Metabolism Of Lipids Flashcards
1
Q
What is cholesterol often referred to as?
A
The most feared among lipids
2
Q
How are lipids characterized in terms of their nature?
A
Hydrophobic and non-polar
3
Q
What percentage of body weight do lipids constitute in humans?
A
15-20%
4
Q
What are triacylglycerols also known as?
A
Triglycerides
5
Q
What is the primary role of triacylglycerols in the body?
A
Energy reserve
6
Q
How much energy do triacylglycerols yield per gram?
A
9 Cal/g
7
Q
What is the energy yield of carbohydrates and proteins per gram?
A
4 Cal/g
8
Q
What is the main reason fat is used as a fuel reserve in the body?
A
Highly concentrated form of energy
9
Q
What is the storage form of fat in the body?
A
Triacylglycerol
10
Q
How much fat is typically stored in a healthy adult weighing 70 kg?
A
10-11 kg
11
Q
What is the fuel reserve in calories for 10-11 kg of stored fat?
A
100,000 Cals
12
Q
What happens to body weight if energy is stored as glycogen instead of fat?
A
Weight would increase by at least 55 kg
13
Q
What are the main components of cell membranes?
A
Phospholipids, glycolipids, cholesterol
14
Q
What is the role of cholesterol in the body?
A
Precursor for bile acids and steroid hormones
15
Q
What are chylomicrons?
A
Lipoproteins that transport dietary lipids
16
Q
What are the different types of lipoproteins mentioned?
A
- Chylomicrons
- VLDL
- LDL
- HDL
17
Q
What is the process of breaking down triacylglycerol called?
A
Lipolysis
18
Q
What enzyme is responsible for the mobilization of fat from adipose tissue?
A
Hormone-sensitive triacylglycerol lipase
19
Q
True or False: Insulin increases the activity of hormone-sensitive TG-lipase.
A
False
20
Q
What happens to glycerol produced in lipolysis?
A
Transported to liver for activation
21
Q
What is the fate of free fatty acids released in adipocytes?
A
Transported in bound form to albumin
22
Q
What percentage of energy from fat comes from the oxidation of fatty acids?
A
95%
23
Q
What is the term for the process of hydrolyzing TG to free fatty acids during starvation?
A
Triacylglycerol/fatty acid cycle
24
Q
What is β-oxidation?
A
Oxidation of fatty acids on the β-carbon atom
25
What is the process of converting fatty acids into triacylglycerol termed?
Triacylglycerol/fatty acid cycle
## Footnote
This process involves the conversion of fatty acids back into triacylglycerols for storage.
26
What is the primary method of fatty acid oxidation in the body?
β-oxidation
## Footnote
This process occurs mainly in the mitochondria and involves the sequential removal of two-carbon fragments from fatty acids.
27
Define β-oxidation.
The oxidation of fatty acids on the β-carbon atom
## Footnote
This process results in the sequential removal of acetyl CoA.
28
In which cellular compartments does fatty acid oxidation occur?
Cytosol and mitochondrial matrix
## Footnote
The activation of fatty acids occurs in the cytosol, while β-oxidation takes place in the mitochondrial matrix.
29
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
## Footnote
Each stage plays a crucial role in the overall process of fatty acid metabolism.
30
What activates fatty acids for β-oxidation?
Acyl CoA formation
## Footnote
Fatty acids are activated to acyl CoA by thiokinases or acyl CoA synthetases.
31
What is required for the activation of fatty acids to acyl CoA?
* ATP
* Coenzyme A
* Mg2+
## Footnote
The activation process involves two steps and utilizes high-energy phosphates from ATP.
32
What enzyme catalyzes the conversion of acyl CoA to acyl-carnitine?
Carnitine acyltransferase I
## Footnote
This enzyme is located on the outer surface of the inner mitochondrial membrane.
33
Fill in the blank: The enzyme that converts acyl-carnitine back to acyl CoA is called _______.
Carnitine acyltransferase II
## Footnote
This enzyme is found on the inner surface of the inner mitochondrial membrane.
34
True or False: The inner mitochondrial membrane is permeable to fatty acids.
False
## Footnote
Fatty acids cannot pass through the inner mitochondrial membrane without being converted to acyl-carnitine.
35
What inhibits the carnitine shuttle during fatty acid oxidation?
Malonyl CoA
## Footnote
Malonyl CoA is a key metabolite involved in fatty acid synthesis and prevents the transport of fatty acids into the mitochondria.
