Biochemistry: Fatty Acid Metabolism
131 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which ketone body is produced when acetoacetate spontaneously decarboxylates?

  • Beta-Hydroxybutyrate
  • Acetone (correct)
  • Acetoacetate
  • Acetyl-CoA

    • What is the primary enzyme responsible for the carboxylation of acetyl-CoA to form malonyl-CoA in fatty acid synthesis?

  • Enoyl-ACP Reductase
  • Beta-Ketoacyl-ACP Reductase
  • Acetyl-CoA Carboxylase (correct)
  • Malonyl-Acyl Transferase

    • During fatty acid biosynthesis, how many carbons are added during each cycle of elongation?

  • 1 carbon
  • 4 carbons
  • 3 carbons
  • 2 carbons (correct)

    • In the fatty acid synthase complex, which of the following activities is NOT part of the complex?

    <p>Malonyl-CoA Synthase</p> Signup and view all the answers

    In which cellular compartment does fatty acid synthesis occur?

    <p>Cytoplasm</p> Signup and view all the answers

    Which of the following is a key distinguishing factor of peroxisomal β-oxidation compared to mitochondrial β-oxidation?

    <p>Shortens very long chain fatty acids</p> Signup and view all the answers

    What is the initial product formed when two molecules of acetyl-CoA condense during ketone body formation?

    <p>Acetoacetyl-CoA</p> Signup and view all the answers

    What is the main fate of excess acetyl-CoA produced during β-oxidation under normal conditions?

    <p>Entry into the citric acid cycle</p> Signup and view all the answers

    What is the direct precursor for the synthesis of ceramide in sphingolipid metabolism?

    <p>Sphinganine</p> Signup and view all the answers

    Which enzyme is responsible for the degradation of glucocerebrosides?

    <p>𝛽-Glucosidase</p> Signup and view all the answers

    In sphingomyelin metabolism, what molecular component is ceramide esterified to?

    <p>Phosphorylcholine</p> Signup and view all the answers

    What condition results from the defective function of sphingomyelinase?

    <p>Niemann-Pick Syndrome</p> Signup and view all the answers

    Which enzyme is responsible for degrading galactocerebrosides?

    <p>𝛽-galactosidase</p> Signup and view all the answers

    What occurs at the end of seven cycles of fatty acid synthesis involving Malonyl-CoA?

    <p>Palmitate is hydrolyzed from ACP</p> Signup and view all the answers

    Which enzyme is identified as the key regulatory enzyme in fatty acid synthesis?

    <p>Acetyl-CoA Carboxylase</p> Signup and view all the answers

    What effect does palmitoyl-CoA have on ACC1?

    <p>It inhibits ACC1 by promoting depolymerization</p> Signup and view all the answers

    Which of the following accurately describes the source of the two-carbon units in fatty acid elongation?

    <p>Malonyl-CoA provides the two-carbon units</p> Signup and view all the answers

    Identify the two processes that occur closely together in the endoplasmic reticulum.

    <p>Fatty acid elongation and desaturation</p> Signup and view all the answers

    How does insulin affect ACC1?

    <p>It enhances its polymerization</p> Signup and view all the answers

    What characterizes the intermediates found in fatty acid synthesis compared to beta-oxidation?

    <p>Fatty acid synthesis intermediates are linked to acyl carrier protein</p> Signup and view all the answers

    What is a critical difference in the location of fatty acid synthesis and beta-oxidation?

    <p>FA synthesis occurs in the cytoplasm, while beta-oxidation occurs in mitochondria and peroxisomes</p> Signup and view all the answers

    Which statement about the relationship between fatty acid synthesis and beta-oxidation is correct?

    <p>Fatty acid synthesis resembles the reverse process of beta-oxidation</p> Signup and view all the answers

    What is a unique characteristic of desaturases involved in fatty acid synthesis?

    <p>They are specific for particular positions of double bonds</p> Signup and view all the answers

    What is the main substrate for glyceroneogenesis?

    <p>Malate</p> Signup and view all the answers

    What is required for the formation of Acyl-CoA from fatty acids?

    <p>ATP and Coenzyme-A</p> Signup and view all the answers

    Which enzyme catalyzes the formation of acylcarnitine from Acyl-CoA?

    <p>Carnitine acyltransferase-1</p> Signup and view all the answers

    What is the yield of ATP from the complete oxidation of Palmitoyl-CoA?

    <p>108 ATP</p> Signup and view all the answers

    Which type of fatty acids requires an additional enzyme for degradation due to cis double bonds?

    <p>Unsaturated fatty acids</p> Signup and view all the answers

    How many carbon atoms are removed in each cycle of beta-oxidation?

    <p>2 carbons</p> Signup and view all the answers

    What is the primary function of fatty acid binding proteins in lipolysis?

    <p>Transport fatty acids in blood to various tissues</p> Signup and view all the answers

    During fatty acid transport into mitochondria, what role does carnitine play?

    <p>It is an acyl group carrier molecule</p> Signup and view all the answers

    Which of the following is true regarding the oxidation of odd-chain fatty acids?

