Finals-Biochemistry-for-Medical-Laboratory-Science-Lecture-Part-2 PDF

BIOCHEMISTRY (LECTURE) Lesson #9: Lipid Metabolism Triacylglycerol Storage and Mobilization Digestion and Absorption of Lipids...

BIOCHEMISTRY (LECTURE) Lesson #9: Lipid Metabolism Triacylglycerol Storage and Mobilization Digestion and Absorption of Lipids Definition Definition Ø Most cells in the body have limited Ø The first step in the digestion of capability for storage of TAGs. triacylglycerols and phospholipids Ø However, this activity is the major begins in the mouth as lipids function of specialized cells called encounter saliva. adipocytes, found in adipose tissue. Ø Chewing with the action of Adipose tissue can be primarily emulsifiers enables the digestive found beneath the skin. It is the insulator against enzyme (lipase) to do their the excessive heat loss also it provides organs tasks. with protection against physical shock. Ø An adipocyte is a triacylglycerol- Ø Lipids = source of energy. storing cell. Enzyme: Lipase Ø Adipose tissue is tissue that contains Ø Triacylglycerol (TAG) large numbers of adipocyte cells. Ø As a result, the fats become tiny droplets and separate from the watery components. Ø In the stomach, gastric lipase starts to break down triacylglycerols into diglycerides and fatty acids. The use of TAGs stored in adipose tissue for energy production is triggered by several Ø As stomach contents enter the hormones. small intestine, bile combines o Epinephrine and Glucagon – stimulates the separated fats with its own fat mobilization. watery fluids. HSL – Hormone Sensitive Lipase Ø Bile contains bile salts, o Inactive after phosphorylation active lecithin, and substances derived cAMP – Cyclic Adenosine Monophosphate from cholesterol, so it acts as an o Serves as the second messenger. emulsifier. o Signal transduction. Ø As pancreatic lipase enters the Ø The overall process of tapping the body’s small intestine, it breaks down the triacylglycerol energy reserves (adipose tissue) for fats into free fatty acids and energy is called triacylglycerol mobilization. monoglycerides. Ø Triacylglycerol mobilization is the hydrolysis of Ø Bile salts envelop the fatty acids and monoglycerides triacylglycerols stored in adipose tissue, followed by to form micelles. release into the bloodstream of the fatty acids and glycerol so produced. Ø Triacylglycerol mobilization is an ongoing process. On the average, about 10% pf the TAGs in adipose Ø Lipid Metabolism tissue are replaced daily by new triacylglycerol molecules. Ø Triacylglycerol energy reserves (fat reserves) are the human body’s major source of stored energy. Ø Energy reserves associated with protein, glycogen, and glucose are small to very small when compared to fat reserves. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Glycerol Metabolism Fatty Acid Activation Definition Ø The outer mitochondrial membrane is the site of fatty Ø Glycerol metabolism primarily involves processes acid activation, the first stage of fatty acid oxidation. considered in the previous chapter. After entering the Free fatty acid to Acyl CoA bloodstream, glycerol travels to the liver or kidneys, o Enzyme: Acyl CoA Synthetase where it is converted, in a two-step process, to dihydroxyacetone phosphate. Main Idea: To convert glycerol to DHAP In activation, this reaction requires the expenditure of 2 high energy phosphate bonds from a single ATP molecule. o From ATP to AMP. Result: 2Pi 1. The first step involves phosphorylation of a primary - 2 ATP consumed hydroxyl group of the glycerol. Ø Here, the fatty acid is converted to a high-energy Phosphorylation derivative of coenzyme A. reactants are the fatty acid, From Glycerol to Glycerol-3-Phosphate coenzyme A, and a molecule of ATP. o Enzyme: Glycerol kinase Ø The activated fatty acid-CoA molecule is called acyl CoA. Ø The difference between the designations acyl CoA is 2. In the second step, glycerol’s secondary alcohol that acyl refers to a random-length fatty acid carbon group (C-2) oxidized to a ketone. chain that is covalently bonded to coenzyme A, Oxidation whereas acetyl refers to a two-carbon chain Glycerol-3-Phosphate to Dihydroxyacetone covalently bonded to coenzyme A. phosphate Fatty Acid Transport o Enzyme: Glycerol-3-Phosphate Ø Acyl CoA is too large to pass through the inner dehydrogenase mitochondrial membrane to the mitochondrial matrix, where the enzymes needed for fatty acid oxidation. Carnitine Shuttle System o Acyl CoA + Carnitine = Acyl Carnitine Ø The following equation represents the overall reaction for the metabolism of glycerol: DHAP is intermediate in the glycolysis and gluconeogenesis. Oxidation of Fatty Acids 3 Parts to the Process by which Fatty Acids are Broken Down to Obtain Energy (ATO) 1. The fatty acids must be activated by bonding to coenzyme A. 2. The fatty acid must be transported into the mitochondrial matrix by a shuttle mechanism. 