Lipid Biochemistry

Question 1

is cholesterol hydrophobic or philic?

Answer 1

hydrophobic

Question 2

are the majority of cholesterols esterified or not?

Answer 2

majority is esterifies…70%

Question 3

where do you find the esterified cholesterol in lipoproteins?

Answer 3

on the interior of the lipoprotein and the unesterified is on the outside

Question 4

what organ is in charge of cholesterol synthesis and what percent does it make?

Answer 4

liver makes close to 80% of it

Question 5

give the rate limiting enzyme in cholesterol synthesis

Answer 5

HMG CoA reductase

Question 6

what hormone increases the action of HMG CoA reductase?

Answer 6

insulin

Question 7

intermediates in the synthesis of cholesterol can lead to 3 types of important molecules…name them

Answer 7

ubiquinone
signal transduction molecules like Rho and Ras
complex glycoproteins

Question 8

what is the name of the transcription factor that upregulates the production of HMG CoA reductase and the LDL receptor?

Answer 8

SREBP-2

Question 9

what molecule is in charge of whether SREBP-2 is transcribed?

Answer 9

SCAP

Question 10

what two things can inhibit SCAP?

Answer 10

intracellular cholesterol and LDL cholesterol

Question 11

if you inhibit SCAP…what happens to HMG CoA reductase and LDL receptors?

Answer 11

production drops because you have less SREBP-2

Question 12

what are the two ways to get cholesterol in a cell?

Answer 12

synthesis and uptake

Question 13

what are the two ways to rid of cholesterol from a cell?

Answer 13

either secrete as bile salt or store it

Question 14

if you have high cholesterol diet..what happens to the LDL receptors on the cells?

Answer 14

they begin to disappear because of the loss of SCAP action and ultimate loss of SREBP-2

Question 15

what is the enzyme that helps store cholesterol?

Answer 15

ACAT

Question 16

what can cause ACAT to decrease its activity?

Answer 16

saturated fats…ACAT uses PUFA to help store cholesterol by esterifying it…but with saturated fats it gets blocked

Question 17

what two ways does saturated fat lead to high cholesterol?

Answer 17

blocks LDL receptors from working

blocks ACAT from storing cholesterol

Question 18

what enzyme turns cholesterol into bile acids?

Answer 18

7a hydroxylase

Question 19

what molecule has to attach to bile acids for them to be secreted?

Answer 19

fiber

Question 20

what happens to bile acids on a low fiber diet?

Answer 20

the bile acids are not able to get secreted since no fiber and will travel back to the liver and be turned back into cholesterol via enterohepatic circulation

Question 21

name three roles of bile acids

Answer 21

1. essential for fat digestion
2. absorb fat vitamins
3. eliminate cholesterol from body

Question 22

what percent of bile acids are reabsorbed? and the percent that is not…what is it representative of?

Answer 22

almost 99%…the slight percent that is not is the only way to rid of cholesterol from the body

Question 23

what is the role of lipoproteins?

Answer 23

to transfer triglycerides, phospholipids and cholesterol

Question 24

order the four lipoproteins in increasing density

Answer 24

chylomicrons
VLDL
LDL
HDL

Question 25

how is density of a lipoprotein related to size and triglyceride content?

Answer 25

inversely...larger the size lower the density | more triglyceride...lower the density

Question 26

how is density of a lipoprotein related to protein and phospholipid content?

Answer 26

directly...more protein means higher density

Question 27

what is the role of apoprotein C?

Answer 27

it activates lipoprotein lipase

Question 28

where is apoprotein C found?

Answer 28

mainly in peripheral tissues...like endothelial cells

Question 29

what is the role of lipoprotein lipase?

Answer 29

to break up the lipoproteins and take off triglycerides around the tissues that will be able to store the triglycerides

Question 30

where are apoproteins B and E found and what is their role?

Answer 30

they are found at the liver and help get LDL and IDL back into the liver

Question 31

what lipoprotein is made and released by the liver

Answer 31

VLDL

Question 32

what are the two sources of cholesterol/tricglycerides for the peripheral tissue?

Answer 32

chylomicrons from diet and VLDL from liver

Question 33

at the peripheral tissue, what happens to VLDL and what does the peripheral tissue release back to the liver?

Answer 33

its triglycerides get clipped by lipoprotein lipase..apo C denpendent then releases LDL and IDL to go back to the liver

Question 34

what can nascent HDL do at peripheral tissue?

Answer 34

bind apoprotein A and pick up cholesterol...

Question 35

if HDL picks up cholesterol at peripheral tissue...what happens next?

Answer 35

LCAT esterifies the cholesterol in HDL

Question 36

what is the role of CETP in HDL molecules?

Answer 36

it can change cholesterol into VLDL, LDL or IDL or chylomicrons

Question 37

after HDL has picked up cholesterol from periphery and then let it get turned into LDL/IDL/VLDL/chylomicrons..what happens to the HDL and remnants of cholesterol?

Answer 37

they get internalized and destroyed at the liver

Question 38

what lipoprotine drives cholesterol from periphery to the liver?

Answer 38

HDL!!

Question 39

what molecule takes the longest to be picked up by periphery or liver?

Answer 39

LDL...hence why we measure LDL in blood