Synthesis of FA's involves a series of reactions all of which occur on the FA synthase complex. Which of the following most accurately represents the sequence of these reactions? A) Condensation, reduction, dehydration, reduction B) Condensation, reduction, hydration, reduction C) Condensation, oxidation, dehydration, oxidation D) Condensation, oxidation, hydration, oxidation
A) Condensation, reduction, dehydration, reduction
A pharmaceutical company is developing a new drug that inhibits FA synthesis in obese (BMI >30) patients. The drug is supposed to prevent the insulin-dependent activation of the rate limiting enzyme of FA synthesis. TO check the efficacy of drug candidates in cell cultures, the inhibition of which of the following enzymes would serve as a suitable marker? A) Long-chain acyl CoA dehydrogenase B) protein phosphatase C) Glycogen phosphorylase D) Protein kinase B (PKB) E) Protein Kinase A (PKA)
B) Protein phosphatase
The correct sequence of steps for shortening of a fatty acyl CoA by two carbons is: A) dehydration, hydration, oxidation, and thiolytic cleavage B) Thiolytic cleavage, hydration, oxidation, and acylation C) Oxidation, hydration, oxidation, and thiolytic cleavage D) Oxidation, hydration, dehydration, and thiolytic cleavage E) Hydration, oxidation, oxidation, and thiolytic cleavage
C) Oxidation, hydration, oxidation, and thiolytic cleavage
Beta-oxidation of an odd-chain FA produces several 2C and one 3C molecules. The after enters the TCA cycle in the form of which compound? A) Citrate B) Isocitrate C) Alpha-ketoglutarate D) Succinyl CoA E) Malate
D) Succinyl CoA
What is a glycerolipid?
A fatty acid derivative with a glycerol backbone (Mono, di, and tri- acylglycerides
What is a glycerophospholipid?
2 fatty acids attached to a glycerol backbone - Phosphate is esterified with a head group
What is a major source of carbon for fatty acid synthesis?
Dietary carbons -> need carbs in diet to synthesize fats
Where does fatty acid synthesis primarily occur?
IN the liver
Fatty acid synthesis primarily occurs in the liver but can also occur in what 4 locations?
Adipose tissue, brain, kidneys, and lactating mammary glands
What is the end product of fatty acid synthesis in humans?
Palmitic acid -> 16C
Where does phase 1 of fatty acid synthesis occur?
made in mito but needed in cytoplasm
What is the goal of phase 1 of fatty acid synthesis?
To get acetyl CoA into the cytosol
How does acetyl CoA get to the cytosol in fatty acid synthesis?
What ate the steps of the citrate shuttle from oxaloacetate back to oxaloacetate?
Oxaloacetate + acetyl coA -> citrate -> citrate in cytoplasm -> oxaloacetate + acetyl coA
In the first step of the carnitine shuttle, what enzyme is used for the condensationof acetyl CoA and oxaloacetate to form citrate?
During the carnitine shuttle pathway, what enzyme converts citrate back to acetyl coA and oxaloacetate?
What is the purpose of phase 2 of fatty acid synthesis?
Synthesis of malonyl CoA
What is the rate limiting step and enzyme of fatty acid synthesis?
Phase II; acetyl CoA carboxylase
What Cofactor is needed for acetyl coA carboxylase in fatty acid synthesis?
What enzyme is used to convert acetyl CoA to malonyl coA in fatty acid synthesis and what cofactor is needed?
Acetyl CoA carboxylase; biotin
What is the inactive and active form of malonyl coA?
Dimeric form = inactive Polymeric form = active
How many carbons are in malonyl coA?
____________ is a regulator. It inhibits carnitine acyltranserase, the rate limiting step in FA degradation
Malonyl CoA (substrate for fatty acid synthase (FAS)) - This prevents FA synthesis and degradation from occurring simultaneously
What is the purpose of phase 3 of fatty acid synthesis?
Fatty acid chain synthesis
What enzyme is used to convert malonyl CoA to Palmitate in fatty acid synthesis?
Fatty acid synthase
The reactions of fatty acid synthesis occur on the _________ __________ __________ complex
Fatty Acid Synthase
Where is the fatty acid synthase complex located?