3. The fatty acid must be repeatedly oxidized, cycling through a series of four reactions, to produce acetyl CoA, FADH2 and NADH. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Reactions of the β-Oxidation Pathway Ø Step #4: Chain Cleavage Ø The β-oxidation pathway The fatty acid chain is broken between the a and is a repetitive series of b carbons by reaction with coenzyme A four biochemical reactions molecule. The result is an acetyl CoA molecule that degrades acyl CoA to and a new acyl CoA molecule that is shorter by acetyl CoA by removing two carbon atoms than its predecessor. two carbon atoms at a o Β-Ketoacyl CoA to Acyl CoA with two time with FADH2 and fewer carbon atoms to Acetyl CoA NADH also being - Enzyme: Thiolase produced. Ø For a saturated fatty acid, the β-oxidation pathway involves the following functional group changes Ø Result: at the β carbon and the 1 Acetyl CoA following reaction types. 1 NADH 1 FADH2 Ø The new acyl CoA molecule Ø Step #1: Oxidation (dehydrogenation) (now shorter by two carbons) Hydrogen atoms are removed from the a and b is recycled through the same carbons, creating a double bond between these set of four reactions again. two carbon atoms. FAD is the oxidizing agent, Ø This yields another acetyl and a FADH2 molecule is a product. CoA, a two-carbon-shorter o Acyl CoA (single bond) to trans-Enoyl new acyl CoA, FADH2 and CoA (double bond) NADH. - Enzyme: Acyl CoA dehydrogenase Ø Recycling occurs again and again, until the entire fatty acid is converted to acetyl CoA. Ø Thus, the fatty acid carbon chain is sequentially degraded, Ø Step #2: Hydration two carbons at a time. A molecule of water is added across the trans Ø The number of repetitions of the b-oxidation pathway double bond, producing a secondary alcohol at that are needed to produce the acetyl CoA is always the β-carbon position. one less than the number of acetyl CoA molecules o trans-Enoyl CoA (double bond) to L-β- produced because the last repetition produces two Hydroxyacyl CoA (single bond) acetyl CoA molecules as a C4 unit splits into two C2 - Enzyme: Enoyl CoA hydratase units. Fatty Acid = # of Carbons Acetyl CoA = # of Fatty Acids divide by 2 Ø Step #3: Oxidation (dehydrogenation) Repetitive Sequence = Acetyl CoA – 1 The β-hydroxy group is oxidized to a ketone o Repetitive Sequence = FADH2 / NADH functional group with NAD+ serving as the oxidizing agent. ATP Production from o L-β-Hydroxyacyl CoA (single bond) to Fatty Acid Oxidation β-Ketoacyl CoA (double bond) Definition - Enzyme: β-Hydroxyacyl CoA Ø Let us calculate ATP dehydrogenase production for the oxidation of a specific fatty acid molecule, stearic acid (18:0), and compare it with that from glucose. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Ø Gross ATP: 60 ATP + 7.5 ATP + 12.5 ATP = 80 ATP Ø Figure on the left shows Ø Fatty Acid Activation: that for each four-reaction 2 ATP sequence except the last Ø Net ATP Production: one, 1 FADH2 molecule, 80 ATP – 2 ATP = 78 ATP 1 NADH molecule, and 1 acetyl CoA molecule is Ketone Bodies produced. Definition Ø In the final four-reaction Ø Ordinarily, when there is adequate balance between sequence, two acetyl CoA lipid and carbohydrate metabolism, most of the acetyl molecules are produced CoA produced from the β-oxidation pathway is in addition to the FADH2 further processes through the citric acid cycle. and NADH molecules. Ø Certain body conditions upset the lipid-carbohydrate Ø Eight repetitions of the balance required for acetyl CoA generated by fatty β-oxidation pathway are acids to be processed by the citric acid cycle. required for the oxidation Dietary intake high in fat and low in of stearic acid, an 18-carbon acid. carbohydrates. Ø These eight repetitions of the pathway produce 9 Diabetic conditions, where the body cannot acetyl CoA molecules, 8 FADH2 molecules and 8 adequately process glucose even though it is NADH molecules. present. Prolonged fasting conditions, including starvation. Types of Ketone Bodies