36
What are the four reactions that occur in each cycle of β-oxidation?
* Oxidation
* Hydration
* Oxidation
* Cleavage
## Footnote
Each reaction is catalyzed by specific enzymes that facilitate the breakdown of fatty acids.
37
What is the final product of each cycle of β-oxidation?
Acetyl CoA
## Footnote
Each cycle liberates a two-carbon unit, acetyl CoA, from the fatty acid chain.
38
What is the total ATP yield from one molecule of palmitoyl CoA after β-oxidation?
129 ATP
## Footnote
This includes ATP generated during β-oxidation and the citric acid cycle.
39
How many cycles of β-oxidation occur for palmitoyl CoA?
7 cycles
## Footnote
Each cycle removes two carbons from the fatty acid chain until it is completely oxidized.
40
What is the efficiency of energy conservation by fatty acid oxidation?
40%
## Footnote
This is based on the energy yield from the complete oxidation of palmitic acid.
41
What are the products of the overall reaction for each cycle of β-oxidation?
* C(n-2) Acyl CoA
* Acetyl CoA
* FADH2
* NADH
* H+
## Footnote
This reaction reflects the breakdown of fatty acids into usable energy forms.
42
What is the primary function of carnitine in fatty acid metabolism?
Transport of activated fatty acids (acyl CoA) into mitochondria
## Footnote
The carnitine shuttle is essential for fatty acid oxidation.
43
What syndrome is associated with a deficiency in medium chain acyl CoA dehydrogenase?
Sudden Infant Death Syndrome (SIDS)
## Footnote
It is estimated that at least 10% of SIDS cases are due to this deficiency.
44
What is the estimated frequency of medium chain acyl CoA dehydrogenase deficiency?
1 in 10,000 births
## Footnote
This condition is more prevalent than phenylketonuria.
45
What is the principal energy source for infants shortly after feeding?
Glucose
## Footnote
After a few hours, glucose levels decrease, requiring an increase in fatty acid oxidation.
46
What causes the sudden death in infants with MCAD deficiency?
Blockade in β-oxidation
## Footnote
This is due to the inability to oxidize fatty acids for energy.
47
What is Jamaican vomiting sickness caused by?
Eating unripe ackee fruit containing hypoglycin A
## Footnote
This toxin inhibits acyl CoA dehydrogenase.
48
What is the first step in β-oxidation of fatty acids?
Activation of fatty acid to acyl CoA
## Footnote
This step requires ATP and CoA.
49
What is the end product of β-oxidation of palmitic acid (16 carbons)?
8 Acetyl CoA
## Footnote
This process involves seven cycles of β-oxidation.
50
What is the fate of odd carbon chain fatty acids during β-oxidation?
Produce propionyl CoA, which is converted to succinyl CoA
## Footnote
This conversion is essential for entry into the citric acid cycle.
51
What vitamin is required for the conversion of methylmalonyl CoA to succinyl CoA?
Vitamin B12
## Footnote
This is crucial for proper metabolic function.
52
What are the two types of methylmalonic acidemias?
* Due to deficiency of vitamin B12
* Due to defect in methylmalonyl CoA mutase
## Footnote
Both types lead to accumulation of methylmalonic acid.
53
What is a characteristic of oxidation of unsaturated fatty acids compared to saturated fatty acids?
Provides less energy due to double bonds
## Footnote
Additional enzymes (isomerase and epimerase) are needed to facilitate the process.
54
Where does β-oxidation of fatty acids occur in peroxisomes?
In a modified form, leading to the formation of H2O2
## Footnote
This process does not produce ATP but generates heat.
55
What is Zellweger syndrome?
A disorder characterized by the absence of peroxisomes in tissues
## Footnote
It leads to accumulation of long-chain fatty acids in the brain, liver, and kidney.
56
What is α-oxidation of fatty acids?
Removal of one carbon unit at a time from the α-carbon of fatty acid
## Footnote
This process does not involve the binding of fatty acids to coenzyme A.
57
What is Refsum's disease characterized by?
Cerebral ataxia and peripheral neuropathy
## Footnote
It involves accumulation of phytanic acid due to a defect in α-oxidation.
58
What prevents phytanic acid from undergoing β-oxidation?
Presence of a methyl group on carbon-3
## Footnote
This necessitates initial α-oxidation before β-oxidation can occur.
59
What is Refsum’s disease caused by?
A defect in -oxidation due to the deficiency of the enzyme phytanic acid -oxidase.
