Lipid Digestion Flashcards
What is a lipid?
Water insoluble biological compound soluble in fat solvents
What properties define whether a substance is called a lipid or not?
Solubility properties
Give some examples of lipids
Fatty acids, TAG, TG, cholesterol, membrane phospholipids, steroid hormones, etc.
Describe the structure of a fatty acid
Long chain carboxylic acid
What is the name for a 16C saturated FA?
Palmitic acid (ionized form = palmitate)
From which end does the numbering system using ω start? α?
Hydrocarbon end; Acid end
What is a 18C monounsaturated FA?
Oleate
What is the major dietary lipid?
Triacylglycerol (TAG)
What composes bile salts?
Cholesterol esters (planar ring structure with hydroxyl groups facing towards hydrophilic surface, and steroidal surface facing hydrophobic areas)
WhatdigestsTGintomonoacylglycerolsanddiacylglycerols?
Lipase (gastric or pancreatic)
What protein binds to lipase and stabilizes it by displacing a bile salt in a micelle?
Colipase
What enzyme cleaves cholesterol esters?
Cholesterol esterase
What enzyme cleaves FA from TAG at the 2 position?
phospholipaseA2
Through what circulation are bile salts returned to the liver?
enterohepatic circulation
How much (percentage) of the bile salt pool is excreted?
5%
How is a FA activated?
Acylated by addition of CoAsh (high energy thioester) utilizing ATP to AMP, produces FA‐CoA
How many high energy phosphate bonds are required for FA activation in their oxidative
catabolism?
2
What carries FA into the lymphatic system?
Chylomicrons
What composes most of a chylomicron?
TAG’s
Are cholesterols present in chylomicrons?
Yes (hydroxyl groups pointed out)
If the B –apoprotein gene is going to produce a protein destined for the liver how much of the
AA transcript is produced?
100%, thus its termed ApoB‐100
If the B –apoprotein gene is going to produce a protein destined for the intestine how much of
the AA transcript is produced?
48%, thus ApoB‐48
What transfers proteins to ApoB particles?
Micosomal TG transfer protein (MTP)
What organelle is responsible for apo particle maturation and secetion?
Golgi
Where are chylomicrons synthesized?
Intestinal epithelial cell
Where is a TG converted to 2‐MG or FA ? (free fatty acids)
Intestional Lumen
Where is the TG resynthesized?
Intestinal epithelial cell
Where are nascent chylomicons?
Lymph
What forms a mature chylomicron?
ApoCII added by HDL+ApoE
What activates mature CM?
LPL
Where does the released FA travel to?
Muscles, adipose tissue, etc.
Where does the glycerol travel to?
Liver (glycerol cycle)
Does the same glycerol cleaved take part in TAG resynthesis for instance in adipocytes?
No, it’s a new glycerol molecule
What are some examples of lipids? (8)
- fatty acids
- TAGs or triglycerides
- membrane phospholipids
- cholesterol
- steroid hormones
- vitamins
- 2nd messengers
- PGs
When is a fatty acid saturated?
no double bonds within the long chain hydrocarbon
T/F Fatty acids are fuel molecules in metabolism
True
What is the major source of dietary fatty acids?
TAG
What gives bile acids and salts their hydrophilic and hydrophobic side to allow them to be detergents?
-OH groups are all on the same side so the side with the -OH is hydrophilic
Outline the steps in digestion of TAG to formation of chylomicrons
- TG in intestinal lumen converted to 2-MG and fatty acids
- Resynthesized into triglycerides
- Starts to assemble into small ApoB-48 particles at RER
- Incorporated into chylomicrons
- Onto the golgi complex
- Packaged for secretion for lymph
- MTP is microsomal TG transfer protein
Which digestive enzyme requires protein colipase to stabilize and localize lipase near the bile salt-TG particle?
pancreatic lipase
What are the enzymes in order of introduction of the TG to the chylomicrons?
- lingual lipase (short and medium TAG)
- gastric lipase
- pancreatic lipase (lipase, colipase, bile salts)
If short or medium chains of TAG are present in the digestion process, what enzymes are necessary?
only lingual lipase as this will allow it to bypass the gut and go straight to the liver
T/F Bile salts are recycled by entero-hepatic circulation
True, 95% saved
Describe the intestinal resynthesis of TG
- activation of fatty acids
- TAG synthesis
- 2-MG
- DAG
- TAG
Where do chylomicrons go?
lymph
Where does the lipase activity to make FA occur? Where are chylomicrons made?
- gut lumen of the cell contains the lipase activity
- chylomicrons are made in mucosal cells
What is present outside on the structure of a lipoprotein?
cholesterol, peripheral apoprotein, amphipathic lipids
What is found in the interior of a lipoprotein?
choseserol ester, TAG, core of nonpolar lipids
What is the composition of a chylomicron in order of most to least?
TG>phospholipid>protein>cholesterol ester>cholesterol
What structure of the chylomicron will tell it the direction to take?
HDL + ApoE, ApoCii
What has the B-apoprotein gene?
VLDLs in the liver
If the B-apoprotein gene from the RER is sent to the liver, which gene will be present? Intestine?
Apo B-100 will be present in liver with 100% translated
Apo B-48 produced 48% of polypeptide due to RNA editing causing a stop codon
T/F For chylomicron synthesis to occur, an MTP is required
True, microsomal TG transfer protein
Where does the chylomicron go after it becomes a larger ApoB particle?
To golgi for maturation and secretion
Describe the path of chylomicrons wrt to the cellular components
- brush border villae
- SER and RER
- Golgi
- chylomicrons
- lymph
What is the role of chylomicrons?
transport dietary TG
What is a water insoluble biological compound solubine in fat solvents such as alcohol, ether, chloroform which is defined by solubility properties?
lipid
