Metabolism Of Lipids Flashcards
What is cholesterol often referred to as?
The most feared among lipids
How are lipids characterized in terms of their nature?
Hydrophobic and non-polar
What percentage of body weight do lipids constitute in humans?
15-20%
What are triacylglycerols also known as?
Triglycerides
What is the primary role of triacylglycerols in the body?
Energy reserve
How much energy do triacylglycerols yield per gram?
9 Cal/g
What is the energy yield of carbohydrates and proteins per gram?
4 Cal/g
What is the main reason fat is used as a fuel reserve in the body?
Highly concentrated form of energy
What is the storage form of fat in the body?
Triacylglycerol
How much fat is typically stored in a healthy adult weighing 70 kg?
10-11 kg
What is the fuel reserve in calories for 10-11 kg of stored fat?
100,000 Cals
What happens to body weight if energy is stored as glycogen instead of fat?
Weight would increase by at least 55 kg
What are the main components of cell membranes?
Phospholipids, glycolipids, cholesterol
What is the role of cholesterol in the body?
Precursor for bile acids and steroid hormones
What are chylomicrons?
Lipoproteins that transport dietary lipids
What are the different types of lipoproteins mentioned?
- Chylomicrons
- VLDL
- LDL
- HDL
What is the process of breaking down triacylglycerol called?
Lipolysis
What enzyme is responsible for the mobilization of fat from adipose tissue?
Hormone-sensitive triacylglycerol lipase
True or False: Insulin increases the activity of hormone-sensitive TG-lipase.
False
What happens to glycerol produced in lipolysis?
Transported to liver for activation
What is the fate of free fatty acids released in adipocytes?
Transported in bound form to albumin
What percentage of energy from fat comes from the oxidation of fatty acids?
95%
What is the term for the process of hydrolyzing TG to free fatty acids during starvation?
Triacylglycerol/fatty acid cycle
What is β-oxidation?
Oxidation of fatty acids on the β-carbon atom
What is the process of converting fatty acids into triacylglycerol termed?
Triacylglycerol/fatty acid cycle
This process involves the conversion of fatty acids back into triacylglycerols for storage.
What is the primary method of fatty acid oxidation in the body?
β-oxidation
This process occurs mainly in the mitochondria and involves the sequential removal of two-carbon fragments from fatty acids.
Define β-oxidation.
The oxidation of fatty acids on the β-carbon atom
This process results in the sequential removal of acetyl CoA.
In which cellular compartments does fatty acid oxidation occur?
Cytosol and mitochondrial matrix
The activation of fatty acids occurs in the cytosol, while β-oxidation takes place in the mitochondrial matrix.
What are the three stages of β-oxidation?
- Activation of fatty acids in the cytosol
- Transport of fatty acids into mitochondria
- β-oxidation proper in the mitochondrial matrix
Each stage plays a crucial role in the overall process of fatty acid metabolism.
What activates fatty acids for β-oxidation?
Acyl CoA formation
Fatty acids are activated to acyl CoA by thiokinases or acyl CoA synthetases.
What is required for the activation of fatty acids to acyl CoA?
- ATP
- Coenzyme A
- Mg2+
The activation process involves two steps and utilizes high-energy phosphates from ATP.
What enzyme catalyzes the conversion of acyl CoA to acyl-carnitine?
Carnitine acyltransferase I
This enzyme is located on the outer surface of the inner mitochondrial membrane.
Fill in the blank: The enzyme that converts acyl-carnitine back to acyl CoA is called _______.
Carnitine acyltransferase II
This enzyme is found on the inner surface of the inner mitochondrial membrane.
True or False: The inner mitochondrial membrane is permeable to fatty acids.
False
Fatty acids cannot pass through the inner mitochondrial membrane without being converted to acyl-carnitine.
What inhibits the carnitine shuttle during fatty acid oxidation?
Malonyl CoA
Malonyl CoA is a key metabolite involved in fatty acid synthesis and prevents the transport of fatty acids into the mitochondria.
What are the four reactions that occur in each cycle of β-oxidation?
- Oxidation
- Hydration
- Oxidation
- Cleavage
Each reaction is catalyzed by specific enzymes that facilitate the breakdown of fatty acids.
What is the final product of each cycle of β-oxidation?
Acetyl CoA
Each cycle liberates a two-carbon unit, acetyl CoA, from the fatty acid chain.