Describe the structure of fatty acid synthase
- Large multi-enzyme complex - Composedof 2 identical dimers - 2 dimers arranged head to tail - Each has 7 enzyme activities and an acyl carrier protein (ACP)
What is the flexible arm of ACP made of?
List the basic reactions of fatty acid synthesis
Activation -> Condensation -> Reduction -> Dehydration -> Reduction -> Product release and cycle repeats
What are sources of NADPH for fatty acid synthesis?
Malic enzyme and PPP
Where does acetyl coA bind in fatty acid synthesis?
To cysteine on FAS
Where does malonyl coA bind during fatty acid synthesis?
Cysteine on ACP
What directly stimulates ATP citrate lyase in fatty acid synthase?
What induces gene expression of ATP citrate lyase in fatty acid synthesis?
What counteracts gene expression of ATP citrate lyase in fatty acid synthesis??
PUFAs and leptin
What allosterically stimulates acetyl CoA carboxylase in fatty acid synthesis?
What allosterically inhibits acetyl coA carboxylase?
Long chain fatty acids palmitate
Does phosphorylation of acetyl coA carboxylase turn it on or off?
Off - Dephosphorylation turns it on
________ dephosphorylates acetyl CoA carboxylase, therefore activating it, via activation of protein phosphatase
__________ and ___________ phosphorylate acetyl CoA carboxylase, therefore inhibiting it, via protein kinase A
Epinephrine and glucagon
_________ phosphorylates acetyl coA carboxylase, therefore inhibiting it, via activation of AMP kinase (energy sensor)
What kind of diet is gene expression of acetyl coA carboxylase up-regulated by?
High carb/low fat diet
What allosteric effect does the presence of phosphorylated sugars have on FAS?
What 2 hormones increase synthesis of FAS?
Insulin and glucocorticoids
What type of diet increases FAS synthesis?
High carb/low fat
What type of diet lowers synthesis of FAS?
High fat diets - Starvation too!
What effect does high PUFA content have on FAS?
Suppresses its synthesis
Where does elongation of FAs occur?
Smooth endoplasmic reticulum or mitochondria
What type of cells need longer fatty acids (C18-C24)?
The SER pathway of FA elongation uses ___________ as carbon donor
Mitochondria pathway of FA elongation uses ________ as carbon donor
Desaturation of FAs introduces what?
Where does desaturation of FAs occur?
What is desaturation of FAs catalyzed by?
Acyl CoA desaturases
How many desaturases do humans have?
4 (Delta 4, 5, 6, and 9)
T/F: FA with double bond beyond carbon 9 and 10 cant be synthesized in humans
Dietary _______ induces expression of delta 9 desaturases, suppresses all others
Gene expression of desaturases is suppressed by what?
Gene expression of desaturases is induced by what?
Linoleic acid is what type of essential FA?
Linolenic acid is what type of essential FA?
Linoleic acid is used to make ___________ acid
Arachidonic - Precursor for eicosanoids (prostaglandins, eukotrienes, and thromboxanes)
Linolenic acid is used to make _____________ and ________________ acid
Eicosapentanoic (EPA) and DHA
The outer mitochondrial membrane is not permeable to what?
The inner mitochondrial membrane is not permeable to what?
What is the purpose of phase 1 of fatty acid oxidation?
Transport of free fatty acids into the mitochondrial matrix via carnitine shuttle
Where does phase one of fatty acid oxidation occur?
Where does phase 2 of fatty acid oxidation occur?
In mitochondrial matrix - This is beta oxidation
What is the purpose of phase 2 of fatty acid oxidation?
Beta oxidation of FAs
What can diffuse into mitochondria in terms of fatty acids?
Short and medium chain FAs
What needs to be actively transported into mitochondria in terms of fatty acids?
Long chain and very long chain FAs
Where are very long chain FAs oxidized to LCFAs before using carnitine shuttle?
What enzyme is used in phase one (activation) of fatty acid oxidation?
Fatty acyl CoA synthetase
Where is fatty acyl CoA synthetase located?(FA oxidation)
Outer mito-membrane - Reaction catalyzed on cytoplasmic side of membrane
What type of bond is formed between FAs and CoA to form FACoA during FA oxidation?
What s the rate limiting enzyme in FA degradation?
Carnitine palmitoyltransferase I (CPT-I)
Where is CPT-I located? (FA oxidation)
What is the role of CPT-I in FA oxidation?