    <p>They yield Acetyl-CoA and propionyl-CoA</p> Signup and view all the answers

    Which enzyme is NOT involved in the beta-oxidation of fatty acids?

    <p>Carnitine acyltransferase-1</p> Signup and view all the answers

    Which enzyme is responsible for hydrolyzing the ester bond at C1 of glycerol?

    <p>PLA1</p> Signup and view all the answers

    Which phospholipid acts as a signal for macrophages to engulf cells?

    <p>Phosphatidylserine</p> Signup and view all the answers

    What role does diacylglycerol play in the synthesis of phosphatidylethanolamine and phosphatidylcholine?

    <p>It is a precursor that reacts with CDP-ethanolamine and CDP-choline.</p> Signup and view all the answers

    Phospholipid turnover involves which of the following processes?

    <p>Rapid replacement of fatty acids.</p> Signup and view all the answers

    What is the primary function of phosphatidylcholine in biological membranes?

    <p>Serving as a surfactant.</p> Signup and view all the answers

    Which phospholipase hydrolyzes both ester bonds at C1 and C2 of glycerol?

    <p>PLB</p> Signup and view all the answers

    The synthesis of phosphatidylserine primarily involves which initial substrate?

    <p>Ethanolamine</p> Signup and view all the answers

    Which of the following statements about phospholipid degradation by phospholipases is true?

    <p>PLC cleaves the phosphodiester bond between glycerol and phosphate.</p> Signup and view all the answers

    What is the main component that contributes to 25% of all phospholipids in humans?

    <p>Phosphatidylethanolamine</p> Signup and view all the answers

    Which of the following best describes the relationship between CTP and phospholipid synthesis?

    <p>CTP is consumed to convert phospho-ethanolamine to CDP-ethanolamine.</p> Signup and view all the answers

    What is the primary function of glutamine synthetase in nitrogen metabolism?

    <p>Facilitates the conversion of glutamate to glutamine</p> Signup and view all the answers

    Which pathway is primarily responsible for the synthesis of glutamate?

    <p>Transamination with α-ketoglutarate</p> Signup and view all the answers

    Which of the following amino acids is considered essential?

    <p>Leucine</p> Signup and view all the answers

    When nitrogen uptake exceeds nitrogen excretion, what condition is indicated?

    <p>Positive nitrogen balance</p> Signup and view all the answers

    Which reaction is primarily involved in the transfer of amino groups during amino acid biosynthesis?

    <p>Transamination reactions</p> Signup and view all the answers

    What is the role of pyridoxal-5'-phosphate (PLP) in transamination reactions?

    <p>It binds the amino acid and facilitates its transfer</p> Signup and view all the answers

    Which two amino acid pairs are most important for nitrogen disposal in the urea cycle?

    <p>Oxaloacetate and aspartate</p> Signup and view all the answers

    What distinguishes essential amino acids from nonessential ones?

    <p>Essential amino acids must be obtained through diet.</p> Signup and view all the answers

    Which mechanism describes the interaction of PLP with the donor amino acid during transamination?

    <p>Ping-pong mechanism</p> Signup and view all the answers

    What is the primary function of glutamine synthetase in nitrogen metabolism?

    <p>Conversion of glutamate to glutamine</p> Signup and view all the answers

    Which of the following pathways leads to the synthesis of glutamate?

    <p>Ammonium assimilation via glutamine synthase</p> Signup and view all the answers

    Which amino acid is considered nonessential due to its ability to be synthesized by the body?

    <p>Alanine</p> Signup and view all the answers

    What is described as a positive nitrogen balance in organisms?

    <p>Nitrogen intake exceeds nitrogen excretion</p> Signup and view all the answers

    Which enzyme is responsible for catalyzing the transamination reaction for amino acid synthesis?

    <p>Transaminases</p> Signup and view all the answers

    Which of the following amino acids is classified as essential and must be obtained through diet?

    <p>Valine</p> Signup and view all the answers

    What biochemical process is directly associated with nitrogen assimilation?

    <p>Incorporation of inorganic nitrogen into organic compounds</p> Signup and view all the answers

    In the context of amino acid production, what is the role of glutamate dehydrogenase?

    <p>Catalyzing the deamination of glutamate to alpha-ketoglutarate</p> Signup and view all the answers

    Which compound is essential for the nitrogen fixation process carried out by the nitrogenase complex?

    <p>ATP</p> Signup and view all the answers

    Which of the following is true regarding the activity of the nitrogenase complex?

    <p>It involves two proteins: dinitrogenase and dinitrogenase reductase</p> Signup and view all the answers

    What is the primary function of glutamine synthetase in nitrogen metabolism?

    <p>Catalyzes the formation of glutamine from glutamate and ammonium</p> Signup and view all the answers

    Which of the following describes the role of glutamate synthase in amino acid biosynthesis?

    <p>It utilizes glutamine as a nitrogen donor to produce glutamate</p> Signup and view all the answers

    Which amino acids must be obtained from the diet due to the inability of humans to synthesize them?

