Fat catabolism Flashcards
How can we obtain fatty acids for catabolism ?
- diet
- stored fats (triglycerols - adipocytes)
- newly synthesized fats (triglycerols that the body makes)
What are triglycerols?
These are 3 long chain fatty acid chains esterified to the glycerol backbone.
What are the major functions of triglycerols?
- energy (~80%)
- more reduced, less hydrated than glycogen so can stockpile (adipocytes,better storage than glucose)
What happens in stage one of fat catabolism?
The long chain fatty acid is catabolised to form acetyl units in the form of acetyl co A
What is the name of stage one of fatty acid catabolism?
Where does it occurs?
Beta-oxidation
Occurs in the mitochondrial matrix.
What happens in stage 2 of fat catabolism?
Acetyl groups are oxidised in the citric acid cycle.
What happens in stage 3 of fat catabolism?
Electrons are derived from oxidations of stages 1&2 pass to O2.
Via the mitochondrial respiratory chain ATP synthesis by oxidative phosphorylation
How are TAGs stored?
within lipid droplets core of Tags and sterol esters.
surrounded by monolayer o phospholipids
What is the surface of the adipocyte droplet coated in ?
Protein called perilipin - a protein which restricts untimely access to TAGs.
What receptors do adipocytes have?
adrenaline and glucagon - low blood glucose.
What do adrenaline and glucagon receptors activate on adipocytes?
Adenylyl cyclase - increase cAMP = activation of PKA
What does protein kinase do?
It mobilises a number of different responses in the cell - it phosphorylates perilipins and other proteins to ‘open’ the lipid droplet.
What activity does PKA allow for?
3 cytosolic lipases including hormone sensitive lipase = degrade TAGs to liberate f.a
What does the dissociated perilipin do ?
Stimulates the first lipase - allows access into lipid.
Tri - di.
What does the phosphorylated perilipin do?
It associated with the phosphorylated HSL - allowing access and convert tri to di.
What is the role of monoacylglycerol?
To hydrolyze monoacylglycerol.
Where do the released fatty acids from the adipocyte go?
Into the blood bound to serum albumin. go to liver, skeletal muscle and enter via fatty acid transporter protein.
What do all of the lipases do?
Hydrolyse ester linkages in tri/di and mono - acyl glycerol.
Liberating them
What happens when the fatty acids dissociate from the serum albumen?
They go through the fatty acid transporter protein into cytosol of cells which need energy.
Where does beta oxidation fatty acid occur?
In the mitochondria, where fatty acid chains less than 14 carbon can enter.
How are fatty acid chains longer than 14 carbon helped into the mitochrondria?
By activation and use of enzymes and transporter protein in inner mitochondrial membrane.
What happens initially in fatty acid activation?
They are energised using fatty acid acyl-CoA synthetase isoenzymes.
What is the role of fatty acyl coA synthetase?
It energises fatty acids - activating them.
- catalyses the formation of thioester linkage to yield fatty acyl CoA (ATP)
Is fatty acyl CoA high energy compound more amenable to catabolism than fatty acids?
Yes
Where is fatty acyl coA synthetase?
Outer mitochondrial membrane.
How are fa longer than 14C transported into the mitochondrial matrtix?
Acyl-carnitine transporter called the carnitine shuttle
How does fa acyl CoA join to the carnitine shuttle?
hydrolysed (more interactive)
attaches to the -OH of carnitine in outer mm
Catalysed: carnitine acyl-transferase-1
What is the enzyme transfer involved in the mm?
Fatty acid group enzymatically transferred to intramitochondrial CoA
Catalysed: carnitine acyl-transferase-2
What happens during the dehydrogenation-dehydrogenase beta oxidation pathway?
Removes 2H+ to FAD = FADH2
Double bond produced
What are the 4 enzymes in the beta-oxidation pathway?
- dehydrogenase
- hydratase
- dehydrogenase
- thiolase
What happens during the hydration - hydratase beta oxidation pathway?
H20 is added to form a double bond
1 H20 input
What happens during dehydrogenation - dehydrogenase?
Removes 2H+ to NAD+ = NADH + H
1 NADH and H is formed.
How many times are the 4 steps of the Beta oxidation carried out for the complete conversion of 16C palmitoyl-CoA to 8 molecules of Acetyl-CoA?
7 times
How much energy is obtained from the beta oxidation of 16C palmitoyl CoA?
Lots - 7FADH2 and 7NADH - delivers electrons to respiratory chain and 8 acetyl COA to enter citric acid cycle.
How many kilojoules does the beta oxidation pathway yield in comparison to glycolysis?
~9800kj/mol (1 palmitate to CO2 and H20)
~ 2380kj/mol (1 glucose)
What configuration are double bonds usually in ?
Cis configuration (H atom same side)
Which type of fatty acids have double bonds?
Unsaturated
mono - one
poly - more than one
What two extra enzymes are needed to catabolise unsaturated fatty acids during beta oxidation?
Isomerase (cis - trans)
Reductase (Poly)
Where are fatty acids stored in higher vertebrates?
adipocytes
What is the name of the major storage fat?
Triacyglycerols
What tissues use a lot of fatty acids for energy?
Liver, skeletal muscle
Are fatty acids more or less reduced than glucose?
Much more reduced.
Why are TAGs a better storage form of energy than glycogen?
Highly concentrated
Reduced
Anhydrous
What part of the cell does fatty acid beta-oxidation take place?
Inside mitochondria.
What does fatty acid activation involve?
Fatty acyl coA synthetase = Fatty acyl coA