What is the total ATP yield from one molecule of palmitoyl CoA after β-oxidation?
129 ATP
This includes ATP generated during β-oxidation and the citric acid cycle.
How many cycles of β-oxidation occur for palmitoyl CoA?
7 cycles
Each cycle removes two carbons from the fatty acid chain until it is completely oxidized.
What is the efficiency of energy conservation by fatty acid oxidation?
40%
This is based on the energy yield from the complete oxidation of palmitic acid.
What are the products of the overall reaction for each cycle of β-oxidation?
- C(n-2) Acyl CoA
- Acetyl CoA
- FADH2
- NADH
- H+
This reaction reflects the breakdown of fatty acids into usable energy forms.
What is the primary function of carnitine in fatty acid metabolism?
Transport of activated fatty acids (acyl CoA) into mitochondria
The carnitine shuttle is essential for fatty acid oxidation.
What syndrome is associated with a deficiency in medium chain acyl CoA dehydrogenase?
Sudden Infant Death Syndrome (SIDS)
It is estimated that at least 10% of SIDS cases are due to this deficiency.
What is the estimated frequency of medium chain acyl CoA dehydrogenase deficiency?
1 in 10,000 births
This condition is more prevalent than phenylketonuria.
What is the principal energy source for infants shortly after feeding?
Glucose
After a few hours, glucose levels decrease, requiring an increase in fatty acid oxidation.
What causes the sudden death in infants with MCAD deficiency?
Blockade in β-oxidation
This is due to the inability to oxidize fatty acids for energy.
What is Jamaican vomiting sickness caused by?
Eating unripe ackee fruit containing hypoglycin A
This toxin inhibits acyl CoA dehydrogenase.
What is the first step in β-oxidation of fatty acids?
Activation of fatty acid to acyl CoA
This step requires ATP and CoA.
What is the end product of β-oxidation of palmitic acid (16 carbons)?
8 Acetyl CoA
This process involves seven cycles of β-oxidation.
What is the fate of odd carbon chain fatty acids during β-oxidation?
Produce propionyl CoA, which is converted to succinyl CoA
This conversion is essential for entry into the citric acid cycle.
What vitamin is required for the conversion of methylmalonyl CoA to succinyl CoA?
Vitamin B12
This is crucial for proper metabolic function.
What are the two types of methylmalonic acidemias?
- Due to deficiency of vitamin B12
- Due to defect in methylmalonyl CoA mutase
Both types lead to accumulation of methylmalonic acid.
What is a characteristic of oxidation of unsaturated fatty acids compared to saturated fatty acids?
Provides less energy due to double bonds
Additional enzymes (isomerase and epimerase) are needed to facilitate the process.
Where does β-oxidation of fatty acids occur in peroxisomes?
In a modified form, leading to the formation of H2O2
This process does not produce ATP but generates heat.
What is Zellweger syndrome?
A disorder characterized by the absence of peroxisomes in tissues
It leads to accumulation of long-chain fatty acids in the brain, liver, and kidney.
What is α-oxidation of fatty acids?
Removal of one carbon unit at a time from the α-carbon of fatty acid
This process does not involve the binding of fatty acids to coenzyme A.
What is Refsum’s disease characterized by?
Cerebral ataxia and peripheral neuropathy
It involves accumulation of phytanic acid due to a defect in α-oxidation.
What prevents phytanic acid from undergoing β-oxidation?
Presence of a methyl group on carbon-3
This necessitates initial α-oxidation before β-oxidation can occur.
What is Refsum’s disease caused by?
A defect in -oxidation due to the deficiency of the enzyme phytanic acid -oxidase.
What dietary restriction is advised for patients with Refsum’s disease?
Patients should not consume diets containing chlorophyll (i.e., green leafy vegetables).
What is the process of -oxidation of fatty acids?
It involves hydroxylation followed by oxidation of the -carbon present as a methyl group.
What are the requirements for the -oxidation reaction?
Cytochrome P450, NADPH, O2, and specific enzymes.
What is metabolic water?
Water produced during the oxidation of fatty acids and aerobic respiration.
Which animal can store lipids in its hump for energy and water supply?
Camel.
What is the significance of metabolic water in the kangaroo rat?
It allows the kangaroo rat to live indefinitely without water by consuming only oil-rich seeds.
What are ketone bodies?
Compounds namely acetone, acetoacetate, and -hydroxybutyrate.