    <p>Methionine, leucine, and histidine</p> Signup and view all the answers

    What is the primary nitrogen source for amino acid synthesis in plants and prokaryotes?

    <p>Ammonium and nitrate sources</p> Signup and view all the answers

    In eukaryotes, which pathway primarily utilizes glutamate dehydrogenase for nitrogen excretion?

    <p>Reversible conversion of alpha-ketoglutarate to ammonia</p> Signup and view all the answers

    Which component is essential for the reaction catalyzed by glutamate synthase?

    <p>NADPH</p> Signup and view all the answers

    What distinguishes essential amino acids from nonessential amino acids?

    <p>Essential amino acids cannot be produced by the human body</p> Signup and view all the answers

    What type of reaction does glutamine synthetase mediate?

    <p>Formation of glutamine from glutamate and ammonium</p> Signup and view all the answers

    Why is the reaction of glutamate dehydrogenase primarily running in reverse in eukaryotes?

    <p>To excrete excess nitrogen as ammonia</p> Signup and view all the answers

    What role does ATP play in the reaction catalyzed by glutamine synthetase?

    <p>It activates glutamate for subsequent nitrogen transfer</p> Signup and view all the answers

    Which of the following nitrogen-containing molecules is least reactive?

    <p>N2</p> Signup and view all the answers

    What is the primary role of the nitrogenase complex?

    <p>Reduction of atmospheric nitrogen to ammonia</p> Signup and view all the answers

    Which enzyme is responsible for transferring electrons from NADH to the dinitrogenase in the nitrogenase complex?

    <p>Dinitrogenase reductase</p> Signup and view all the answers

    Which of the following statements accurately describes nitrogen fixation?

    <p>Only some prokaryotes can perform it.</p> Signup and view all the answers

    What defines positive nitrogen balance in a biological system?

    <p>Nitrogen intake exceeds nitrogen excretion.</p> Signup and view all the answers

    Which of the following amino acids is classified as nonessential?

    <p>Glutamate</p> Signup and view all the answers

    What is the net result of the nitrogen fixation reaction as described?

    <p>1 N2 is converted into 2 NH3.</p> Signup and view all the answers

    Which of the following processes involves the incorporation of inorganic nitrogen into organic molecules?

    <p>Nitrogen assimilation</p> Signup and view all the answers

    What is a characteristic of the speed of nitrogen fixation by the nitrogenase complex?

    <p>It operates very slowly, at about 6 reactions per second.</p> Signup and view all the answers

    Which term best describes the overall reaction catalyzed by the nitrogenase complex?

    <p>Endothermic and requires significant energy</p> Signup and view all the answers

    Which process is required to incorporate nitrogen from nitrate?

    <p>Reduction to ammonium</p> Signup and view all the answers

    What is the primary function of glutamine synthetase?

    <p>To catalyze the conversion of glutamate to glutamine</p> Signup and view all the answers

    Which enzyme is responsible for the reductive amination of a-ketoglutarate?

    <p>Glutamate synthetase</p> Signup and view all the answers

    Which condition describes the predominant reaction direction of glutamate dehydrogenase in eukaryotes?

    <p>Excretion of nitrogen</p> Signup and view all the answers

    How do essential and nonessential amino acids differ for animals?

    <p>Essential amino acids cannot be synthesized by animals.</p> Signup and view all the answers

    What is required for the reaction catalyzed by glutamate synthetase?

    <p>NADPH</p> Signup and view all the answers

    Which biochemical pathway leads to the production of glutamate?

    <p>Transamination</p> Signup and view all the answers

    What primarily characterizes how organic nitrogen moves through ecosystems?

    <p>As amino acids</p> Signup and view all the answers

    Which substance is produced as a byproduct during the synthesis of glutamate from a-ketoglutarate?

    <p>NADP+</p> Signup and view all the answers

    Which amino acids can humans not synthesize biosynthetically?

    <p>Methionine, Valine, Tryptophan</p> Signup and view all the answers

    What occurs during a positive nitrogen balance?

    <p>Children experience growth.</p> Signup and view all the answers

    Which amino acid is most frequently the donor in transamination reactions?

    <p>Glutamate</p> Signup and view all the answers

    What is a primary function of pyridoxal-5'-phosphate (PLP) in transamination reactions?

    <p>It forms a Schiff base with donor amino acids.</p> Signup and view all the answers

    Which of the following statements correctly describes transamination reactions?

    <p>They are catalyzed by aminotransferases.</p> Signup and view all the answers

    What is a characteristic of branched chain amino acids (BCAAs) in amino acid metabolism?

    <p>They facilitate nitrogen transfer from the liver to other tissues.</p> Signup and view all the answers

    Which reaction is crucial for the disposal of nitrogen through the urea cycle?

    <p>Transamination with glutamate.</p> Signup and view all the answers

    What type of mechanism does the transamination reaction employ?

    <p>Ping-pong mechanism.</p> Signup and view all the answers

    Which cofactor is required for the synthesis and degradation of amino acids involving transaminases?

    <p>Pyridoxal-5'-phosphate</p> Signup and view all the answers

    Which pair of amino acids is essential for the glucose-alanine cycle?

