TAGs with apolipoproteins (APO) and other lipids which are released in the lymphatic system and enter the blood via the thoracic duct

Question 4

The major source for TAG synthesis in the liver/hepatocytes are?

Answer 4

** Glucose(carbohydrates) **

Acetyl CoA and Glycerol

Question 5

What is different in TAG synthesis in the liver regarding glycerol compared to other processed in the intestine and adipocytes?

Answer 5

Glycerol is able to be made into Glycerol3P by glycerol kinase unique to liver TAG syn

Question 6

Intestinal cells use MAG as a backbone, Hepatocytes use G3P as a backbone for TAG synthesis and what do adipocytes use?

Answer 6

G3P as well!

Question 7

In the liver, what is the final product of TAG synthesis?

Answer 7

Very Low Density lipoproteins (VLDL), released into blood

Question 8

For storage of TAGs in adipocytes, glucose via insulin activated GLUT4 transporter is used along with what other two sources?

Answer 8

The chylomicron from intestines and VLDL from the liver

Question 9

How are chylomicrons and VLDL broken down to form FAs in adipocytes?

Answer 9

Via capillary lipoprotein lipase***

Question 10

DAGs and some TAGs are broken down via HORMONE sensitive lipase (HSL) which is activated by glucagon, E/NE and inhibited by insulin (fed state). How are DAGs and MAGs are broken down?

Answer 10

LPL lipoprotein lipase for DAGs

MAGs via monoacylglycerol lipase

Question 11

How are short chain FA transported compared to longchain fatty acids?

Answer 11

Short are able to travel within the blood freely

Long bind to albumin (carrier protein) for trasnport

Question 12

HSL is modulated by hunger and exercise. Glucagon, epinephrine and norepinephrine will _______ HSL making it active to promote lipolysis in adipocytes while insulin will do what?

Answer 12

Phosphorylate HSL to become active

Insulin dephosphorylates to inactivate and stop lipolysis

Question 13

What is the main lipase to breakdown TAGs after further experiments?

Answer 13

ATGL adipose triglyceride lipase

Question 14

During hunger and exercise, Glucagon/epinerphrin bind to GPCR which activates AC and PKA which will phospharylate perilipin to its active form, which makes HSL into its active form by phosphorylation to break down DAGs. What is perilipin?

Answer 14

A protein that coats lipid droplets in adipocytes, preventing activation. Overexpression inhibits lipolysis and without perilipin, there would be lots of fat break down

Question 15

What is the main substrate that forms cholesterol?

Answer 15

acetyl CoA

Question 16

Lipoproteins are vehicles for transport of cholesterol, TAGS and other things. They contribute to lipid metabolism by doing what two things?

Answer 16

1. Serve as ligands that bind to receptors to internalize lipoproteins
2. Activate Enzymes

Question 17

What are the 5 different types of lipoproteins?

Answer 17

chylomicron from intestine
VLDL from liver
IDL
LDL
HDL

Question 18

HDL contains mainly proteins and little fats and cholesterol, this is why it is considered a good fat. What is the main contributor to Chylomicrons, VLDL and IDLs and what is the main contributor to LDLs?

Answer 18

Chylomicrons, VLDL, and IDLs are most TAGs

LDLs are more than 50% cholesterol, this is why they are considered bad fats

Question 19

Chylomicrons are formed from dietary fats, is the largest lipoprotein, least dense and has high TAG content. What are the 3 apolipoproteins on the outer shell?

Answer 19

unique to it ApoB48 which facilitates transport
ApoCII which activates capillary lipoprotein lipase to store in adipocytes!
ApoE facilitates uptake into liver

Question 20

VLDL from liver have the same ApoCII to activate capillary lipoprotein lipase and ApoE for uptake into liver, what is the different B protein that it has?

Answer 20

ApoB100: binds to LDL and makes sure it is taken up and not allowed in blood (increase cholesterol)

Question 21

IDL have both ApoB100 and ApoE while LDL only have?

Answer 21

ApoB100

Question 22

HDL are the smallest and most dense and consist mainly of proteins. It has ApoCII and ApoE like the others but has ApoAI which does what?

Answer 22

activates an enzyme to convert cholesterol into cholesterol ester

Question 23

The chylomicron is formed in the intestines and ApoCII and ApoE are added by HDL. capillary lipoprotein lipase cleaves apocII leaving it withApoE and ApoB48 which then does what?

Answer 23

binds to ApoE receptor in liver

Question 24

VLDL are assembled in the liver and have all 3 Apo. Capillary lipoprotein lipase cleaves ApoCII and gives back to HDL, leaving you with IDL. IDL via hepatic lipoprotein lipase cleaves ApoE, leaving you with LDL. What does LDL do?

Answer 24

Bind to LDL receptor on target cell for uptake. If the receptors are defective, resulting in LDL in the bloodstream, can lead to atherosclerosis

Question 25

How is LDL uptaken into the plasma membrane?

Answer 25

Via receptor mediated endocytosis:

LDL binds receptor, endocytosed, lysosomes degrade, releasing cholesterol, receptor vesicle is recycled

Question 26

HDL from liver picks up APOAI from peripheral tissue and via LCAT cholesterol is esterified forming a sphere. HDL donates and receives APOCII and APOE from?

Answer 26

CHYLOMICRONS ***

HDLs are crucial for chylomicron maturation

Question 27

HDL-C is negatively associated with CAD, it removes LDL from periphery and trasnports its to the liver where?

Answer 27

LDLs will be recycled and processed

Question 28

What gives APOCII and APOE to the chylomicrons?

Answer 28

HDL

Question 29

What are some of the main product of lipoproteins?

Answer 29

Making cells, hormones, energy, fat storage, cholesterol, bile

Question 30

Type I hyperlipoproteinemia (familial hyperchylomicronemia) is caused by what defect?

Answer 30

Deficiency in APOCII or a defective capillary lipoprotein lipase which leads to an increased in TAGs (ALOT 5 fold, have xanthomas) and chylomicrons

Question 31

Type II hyperlipoproteinemia (familial hypercholesterolemia) is caused by what defect?

Answer 31

LDL receptor is completely (IIa) or partially (IIb) defective leading to increased cholesterol, increased LDL and increase VLDL and TAGs in IIb