Which two ketone bodies are considered true ketones?
Acetone and acetoacetate.
Where does ketogenesis occur?
In the liver.
What is the precursor for ketone bodies?
Acetyl CoA.
What enzyme catalyzes the condensation of two moles of acetyl CoA?
Thiolase.
What is the role of HMG CoA synthase in ketogenesis?
It regulates the synthesis of ketone bodies.
What happens to acetoacetate during ketone body metabolism?
It can undergo spontaneous decarboxylation to form acetone.
Which tissues can utilize ketone bodies?
Skeletal muscle, cardiac muscle, renal cortex, etc.
Which tissues cannot utilize ketone bodies?
Erythrocytes (they lack mitochondria).
What is the brain’s ability to utilize fatty acids for energy?
Very limited; ketone bodies can meet 50-70% of the brain’s energy needs.
What is the result of prolonged starvation regarding ketone bodies?
Ketone bodies become the major fuel source for the brain and central nervous system.
What is the process by which -hydroxybutyrate is used?
It is converted to acetoacetate and metabolized.
What is the consequence of overproduction of ketone bodies?
Ketonemia, where concentration in blood increases.
What does the term ketonuria represent?
The excretion of ketone bodies in urine.
What is ketosis?
The overall condition involving ketonemia and ketonuria.
What is the smell associated with ketosis?
The smell of acetone.
What condition is associated with uncontrolled diabetes mellitus?
Ketosis, which can lead to diabetic ketoacidosis.
What is the difference between starvation and ketoacidosis?
Starvation is not accompanied by ketoacidosis.
What is the role of insulin in fatty acid synthesis?
It promotes fatty acid synthesis by stimulating the conversion of pyruvate to acetyl CoA.
What makes linoleic and linolenic acids essential to mammals?
The lack of ability to introduce double bonds in fatty acids beyond C9 and C10.
What is methylmalonic acidemia caused by?
Deficiency of vitamin B12 or a defect in methyl malonyl CoA mutase.
What syndrome is attributed to a blockade in -oxidation of fatty acids?
Sudden infant death syndrome (SIDS).
What is Jamaican vomiting sickness caused by?
Consumption of unripe ackee fruit containing hypoglycin A.
What are the effects of Zellweger syndrome?
Absence of peroxisomes in tissues, preventing oxidation of long-chain fatty acids.
What is Ketonemia primarily due to?
Increased production of ketone bodies rather than deficiency in their utilization.
What does Ketonuria represent?
The excretion of ketone bodies in urine.
What is the overall picture of ketonemia and ketonuria commonly referred to as?
Ketosis.
What is a common feature of ketosis?
Smell of acetone in breath.
What is starvation accompanied by?
Increased degradation of fatty acids to meet energy needs.
What causes an overproduction of acetyl CoA during starvation?
Inability to fully handle acetyl CoA by the citric acid cycle.
What is the result of the impaired TCA cycle during starvation?
Accumulation of acetyl CoA and overproduction of ketone bodies.
What does the appearance of ketone bodies in urine indicate?
Active fat metabolism.
What dietary changes do weight loss programs often encourage?
Reduction in carbohydrate and total calorie intake.
What is diabetes mellitus associated with?
Insulin deficiency.
What leads to the accumulation of acetyl CoA in severe diabetes?
Impaired carbohydrate metabolism and increased lipolysis.
What does the concentration of ketone bodies in blood plasma reach in severe diabetes?
Up to 100 mg/dl.
What promotes ketone body formation?
Increased ratio of glucagon to insulin.
What are ketogenic substances?
Fatty acids and certain amino acids (e.g., leucine, lysine, tyrosine).
What are antiketogenic substances?
Glucose, glycerol, and glucogenic amino acids (e.g., glycine, alanine, serine, glutamate).
True or False: Both acetoacetate and β-hydroxybutyrate are weak acids.
False.
What can an increase in ketone body concentration in blood cause?
Acidosis.
What is diabetic ketoacidosis?
A dangerous condition that can result in coma or death if untreated.
What is the primary source of carbon atoms for fatty acid synthesis?
Acetyl CoA.
What provides the reducing equivalents for fatty acid synthesis?
NADPH.
What supplies energy for fatty acid formation?
ATP.
What is the first stage of fatty acid synthesis?
Production of acetyl CoA and NADPH.
What enzyme carboxylates acetyl CoA to form malonyl CoA?
