Cardio - Biochemistry - Fatty Acids; Cholesterol Transport Flashcards
Which carbon on a fatty acid is the α carbon?
The β carbon?
The ω carbon?
α - carbon 2
β - carbon 3
ω - last carbon
Dissect what each part of this name means:
20:5(Δ5,8,11,14,17) Eicosapentaenoic acid (EPA)
20 carbons
5 double bonds
unsaturated (-enoic)
double bonds at carbons 5, 8, 11, 14, and 17
Dissect what each part of this name means:
18:1(Δ9) Octaecenoic acid
18 carbons
1 double bond
unsaturated (-enoic)
double bond starting at carbon 9
What type of omega fat is this?
Omega-3
(double bond 3rd carbon if you start at the end [omega - ω])
Describe the difference in energy storage timeframes between triglycerides (triacylglycerols) and glycogen.
Glycogen = Short-term energy (< 12 hrs)
Triglycerides = Long-term energy (> 12 hrs)
Describe the relative membrane fluidity of saturated and unsaturated fatty acids.
Saturated = less fluid (can pack closely)
Unsaturated = more fluid (kinks don’t pack tightly)
Explain the structure of a 16:0 fatty acid.
It is a saturated FA with 16 carbons and no double bonds
How would you distinguish saturated vs. unsaturated fatty acids using common nomenclature?
Saturated = “anoic acid”
(e.g. 18:0 octadecanoic acid)
Unsaturated = “enoic acid”
(e.g. 18:1(Δ7) trans-7-octadecenoic acid)
What pathologic conditions are implicated with a high consumption of unsaturated fats (e.g. lauric (12:0), myristic (14:0), palmitic (16:0), or stearic (18:0) acid)?
Increased risk of atherosclerosis, coronary heart disease, and CVA
Describe the recommended consumption of omega(ω)-fatty acids ratios.
Omega-6 and omega-3 between a 1:1 and 4:1 ratio of consumption, respectively.
What are some example health benefits of Omega-3 FA consumption?
Protective against:
CVD, unhealthy inflammatory responses, poor neuronal responses in brain and retina, CVA, cancer
Describe the structure of palmitic acid in regards to number of carbons and number of double bonds.
And palmitoleic acid?
And stearic acid?
Place an asterisk next to the saturated fats.
16: 0 - saturated*
16: 1 - monounsaturated
18: 0 - saturated*
Describe the structure of oleic acid in regards to number of carbons and number of double bonds.
And α-linolenic acid?
And linoleic acid?
18: 1 - monounsaturated
18: 3 - polyunsaturated (ω-3)
18: 2 - polyunsaturated (ω-6)
Name a few ω-3 fatty acids.
α-linolenic,
eicosapentaenoic acid (EPA),
docosahexaenoic acid (DHA)
Name a few ω-6 fatty acids.
Linoleic acid,
arachidonic acid
Identify if each of the following is either an ω-3 or ω-6 fatty acid (identify the two that are essential with an asterisk):
Docosahexaenoic acid (DHA)
Linoleic acid
α-linolenic
Eicosapentaenoic acid (EPA)
Arachidonic acid
ω-3
*ω-6
*ω-3
ω-3
ω-6
How do you distinguish the type of omega acid between Linolenic acid and linoleic acid?
Linolenic acid - 1st “n” is 3 letters away from the end = ω-3
Linoleic acid - 1st “n” is 6 letters away from end = ω-6
True/False.
Most naturally occuring double bonds in fatty acids are trans double bonds.
False.
Most are cis but processing creates trans double bonds
(extra unhealthy ‘trans fats’)
True/False.
Too many ω-3 fatty acids outcompete ω-6 fatty acids for enzymatic rate limiting steps and are often the cause of decreases in the postitive effects associated with ω-6 fatty acids.
False.
Too many ω-6 fatty acids outcompete ω-3 fatty acids for enzymatic rate limiting steps and are often the cause of decreases in the postitive effects associated with ω-3 fatty acids.
From what fatty acid are prostaglandins derived?
Arachidonic acid (ARA) (an ω-6 fatty acid)
Which fatty acid stored on a triacylglycerol molecule is often the unsaturated one?
How are fatty acids freed from storage for usage when needed?
The one attached to the second carbon on the glycerol backbone;
they are hydrolyzed from the glycerol backbone (and released from their triglyceride storage form)
Describe the functions of triacylglycerols (triglycerides).
