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Biochemistry: Metabolism Of Lipids > Metabolism Of Lipids > Flashcards

Metabolism Of Lipids Flashcards

1
Q

What is cholesterol often referred to as?

A

The most feared among lipids

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2
Q

How are lipids characterized in terms of their nature?

A

Hydrophobic and non-polar

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3
Q

What percentage of body weight do lipids constitute in humans?

A

15-20%

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4
Q

What are triacylglycerols also known as?

A

Triglycerides

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5
Q

What is the primary role of triacylglycerols in the body?

A

Energy reserve

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6
Q

How much energy do triacylglycerols yield per gram?

A

9 Cal/g

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7
Q

What is the energy yield of carbohydrates and proteins per gram?

A

4 Cal/g

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8
Q

What is the main reason fat is used as a fuel reserve in the body?

A

Highly concentrated form of energy

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9
Q

What is the storage form of fat in the body?

A

Triacylglycerol

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10
Q

How much fat is typically stored in a healthy adult weighing 70 kg?

A

10-11 kg

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11
Q

What is the fuel reserve in calories for 10-11 kg of stored fat?

A

100,000 Cals

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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

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13
Q

What are the main components of cell membranes?

A

Phospholipids, glycolipids, cholesterol

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14
Q

What is the role of cholesterol in the body?

A

Precursor for bile acids and steroid hormones

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15
Q

What are chylomicrons?

A

Lipoproteins that transport dietary lipids

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16
Q

What are the different types of lipoproteins mentioned?

A
  • Chylomicrons
  • VLDL
  • LDL
  • HDL
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17
Q

What is the process of breaking down triacylglycerol called?

A

Lipolysis

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18
Q

What enzyme is responsible for the mobilization of fat from adipose tissue?

A

Hormone-sensitive triacylglycerol lipase

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19
Q

True or False: Insulin increases the activity of hormone-sensitive TG-lipase.

A

False

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20
Q

What happens to glycerol produced in lipolysis?

A

Transported to liver for activation

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21
Q

What is the fate of free fatty acids released in adipocytes?

A

Transported in bound form to albumin

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22
Q

What percentage of energy from fat comes from the oxidation of fatty acids?

A

95%

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23
Q

What is the term for the process of hydrolyzing TG to free fatty acids during starvation?

A

Triacylglycerol/fatty acid cycle

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24
Q

What is β-oxidation?

A

Oxidation of fatty acids on the β-carbon atom

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25
Q

What is the process of converting fatty acids into triacylglycerol termed?

A

Triacylglycerol/fatty acid cycle

This process involves the conversion of fatty acids back into triacylglycerols for storage.

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26
Q

What is the primary method of fatty acid oxidation in the body?

A

β-oxidation

This process occurs mainly in the mitochondria and involves the sequential removal of two-carbon fragments from fatty acids.

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27
Q

Define β-oxidation.

A

The oxidation of fatty acids on the β-carbon atom

This process results in the sequential removal of acetyl CoA.

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28
Q

In which cellular compartments does fatty acid oxidation occur?

A

Cytosol and mitochondrial matrix

The activation of fatty acids occurs in the cytosol, while β-oxidation takes place in the mitochondrial matrix.

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29
Q

What are the three stages of β-oxidation?

A
  • 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.

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30
Q

What activates fatty acids for β-oxidation?

A

Acyl CoA formation

Fatty acids are activated to acyl CoA by thiokinases or acyl CoA synthetases.

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31
Q

What is required for the activation of fatty acids to acyl CoA?

A
  • ATP
  • Coenzyme A
  • Mg2+

The activation process involves two steps and utilizes high-energy phosphates from ATP.

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32
Q

What enzyme catalyzes the conversion of acyl CoA to acyl-carnitine?

A

Carnitine acyltransferase I

This enzyme is located on the outer surface of the inner mitochondrial membrane.

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33
Q

Fill in the blank: The enzyme that converts acyl-carnitine back to acyl CoA is called _______.