60
What dietary restriction is advised for patients with Refsum’s disease?
Patients should not consume diets containing chlorophyll (i.e., green leafy vegetables).
61
What is the process of -oxidation of fatty acids?
It involves hydroxylation followed by oxidation of the -carbon present as a methyl group.
62
What are the requirements for the -oxidation reaction?
Cytochrome P450, NADPH, O2, and specific enzymes.
63
What is metabolic water?
Water produced during the oxidation of fatty acids and aerobic respiration.
64
Which animal can store lipids in its hump for energy and water supply?
Camel.
65
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.
66
What are ketone bodies?
Compounds namely acetone, acetoacetate, and -hydroxybutyrate.
67
Which two ketone bodies are considered true ketones?
Acetone and acetoacetate.
68
Where does ketogenesis occur?
In the liver.
69
What is the precursor for ketone bodies?
Acetyl CoA.
70
What enzyme catalyzes the condensation of two moles of acetyl CoA?
Thiolase.
71
What is the role of HMG CoA synthase in ketogenesis?
It regulates the synthesis of ketone bodies.
72
What happens to acetoacetate during ketone body metabolism?
It can undergo spontaneous decarboxylation to form acetone.
73
Which tissues can utilize ketone bodies?
Skeletal muscle, cardiac muscle, renal cortex, etc.
74
Which tissues cannot utilize ketone bodies?
Erythrocytes (they lack mitochondria).
75
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.
76
What is the result of prolonged starvation regarding ketone bodies?
Ketone bodies become the major fuel source for the brain and central nervous system.
77
What is the process by which -hydroxybutyrate is used?
It is converted to acetoacetate and metabolized.
78
What is the consequence of overproduction of ketone bodies?
Ketonemia, where concentration in blood increases.
79
What does the term ketonuria represent?
The excretion of ketone bodies in urine.
80
What is ketosis?
The overall condition involving ketonemia and ketonuria.
81
What is the smell associated with ketosis?
The smell of acetone.
82
What condition is associated with uncontrolled diabetes mellitus?
Ketosis, which can lead to diabetic ketoacidosis.
83
What is the difference between starvation and ketoacidosis?
Starvation is not accompanied by ketoacidosis.
84
What is the role of insulin in fatty acid synthesis?
It promotes fatty acid synthesis by stimulating the conversion of pyruvate to acetyl CoA.
85
What makes linoleic and linolenic acids essential to mammals?
The lack of ability to introduce double bonds in fatty acids beyond C9 and C10.
86
What is methylmalonic acidemia caused by?
Deficiency of vitamin B12 or a defect in methyl malonyl CoA mutase.
87
What syndrome is attributed to a blockade in -oxidation of fatty acids?
Sudden infant death syndrome (SIDS).
88
What is Jamaican vomiting sickness caused by?
Consumption of unripe ackee fruit containing hypoglycin A.
89
What are the effects of Zellweger syndrome?
Absence of peroxisomes in tissues, preventing oxidation of long-chain fatty acids.
90
What is Ketonemia primarily due to?
Increased production of ketone bodies rather than deficiency in their utilization.
91
What does Ketonuria represent?
The excretion of ketone bodies in urine.
92
What is the overall picture of ketonemia and ketonuria commonly referred to as?
Ketosis.
93
What is a common feature of ketosis?
Smell of acetone in breath.
94
What is starvation accompanied by?
Increased degradation of fatty acids to meet energy needs.
95
What causes an overproduction of acetyl CoA during starvation?
Inability to fully handle acetyl CoA by the citric acid cycle.
96
What is the result of the impaired TCA cycle during starvation?
Accumulation of acetyl CoA and overproduction of ketone bodies.
97
What does the appearance of ketone bodies in urine indicate?
Active fat metabolism.
98
What dietary changes do weight loss programs often encourage?
Reduction in carbohydrate and total calorie intake.
99
What is diabetes mellitus associated with?
Insulin deficiency.
100
What leads to the accumulation of acetyl CoA in severe diabetes?
Impaired carbohydrate metabolism and increased lipolysis.
101
What does the concentration of ketone bodies in blood plasma reach in severe diabetes?
Up to 100 mg/dl.
102
What promotes ketone body formation?
Increased ratio of glucagon to insulin.
103
What are ketogenic substances?
Fatty acids and certain amino acids (e.g., leucine, lysine, tyrosine).
104
What are antiketogenic substances?