Ø Kreb’s Cycle Acetoacetate 3 NADH x 2.5 ATP = 7.5 ATP β-Hydroxybutyrate 1 FADH2 x 1.5 ATP = 1.5 ATP Acetone 1 GTP x 1 ATP = 1 ATP Ø Chemically, these three structures are closely related. o Always 10 ATP The relationships are most easily seen if the focus o 10 ATP = 9 Acetyl CoA starts with the molecule acetate. Problem Solving Ø What is the net ATP production for the complete 1. Reduction of the ketone group present in acetoacetate oxidation of lauric acid, the C12 saturated fatty acid, to a secondary alcohol produces β-hydroxybutyrate. to CO2 and H2O? Acetoacetate to β-hydroxybutyrate 1 Acetyl CoA = 10 ATP o Enzyme: Reducing agent 1 NADH = 2.5 ATP 1 FADH2 = 1.5 ATP 2. Decarboxylation of acetoacetate produces acetone. Acetoacetate to Acetone o Enzyme: Decarboxylation BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Ø Step #3: Chain Cleavage Ketogenesis HMG-CoA is then cleaved to acetyl CoA and Ø Ketogenesis is the metabolic pathway by which acetoacetate. ketone bodies are synthesized from Acetyl CoA. o HMG-CoA to Acetoacetate and Acetyl Ø Items to consider about this process prior to looking CoA at the actual steps in this four-step process are: - Enzyme: HMG-CoA lyase 1.The primary site for the process is liver mitochondria. 2. The first ketone body to be produced is acetoacetate. This production occurs in Step 3 of ketogenesis. 3. Some of the acetoacetate produced in Step 3 is converted to the second ketone body, β- Ø Step #4: Reduction hydroxybutyrate, in Step 4 of ketogenesis. Acetoacetate is reduced to β-hydroxybutyrate. 4. The acetoacetate and β-hydroxybutyrate The reducing agent is NADH. synthesized by ketogenesis in the liver are o Acetoacetate to β-hydroxybutyrate released to the bloodstream where acetone, the - Enzyme: β-hydroxybutyrate third ketone body, is produced. dehydrogenase 5. Acetoacetate is somewhat unstable and can Ø Clinical Significance spontaneously or enzymatically lose its carboxyl Ketoacidosis – during uncontrolled diabetes. Too group to form acetone. much production of ketone bodies within the 6. The ketone body acetone present in the body. Diabetic ketone acidosis. bloodstream is a volatile substance that is mainly Ketogenic – e.g., ketogenic diet excreted by exhalation. 7. The amount of acetone present is usually small Lipogenesis compared to the concentrations of the other two Definition ketone bodies. Ø Is the metabolic pathway by which fatty acids are The Process of Ketogenesis synthesized from acetyl CoA. Ø Step #1: First Condensation Ø Is not simple a reversal of the steps for degradation of Ketogenesis begins as two acetyl CoA molecules fatty acids (the β-oxidation pathway). combine to produce acetoacetyl CoA, a reversal Features of Lipogenesis of the last step of the β-oxidation pathway. o 2 Acetyl CoA to Acetoacetyl CoA Lipogenesis Lipolysis - Enzyme: Thiolase 1. Lipogenesis occurs in 1. Degradation of fatty the cell cytosol. acids occurs in the 2. Lipogenesis enzymes mitochondrial matrix. are collected into a 2. The enzymes multienzyme involved in fatty acid complex called fatty degradation are not acid synthase. physically associated, 3. Lipogenesis so the reaction steps Ø Step #2: Second Condensation intermediates are are independent. Acetoacetyl CoA then reacts with a third acetyl bonded to ACP (acyl 3. The carrier for fatty CoA and water to produce 3-hydroxy-3- carrier protein) acid degradation methylglutaryl CoA (HMG-CoA) and CoA— 4. Fatty acid synthesis intermediates is CoA. is dependent on the 4. Fatty acid SH. reducing agent degradation is o Acetoacetyl CoA and Acetyl CoA to NADPH. dependent on the HMG-CoA 5. Fatty acids are built oxidizing agents - Enzyme: HMG-CoA synthase up two carbons at a FAD and NAD+. time during 5. Fatty acids are synthesis. broken down two 6. In lipogenesis, acetyl carbons at a time CoA is used to form during degradation. malonyl ACP, which 6. CoA derivatives are becomes the carrier involved in all steps of the two carbon of fatty acid units. degradation. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) When does Lipogenesis occurs? Ø Lipogenesis occurs in well fed condition. The Malonyl CoA so produced then reacts with Ø Conditions Favoring Lipogenesis ACP to produce malonyl ACP. Excess of free glucose after heavy carbohydrate meals. Insulin promotes lipogenesis. Where does Lipogenesis occur? Ø Predominant site for Lipogenesis Liver Cytoplasm Ø Other tissues for Lipogenesis Ø Chain Elongation Intestine Step #1: Condensation Mammary Glands o Acetyl ACP and Malonyl ACP Reasons for Lipogenesis condense together to form Acetoacetyl Ø Free excess Glucose can’t be stored as it is in body ACP cells and tissues. Ø Free excess Glucose is first converted and stored in the form of Glycogen. Ø Storage of Glycogen is limited. Ø In a well-fed condition after limited storage of Glycogen. Ø When still there remains Free Excess Glucose. Ø This Free Excess Glucose is oxidized to Pyruvate via Glycolysis. Ø Further Pyruvate to Acetyl-CoA via PDH Complex reaction. Step #2: First Hydrogenation Ø This Acetyl-CoA when excess is then diverted for o The Keto Group of the Acetoacetyl Lipogenesis. Complex, which involves the β-carbon Triacylglycerols (TAG) atoms, is reduced to the corresponding Ø To transform free excess Glucose to Acetyl-CoA alcohol by NADPH. further into Fatty acids. Ø Fatty acids are stored as TAG. Ø Storageable form of Lipid (TAG). Ø TAG in Adipocytes can be stored in unlimited amounts. 2 Parts of Lipogenesis Step #3: Dehydration Ø ACP Complex Formation – it shows that all o The alcohol produced in Step 2 is intermediates in lipogenesis are bound to ACP-SH or dehydrated to introduce a double bond also known as acyl carrier proteins. into the molecule (between the α and β 1. Acetyl ACP Formation (C2) carbons) C2 to ACP 2. Malonyl ACP Formation (C3) Carboxylation Step #4: Second Hydrogenation C3 to ACP o The double bons introduced in Step 3 is converted to a single bond through hydrogenation. o As in Step 2, NADPH is the reducing agent. o This reaction occurs only when cellular ATP levels are high. o It is catalyzed by Acetyl CoA Carboxylase Complex, which requires both Mn2+ion and the B Vitamin Biotin for its activity. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Fate of Fatty Acid-Generated Acetyl CoA Citric Acid Cycle (Krebs Cycle) Ø Acetyl-CoA enters the Citric Acid Cycle, where it combines with oxaloacetate to form citrate. Ø Through a series of enzymatic reactions, citrate is converted back to oxaloacetate, producing ATP, NADH, and FADH2, which are used for energy production. Lipogenesis and Citric Acid Cycle Intermediates Relationship between Lipogenesis and Citric Acid Cycle Intermediates Ø The intermediates in the last four steps of the Citric Acid Cycle are all C4 molecules. Ketogenesis Ø In the liver, during periods of low carbohydrate availability (e.g., fasting, low-carbohydrate diets, or uncontrolled diabetes), acetyl-CoA is converted into ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone). Ø Ketone bodies can be used as an alternative energy source by peripheral tissues, including the brain, during prolonged fasting or Ø The last four intermediates of the Citric Acid Cycle carbohydrate restriction. bear the following relationship to each other. Cholesterol Synthesis Succinate Ø Acetyl-CoA is the starting material for the biosynthesis of cholesterol. Ø The intermediate C4 carbon chains of Lipogenesis The process begins with the bear the following relationship to each other. conversion of Acetyl-CoA Butyrate into HMG-CoA (3-hydroxy-3-methylglutaryl- CoA), which is then reduced to Ø Note two important contrasts in these compound mevalonate by the enzyme sequences: HMG-CoA reductase. The Citric Acid intermediates involve C4 diacids Ø Mevalonate undergoes a series and the Lipogenesis intermediates involve C4 of reactions to monoacids. eventually form The order in which the various acid derivative cholesterol, a vital types are encountered in Lipogenesis is the component of cell membranes and precursor for reverse of the order in which they are steroid hormones and bile acids. encountered in the Citric Acid Cycle. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Fatty Acid Synthesis Fatty Acid Biosynthesis Ø Although Acetyl-CoA is produced from fatty acids Ø The buildup of excess Acetyl CoA when dietary during oxidation, it can also be used for fatty acid intake exceeds energy needs to leads to accelerated synthesis. In the cytoplasm, Acetyl-CoA is converted fatty acid biosynthesis. into Malonyl-CoA by Acetyl-CoA carboxylase. Cholesterol Biosynthesis Ø As with fatty acid biosynthesis, cholesterol biosynthesis occurs primarily when the body is in an Acetyl CoA—rich state. B Vitamins and Lipid Metabolism Thiamin (Vitamin B1) Ø Is a precursor for the coenzyme Thiamine Pyrophosphate (TPP), which is essential for the Pyruvate dehydrogenase complex. Ø This complex