Acetyl CoA carboxylase.
What is required for the carboxylation of acetyl CoA?
ATP and biotin.
What is the role of fatty acid synthase (FAS) complex?
Catalyzes all reactions in fatty acid synthesis.
How many different enzymes does each monomer of FAS possess?
Seven different enzymes.
What happens if the fatty acid synthase complex dissociates?
Loss of enzyme activities.
What is the main difference between eukaryotic and prokaryotic fatty acid synthesis?
Eukaryotes use a multifunctional enzyme complex, while prokaryotes use a multienzyme complex with a separate acyl carrier protein.
What is the role of Acyl Carrier Protein (ACP) in fatty acid synthesis?
ACP is involved in the transfer of acyl groups during the synthesis of fatty acids such as palmitate.
ACP is a key component of fatty acid synthase in eukaryotes.
What is the primary product of fatty acid synthesis described in the text?
Palmitate
Palmitate is a 16-carbon fully saturated fatty acid produced at the end of the synthesis process.
How many cycles are involved in the synthesis of palmitate?
7 cycles
Each cycle adds a two-carbon unit to the growing fatty acid chain.
What are the starting materials for the synthesis of palmitate?
Acetyl CoA and malonyl CoA
Acetyl CoA contributes two carbons, while the remaining 14 carbons come from malonyl CoA.
Fill in the blank: The enzyme that catalyzes the transfer of the acetyl unit to cysteine in fatty acid synthesis is called _______.
acetyl CoA-ACP transacylase
What is the function of malonyl CoA-ACP transacylase in fatty acid synthesis?
It transfers malonate from malonyl CoA to ACP
This step is crucial for adding carbon units to the growing fatty acid chain.
Which enzyme reduces the ketoacyl group to a hydroxyacyl group during fatty acid synthesis?
β-Ketoacyl-ACP reductase
What is the overall reaction for the synthesis of palmitate?
Acetyl CoA + 7 ATP + 14 NADPH + 14 H+ → Palmitate + 8 CoA + 7 ADP + 7 Pi + 6 H2O
True or False: The fatty acid synthase complex is a dimer composed of two identical subunits.
True
What is the significance of the fatty acid synthase (FAS) complex organization?
It provides efficiency and coordination in fatty acid synthesis
The multienzyme complex prevents interference from other cellular reactions.
Which enzyme controls a committed step in fatty acid synthesis?
Acetyl CoA carboxylase
How does citrate affect acetyl CoA carboxylase activity?
Citrate promotes polymer formation, increasing fatty acid synthesis.
What hormonal factors influence acetyl CoA carboxylase activity?
Insulin activates while glucagon, epinephrine, and norepinephrine inactivate it.
Fill in the blank: High carbohydrate or fat-free diets increase the synthesis of acetyl CoA carboxylase and _______.
fatty acid synthase
What is the primary source of NADPH for fatty acid synthesis?
Hexose monophosphate shunt
About 50-60% of required NADPH comes from this pathway.
What enzyme is responsible for the formation of unsaturated fatty acids?
Fatty acyl CoA desaturase
What is the role of flavin-dependent cytochrome b5 reductase in fatty acid metabolism?
It is involved in the desaturation of fatty acids
This process requires NADH and molecular O2.
List the components necessary for the overall reaction of palmitate synthesis.
- Acetyl CoA
- ATP
- NADPH
- H+
What happens to malonyl group during the synthesis process?
It loses CO2 during the reaction catalyzed by β-Ketoacyl ACP synthase.
What are the two functional subunits involved in fatty acid synthesis?
Malonyl and Acetyl
These subunits are crucial for the synthesis of fatty acids.
What is the role of ketoacyl synthase in fatty acid synthesis?
Catalyzes the condensation of acetyl and malonyl groups
This is a key step in the fatty acid elongation process.
Which fatty acids are synthesized from stearate and palmitate?
Stearic acid and palmitoleic acid
These fatty acids are synthesized through specific pathways in mammals.
What essential fatty acids must be included in the human diet?
- Linoleic acid (18:2; 9,12)
- Linolenic acid (18:3; 9,12,15)
These acids cannot be synthesized by mammals and must be obtained from the diet.
What is arachidonic acid and how is it synthesized?
Arachidonic acid (20:4; 5,8,11,14) can be synthesized from linoleic acid by desaturation and chain elongation
It is a precursor for eicosanoids.
