Flashcards in Biochemistry- lipid catabolism Deck (32)
What are essential fatty acids?
Polyunsaturated fatty acids which can not be made by the body but are required by the body and therefore must be consumed.
What can deficiencies in essential fatty acids cause?
These can lead to membrane disorders, increased skin permeability and mitochondrial damage.
Which vitamins are fat-soluble?
A, D E and K
Give examples of simple lipids
fatty acids, triglycerides, waxes
Give examples of compound lipids
phospholipids, glycolipids, lipoprotein
Give examples of steroids?
Cholesterol, steroid hormones
Are fatty acids aliphatic?
yes- this means they have no rings
Do most fatty acids, and the ones in our bodies, contain an even or an odd number of carbon atoms?
Even- usually 2-20 but there can be more
Do branched fatty acids, or fatty acids with an odd number of C atoms exist?
yes, but these are rare
Are double bonds usually in the cis or trans configuration
Explain what a cis fatty acid is
Cis: the adjacent hydrogen atoms are on the same side of the double bond. The rigidity of the double bond freezes its conformation and causes the chain to bend and restricts the conformational freedom of the fatty acid.
When a chain has main cis bonds, it becomes quite curved. The result is, when fatty acids are in phospholipids in a bilayer or TAG in a lipid droplet, the fatty acids can not be as closely packed.
Explain what a trans fatty acid is
The two hydrogen atoms are bound to opposite sides of the double bond.
As a result, they do not cause the chain to bend much, and the shape is similar to straight fatty acids.
What is the most common fatty acid in the body?
How many carbon atoms does it have?
How many double bonds does it have?
It has 16 carbon atoms and no double bonds
How many carbon atoms and double bonds does stearic acid have?
It has 18 carbon atoms and no double bonds
How many carbon atoms and double bonds does oleic acid have?
It has 18 carbon atoms and 1 double bond
If carbon atoms in a fatty acid are labelled using the greek alphabet, which carbon atom is the alpha atom and which is the omega atom?
The carbon atom adjacent to the carboxyl group is the alpha atom, and the carbon atom furthest away is the omega atom, no matter how many atoms are in between.
Fatty acids with up to how many carbon atoms are liquids at room temperature?
Up to 8 carbon atoms
What is the effect of double bonds on the melting point of fatty acids?
It lowers the melting point
What are the main products of fat digestion?
Which of these are readily absorbed by epithelial cells?
Glycerol (readily absorbed by epithelial cells)
What happens to chylomicrons are muscle and adipose tissue?
They are attacked by lipoprotein lipase which cleaves them. Free fatty acids are then taken into the cells and are either resynthesised to form TAG in adipose tissue for storage or are oxidised to produce energy (in muscle). This depends on how much is available.
What is the name for the breakdown of lipids?
What initially happens to the stored fat in lipolysis?
It is cleaved by a hormone-sensitive lipase e.g. adrenaline-sensitive lipase
What has to happen to fatty acids before they can be oxidised?
How much energy is required to do this?
Where does this occur?
They have to be activated by being linked to coA. This forms acyl coA. This requires 2 ATPs.
It occurs in the cytoplasm.
What is acyl coA?
It is formed from the linkage of fatty acids to coA. It has an undefined number of carbons, which depends on the number of carbons in the fatty acid chain.
Where does further oxidation of acyl coA occur?
In the matrix of the mitochondrion.
How is the fatty acid from acyl coA transported into the mitochondrial matrix?
In the cytoplasm, fatty acids are transferred from acyl-coA to a carrier protein called carnitine, which can be transported across the inner mitochondrial matrix by a specialacyl-carnitine transporter, which also transports carnitine out of the matrix.
In the matrix, the acyl group is cleaved off of carnitine and transferred onto another coA.
The remaining carnitine is moved back out and the cycle can continue.
What is beta oxidation?
This a cycle of reactions which occurs in the mitochondrial matrix. There are 4 steps in each cycle.
Acyl coA which has been brought into the matrix is the substrate.
The products are one 2-carbon acetyl coA, a new acyl coA which is 2 carbons shorter than the previous one, 1FADH2, 1 NADH+ H+ (as there are 2 oxidation reactions in the cycle).
What is required for the oxidation of unsaturated fatty acids, odd-chain fatty acids and branched chain fatty acids?
Additional enzymes. The oxidation of these fatty acids usually yields less ATP.
What happens to the glycerol that is produced after cleavage of TAG?
It is activated to glycerol-3-phosphate by glycerol kinase which is present in the liver and kidney, but absent from skeletal muscle, heart muscle and adipose tissue. It is then dehydrogenated to dihydroxyacetone phosphate which is an intermediate in glycolysis, and therefore it can enter mainstream metabolism.