Lecture 23: Lipid Metabolism Flashcards
1
Q
Know the structure of a triacylglycerol
A
See slide 3 for breakdown
- Need to review slide 4 pretty hard too.
2
Q
Describe Lipid Digestion
A
- TAGs present in diet broken down to FA for absorption.
- Intestinal enzymes called lipases released by pancreas digest TAG.
- Breakdown depends on length of fatty acids in the TAG.
- Lingual and gastric lipase present in tongue and stomach, respectively, digest short and medium chain FA in TAG (<12 carbons), e.g., TAGs in milk.
3
Q
Describe the action of bile salts
A
- Fats are emulsified by bile salts in small intestine.
- Emulsification - suspension into small particles in the aqueous environment.
- Bile salts are amphipathic (have hydrophobic and hydrophilic components)
- Contraction of gall bladder to release bile salts and other pancreatic enzymes is stimulated by the gut hormone cholecystokinin.
4
Q
Describe pancreatic lipase
A
- Emulsification greatly increases the surface area of fats.
- Become the substrate of pancreatic lipase.
- Another hormone called secretin released in response to acidic material.
- Causes release of bicarbonate which increases the pH to 6, optimal for intestinal enzymes.
- Pancreatic lipase digests all lengths of FA. Forms FA and 2-monoacylglycerol (2-MAG).
- Pancreas also produces esterase which removes FA from cholesterol esters.
- And phospholipase A2 which removes FA from phospholipids.
5
Q
Describe the absorption of dietary lipids
A
- Short and medium chain FA (C4-C12) are absorbed into intestinal epithelial cells.
- Enter portal blood and are transported into liver bound to serum albumin.
- Long chain FAs and 2-MAGs are packaged into micelles and emulsified by bile salts.
- Other lipids such as cholesterol, lyso PLs and fat soluble vitamins are packaged into micelles.
- Lipids are absorbed across microvilli, bile salts are left in gut.
6
Q
Describe the synthesis of chylomicrons
A
- Within intestinal cells the FA and MAGs are condensed to form TAG (in smooth ER).
- Then packaged into chylomicrons which contain proteins, phospholipids, cholesterol and fat soluble vitamins.
- Major apoprotein is B48.
- See Slide 10-11
7
Q
Describe the transport of lipids in blood
A
- Nascent chylomicrons are secreted by intestinal epithelial cells by exocytosis.
- Secreted into lymphatic system.
- Enter blood via thoracic duct.
- Accept proteins from HDL within lymph and blood, convert into mature chylomicrons.
- ApoE and apoCII most imp.
- ApoE recognized by receptors on surface of liver cells allowing endocytosis.
- ApoCII activates lipoprotein lipase present on capillary endothelial cells in muscle and adipose tissue which digests chylomicrons.
- See slide 13-16
8
Q
Describe the utilization of fatty acids of fuel
A
- Requires 3 steps:
1. Mobilization – TAGs in adipose tissue broken to FA and glycerol, released and transported to energy requiring tissue.
2. Activation - Fatty acids must be activated and transported into mitochondria.
3. Degradation - Stepwise breakdown of FA into acetyl CoA which is then processed in TCA cycle.
9
Q
Review slides 18-30
A
Ow.
10
Q
Describe unsaturated and odd chain fatty acid degradation
A
- Require 2 additional enzymes
- isomerase and reductase
- Odd numbered double bonds handled by isomerase
- Even numbered by reductase and isomerase
- Odd chain – give rise to propionyl CoA and acetyl CoA
- Propionyl CoA converted to Succinyl CoA and then enters TCA cycle –conversion requires vitamin B12 a.k.a cobalamin.
11
Q
See slides 32-33
A
Yay
12
Q
Describe links between lipid and carbohydrate oxidation
A
- Acetyl CoA formed from FA enters TCA cycle.
- Combines with Oxaloacetate (OAA) to form citrate.
- If OAA low (due to low carb) acetyl CoA not utilized
- “Fats burn in the flame of carbohydrates”
- In fasting or diabetes OAA consumed to glucose by gluconeogenesis.
- Acetyl CoA condenses to form ketone bodies
- See slides 35-38