- Long-term energy storage
- Cushioning for organs
- Thermal insulation (thermogenin and brown fat)
- Absorption and transport of fat soluble vitamins (A,D,E,K)
As dietary lipids are ingested and pass into the intestines, how are the gallbladder and pancreas involved in their digestion?
What hormone triggers these reactions?
CCK (cholecystokinin) is released from the intestinal mucosa
–>
causing bile (gallbladder) and lipase (pancreatic) secretion
How is dietary fat broken down in the gut?
Cholecystokinin causes bile/lipase secretion
–>
Bile emulsifies the fat
–>
Lipase cuts fatty acids off the triacylglycerols (triglycerides)
–>
Intestinal mucosa take up the fatty acids
After being absorbed by the intestinal mucosa, how do fatty acids make their way to the peripheral cells?
Triglycerides are
(1) resynthesized,
(2) incorporated into chylomicrons (with cholesterol and apolipoproteins),
(3) released into blood and lymph to reach (but not yet enter!) peripheral cells (e.g. adipocytes)
Describe the makeup of a chylomicron.
Triglycerides and cholesteryl esters form the hydrophobic core;
ApoB-48, ApoC-II, cholesterol, and phospholipids make up the hydrophilic exterior
What must a cell do to access the energy stored within chylomicrons?
It must increase its secretion of lipoprotein lipase in order to “flag down” the chylomicron and stimulate ApoC-II to breakdown triglycerides
What is the role of lipoprotein lipase?
Capillary triglyceride digestion
–> frees fatty acids from chylomicrons to enter cells
Upon making it from the intestinal mucosa to the blood supply of peripheral tissues (e.g. adipocytes), how do fatty acids make it from their triglyceride storage form inside chylomicrons out and into the peripheral tissues?
apoC-II (apolipoprotein C-11) on the chylomicron activates lipoprotein lipase (a lipase found in the capillary)
The lipoprotein lipase cuts the fatty acids off glycerol so they can enter the peripheral cells and be oxidized for energy or reesterified into storage triglycerides once more.
What is the function of apoC-II?
Where is it found?
To activate lipoprotein lipase;
the chylomicron exterior
What do peripheral tissues (e.g. adipocytes, cardiac muscle) secrete when they need fatty acids for storage and use?
To where is it secreted?
Lipoprotein lipase;
the capillary surface (to contact apoC-II on chylomicron surfaces)
Why is steatorrhea (increased fecal lipids) often seen in individuals with cystic fibrosis or bowel resections?
(Why might this be a problem?)
Thickening of intestinal mucous
—> digestive lipases not secreted
—> lipids not digested / absorbed
(possibly leading to fat-soluble vitamin and essential fatty acid deficiencies)
A patient has a partial bowel resection. You worry she may develop a fat-soluble vitamin or essential fatty acid deficiency.
What might you advise her to incorporate into her diet in order to mitigate these risks?
Short and/or medium-chain fatty acids
–> easier to absorb into the intestinal mucosa (do not require micelle incorporation)
True/False.
Triglyceride (triacylglycerol) synthesis begins with glycerol 3-phosphate.
AND
An activated fatty acid (CoA - S - fatty acid) is then added to the glycerol.
True.
Glycerol 3-phosphate is essential to triglyceride synthesis.
What are two ways the liver produces it?
- Reduction of DHAP (glycerol-P dehydrogenase)
- Phosphorlyation of glycerol (glycerol kinase)
Here are two ways that glycerol 3-phosphate can be produced (for triglyceride synthesis).
Which organ(s) use(s) method 1?
Which organ(s) use(s) method 2?
1. Reduction of DHAP (glycerol-P dehydrogenase)
2. Phosphorlyation of glycerol (glycerol kinase)
- Liver and adipose
- Liver only
The liver is capable of forming both preliminary substrates for triglyceride synthesis (DHAP and glycerol).
Describe the conditions in which both molecules are generated (well-fed or fasting)?
DHAP is generated during the well-fed state
Glycerol is generated during the fasting state
How are fat storages accessed in the fasting state?
Hormone-regulation (glucagon/epinephrine)
Discuss the effect of glucagon and epinephrine on adipose cells.
Mobilizes triglycerides for breakdown into free fatty acids and glycerol
(via hormone-sensitive lipase and perilipin)
Glucagon/epinephrine activate G-protein signaling which causes PKA to activate what lipid mobilization components?
Hormone-sensitive lipase and perilipin
In regards to fatty acid metabolism, glucagon-activated PKA is responsible for activating what two substances?