Transfers fatty acyl from FA-CoA to carnitine forming FA-carnitine
What is CPT-I in FA oxidation inhibited by?
There are 4 steps of beta oxidation. The first step is oxidation using what enzyme?
Acyl CoA dehydrogenase (ACAD)
What are the 4 types of ACADs
Short chain (SCAD) Medium chain (MCAD) Long chain (LCAD) Very long chain (LCAD)
Steps 3-4 of beta oxidation use enoyl CoA hydratase, beta hydroxy acyl CoA dehydrogenase, and acyl CoA acyl transferase or ketothiolase. These 3 enzymes together are called what?
MTFP (mitochondrial trifunnctional protein)
Catabolism of palmitic acid gives ______ ATP
Acetyl CoA generates ______ ATP
Odd numbered FAs are metabolized until _____________ remains
Propionyl CoA (3C)
what enzyme is used to convert propionyl coA to methylmalonyl CoA when degrading odd numbered FAs?
Propionyl CoA carboxylase
What enzyme generates succinyl CoA from methylmalonyl CoA during degradation of odd numbered FAs?
Methylmalonyl CoA mutase
What product of the degradation of odd numbered FAs enters TCA?
VLCFAs are more than _____ carbons
How are unsaturated FAs degraded?
1) Reductase reduces double bond 2) Isomerases moves the disruptive bond
How long does VLCFA oxidation occur in peroxisome?
Until you get a 20 carbon FA
What does VLCFA degradation in peroxisomes produce?
H2O2 - Peroxide can be toxic so catalase converts the hydrogen peroxide into water and oxygen which arent toxic
What enzyme oxidizes the first step of VLCFA oxidation?
Acyl CoA oxidase
_________ is an analog of lysine, not synthesized in the body, and rich in skeletal muscle
Carnitine - Carnitine deficiency is common in strict vegetarians **Without carnitine you dont get beta oxidation**
An autosomal recessive disorder of FA beta oxidation that impairs the breakdown of MCFAs is due to a deficiency of what enzyme?
Patients with an MCAD deficiency depend on what as an energy source?
__________ deficiency leads to secondary carnitine deficiency due to excessive excretion of MCA carnitines in urine
MCAD - C8 FA accumulates in liver and interferes with urea cycle leading to elevated levels of ammonia
Gluconeogenesis is impaired in MCAD deficiency die to low activity of what enzyme?
Pyruvate carboxylase (due to low ATP and acetyl coA)
Ketone bodies are water-soluble and acidic compounds. What are the three ketone bodies/
Acetoacetate Beta hydroxybutyrate Acetone
Where are ketone bodies produced?
IN LIVER ONLY
Where in hepatocytes does synthesis of ketone bodies occur?
What three organs utilize ketone bodies
Brain (only when starving), muscle and kidneys - RBCs cannot utilize ketone bodies for energy
1 acetate yields _____ ATP
23 -> 24 from acetyl CoA, minus 1 from activation of acetoacetate
1 beta hydroxybutyrate yields _____ ATP
26 -> 3 from NADH, 24 from 2 acetyl CoA , minus 1 from activationof acetoacetate
What is the primary energy source during the first few hours of fasting?
Blood glucose followed by glycogen stored in muscle and liver - Next would be gluconeogenesis in liver
What is the primary energy source after 1 day of fasting?
TAGs stored in adipose tissue - TAGs broken down to release FA which undergo beta oxidation
What s the primary energy source after 3 days of fasting?
Ketone bodies made in liver and proteins in muscles are broken down - Glycerol from TAGs and glucogenic AAs from proteins enter gluconeogenesis -> supplies energy to brain and RBCs
What is the primary energy source after 1-2 weeks of starvation?
Brain switches to ketone bodies as major energy source
What s the primary energy source after 2-3 months of starvation?
TAGs depleted, proteins main source -> coma and death
__________ ____________ occurs in fasting, during pregnancy and in babies, and after prolonged exercise and is a mild to moderate increase in ketone bodies
______________ _____________ occurs when glucagon/insulin ratio is increased, favoring FA breakdown.
What are the steps of diabetic ketosis?
Glucose cant enter liver or adipose tissue: 1) OAA level drops 2) CAC 3) Free FAs are released from adipose tissue 4) Ketone bodies form 5) Blood pH drops 6) Coma and death result