converts Pyruvate Ø Malonyl-CoA is then used in (from Glycolysis) into Acetyl-CoA, the fatty acid synthase which is necessary for entering the complex to elongate Citric Acid Cycle and Lipid fatty acid chains, Synthesis. producing palmitate, Riboflavin (Vitamin B2) which can be further Ø Is a component of the coenzymes modified into other FAD (Flavin Adenine Dinucleotide) fatty acids. and FMN (Flavin Mononucleotide). Ø These coenzymes are crucial in the beta-oxidation of fatty acids, where Ø Acetyl-CoA serves they participate in the as a precursor for the dehydrogenation steps, helping to synthesis of certain generate acetyl-CoA from fatty acids. amino acids and other important Niacin (Vitamin B3) biomolecules. Ø Is converted into NAD+ For example, (Nicotinamide Adenine Acetyl-CoA can Dinucleotide) and NADP+ be used in the (Nicotinamide Adenine production of the Dinucleotide Phosphate), which amino acid leucine are key coenzymes in oxidation- or in the formation reduction reactions. of acetylcholine, a Ø NAD+ is required for the neurotransmitter. oxidation of fatty acids during beta-oxidation, while NADP+ is involved in the synthesis of fatty Relationships between Lipid acids. and Carbohydrate Metabolism Oxidation in the Citric Acid Cycle Ø Both lipids (Fatty Acids and Glycerol) and carbohydrates (Glucose) supply Acetyl CoA for the operation of this cycle. Pyridoxine (Vitamin B5) Ketone Body Formation Ø Is involved in amino acid Ø This process is of major importance when there is metabolism, which intersects imbalance between lipid and carbohydrate metabolic with Lipid Metabolism, processes. The imbalance is caused by inadequate particularly in the production of glucose metabolism during times of adequate lipid carnitine, a molecule necessary metabolism. for transporting fatty acids into the mitochondria for beta- oxidation. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Biotin (Vitamin B7) Ø Is a coenzyme for carboxylase enzymes, such as Acetyl-CoA carboxylase, which is critical in the first step of fatty acid synthesis. Ø It is also involved in the catabolism of odd-chain fatty acids, which require the conversion of propionyl-CoA to succinyl-CoA. Folate (Vitamin B9) Ø Is involved in the transfer of one-carbon units during the synthesis of nucleotides and amino acids. Ø Its role in lipid metabolism is more indirect, influencing homocysteine levels, which can affect cardiovascular health and lipid profiles. Cobalamin (Vitamin B12) Ø Is necessary for the conversion of methylmalonyl-CoA to succinyl-CoA, a critical step in the catabolism of odd- chain fatty acids. This reaction prevents the accumulation of methylmalonic acid, which could otherwise disrupt lipid metabolism. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Lesson #10: Protein Metabolism d. The enzyme carboxypeptidase is active. o Small Intestine Protein Digestion and Absorption Process Amino Acid Utilization Ø Protein metabolism is a supporting role. Definition Ø In overall metabolism, within a normal diet, Ø Amino acids produced from the digestion of proteins carbohydrate and fats supplies almost 90% of the enter the amino acid pool of the body. energy needed within the body. 10% is from the Ø The amino acid pool is the total supply of free amino Protein. acids available for use in the human body. Ø Stomach Ø Sources of Amino Acids: The digestion process happens in the stomach. Dietary Protein o HCl pH: 1.5-2.0 (highly acidic) Protein Turnover (happens in the liver) o Pepsin: hydrolyzes about 10% of the Biosynthesis (happens in the liver) peptide bonds in proteins. Protein Turnover - HCl and Pepsin is from hormone Ø Protein Turnover is the repetitive process in gastrin. which proteins are degraded and Ø Small Intestine resynthesized within the human body. Production of Secretin Ø Within the human body, proteins o Secretin stimulates the pancreatic are continually being degraded production. Produces bicarbonate ions. (hydrolyzed) to amino acids - Bicarbonate Ions = base (basic) and resynthesized. Disease, injury, and “wear and tear” Varies from few minutes to several hours. Ø Healthy adult about 2% of the body’s protein is broken down and resynthesized every day. Biosynthesis Ø Biosynthesis of amino acids by the liver also supplies the amino acid pool with amino acids. However, only the nonessential amino acids can be produced in this manner. Ø 11 Nonessential Amino Acids Polar Neutral Amino Acids Polar Basic Amino