Hormone-sensitive lipase;
perilipin
What is the role of perilipin?
Guards triglycerides inside fat droplets from being hydrolyzed by hormone-sensitive lipase
(until both HSL and perilipin are phosphorylated by PKA)
True/False.
PKA causes a conformational shift in hormone-sensitive lipase to expose triglycerides for activated perilipin to digest.
False.
PKA causes a conformational shift in perilipin to expose triglycerides for activated hormone-sensitive lipase to digest.
What happens when PKA phosphorylates the perilipin protein coat in triglyceride storage sites?
Perilipin undergoes a conformational change allowing lipase to reach stored triglycerides
During the fasting state, how does hormone-sensitive lipase address the body’s increased energy needs?
By breaking down triglycerides into free fatty acids and glycerol
(the FFA enter the bloodstream and are distributed to needy cells)
A fasting myocyte is in need of high-energy free fatty acids. What carries free fatty acids through the bloodstream from adipocytes to myocytes?
Serum albumin
If the body breaks down large amounts of triglycerides during fasting, there will be an increased amount of glycerol in the blood and liver.
What will happen to all the serum glycerol once the energy deficit is corrected?
All goes to the liver for:
- gluconeogenesis (for remaining body needs)
- triglyceride synthesis
During what state do muscles secrete lipoprotein lipase?
How is this different than other cells?
During the fasting state (when glucose is being saved for the brain);
other cells (liver and adipose cells) use lipoprotein lipase during the well-fed state to replenish energy stores
In the fasting state (low insulin), describe the expression of lipoprotein lipase in adipocytes, hepatocytes, and muscle cells
Adipocytes = low expression (provide energy from stores)
Hepatocytes = low expression (provide energy)
Myocytes = high expression (need alternative fuel)
What organ is constantly expressing lipoprotein lipase?
Why?
Cardiac cells;
the heart gets 60-90% of its energy from free fatty acids
What is the main pathway for oxidizing fatty acids?
What tissues use this breakdown pathway most frequently?
β-oxidation;
tissues with a high energy or metabolic requirement (e.g. cardiac muscle tissue)
What enzyme activates fatty acids?
Fatty acyl - CoA synthetase
In triglyceride synthesis, an activated fatty acid (CoA attached) is first attached (via acyl transferase) to the carbon 1 on a glycerol 3-phosphate.
Then, a second activated fatty acid is attached (via acyl transferase) to the carbon 2 on a glycerol 3-phosphate.
What happens next?
The phosphate is removed from glycerol 3-phosphate,
then the 3rd carbon receives an activated fatty acid as in the other steps
Where in the cell does β-oxidation take place?
What must occur in order for a fatty acid to be transported into the mitochondria for β-oxidation?
The mitochondrial matrix;
fatty acid activation by CoA
The carnitine shuttle exists to take a fatty acid-CoA from the cytosol to the mitochondrial matrix.
What two enzyme are involved in this shuttle system and where are they located?
Carnitine acyl transferase I (CAT I) - outer membrane
Carnitine acyl transferase II (CAT II) - inner membrane
At what point is a fatty acid committed to the β-oxidation pathway?
Upon entering the mitochondria
(via the carnitine shuttle)
When is β-oxidation used?
It is stimulated by:
Fasting state,
exercise;
glucagon, epinephrine
How are fatty acyl - CoA (activated fatty acids) transported into the mitochondria?
They are turned into fatty acyl - carnitine,
passed through the carnitine shuttle,
and turned back into fatty acyl - CoA
In what organs is carnitine produced?
What is the body’s main source of carnitine?
The liver and kidney;
dietary meats
What is the inheritance pattern of a primary carnitine deficiency?
What causes it?
Autosomal recessive;
a defect in either carnitine acyl transferase I or II
A carnitine acyl transferase I (CAT I) deficiency mainly affects what organ(s)?
The liver
A carnitine acyl transferase II (CAT II) deficiency mainly affects what organ(s)?
Cardiac and skeletal muscle
What is a typical dietary treatment for secondary carnitine deficiencies?
High carbohydrates
Low long-chain fatty acids
Carnitine supplementation
Secondary carnitine deficiency typically presents due to what type of conditions?
The body not being provided enough carnitine
E.g. Liver disease
Vegetarian diets
Increasing carnitine needs (pregnancy, trauma)
Malnutrition
Which (if any) cells do not utilize β-oxidation pathways?