    <p>Pyruvate/alanine</p> Signup and view all the answers

    What metabolic process occurs when negative nitrogen balance is evident?

    <p>Potential malnutrition.</p> Signup and view all the answers

    What condition results when nitrogen uptake is less than nitrogen excretion?

    <p>Negative nitrogen balance</p> Signup and view all the answers

    Which amino acid pair is primarily involved in the urea cycle for nitrogen disposal?

    <p>Aspartate / Oxaloacetate</p> Signup and view all the answers

    What is NOT a function of pyridoxal-5'-phosphate (PLP) in transamination reactions?

    <p>Acting as a coenzyme for amino acid transport</p> Signup and view all the answers

    Which metabolic mechanism aids in transporting nitrogen from the liver to other tissues?

    <p>Branched chain amino acids (BCAA)</p> Signup and view all the answers

    What is the primary source of nitrogen required for biosynthetic reactions?

    <p>Dietary amino acids</p> Signup and view all the answers

    What type of reaction is characterized as reversible and involves the synthesis and degradation of amino acids?

    <p>Transamination</p> Signup and view all the answers

    What cofactor is essential for the transfer of one carbon groups in amino acid metabolism?

    <p>THF or SAM</p> Signup and view all the answers

    Which amino acid is most commonly the donor in transamination reactions?

    <p>Glutamate</p> Signup and view all the answers

    What describes the mechanism by which PLP transfers NH2 groups to acceptor keto acids during transamination?

    <p>Ping-pong mechanism</p> Signup and view all the answers

    What mechanism primarily involves breaking bonds to generate new amino acids from keto acids?

    <p>Transamination</p> Signup and view all the answers

    Which enzyme is responsible for the initial step in the nitrogen fixation process?

    <p>Dinitrogenase</p> Signup and view all the answers

    What essential function does nitrogen assimilation serve in organisms?

    <p>Incorporating inorganic nitrogen into organic molecules</p> Signup and view all the answers

    How many electrons are required in total for the nitrogen fixation reaction to occur?

    <p>8 electrons</p> Signup and view all the answers

    Which of the following compounds is not directly involved in the nitrogen fixation reaction mediated by the nitrogenase complex?

    <p>Nitrate (NO3-)</p> Signup and view all the answers

    What distinguishes essential amino acids from nonessential amino acids?

    <p>Essential amino acids cannot be synthesized by the body.</p> Signup and view all the answers

    Which reaction is catalyzed by transaminases/aminotransferases?

    <p>Transfer of amino groups between amino acids and alpha-keto acids</p> Signup and view all the answers

    What characterizes a positive nitrogen balance in an organism?

    <p>Nitrogen intake exceeds excretion</p> Signup and view all the answers

    What is the significance of the nitrogenase complex having a slow reaction rate of 6 per second?

    <p>It highlights the complexity of the nitrogen fixation process.</p> Signup and view all the answers

    What does the term 'nitrogen balance' specifically refer to in biological systems?

    <p>The difference between nitrogen intake and nitrogen excretion.</p> Signup and view all the answers

    What must happen to nitrate before it can be incorporated into organic nitrogen molecules?

    <p>It must be reduced to ammonium.</p> Signup and view all the answers

    Which enzyme is responsible for the nitrogen donation during the synthesis of glutamate from a-ketoglutarate?

    <p>Glutamate synthase</p> Signup and view all the answers

    What is the role of NADPH in the reaction catalyzed by glutamate synthase?

    <p>It serves as a reducing agent in the formation of glutamate.</p> Signup and view all the answers

    Which statement best describes the ability of animals to synthesize amino acids?

    <p>Animals can synthesize some but require certain essential amino acids from their diet.</p> Signup and view all the answers

    What is the primary fate of amino groups transferred from glutamate in amino acid biosynthesis?

    <p>They are involved in the synthesis of other amino acids.</p> Signup and view all the answers

    What does glutamate dehydrogenase primarily generate in eukaryotes?

    <p>NH4+ for nitrogen excretion</p> Signup and view all the answers

    What distinguishes the capabilities of glutamine synthetase in prokaryotes and plants from those in animals?

    <p>Animals lack the enzyme glutamine synthetase entirely.</p> Signup and view all the answers

    What is the significance of ATP in the reaction catalyzed by glutamine synthetase?

    <p>It provides energy for the incorporation of ammonium.</p> Signup and view all the answers

    Which process is primarily responsible for the synthesis of nonessential amino acids in animals?

    <p>Transamination reactions</p> Signup and view all the answers

    Which compound must be present to facilitate the direct amination of a-ketoglutarate?

    <p>NADH</p> Signup and view all the answers

    Study Notes

    Phytanic Acid

    • Phytanic acid is derived from phytol, a component of chlorophyll found in green vegetables.
    • Phytanic acid is oxidized in peroxisomes.