Glucose, glycerol, and glucogenic amino acids (e.g., glycine, alanine, serine, glutamate).
105
True or False: Both acetoacetate and β-hydroxybutyrate are weak acids.
False.
106
What can an increase in ketone body concentration in blood cause?
Acidosis.
107
What is diabetic ketoacidosis?
A dangerous condition that can result in coma or death if untreated.
108
What is the primary source of carbon atoms for fatty acid synthesis?
Acetyl CoA.
109
What provides the reducing equivalents for fatty acid synthesis?
NADPH.
110
What supplies energy for fatty acid formation?
ATP.
111
What is the first stage of fatty acid synthesis?
Production of acetyl CoA and NADPH.
112
What enzyme carboxylates acetyl CoA to form malonyl CoA?
Acetyl CoA carboxylase.
113
What is required for the carboxylation of acetyl CoA?
ATP and biotin.
114
What is the role of fatty acid synthase (FAS) complex?
Catalyzes all reactions in fatty acid synthesis.
115
How many different enzymes does each monomer of FAS possess?
Seven different enzymes.
116
What happens if the fatty acid synthase complex dissociates?
Loss of enzyme activities.
117
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.
118
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.
## Footnote
ACP is a key component of fatty acid synthase in eukaryotes.
119
What is the primary product of fatty acid synthesis described in the text?
Palmitate
## Footnote
Palmitate is a 16-carbon fully saturated fatty acid produced at the end of the synthesis process.
120
How many cycles are involved in the synthesis of palmitate?
7 cycles
## Footnote
Each cycle adds a two-carbon unit to the growing fatty acid chain.
121
What are the starting materials for the synthesis of palmitate?
Acetyl CoA and malonyl CoA
## Footnote
Acetyl CoA contributes two carbons, while the remaining 14 carbons come from malonyl CoA.
122
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
123
What is the function of malonyl CoA-ACP transacylase in fatty acid synthesis?
It transfers malonate from malonyl CoA to ACP
## Footnote
This step is crucial for adding carbon units to the growing fatty acid chain.
124
Which enzyme reduces the ketoacyl group to a hydroxyacyl group during fatty acid synthesis?
β-Ketoacyl-ACP reductase
125
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
126
True or False: The fatty acid synthase complex is a dimer composed of two identical subunits.
True
127
What is the significance of the fatty acid synthase (FAS) complex organization?
It provides efficiency and coordination in fatty acid synthesis
## Footnote
The multienzyme complex prevents interference from other cellular reactions.
128
Which enzyme controls a committed step in fatty acid synthesis?
Acetyl CoA carboxylase
129
How does citrate affect acetyl CoA carboxylase activity?
Citrate promotes polymer formation, increasing fatty acid synthesis.
130
What hormonal factors influence acetyl CoA carboxylase activity?
Insulin activates while glucagon, epinephrine, and norepinephrine inactivate it.
131
Fill in the blank: High carbohydrate or fat-free diets increase the synthesis of acetyl CoA carboxylase and _______.
fatty acid synthase
132
What is the primary source of NADPH for fatty acid synthesis?
Hexose monophosphate shunt
## Footnote
About 50-60% of required NADPH comes from this pathway.
133
What enzyme is responsible for the formation of unsaturated fatty acids?
Fatty acyl CoA desaturase
134
What is the role of flavin-dependent cytochrome b5 reductase in fatty acid metabolism?
It is involved in the desaturation of fatty acids
## Footnote
This process requires NADH and molecular O2.
135
List the components necessary for the overall reaction of palmitate synthesis.
* Acetyl CoA
* ATP
* NADPH
* H+
136
What happens to malonyl group during the synthesis process?
It loses CO2 during the reaction catalyzed by β-Ketoacyl ACP synthase.
137
What are the two functional subunits involved in fatty acid synthesis?
Malonyl and Acetyl
## Footnote
These subunits are crucial for the synthesis of fatty acids.
138
What is the role of ketoacyl synthase in fatty acid synthesis?
Catalyzes the condensation of acetyl and malonyl groups
## Footnote
This is a key step in the fatty acid elongation process.
139
Which fatty acids are synthesized from stearate and palmitate?
Stearic acid and palmitoleic acid
## Footnote
These fatty acids are synthesized through specific pathways in mammals.
140
What essential fatty acids must be included in the human diet?
* Linoleic acid (18:2; 9,12)
* Linolenic acid (18:3; 9,12,15)
## Footnote
These acids cannot be synthesized by mammals and must be obtained from the diet.
