Lipids - Digestion

Question 1

What is the major digestive enzyme of TGs + specificity & cofactor

Answer 1

pancreatic lipase, sn-1&3 positions, colipase

Question 2

what is the major digestive enzyme of phospholipids + specificity

Answer 2

phospholipase A2, sn-2 position

Question 3

what is the major digestive enzyme of cholesterol + specificity

Answer 3

cholesterol esterase, non-specific

Question 4

what enzymes are important for infant digestions & why

Answer 4

gastric and lingual lipase because they have little pancreatic lipase

Question 5

what initiates lipid digestion

Answer 5

acid-stable lingual lipase

Question 6

how does the small intestine digest fat

Answer 6

fat to emulsified fat (via bile)
emulsified fat (TGs) to MGs/FAs (via pancreatic lipase)

Question 7

how do lingual lipase, gastric lipase, and pancreatic/co-lipase differ (hydrolysis site)

Answer 7

lingual: hydrolyzes at sn-3 (minor role)
gastric: hydrolyzes at sn-3
pancreatic/co-lipase: hydrolyzes at sn-1&3

Question 8

what enzyme digests phospholipids, where does it hydrolyze

Answer 8

mainly phosphatidylcholine, hydrolyzes at sn-2

Question 9

30-40% of dietary cholesterol is present as ester? T or F

Answer 9

false, 10-15%

Question 10

when cholesterol esters are digested, only free cholesterol is absorbed, T or F

Answer 10

true

Question 11

is pancreatic cholesterol esterase secreted as inactive or active?

Answer 11

active

Question 12

where does pancreatic cholesterol esterase hydrolyze?

Answer 12

all positions

Question 13

what is required before lipids are absorbed, how?

Answer 13

• have to cross the unstirred water layer
• mixed micelles are the most soluble/cross easiest

Question 14

what are the 2 steps of lipid absorption/uptake into enterocyte

Answer 14

1. passive diffusion: glycerol, SCFA, MCFA via micelle delivery
2. carrier mediated transporters on BBM: fatty acid binding protein (FABP) & NPC1L1 protein

Question 14

what is NPC1L1

Answer 14

Niemann Pick C1 like 1 protein, major sterol transporter

Question 15

steroid compounds from plants that are similar to cholesterols are what?

Answer 15

phytosterols

Question 15

how can plant sterols help reduce/lower cholesterol?

Answer 15

compete for inclusion in micelles/transport by NPC1L1 = less cholesterol being absorbed

Question 16

how to plant sterols differ from cholesterol for absorption

Answer 16

they’re exported out of intestinal lumen & excreted

Question 17

how are bile acids recycled

Answer 17

enterohepatic circulation: before reaching large intestine BAs are reabsorbed by specialised mucosa and carried back to liver in portal venous blood

Question 18

what are the two ways enterocyte lipids are re-esterified/re-formed

Answer 18

1. monoacylglycerol pathway (major)
2. glycerol-3-phosphate pathway (minor)

Question 19

what is the monoacylglycerol pathway + where are the enzymes found

Answer 19

taking the products of lipid digestion and putting them back together, enzymes found in ER
- sn-2 MAG to DAG (via MGAT)
- DAG to TG (via DGAT)

Question 20

what is the glycerol-3-phosphate pathway and when does it occur

Answer 20

occurs when 2-MAG is lacking
- G3P to DAG (via GPAT/phosphatide phosphatase)
- DAG to TG (via DGAT)

Question 21

cholesterol esterase and Acyl CoA cholesterol acyltransferase (ACAT) are the enzymes involved in what

Answer 21

reformation of cholesterol ester in enterocyte
cholesterol + FA = cholesterol ester (via ACAT)

Question 22

phospholipids are re-formed from lysophospholipids via what process

Answer 22

reacylation