Where does the synthesis of palmitate occur?
In the cytosol
Palmitate is the end product of fatty acid synthase reactions.
What are the two sites where chain elongation occurs?
- Mitochondria
- Endoplasmic reticulum (microsomes)
These sites utilize different mechanisms for elongating fatty acid chains.
What is the main enzyme group responsible for fatty acid chain elongation?
Elongases
These enzymes facilitate the addition of carbon units to fatty acids.
How does mitochondrial chain elongation differ from fatty acid synthesis?
It is almost a reversal of β-oxidation of fatty acids
Acetyl CoA molecules are added to lengthen the fatty acid chain.
What is the primary precursor for triacylglycerol synthesis?
Acyl CoA
Fatty acids must be activated to acyl CoA before they can be used.
In which tissues does triacylglycerol synthesis primarily occur?
- Liver
- Adipose tissue
These tissues are the main sites for TG synthesis.
What are the two mechanisms for synthesizing glycerol 3-phosphate?
- Glycerol kinase in the liver
- Conversion from dihydroxyacetone phosphate (DHAP)
DHAP is produced during glycolysis and is reduced to glycerol 3-phosphate.
What is the end product of the triacylglycerol synthesis pathway?
Triacylglycerol
The process involves several intermediates including lysophosphatidic acid and diacylglycerol.
What is the typical composition of fatty acids in triacylglycerol?
- Saturated fatty acid on carbon 1
- Unsaturated fatty acid on carbon 2
- Either type on carbon 3
This composition affects the physical properties of triacylglycerols.
What is the primary function of phospholipids?
Membrane structure and function
They also play roles in blood clotting and supply arachidonic acid.
What are the starting materials for phospholipid synthesis?
- Phosphatidic acid
- 1,2-diacylglycerol
These intermediates are produced during triacylglycerol synthesis.
What happens to choline and ethanolamine during phospholipid synthesis?
They are phosphorylated and then combine with CTP
This leads to the formation of CDP-choline and CDP-ethanolamine.
How is phosphatidylserine synthesized?
By exchanging the ethanolamine group of phosphatidyl ethanolamine with free serine
This reaction is reversible.
What is cardiolipin and its unique property?
A phospholipid possessing antigenic properties
It is formed from phosphatidylglycerol and plays a role in mitochondrial function.
What distinguishes plasmalogens from other phospholipids?
Fatty acid at carbon 1 bound by an ether linkage
Plasmalogens have unique functions, including platelet activation.
What is the structure of diacylglycerol?
Diacylglycerol consists of a glycerol backbone with two acyl groups attached to it
Diacylglycerol is a key intermediate in the synthesis of triacylglycerol and phospholipids.
What is the role of acyltransferase in lipid metabolism?
Acyltransferase catalyzes the transfer of acyl groups to form diacylglycerol and phospholipids
This enzyme plays a crucial role in the biosynthesis of lipids.
Fill in the blank: Phosphatidic acid is a precursor for the synthesis of _______.
triacylglycerol and phospholipids
What are the primary components of phospholipids?
Phospholipids are composed of a glycerol backbone, two fatty acid chains, and a phosphate group
The phosphate group may be further modified by alcohols such as choline or ethanolamine.
True or False: Cardiolipin is also known as diphosphatidylglycerol.
True
What is the function of phosphatidylglycerol?
Phosphatidylglycerol is involved in the structure of membranes and signaling pathways
It plays a significant role in mitochondrial membranes.
List the enzymes involved in the biosynthesis of phospholipids.
- Choline kinase
- Phosphocholine cytidyltransferase
- Phosphatidate phosphohydrolase
- Phosphocholine diacylglycerol transferase
- CTP–Phosphatidate cytidyltransferase
- CDP–Diacylglycerol inositol transferase
Fill in the blank: Glycerol 3-phosphate is also known as _______.
dihydroxyacetone phosphate
What is the significance of CDP-diacylglycerol in lipid metabolism?
CDP-diacylglycerol serves as an important intermediate in the synthesis of various phospholipids
It is crucial for the formation of phosphatidylinositol and cardiolipin.
What is the role of CTP in the biosynthesis of phospholipids?
CTP provides the cytidine monophosphate (CMP) required for the synthesis of CDP-diacylglycerol
This reaction is essential for creating the activated diacylglycerol precursor.
True or False: Phosphatidylserine is synthesized from serine and phosphatidic acid.
True