141
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
## Footnote
It is a precursor for eicosanoids.
142
Where does the synthesis of palmitate occur?
In the cytosol
## Footnote
Palmitate is the end product of fatty acid synthase reactions.
143
What are the two sites where chain elongation occurs?
* Mitochondria
* Endoplasmic reticulum (microsomes)
## Footnote
These sites utilize different mechanisms for elongating fatty acid chains.
144
What is the main enzyme group responsible for fatty acid chain elongation?
Elongases
## Footnote
These enzymes facilitate the addition of carbon units to fatty acids.
145
How does mitochondrial chain elongation differ from fatty acid synthesis?
It is almost a reversal of β-oxidation of fatty acids
## Footnote
Acetyl CoA molecules are added to lengthen the fatty acid chain.
146
What is the primary precursor for triacylglycerol synthesis?
Acyl CoA
## Footnote
Fatty acids must be activated to acyl CoA before they can be used.
147
In which tissues does triacylglycerol synthesis primarily occur?
* Liver
* Adipose tissue
## Footnote
These tissues are the main sites for TG synthesis.
148
What are the two mechanisms for synthesizing glycerol 3-phosphate?
* Glycerol kinase in the liver
* Conversion from dihydroxyacetone phosphate (DHAP)
## Footnote
DHAP is produced during glycolysis and is reduced to glycerol 3-phosphate.
149
What is the end product of the triacylglycerol synthesis pathway?
Triacylglycerol
## Footnote
The process involves several intermediates including lysophosphatidic acid and diacylglycerol.
150
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
## Footnote
This composition affects the physical properties of triacylglycerols.
151
What is the primary function of phospholipids?
Membrane structure and function
## Footnote
They also play roles in blood clotting and supply arachidonic acid.
152
What are the starting materials for phospholipid synthesis?
* Phosphatidic acid
* 1,2-diacylglycerol
## Footnote
These intermediates are produced during triacylglycerol synthesis.
153
What happens to choline and ethanolamine during phospholipid synthesis?
They are phosphorylated and then combine with CTP
## Footnote
This leads to the formation of CDP-choline and CDP-ethanolamine.
154
How is phosphatidylserine synthesized?
By exchanging the ethanolamine group of phosphatidyl ethanolamine with free serine
## Footnote
This reaction is reversible.
155
What is cardiolipin and its unique property?
A phospholipid possessing antigenic properties
## Footnote
It is formed from phosphatidylglycerol and plays a role in mitochondrial function.
156
What distinguishes plasmalogens from other phospholipids?
Fatty acid at carbon 1 bound by an ether linkage
## Footnote
Plasmalogens have unique functions, including platelet activation.
157
What is the structure of diacylglycerol?
Diacylglycerol consists of a glycerol backbone with two acyl groups attached to it
## Footnote
Diacylglycerol is a key intermediate in the synthesis of triacylglycerol and phospholipids.
158
What is the role of acyltransferase in lipid metabolism?
Acyltransferase catalyzes the transfer of acyl groups to form diacylglycerol and phospholipids
## Footnote
This enzyme plays a crucial role in the biosynthesis of lipids.
159
Fill in the blank: Phosphatidic acid is a precursor for the synthesis of _______.
triacylglycerol and phospholipids
160
What are the primary components of phospholipids?
Phospholipids are composed of a glycerol backbone, two fatty acid chains, and a phosphate group
## Footnote
The phosphate group may be further modified by alcohols such as choline or ethanolamine.
161
True or False: Cardiolipin is also known as diphosphatidylglycerol.
True
162
What is the function of phosphatidylglycerol?
Phosphatidylglycerol is involved in the structure of membranes and signaling pathways
## Footnote
It plays a significant role in mitochondrial membranes.
163
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
164
Fill in the blank: Glycerol 3-phosphate is also known as _______.
dihydroxyacetone phosphate
165
What is the significance of CDP-diacylglycerol in lipid metabolism?
CDP-diacylglycerol serves as an important intermediate in the synthesis of various phospholipids
## Footnote
It is crucial for the formation of phosphatidylinositol and cardiolipin.
166
What is the role of CTP in the biosynthesis of phospholipids?
CTP provides the cytidine monophosphate (CMP) required for the synthesis of CDP-diacylglycerol
## Footnote
This reaction is essential for creating the activated diacylglycerol precursor.
167
True or False: Phosphatidylserine is synthesized from serine and phosphatidic acid.
True