Acids Practice Polar Acidic Amino Acids Ø Determine the location within the human body where o Alanine each of the following aspects of protein digestion o Arginine occurs. o Asparagine a. The enzyme trypsin is active. o Aspartic Acid o Small Intestine o Cysteine b. Large polypeptides are produced. o Glutamic Acid o Stomach o Glutamine c. Protein is denatured by HCl. o Glycine o Stomach o Proline d. Active transport moves amino acids into the o Serine bloodstream. o Tyrosine o Intestinal Lining Nitrogen Balance Ø Based on the information in Figure 26.1, determine Ø Nitrogen Balance the location within the human body where each of the Is the state that results when the amount of following aspects of protein digestion occurs. nitrogen taken into the human body as protein a. The enzyme aminopeptidase is active. equals the amount of nitrogen excreted form the o Small Intestine body in waste materials. b. Peptide bonds are hydrolyzed under the action of pepsin. o Stomach c. Individual amino acids are produced. o Small Intestine BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Ø Negative Nitrogen Balance Transamination and Is when protein degradation exceeds protein Oxidative Deamination synthesis, the amount of nitrogen in the urine 2 Stages of Degradation exceeds the amount of nitrogen ingested (dietary of Amino Acid protein). This is accompanied by a state of tissue 1. The removal of the amino group wasting. 2. The degradation of the remaining carbon skeleton o Examples: - Protein poor diets - Starvation Ø Positive Nitrogen Balance Nitrogen intake exceeds nitrogen output. Indicates that the rate of protein anabolism (synthesis) exceeds that of protein catabolism. o Examples: - Growth - Pregnancy Transamination vs Deamination Ø The release of an amino group from most amino acids requires a two-step process involving Ø Although the overall transamination followed by oxidative deamination. nitrogen balance in the body often varies, the Transamination Deamination relative concentrations Is the removal of an of amino acids within Is the transfer of an amino acid group the amino acid pool Definition amino group to a from an organic remain essentially keto acid. compound. constant. Ø During negative nitrogen balance, the body must Involves two Involves one resort to degradation of proteins that were Molecules molecules: amino molecule: an synthesized for other functions. acid and keto acid amino acid Ø The amino acids from the body’s amino acid pool are Transaminases used in 4 different ways: Enzymes and Deaminase Protein Synthesis (75% Free Amino Acid) aminotransferases Synthesis of nonprotein nitrogen-containing Conversion of compounds (Purine, pyrimidines) essential amino Breakdown of amino Synthesis of nonessential amino acids Conversion acids into acids in order to Production of energy nonessential amino produce energy acids Derivatives of 3 Carboxylic Acids Ø Are particularly important in metabolic reaction. Propionic – a three-carbon monoacid Succinic – a four-carbon monoacid Glutaric – a five-carbon monoacid BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Practice Ø Determine the structural formulas for the products in a transamination reaction in which the reactants are aspartate and pyruvate. Aspartate to Oxaloacetate Pyruvate to Alanine Transamination Reaction Ø Is a biochemical reaction that involves the interchange of the amino group of an α-amino acid with the keto group of an α-keto acid. Ø Determine the structural formulas for the products in a transamination reaction in which the reactants are Ø There are at least 50 aminotransferase enzymes α-ketoglutarate and alanine. associated with transamination reactions. Most are specific for α-ketoglutarate as the amino group acceptor but are less specific for the amino acid. Glutamate is the amino acid produced from the action α-ketoglutarate to Glutamate of α-ketoglutarate specific aminotransferases. Alanine to Pyruvate Initial Effect of Transamination Reactions Ø Is to collect the amino acids from a variety of amino acids into just two amino acids – glutamate (most cells) and alanine (muscle cells) Ø An important exception to the α -ketoglutarate specificity of aminotransferases is found in muscle cells. Here, many aminotransferases have specificity for the keto acid pyruvate. Alanine is the amino acid produced from the action of such pyruvate specific enzymes. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Oxidative Deamination Ø Is a biochemical reaction in which an α-amino acid is converted into an α-keto acid with release of an The Urea Cycle ammonium ion. Definition Ø Oxidative deamination occurs primarily in liver and Ø The urea cycle is the series of biochemical reactions kidney mitochondria. in which urea is produced from ammonium ions and carbon dioxide. Ø Three amino acids are involved in the urea cycle. Arginine Ornithine Citrulline Ø The sum of the transamination and deamination steps o Ornithine and Citrulline are proteins of the degradation of amino acid is: that are not found in proteins a.k.a. non- standard amino acids. Ø Nitrogen Sources Ø The NH4+ so produce, a toxic substance if left to Ammonium Ions (NH4+) accumulate in the body, is then converted to urea in Aspartate the urea cycle. o From blood to liver to kidney to urea Ø Two amino acids, serine and threonine, exhibit different behavior from the other amino acids. They undergo direct deamination by a dehydration- hydration process rather than oxidative deamination. Practice Ø Indicate whether each of the following reaction characteristics is associated with the process of transamination or with the process of oxidative deamination. a. The enzyme glutamate dehydrogenase is active. o Oxidative Deamination b. The coenzyme pyridoxal phosphate is needed. o Transamination Ø Orange-Colored Cats Always Ask For Awesome c. An amino acid is converted into a keto acid with Umbrellas release of ammonium ion. Ornithine, Carbamoyl Phosphate, Citrulline, o Oxidative Deamination Aspartate (enters cycle), Arginosuccinate, d. One of the reactants is an amino acid and one of Fumarate (leaves cycle), Arginine, Urea (leaves the products is an amino acid. cycle) o Transamination Practice Ø Indicate whether each of the following reaction Ø For each of the following urea cycle events identify characteristics is associated with the process of the urea cycle intermediate that is involved. The urea transamination or with the process of oxidative cycle intermediates are ornithine, citrulline, deamination. arginosuccinate, and arginine. a. One of the reactants is a keto acid and one of the a. Intermediate participates in a condensation products is a keto acid. reaction. o Transamination b. Intermediate is produced while urea is formed. b. Enzymes with specificity toward α-ketoglutarate c. Intermediate must be transported from the are often active. mitochondrial matrix to the cytosol. o Transamination d. Intermediate is the product in Step 3 of the urea c. NAD is used as an oxidizing agent. cycle. o Oxidative Deamination d. An aminotransferase enzyme is active. o Transamination BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Ø For each of the following urea cycle events identify the urea cycle intermediate that is involved. The urea cycle intermediates are ornithine, citrulline, arginosuccinate, and arginine. a. Intermediate reacts with carbamoyl phosphate. b. Intermediate must be transported from the cytosol to the mitochondrial matrix. c. Intermediate is a reactant in a hydrolysis reaction. d. Intermediate is the reactant in Step 2 of the urea cycle. Urea Cycle Net Reaction Ø The equivalent of a total of four ATP molecules is expended in the production of one urea molecule. Two ATP molecules are consumed in the production of carbamoyl phosphate, and the equivalent of two ATP molecules is consumed in Step 2 of the urea cycle. The Urea Cycle Ø Glucogenic Amino Acid Is an amino acid that has a carbon-containing degradation product that can be used to produce glucose via gluconeogenesis. Ø Ketogenic Amino Acid Is an amino acid that has a carbon-containing degradation product that can be used to produce ketone bodies. Ø Purely Ketogenic Leucine Lysine Ø Both Glucogenic and Ketogenic Alanine Serine Amino Acid Carbon Skeletons Tyrosine Definition Glycine Ø Each of the 20 amino acid carbon skeletons Threonine undergoes a different Phenylalanine degradation process. Cysteine Ø It is important to Tryptophan consider the products Isoleucine of these 20 degradation Ø Purely Glucogenic sequences: Glutamate Ø 7 Degradation Products of Amino Acids: Proline Pyruvate Valine Acetyl-CoA Glutamine Acetoacetyl-CoA Arginine α-ketoglutarate (intermediates of Citric Acid Asparagine Cycle) Histidine Succinyl-CoA (intermediates of Citric Acid Methionine Cycle) Aspartate Fumarate (intermediates of Citric Acid Cycle) Oxaloacetate (intermediates of Citric Acid Cycle) BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Amino Acid Biosynthesis Ø The oxygen-carrying ability of red blood cells is due Definition to the protein hemoglobin. Ø The nonessential amino acids can be made in 1-3 Hemoglobin is a conjugated protein. steps. Globin – the protein portion Ø The essential amino acids can be made in 7-10 steps Heme – nonprotein portion (contains (observations in microorganisms). 