    Beta-oxidation in Peroxisomes

    • Peroxisomes are organelles that specialize in the shortening of very long-chain fatty acids.
    • Peroxisomes oxidize very long chain fatty acids into medium chain fatty acids.
    • The process halts at octanoyl-CoA.
    • Peroxisomal beta-oxidation does not generate ATP.
    • The initial reaction produces hydrogen peroxide (H2O2), which is neutralized by catalase to form water.

    Beta-oxidation in Peroxisome vs. Mitochondria

    • Peroxisomes carry out the initial stages of the oxidation of very long-chain fatty acids.
    • Mitochondria complete the oxidation of medium-chain fatty acids produced by peroxisomes.

    Ketogenesis and Ketone Bodies

    • Ketogenesis is the process of producing ketone bodies.
    • Ketone bodies include acetoacetate, beta-hydroxybutyrate, and acetone.
    • Ketone bodies are synthesized primarily in the liver from excess acetyl-CoA.
    • Under normal conditions, only small amounts of excess acetyl-CoA are produced, so ketone body production is minimal.

    Ketosis

    • Ketosis is a state in which acetone is produced.
    • Ketosis occurs most significantly during prolonged starvation and uncontrolled diabetes.
    • Acetoacetate spontaneously decarboxylates to form acetone.

    Ketone Body Formation

    • Ketone body formation involves a series of reactions:
      • Two acetyl-CoA molecules condense to form acetoacetyl-CoA.
      • Acetoacetyl-CoA condenses with another acetyl-CoA to form HMG-CoA.
      • HMG-CoA lyase hydrolyzes HMG-CoA into acetoacetate.
      • Acetoacetate spontaneously decarboxylates to form acetone.
      • Acetoacetate can also be reversibly reduced to beta-hydroxybutyrate.
    • Heart and skeletal muscle use ketone bodies for energy.
    • Brain uses ketone bodies as an energy source during prolonged starvation.

    Conversion of Ketone Bodies to Acetyl-CoA

    • Ketone bodies can be converted back into acetyl-CoA.
    • Beta-hydroxybutyrate is converted to acetyl-CoA in the mitochondrial matrix of the liver.

    Fatty Acid Biosynthesis

    • Fatty acid synthesis takes place in the cytoplasm.
    • Intermediates are covalently linked to acyl carrier protein (ACP).
    • ACP is a fatty acid activator in fatty acid biosynthesis.
    • Acetyl-CoA and malonyl-CoA are converted into Acetyl-ACP and Malonyl-ACP, respectively, for fatty acid synthesis.
    • The process involves a four-step repeating cycle: condensation, reduction, dehydration, and reduction.
    • Each cycle extends the fatty acid chain by two carbons.

    Fatty Acid Synthase (FAS)

    • Fatty acid synthase is a multi-enzyme complex composed of distinct enzyme activities:
      • Malonyl-acyl transferase (MAT)
      • Ketosynthase (KS)
      • Keto reductase (KR)
      • Dehydratase (DH)
      • Enoyl reductase (ER)
    • FAS is an X-shaped homodimer, meaning it consists of two identical polypeptide chains.
    • Each polypeptide chain contains seven catalytic domains and an ACP.
    • FAS synthesizes two fatty acids simultaneously.

    Fatty Acid Biosynthesis (Phases 1 and 2)

    • Fatty acid biosynthesis proceeds in two phases:
      • Phase 1: Synthesis of Malonyl-CoA
      • Phase 2: Sequential addition of two-carbon units to synthesize palmitic acid (16:0)
    • Acetyl-ACP and Malonyl-ACP are the substrates for fatty acid biosynthesis.

    Fatty Acid Biosynthesis (Phase 1: Malonyl-CoA formation)

    • Acetyl-CoA carboxylase (ACC1) carboxylates acetyl-CoA to synthesize malonyl-CoA.
    • This reaction is irreversible and is the rate-limiting step in fatty acid biosynthesis.
    • Malonyl-CoA is activated by malonyl-acetyl transferase to form malonyl-ACP.

    Acetyl-ACP Formation

    • Acetyl-CoA reacts with ACP-SH to form acetyl-ACP (activated acetate).
    • Acetyl-ACP is transferred to the ketosynthase (KS) unit of the fatty acid synthase complex.

    Fatty Acid Biosynthesis (Phase 2)

    • The seven steps in phase 2 are:
      1. Condensation of acetyl and malonyl groups to form acetoacetyl-ACP.
      2. Reduction of the beta-carbonyl group to form an alcohol.
      3. Dehydration of the alcohol to form a carbon-carbon double bond.
      4. Reduction of the double bond to form a saturated four-carbon acyl group.
      5. Transfer of the acyl group from ACP to the SH group of beta-ketoacyl synthase (KS).
      6. Condensation of the acyl group with another ACP-linked malonyl group, extending the chain by two carbons.
      7. Hydrolysis of palmitate from ACP by thioesterase (TE).

    Repeated Cycles for Elongation

    • After the first cycle, a four-carbon chain is associated with the ACP arm.
    • This four-carbon chain is transferred back to the KS arm, and a new malonyl-CoA is introduced on the ACP arm.
    • Each subsequent cycle extends the acyl chain by two carbons.
    • After seven cycles, a 16-carbon fatty acid (palmitoyl-ACP) is attached to the ACP arm.
    • Palmitoyl-ACP is hydrolyzed to release free palmitate.