Red blood cells and the brain
What are the 4 repeating reactions of β-oxidation?
- Oxidation
- Hydration
- Oxidation
- Cleavage
How many Acetyl-CoA can be produced from one round of β-oxidation of palmitate (16:0)?
How many NADH can be produced from one round of β-oxidation of palmitate (16:0)?
How many FADH2 can be produced from one round of β-oxidation of palmitate (16:0)?
1 acetyl-CoA
1 NADH
1 FADH2
How many Acetyl-CoA can be produced from complete oxidation of palmitate (16:0)?
How many NADH can be produced from complete oxidation of palmitate (16:0)?
How many FADH2 can be produced from complete oxidation of palmitate (16:0)?
8 acetyl-CoA * 10 ATP per Acetyl-CoA = 80 ATP
7 NADH * 2.5 ATP/NADH = 17.5 ATP
7 FADH2 * 1.5 ATP per FADH2 = 10.5 ATP
What is the total energy yield of β-oxidation of a palmitate (16:0) fatty acid?
108 ATP
(8 acetyl-CoA, 7 NADH, 7 FADH2)
What is the most common inborn error of metabolism and fatty acid oxidation?
Why is this such a problem for fatty acid oxidation?
Medium-chain acyl-CoA dehydrogenase deficiency (MCADD)
This enzyme is the first oxidation enzyme of fatty acid oxidation and it targets fatty acids of 6 - 10 carbons
Does an individual with medium-chain acyl-CoA dehydrogenase deficiency (MCADD) need to worry if they are eating only long-chain fatty acids?
How is this disorder managed?
YES!
Long-chain fatty acids will be oxidized into medium chain lengths and, at that point, will be unable to be broken down;
low fat / high carb diet
How is medium chain acyl-CoA dehydrogenase diagnosed?
It has an association with what fatal infantile disorder?
High 6 - 10 mono- and dicarboxylic acids in the blood/urine;
SIDS
When normal β-oxidation is inhibited, medium-chain length fatty acids can be oxidized by __-fatty acid oxidation.
Where does this reaction take place?
ω;
the ER of liver and kidney cells.
What is the unique product of ω-fatty acid oxidation?
Dicarboxylic acid (succinate)
What is a diagnostic sign of medium-chain acyl-CoA dehydrogenase deficiency (MCADD)?
An increase in urine [dicarboxylic acids];
β-oxidation is inhibited and those dicarboxylic acids can’t be oxidized further in mitochondria (so they are ω-oxidized in the ER)
An odd-chain fatty acid can be oxidized but it will end in propionyl-CoA, a 3-carbon structure activated by CoA.
What is the final product of propionyl-CoA after subsequent reactions?
Succinyl-CoA - a citric acid cycle intermediate
Even-chain fatty acids end in production of two:
Odd-chain fatty acids end in production of:
Acetyl-CoA;
one propionyl-CoA, one acetyl-CoA
What vitamin cofactors are needed to convert propionyl-CoA to succinyl-CoA?
(Note: 2 reactions –> 2 vitamins)
- Biotin (vitamin B7)
- Cobalamin (vitamin B12)
What reaction does biotin facilitate in odd chain fatty acid oxidation?
Adds CO2 to propionyl-CoA to form methylmalonyl-CoA
Methylmalonyl-CoA mutase is used in odd chain fatty acid oxidation.
Describe the function and cofactor required by this enzyme.
Converts L-methylmalonyl-CoA to succinyl-CoA
Requires vitamin B12 (cobalamin)
What enzymatic defect of odd-chain fatty acid oxidation can lead to methylmalonic acidemia?
Defect in methylmalonyl-CoA mutase
(unable to oxidize odd chain fatty acids *inability to replenish key citric acid cycle intermediates)
propionyl-CoA buildup
Where are very long-chain fatty acids oxidized?
What is considered a very long-chain fatty acid?
Peroxisomes;
>20 carbons in a chain
What are the two unique aspects of oxidation of very long-chain fatty acids in peroxisomes as compared to normal β-oxidation in the mitochondrial matrix?
- No carnitine shuttle required for entry into peroxisomes
- Initial oxidation produces H2O2 and FAD
Zellweger Syndrome, as well as X-linked adrenoleukodystrophy, result in what primary clinical/laboratory sign?
Why is this?
Elevated levels of very long-chain fatty acids;
they are both disorders of peroxisomal very long chain fatty acid oxidation