A

Carnitine acyltransferase II

This enzyme is found on the inner surface of the inner mitochondrial membrane.

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34
Q

True or False: The inner mitochondrial membrane is permeable to fatty acids.

A

False

Fatty acids cannot pass through the inner mitochondrial membrane without being converted to acyl-carnitine.

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35
Q

What inhibits the carnitine shuttle during fatty acid oxidation?

A

Malonyl CoA

Malonyl CoA is a key metabolite involved in fatty acid synthesis and prevents the transport of fatty acids into the mitochondria.

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36
Q

What are the four reactions that occur in each cycle of β-oxidation?

A
  • Oxidation
  • Hydration
  • Oxidation
  • Cleavage

Each reaction is catalyzed by specific enzymes that facilitate the breakdown of fatty acids.

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37
Q

What is the final product of each cycle of β-oxidation?

A

Acetyl CoA

Each cycle liberates a two-carbon unit, acetyl CoA, from the fatty acid chain.

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38
Q

What is the total ATP yield from one molecule of palmitoyl CoA after β-oxidation?

A

129 ATP

This includes ATP generated during β-oxidation and the citric acid cycle.

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39
Q

How many cycles of β-oxidation occur for palmitoyl CoA?

A

7 cycles

Each cycle removes two carbons from the fatty acid chain until it is completely oxidized.

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40
Q

What is the efficiency of energy conservation by fatty acid oxidation?

A

40%

This is based on the energy yield from the complete oxidation of palmitic acid.

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41
Q

What are the products of the overall reaction for each cycle of β-oxidation?

A
  • C(n-2) Acyl CoA
  • Acetyl CoA
  • FADH2
  • NADH
  • H+

This reaction reflects the breakdown of fatty acids into usable energy forms.

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42
Q

What is the primary function of carnitine in fatty acid metabolism?

A

Transport of activated fatty acids (acyl CoA) into mitochondria

The carnitine shuttle is essential for fatty acid oxidation.

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43
Q

What syndrome is associated with a deficiency in medium chain acyl CoA dehydrogenase?

A

Sudden Infant Death Syndrome (SIDS)

It is estimated that at least 10% of SIDS cases are due to this deficiency.

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44
Q

What is the estimated frequency of medium chain acyl CoA dehydrogenase deficiency?

A

1 in 10,000 births

This condition is more prevalent than phenylketonuria.

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45
Q

What is the principal energy source for infants shortly after feeding?

A

Glucose

After a few hours, glucose levels decrease, requiring an increase in fatty acid oxidation.

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46
Q

What causes the sudden death in infants with MCAD deficiency?

A

Blockade in β-oxidation

This is due to the inability to oxidize fatty acids for energy.

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47
Q

What is Jamaican vomiting sickness caused by?

A

Eating unripe ackee fruit containing hypoglycin A

This toxin inhibits acyl CoA dehydrogenase.

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48
Q

What is the first step in β-oxidation of fatty acids?

A

Activation of fatty acid to acyl CoA

This step requires ATP and CoA.

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49
Q

What is the end product of β-oxidation of palmitic acid (16 carbons)?

A

8 Acetyl CoA

This process involves seven cycles of β-oxidation.

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50
Q

What is the fate of odd carbon chain fatty acids during β-oxidation?

A

Produce propionyl CoA, which is converted to succinyl CoA

This conversion is essential for entry into the citric acid cycle.

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51
Q

What vitamin is required for the conversion of methylmalonyl CoA to succinyl CoA?

A

Vitamin B12

This is crucial for proper metabolic function.

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52
Q

What are the two types of methylmalonic acidemias?

A
  • Due to deficiency of vitamin B12
  • Due to defect in methylmalonyl CoA mutase

Both types lead to accumulation of methylmalonic acid.

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53
Q

What is a characteristic of oxidation of unsaturated fatty acids compared to saturated fatty acids?

A

Provides less energy due to double bonds

Additional enzymes (isomerase and epimerase) are needed to facilitate the process.

