Lipid and cholesterol metabolism Flashcards
What is the difference between saponifiable and non-saponifiable dietary lipids?
Saponifiable lipids have ester group and can react with NaOH to form carboxylic acid salt+alcohol (triglycerides, phosphlipids, sphingolipids)
Non-saponifiable lipids have no ester group, cannot react with NaOH (e..g . derive lipids like eicosanoids, bile salts, sterols, Vit D)
Are lipids hydrophobic or hydrophilic?
Hydrophobic, needs micellar structures for their transportation in aqueous medium
What is the main component of dietary lipids?
Triglycerides make up 90% of dietary lipids,
remaining include cholesterol, cholesterol ester, fatty acids, phospholipids
How are triglycerides stored?
In anhydrous form in adipose tissue
How are triglycerides transported?
in lipoprotein particles in blood
What is saturated fat?
no double bond
What is unsaturated fat?
1 or more double bond
What is the relation between the number of double bonds and the melting temperature of lipids?
The more the double bonds, the lower melting temperature of the lipids.
When there are more double bonds, there are more kinks in the structure and thus FA does not pack well together
The more unsaturated the FAs in the phospholipid membrane, the _____________ the membrane fluidity?
greater
Why do more unsaturated fatty acids become rancid faster?
The double bonds can be cleaved by free-radical reactions involving molecular oxygen, and highly volatile aldehydes and ketones will be released
What are trans fats?
Trans C=C bonds are introduced by partial hydrogenation of cis-unsaturated fats. Removes most double bonds, reforms some and alters FA shape.
What are omega 3 and omega 6 fatty acids used for?
Synthesis of eicosanoids (prostaglandins, thromboxanes and leukotrienes)
How do trans C=C bonds in omega 3 and omega 6 fatty acids affect formation of eicosanoids?
Cyclooxygenase and lipooxygenase are less effective on FAs with trans C=C bonds.
What are the other negative side effects of transfats?
High amount of transfat in fiet, incorporation in PL membranes, lowered membrane fluidity as transfats pack more effectively. Abnormal cellular function and higher risk of coronary heart disease and atherosclerosis
What are the two sources of lipids in our body?
Diet, and de novo synthesis from acetyl-CoA
What does hydrolysis of triglyceride yield?
Fatty acids and glycerol
Why can’t triglycerides form micelles or bilayers like phospholipids?
Triglycerides have no polar groups and form aggregates in adipocytes
Where does digestion of triglycerides occur mainly?
In the duodenum
What is TG digested by?
Lipase
What are the different types of lipase?
Lingual lipase (salivary gland) Gastric lipase (stomach) Pancreatic lipase (main enzyme) Colipase (binds to dietary TG and pancreatic lipase simultaneously to allow active site of lipase to access TG)
Describe the break down of TG
TG—Pancreatic lipase—> 2-mono-acylglycerol + 2 FFAs
How are cholesterol esters digested?
CE—Pancreatic cholesterol esterase—> FFA+ cholesterol
How is membrane phospholipid digested?
Membrane PL—Phospholipid A2—> FFA +Lysophospholipid
What is the function of bile salts in digestion of dietary lipids?
Bile salts emulsify fats into small droplets to increase the surface area. Lipid digestion occurs at lipid-water surface.