    Net Reaction for Palmitate Synthesis

    • 8 Acetyl-CoA + 14 NADPH + 17 H+ + 7 ATP → Palmitate + 14 NADP+ + 7 ADP + 7 Pi + 8 CoASH + 6 H2O

    Acetyl-CoA Carboxylase (ACC)

    • Acetyl-CoA carboxylase (ACC1) is a key enzyme in fatty acid synthesis.
    • ACC1 catalyzes the rate-limiting step in fatty acid synthesis.
    • ACC exists in active and inactive forms:
      • Active form: Polymerized, dephosphorylated dimer.
      • Inactive form: Phosphorylated monomer.

    Allosteric Regulation of ACC1

    • Activators:
      • Citrate: A feedforward activator that promotes polymerization of ACC1.
    • Inhibitors:
      • Palmitoyl-CoA: The end product of fatty acid synthesis, which depolymerizes ACC1 and inhibits activity.

    Hormonal Regulation of ACC1

    • Insulin: Dephosphorylates and activates ACC1.
    • Epinephrine and glucagon: Phosphorylate and inhibit ACC1.

    Fatty Acid Elongation and Desaturation

    • Fatty acid elongation and desaturation are closely integrated processes.
    • Both processes occur in the endoplasmic reticulum (ER).
    • Palmitic acid is first activated to palmitoyl-CoA for elongation and desaturation.
    • For elongation, malonyl-CoA provides a two-carbon unit.
    • Elongases are enzymes that synthesize longer chain fatty acids.
    • Desaturases are enzymes that synthesize unsaturated fatty acids.
    • Mammals lack the enzymes to introduce a double bond beyond carbon 9.
    • Fatty acids containing double bonds beyond carbon 9 are supplied by the diet (essential fatty acids, EFAs).
    • Desaturases are specific for the position of the double bond.

    Nitrogen in Biological Systems

    • Nitrogen is an essential element for life.
    • Nitrogen exists in different forms - atmospheric nitrogen (N2), ammonia (NH3), ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-).
    • Nitrogen gas in the atmosphere is inert and unavailable for use by organisms.
    • Nitrogen fixation is the process of converting atmospheric nitrogen into a usable form – ammonia.
    • Nitrogen fixation is carried out by some prokaryotes, which possess the nitrogenase enzyme complex.

    Nitrogenase Complex

    • The nitrogenase complex is a key enzyme responsible for nitrogen fixation.
    • It consists of two proteins: dinitrogenase and dinitrogenase reductase, both containing iron.
    • Dinitrogenase reductase transfers electrons from NADH to dinitrogenase.
    • Dinitrogenase then reduces N2 to ammonia (NH3).
    • This process requires a significant amount of energy.

    Nitrogen Assimilation

    • Nitrogen assimilation is the process of incorporating inorganic nitrogen into organic molecules, primarily amino acids.
    • Glutamine synthetase catalyzes the first step in nitrogen assimilation.
    • It converts glutamate and ammonia into glutamine using ATP.

    Glutamate Synthase

    • Glutamine acts as a nitrogen donor for the reductive amination of α-ketoglutarate, catalyzed by glutamate synthase, which is present only in prokaryotes and plants.
    • Glutamate synthase requires NADPH as a cofactor.

    Direct Amination of α-Ketoglutarate

    • Glutamate dehydrogenase catalyzes the direct amination of α-ketoglutarate, forming glutamate.
    • This reaction is reversible but primarily runs in reverse in eukaryotes to generate ammonia for nitrogen excretion.
    • It plays a minor role in nitrogen assimilation.

    Essential and Nonessential Amino Acids

    • Plants and prokaryotes can synthesize all twenty amino acids.
    • Animals can synthesize only nonessential amino acids and must obtain essential amino acids from their diet.

    Nitrogen Balance

    • Nitrogen balance refers to the equilibrium between nitrogen intake and excretion.
    • Positive nitrogen balance: Intake exceeds excretion, often occurring in children during growth.
    • Negative nitrogen balance: Excretion exceeds intake, caused by malnutrition or disease.

    Amino Acid Metabolism

    • Amino acids are the primary source of nitrogen for biosynthesis.
    • Dietary amino acids may not be available in the optimal proportions required, and metabolic mechanisms are needed to balance and utilize them.
    • Branched-chain amino acids (BCAAs) play a vital role in transporting nitrogen from the liver to other tissues.
    • Amino acids are transported across cell membranes by specific proteins.

    Overview of Amino Acid and Nucleotide Biosynthesis

    • Several key types of reactions are involved:
      • Transamination reactions catalyzed by aminotransferases using pyridoxal phosphate (PLP) as a cofactor.
      • Transfer of one-carbon groups using tetrahydrofolate (THF) or S-adenosylmethionine (SAM) cofactors.
      • Transfer of amino groups from glutamine.