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54
Q

Where does β-oxidation of fatty acids occur in peroxisomes?

A

In a modified form, leading to the formation of H2O2

This process does not produce ATP but generates heat.

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55
Q

What is Zellweger syndrome?

A

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.

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56
Q

What is α-oxidation of fatty acids?

A

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.

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57
Q

What is Refsum’s disease characterized by?

A

Cerebral ataxia and peripheral neuropathy

It involves accumulation of phytanic acid due to a defect in α-oxidation.

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58
Q

What prevents phytanic acid from undergoing β-oxidation?

A

Presence of a methyl group on carbon-3

This necessitates initial α-oxidation before β-oxidation can occur.

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59
Q

What is Refsum’s disease caused by?

A

A defect in -oxidation due to the deficiency of the enzyme phytanic acid -oxidase.

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60
Q

What dietary restriction is advised for patients with Refsum’s disease?

A

Patients should not consume diets containing chlorophyll (i.e., green leafy vegetables).

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61
Q

What is the process of -oxidation of fatty acids?

A

It involves hydroxylation followed by oxidation of the -carbon present as a methyl group.

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62
Q

What are the requirements for the -oxidation reaction?

A

Cytochrome P450, NADPH, O2, and specific enzymes.

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63
Q

What is metabolic water?

A

Water produced during the oxidation of fatty acids and aerobic respiration.

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64
Q

Which animal can store lipids in its hump for energy and water supply?

A

Camel.

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65
Q

What is the significance of metabolic water in the kangaroo rat?

A

It allows the kangaroo rat to live indefinitely without water by consuming only oil-rich seeds.

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66
Q

What are ketone bodies?

A

Compounds namely acetone, acetoacetate, and -hydroxybutyrate.

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67
Q

Which two ketone bodies are considered true ketones?

A

Acetone and acetoacetate.

68
Q

Where does ketogenesis occur?

A

In the liver.

69
Q

What is the precursor for ketone bodies?

A

Acetyl CoA.

70
Q

What enzyme catalyzes the condensation of two moles of acetyl CoA?

A

Thiolase.

71
Q

What is the role of HMG CoA synthase in ketogenesis?

A

It regulates the synthesis of ketone bodies.

72
Q

What happens to acetoacetate during ketone body metabolism?

A

It can undergo spontaneous decarboxylation to form acetone.

73
Q

Which tissues can utilize ketone bodies?

A

Skeletal muscle, cardiac muscle, renal cortex, etc.

74
Q

Which tissues cannot utilize ketone bodies?

A

Erythrocytes (they lack mitochondria).

75
Q

What is the brain’s ability to utilize fatty acids for energy?

A

Very limited; ketone bodies can meet 50-70% of the brain’s energy needs.

76
Q

What is the result of prolonged starvation regarding ketone bodies?

A

Ketone bodies become the major fuel source for the brain and central nervous system.

77
Q

What is the process by which -hydroxybutyrate is used?

A

It is converted to acetoacetate and metabolized.

78
Q

What is the consequence of overproduction of ketone bodies?

A

Ketonemia, where concentration in blood increases.

79
Q

What does the term ketonuria represent?

A

The excretion of ketone bodies in urine.

80
Q

What is ketosis?

A

The overall condition involving ketonemia and ketonuria.

81
Q

What is the smell associated with ketosis?

A

The smell of acetone.

82
Q

What condition is associated with uncontrolled diabetes mellitus?

A

Ketosis, which can lead to diabetic ketoacidosis.

83
Q

What is the difference between starvation and ketoacidosis?

A

Starvation is not accompanied by ketoacidosis.

84
Q

What is the role of insulin in fatty acid synthesis?

A

It promotes fatty acid synthesis by stimulating the conversion of pyruvate to acetyl CoA.

85
Q

What makes linoleic and linolenic acids essential to mammals?

A

The lack of ability to introduce double bonds in fatty acids beyond C9 and C10.

86
Q

What is methylmalonic acidemia caused by?