4 pyrrole groups with an iron Ø Plants, consumed as food, are the major source of the atom in the center). essential amino acids in humans and animals. o It is the iron atom in heme that interacts with O2. Ø Old red blood cells are broken down in the: Spleen (primary site) Liver (secondary site) Ø Globin – hydrolyzed to amino acids, which become part of the amino acid pool. Ø Iron Atom – becomes part of ferritin, an iron-storage protein, which saves the iron for use in the biosynthesis of new hemoglobin molecules. Ø Tetrapyrrole – degraded to bile pigments that are eliminated in feces and to a lesser extent in urine. Heme Degradation Ø Step #1: Degradation of heme begins with a ring- opening reaction in which a single atom is removed. Ø The starting materials for the biosynthesis of 11 The product is called biliverdin. nonessential amino acids are: Molecular oxygen, O2, is required as a reactant. 3-phosphoglycerate Ring opening releases the iron atom to be Pyruvate incorporated into ferritin. Oxaloacetate The product containing the excised carbon atom α-ketoglutarate is carbon monoxide. Ø The lack of phenylalanine hydroxylase caused the metabolic disease phenylketonuria (PKU). Characterized by elevated blood levels of phenylalanine and phenylpyruvate. Ø Step #2: In the second step of heme degradation, Damage to developing brain cells. biliverdin is converted to PKU leads to retarded mental development. bilirubin. Management: This usually occurs in the spleen. o Restrict children’s dietary The bilirubin is then transported phenylalanine to that needed for protein by serum albumin to the liver, synthesis until 6 years old. where it is rendered more water-soluble by the attachment Hemoglobin Catabolism of sugar residues to its Definition propionate side chains (P side Ø Red blood cells deliver oxygen to, and remove chains). The solubilizing sugar carbon dioxide from, body tissues. is glucuronate. Ø Mature red blood cells have no nucleus or DNA. Instead, they are filled with the red pigment hemoglobin. Ø The life span of a red blood cell is about 4 months. BIOCHEMISTRY (LECTURE)  BIOCHEMISTRY (LECTURE) Local Coloration Ø The local coloration associated with a deep bruise is also related to the Solubilized bilirubin from the liver to small pigmentation associated with heme, intestine. biliverdin, and bilirubin. Here the bilirubin diglucuronide is changed, in a Ø The changing color of the bruise as it multistep process, to either stercobilin for heals reflects the dominant degradation excretion in feces or urobilin for excretion in product present at the time as the tissue urine. repairs itself. Interrelationships among Metabolic Pathways Definition Ø Carbohydrate, Lipids, and Protein pathways are not independent of each other but rather are integrally linked. Ø The numerous connections among pathways mean that a change in one pathway can affect many other pathways. Ø A good illustration of the interrelationships among Ø The tetrapyrrole degradation process obtained from pathways emerges from comparing the processes of heme are known as bile pigments because they are eating (feasting), not eating for a short period secreted with the bile (highly colored). (fasting), and not eating for a prolonged period Stercobilin (starvation). o Brownish hue = the reason why poops are brown. - 250-350 mg daily Urobilin o Yellowish hue = the reason why urine are yellow. - 1-2 mg daily Ø When the body is functioning properly, degradation of heme to bilirubin in the spleen = removal of bilirubin from the blood by the liver. Jaundice Ø Jaundice is the condition that occurs when this balance us upset such that bilirubin concentrations in the blood become higher than normal. Ø Can occur because of liver diseases, such as: Infectious hepatitis and cirrhosis, that decrease the liver’s ability to process bilirubin. From spleen malfunction, in which heme is degraded more rapidly than it can be absorbed by the liver. From gallbladder malfunction, usually from an obstruction of the bile duct. BIOCHEMISTRY (LECTURE)