    Transamination Reactions

    • They are reversible reactions involved in both synthesis and degradation of amino acids.
    • Aminotransferases are numerous in eukaryotes, present in both cytoplasm and mitochondria.
    • They specifically recognize the donor amino acid and acceptor keto acid.
    • Glutamate is commonly the donor amino acid.
    • The α-ketoglutarate/glutamate pair and the oxaloacetate/aspartate pair are crucial.

    Pyridoxal-5'-Phosphate (PLP)

    • PLP is a cofactor for transamination reactions, acting as the active form of Vitamin B6.
    • PLP binds to the active site of transaminases.
    • It plays a key role in various reactions, including transamination, racemization, and decarboxylation.

    PLP Schiff Base Formation

    • Transamination involves the formation of a Schiff base between PLP and the donor amino acid.
    • This Schiff base is crucial for the transfer of the amino group.
    • The reaction mechanism involves a series of steps, including bond breaking and formation, leading to the transfer of the amino group from the donor to the acceptor.
    • This process is also known as a ping-pong or double displacement mechanism.

    Why is Nitrogen Important?

    • Nitrogen is an essential nutrient for all forms of life, making up approximately 78% of the air we breathe.
    • We cannot directly utilize nitrogen gas (N2) as it is inert.
    • Nitrogen fixation refers to the process of converting atmospheric nitrogen into usable forms.

    Nitrogen Fixation

    • Performed exclusively by certain prokaryotes (bacteria).
    • Nitrogenase enzyme complex is responsible for N2 reduction to ammonia (NH3).
    • The nitrogenase complex consists of two proteins: dinitrogenase and dinitrogenase reductase.
    • Dinitrogenase reductase transfers electrons from NADH to dinitrogenase.
    • Dinitrogenase then catalyzes the reduction of N2 to NH3.
    • The reaction is energetically demanding, requiring 8 electrons, 16 ATP, and 10 protons.

    Nitrogen Assimilation

    • The process of incorporating inorganic nitrogen (NH4+ or NO3-) into organic molecules.
    • Primarily involves the synthesis of amino acids.
    • Glutamine synthetase catalyzes the incorporation of ammonia into glutamate to form glutamine.
    • Glutamate synthase, found in prokaryotes and plants, utilizes glutamine as a nitrogen donor to reduce α-ketoglutarate to glutamate, requiring NADPH.
    • Glutamate dehydrogenase catalyzes the direct amination of α-ketoglutarate to form glutamate.

    Amino Acid Biosynthesis

    • Plants and prokaryotes are capable of synthesizing all 20 amino acids.
    • Animals can only synthesize a subset of amino acids, known as nonessential amino acids.
    • Essential amino acids must be obtained from the diet.

    Nitrogen Balance

    • Nitrogen balance refers to the equilibrium between nitrogen intake and excretion.
    • Positive nitrogen balance occurs when intake exceeds excretion, commonly seen in growing children.
    • Negative nitrogen balance occurs when excretion exceeds intake, potentially leading to malnutrition.

    Amino Acid Metabolism

    • Amino acids serve as the primary nitrogen source for biosynthetic reactions.
    • Dietary amino acids may not be present in optimal proportions for our needs.
    • Branched-chain amino acids (BCAAs) play a crucial role in transporting nitrogen from the liver to other tissues.

    Overview of Reactions

    • Transamination: Transfer of amino groups catalyzed by pyridoxal phosphate-dependent enzymes (aminotransferases or transaminases).
    • One-carbon group transfer: Utilizing tetrahydrofolate (THF) or S-adenosylmethionine (SAM) cofactors.
    • Glutamine-dependent amino group transfer: Utilizing glutamine as a nitrogen donor.

    Transamination Reactions

    • Reversible reactions involved in both amino acid synthesis and degradation.
    • Aminotransferases are abundant enzymes in eukaryotes, found in both cytoplasm and mitochondria.
    • Glutamate serves as a common donor amino acid in transamination reactions.
    • Pyridoxal-5’-phosphate (PLP) acts as a coenzyme for transaminases.

    Pyridoxal-5’-Phosphate (PLP)

    • PLP is a coenzyme derived from vitamin B6.
    • PLP facilitates transamination reactions by forming Schiff bases with amino acids.
    • PLP also serves as a coenzyme for racemization and decarboxylation reactions.

    Schiff Base Formation

    • PLP forms a Schiff base with the donor amino acid, which is essential for the transamination process.

    Nitrogen Importance

    • Nitrogen is a key element for life, present in many essential molecules like amino acids and nucleic acids.
    • Air is composed of ~78% nitrogen gas (N2).
    • N2 is inert (stable/nonreactive) and cannot be directly used by most organisms.

    Nitrogen Fixation

    • Nitrogen fixation is the process of converting atmospheric N2 into a usable form, usually ammonia (NH3).
    • This process requires significant energy and can only be carried out by certain prokaryotes (nitrogen-fixing bacteria).
    • The nitrogenase complex is a key enzyme involved in nitrogen fixation.