A

Deficiency of vitamin B12 or a defect in methyl malonyl CoA mutase.

87
Q

What syndrome is attributed to a blockade in -oxidation of fatty acids?

A

Sudden infant death syndrome (SIDS).

88
Q

What is Jamaican vomiting sickness caused by?

A

Consumption of unripe ackee fruit containing hypoglycin A.

89
Q

What are the effects of Zellweger syndrome?

A

Absence of peroxisomes in tissues, preventing oxidation of long-chain fatty acids.

90
Q

What is Ketonemia primarily due to?

A

Increased production of ketone bodies rather than deficiency in their utilization.

91
Q

What does Ketonuria represent?

A

The excretion of ketone bodies in urine.

92
Q

What is the overall picture of ketonemia and ketonuria commonly referred to as?

A

Ketosis.

93
Q

What is a common feature of ketosis?

A

Smell of acetone in breath.

94
Q

What is starvation accompanied by?

A

Increased degradation of fatty acids to meet energy needs.

95
Q

What causes an overproduction of acetyl CoA during starvation?

A

Inability to fully handle acetyl CoA by the citric acid cycle.

96
Q

What is the result of the impaired TCA cycle during starvation?

A

Accumulation of acetyl CoA and overproduction of ketone bodies.

97
Q

What does the appearance of ketone bodies in urine indicate?

A

Active fat metabolism.

98
Q

What dietary changes do weight loss programs often encourage?

A

Reduction in carbohydrate and total calorie intake.

99
Q

What is diabetes mellitus associated with?

A

Insulin deficiency.

100
Q

What leads to the accumulation of acetyl CoA in severe diabetes?

A

Impaired carbohydrate metabolism and increased lipolysis.

101
Q

What does the concentration of ketone bodies in blood plasma reach in severe diabetes?

A

Up to 100 mg/dl.

102
Q

What promotes ketone body formation?

A

Increased ratio of glucagon to insulin.

103
Q

What are ketogenic substances?

A

Fatty acids and certain amino acids (e.g., leucine, lysine, tyrosine).

104
Q

What are antiketogenic substances?

A

Glucose, glycerol, and glucogenic amino acids (e.g., glycine, alanine, serine, glutamate).

105
Q

True or False: Both acetoacetate and β-hydroxybutyrate are weak acids.

A

False.

106
Q

What can an increase in ketone body concentration in blood cause?

A

Acidosis.

107
Q

What is diabetic ketoacidosis?

A

A dangerous condition that can result in coma or death if untreated.

108
Q

What is the primary source of carbon atoms for fatty acid synthesis?

A

Acetyl CoA.

109
Q

What provides the reducing equivalents for fatty acid synthesis?

A

NADPH.

110
Q

What supplies energy for fatty acid formation?

A

ATP.

111
Q

What is the first stage of fatty acid synthesis?

A

Production of acetyl CoA and NADPH.

112
Q

What enzyme carboxylates acetyl CoA to form malonyl CoA?

A

Acetyl CoA carboxylase.

113
Q

What is required for the carboxylation of acetyl CoA?

A

ATP and biotin.

114
Q

What is the role of fatty acid synthase (FAS) complex?

A

Catalyzes all reactions in fatty acid synthesis.

115
Q

How many different enzymes does each monomer of FAS possess?

A

Seven different enzymes.

116
Q

What happens if the fatty acid synthase complex dissociates?

A

Loss of enzyme activities.

117
Q

What is the main difference between eukaryotic and prokaryotic fatty acid synthesis?

A

Eukaryotes use a multifunctional enzyme complex, while prokaryotes use a multienzyme complex with a separate acyl carrier protein.

118
Q

What is the role of Acyl Carrier Protein (ACP) in fatty acid synthesis?

A

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.

119
Q

What is the primary product of fatty acid synthesis described in the text?

A

Palmitate

Palmitate is a 16-carbon fully saturated fatty acid produced at the end of the synthesis process.

120
Q

How many cycles are involved in the synthesis of palmitate?

A

7 cycles

Each cycle adds a two-carbon unit to the growing fatty acid chain.

121
Q

What are the starting materials for the synthesis of palmitate?

A

Acetyl CoA and malonyl CoA

Acetyl CoA contributes two carbons, while the remaining 14 carbons come from malonyl CoA.

122
Q

Fill in the blank: The enzyme that catalyzes the transfer of the acetyl unit to cysteine in fatty acid synthesis is called _______.

A

acetyl CoA-ACP transacylase

123
Q

What is the function of malonyl CoA-ACP transacylase in fatty acid synthesis?

A

It transfers malonate from malonyl CoA to ACP

This step is crucial for adding carbon units to the growing fatty acid chain.

124
Q

Which enzyme reduces the ketoacyl group to a hydroxyacyl group during fatty acid synthesis?

A

β-Ketoacyl-ACP reductase

125
Q

What is the overall reaction for the synthesis of palmitate?

A

Acetyl CoA + 7 ATP + 14 NADPH + 14 H+ → Palmitate + 8 CoA + 7 ADP + 7 Pi + 6 H2O

126
Q

True or False: The fatty acid synthase complex is a dimer composed of two identical subunits.

A

True

127
Q

What is the significance of the fatty acid synthase (FAS) complex organization?

A

It provides efficiency and coordination in fatty acid synthesis

The multienzyme complex prevents interference from other cellular reactions.

128
Q

Which enzyme controls a committed step in fatty acid synthesis?

A

Acetyl CoA carboxylase

129
Q

How does citrate affect acetyl CoA carboxylase activity?

A

Citrate promotes polymer formation, increasing fatty acid synthesis.

130
Q

What hormonal factors influence acetyl CoA carboxylase activity?

A

Insulin activates while glucagon, epinephrine, and norepinephrine inactivate it.

131
Q

Fill in the blank: High carbohydrate or fat-free diets increase the synthesis of acetyl CoA carboxylase and _______.

A

fatty acid synthase

132
Q

What is the primary source of NADPH for fatty acid synthesis?

A

Hexose monophosphate shunt

About 50-60% of required NADPH comes from this pathway.

133
Q

What enzyme is responsible for the formation of unsaturated fatty acids?

A

Fatty acyl CoA desaturase

134
Q

What is the role of flavin-dependent cytochrome b5 reductase in fatty acid metabolism?

A

It is involved in the desaturation of fatty acids

This process requires NADH and molecular O2.

135
Q

List the components necessary for the overall reaction of palmitate synthesis.

A
  • Acetyl CoA
  • ATP
  • NADPH
  • H+
136
Q

What happens to malonyl group during the synthesis process?

A

It loses CO2 during the reaction catalyzed by β-Ketoacyl ACP synthase.

137
Q

What are the two functional subunits involved in fatty acid synthesis?

A

Malonyl and Acetyl

These subunits are crucial for the synthesis of fatty acids.

138
Q

What is the role of ketoacyl synthase in fatty acid synthesis?

A

Catalyzes the condensation of acetyl and malonyl groups

This is a key step in the fatty acid elongation process.

139
Q

Which fatty acids are synthesized from stearate and palmitate?

A

Stearic acid and palmitoleic acid

These fatty acids are synthesized through specific pathways in mammals.

140
Q

What essential fatty acids must be included in the human diet?

A
  • 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.

141
Q

What is arachidonic acid and how is it synthesized?

A

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.

142
Q

Where does the synthesis of palmitate occur?

A

In the cytosol

Palmitate is the end product of fatty acid synthase reactions.

143
Q

What are the two sites where chain elongation occurs?

A
  • Mitochondria
  • Endoplasmic reticulum (microsomes)

These sites utilize different mechanisms for elongating fatty acid chains.

144
Q

What is the main enzyme group responsible for fatty acid chain elongation?

A

Elongases

These enzymes facilitate the addition of carbon units to fatty acids.

145
Q

How does mitochondrial chain elongation differ from fatty acid synthesis?

A

It is almost a reversal of β-oxidation of fatty acids

Acetyl CoA molecules are added to lengthen the fatty acid chain.

146
Q

What is the primary precursor for triacylglycerol synthesis?

A

Acyl CoA

Fatty acids must be activated to acyl CoA before they can be used.

147
Q

In which tissues does triacylglycerol synthesis primarily occur?

A
  • Liver
  • Adipose tissue

These tissues are the main sites for TG synthesis.

148
Q

What are the two mechanisms for synthesizing glycerol 3-phosphate?

A
  • Glycerol kinase in the liver
  • Conversion from dihydroxyacetone phosphate (DHAP)

DHAP is produced during glycolysis and is reduced to glycerol 3-phosphate.

149
Q

What is the end product of the triacylglycerol synthesis pathway?

A

Triacylglycerol

The process involves several intermediates including lysophosphatidic acid and diacylglycerol.

150
Q

What is the typical composition of fatty acids in triacylglycerol?

A
  • 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.

151
Q

What is the primary function of phospholipids?

A

Membrane structure and function

They also play roles in blood clotting and supply arachidonic acid.

152
Q

What are the starting materials for phospholipid synthesis?

A
  • Phosphatidic acid
  • 1,2-diacylglycerol

These intermediates are produced during triacylglycerol synthesis.

153
Q

What happens to choline and ethanolamine during phospholipid synthesis?

A

They are phosphorylated and then combine with CTP

This leads to the formation of CDP-choline and CDP-ethanolamine.

154
Q

How is phosphatidylserine synthesized?

A

By exchanging the ethanolamine group of phosphatidyl ethanolamine with free serine

This reaction is reversible.

155
Q

What is cardiolipin and its unique property?

A

A phospholipid possessing antigenic properties

It is formed from phosphatidylglycerol and plays a role in mitochondrial function.

156
Q

What distinguishes plasmalogens from other phospholipids?

A

Fatty acid at carbon 1 bound by an ether linkage

Plasmalogens have unique functions, including platelet activation.

157
Q

What is the structure of diacylglycerol?

A

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.

158
Q

What is the role of acyltransferase in lipid metabolism?

A

Acyltransferase catalyzes the transfer of acyl groups to form diacylglycerol and phospholipids

This enzyme plays a crucial role in the biosynthesis of lipids.

159
Q

Fill in the blank: Phosphatidic acid is a precursor for the synthesis of _______.

A

triacylglycerol and phospholipids

160
Q

What are the primary components of phospholipids?

A

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.

161
Q

True or False: Cardiolipin is also known as diphosphatidylglycerol.

A

True

162
Q

What is the function of phosphatidylglycerol?

A

Phosphatidylglycerol is involved in the structure of membranes and signaling pathways

It plays a significant role in mitochondrial membranes.

163
Q

List the enzymes involved in the biosynthesis of phospholipids.

A
  • Choline kinase
  • Phosphocholine cytidyltransferase
  • Phosphatidate phosphohydrolase
  • Phosphocholine diacylglycerol transferase
  • CTP–Phosphatidate cytidyltransferase
  • CDP–Diacylglycerol inositol transferase
164
Q

Fill in the blank: Glycerol 3-phosphate is also known as _______.

A

dihydroxyacetone phosphate

165
Q

What is the significance of CDP-diacylglycerol in lipid metabolism?

A

CDP-diacylglycerol serves as an important intermediate in the synthesis of various phospholipids

It is crucial for the formation of phosphatidylinositol and cardiolipin.

166
Q

What is the role of CTP in the biosynthesis of phospholipids?

A

CTP provides the cytidine monophosphate (CMP) required for the synthesis of CDP-diacylglycerol

This reaction is essential for creating the activated diacylglycerol precursor.

167
Q

True or False: Phosphatidylserine is synthesized from serine and phosphatidic acid.

A

True

Biochemistry: Metabolism Of Lipids (3 decks)

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