    Nitrogenase Complex

    • The nitrogenase complex is composed of two proteins: dinitrogenase and dinitrogenase reductase.
    • These proteins contain iron and are crucial for the reduction of N2 to NH3.
    • The dinitrogenase reductase transfers electrons from NADH to dinitrogenase.
    • Dinitrogenase utilizes these electrons to reduce N2.
    • The process is relatively slow, with only about 6 reactions per second.

    Nitrogen Assimilation

    • Nitrogen assimilation is the incorporation of inorganic nitrogen (like NH4+ or NO3-) into organic molecules.
    • It primarily involves the incorporation of nitrogen into amino acids.
    • Glutamine synthetase is a key enzyme catalyzing the incorporation of ammonia (NH4+) into glutamate to form glutamine.
    • This reaction requires ATP.
    • If NO3- is the nitrogen source, it must be reduced to NH4+ first.

    Glutamate Synthase

    • Glutamine acts as a nitrogen donor in the reductive amination of α-ketoglutarate.
    • This reaction is catalyzed by glutamate synthase, which is found in plants and prokaryotes but not animals.
    • Glutamate synthase requires NADPH.

    Direct Amination of α-Ketoglutarate

    • Glutamate dehydrogenase catalyzes the direct amination of α-ketoglutarate to form glutamate.
    • This reaction is reversible, but in eukaryotes, it mainly runs in reverse to generate NH4+ for nitrogen excretion.

    Essential and Nonessential Amino Acids

    • Plants and prokaryotes can synthesize all 20 amino acids.
    • Animals can only synthesize nonessential amino acids, requiring essential amino acids from their diet.
    • Humans cannot synthesize three amino acids biosynthetically (histidine, isoleucine, and lysine) but they can be produced as byproducts of other biochemical pathways.

    Nitrogen Balance

    • Nitrogen balance occurs when nitrogen uptake equals nitrogen excretion.
    • Positive nitrogen balance indicates nitrogen uptake exceeding excretion, often seen during growth periods.
    • Negative nitrogen balance indicates nitrogen uptake less than excretion, potentially leading to malnutrition.

    Amino Acid Metabolism

    • Amino acids are the primary source of nitrogen for biosynthetic reactions.
    • Dietary amino acids may not be available in the proportions needed, requiring metabolic regulation.
    • Branched-chain amino acids (BCAAs) play a role in transporting nitrogen from the liver to other tissues.
    • Specific transport proteins facilitate amino acid movement across cell membranes.

    Overview of Reactions in Amino Acid and Nucleotide Biosynthesis

    • Transamination reactions: catalyzed by pyridoxal phosphate-containing enzymes (aminotransferases or transaminases) and involve the transfer of amino groups.
    • One-carbon group transfers: utilize THF or SAM cofactors.
    • Glutamine-dependent amino group transfers: involve transfer of amino groups from glutamine.

    Transamination Reactions

    • Reversible reactions involved in both the synthesis and degradation of amino acids.
    • Aminotransferases are numerous in eukaryotes, present in both cytoplasm and mitochondria.
    • Glutamate is often a donor amino acid, forming the α-ketoglutarate/glutamate pair.
    • The oxaloacetate/aspartate pair is essential for the urea cycle (nitrogen disposal).
    • The pyruvate/alanine pair is crucial for the glucose-alanine cycle (gluconeogenesis).

    Pyridoxal-5'-Phosphate (PLP)

    • PLP is a coenzyme required for transamination reactions.
    • It acts as a vitamin B6 derivative and binds to the active site of transaminases.
    • PLP is also involved in racemization and decarboxylation reactions.

    PLP Forms a Schiff Base

    • PLP forms a Schiff base with the donor amino acid, which is crucial for transamination.
    • The Schiff base formation and subsequent breakage lead to the transfer of the amino group from the donor amino acid to the acceptor keto acid.

    Aminotransferases – Mechanism

    • Aminotransferases utilize a ping-pong or double displacement mechanism.
    • During the process, the amino group is temporarily attached to PLP before being transferred to the acceptor keto acid.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    BMM339 Exam 3 PDF
    Nitrogen Fixation & Incorporation Lecture 2024 PDF

    Description

    Explore the biochemical processes of phytanic acid metabolism and the roles of peroxisomes and mitochondria in fatty acid oxidation. Understand ketogenesis and the production of ketone bodies. This quiz deepens your understanding of essential metabolic pathways.

    More Like This

    Fatty Acid Metabolism and Ketone Bodies Quiz
    16 questions

    Fatty Acid Metabolism and Ketone Bodies Quiz

    WellBeingHawkSEye avatar
    WellBeingHawkSEye
    Fatty Acid Metabolism and Transport Quiz
    9 questions

    Fatty Acid Metabolism and Transport Quiz

    FrugalWilliamsite616 avatar
    FrugalWilliamsite616
    Fatty Acid Metabolism
    36 questions

    Fatty Acid Metabolism

    AffableCognition avatar
    AffableCognition
    Biochemistry of Fatty Acid Metabolism
    15 questions

    Biochemistry of Fatty Acid Metabolism

    TrendyAcademicArt avatar
    TrendyAcademicArt
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser