Irreversible inhibitors

Compounds that inhibit enzymes may either act reversibly, so that the inhibition gradually wears off as the inhibitor is metabolized, or irreversibly, causing chemical modification of the enzyme protein, so that the effect of the inhibitor is prolonged, and only diminishes gradually as the enzyme protein is catabolized and replaced (section 9.1.1). It is important when designing drugs to know whether they act as reversible or irreversible inhibitors. An irreversible inhibitor may only need to...

Classification and naming of enzymes

There is a formal system of enzyme nomenclature, in which each enzyme has a number, and the various enzymes are classified according to the type of reaction catalysed and the substrates, products and coenzymes of the reaction. This is used in research publications, when there is a need to identify an enzyme unambiguously, but for general use there is a less formal system of naming enzymes. Almost all enzyme names end in -ase, and many are derived simply from the name of the substrate acted on,...

Diabetes mellitus a failure of regulation of blood glucose concentration

Diabetes mellitus is an impaired ability to regulate the concentration of blood glucose as a result of a failure of the normal control by insulin. Therefore, the plasma glucose concentration is considerably higher than normal, especially after a meal. When it rises above the capacity of the kidney to reabsorb it from the glomerular filtrate (the renal threshold, 11 mmol L), the result is glucosuria excretion of glucose in the urine. As a result of glucosuria, there is increased excretion of...

Digestion and absorption of fats

The major fats in the diet are triacylglycerols and, to a lesser extent, phospholipids. These are hydrophobic molecules and have to be emulsified to very small droplets (micelles section 4.3.2.2) before they can be absorbed. This emulsification is achieved by hydrolysis to monoacyl- and diacylglycerols and free fatty acids, and also by the action of the bile salts (section 4.3.2.1). 4.3.1 The classification of dietary lipids Four groups of compounds that are metabolically important can be...

Alcohol

A high intake of alcoholic drinks can be a factor in causing obesity, both as a result of the energy yield of the alcohol itself and also because of the relatively high carbohydrate content of many alcoholic beverages. People who satisfy much of their energy requirement from alcohol frequently show vitamin deficiencies, because they are meeting their energy needs from drink, and therefore are not eating enough food to provide adequate amounts of vitamins and minerals. Deficiency of vitamin Bt...

Energy balance and changes in body weight

When energy intake is greater than energy expenditure (positive energy balance) there is increased storage of excess metabolic fuel, largely as adipose tissue similarly, if energy intake is inadequate to meet expenditure (negative energy balance), there is utilization of reserves of adipose tissue. Adipose tissue consists of 80 triacylglycerol (with an energy yield of 37 kJ g) and 5 protein (energy yield 17 kJ g) the remaining 15 is water. Hence, adipose tissue reserves are equivalent to...

Pharmacological treatment of obesity

A number of compounds act either to suppress the activity of the hunger centre in the hypothalamus or to stimulate the satiety centre. Sometimes this is an undesirable side-effect of drugs used to treat disease and can contribute to the undernutrition seen in chronically ill people (section 8.4). As an aid to weight reduction, especially in people who find it difficult to control their food intake, drugs that suppress appetite can be useful. Three compounds are in relatively widespread use as...

Energy costs of physical activity

The most useful way of expressing the energy cost of physical activities is as a multiple of BMR. The physical activity ratio (PAR) for an activity is the ratio of the energy expended while performing the activity to that expended at rest ( BMR). Very gentle, sedentary activities use only about 1.1 1.2 times BMR. By contrast, as shown in Table 5.3, vigorous exertion, such as climbing stairs, cross-country walking uphill, etc. may use 6 8 times BMR. Using data such as those in Table 5.3 and...

Tissue reserves of metabolic fuels

In the fed state, as well as providing for immediate energy needs, substrates are converted into storage compounds for use in the fasting state. There are two main stores of metabolic fuels triacylglycerols in adipose tissue glycogen as a carbohydrate reserve in liver and muscle. In addition, there is an increase in the synthesis of tissue proteins after a meal, as a result of the increased availability of metabolic fuel to provide ATP for protein synthesis (section 9.2.3.3). In the fasting...

Serum cholesterol mmol L

Figure 7.9 The relationship between serum cholesterol and coronary heart disease mortality. From data reported by the Multiple Risk Factor Intervention Trial Research Group (1982) Journal of the American Medical Association 248 1465-1475. 10 12 14 16 18 20 22 saturated fat, energy 10 12 14 16 18 20 22 saturated fat, energy 2 4 6 8 10 polyunsaturated fat, energy 2 4 6 8 10 polyunsaturated fat, energy 100 200 300 400 500 600 700 800 cholesterol, mg day Figure 7.10 The effects of dietary saturated...

Basal metabolic rate BMR

Basal metabolic rate is the energy expenditure by the body when at rest, but not asleep, under controlled conditions of thermal neutrality, and about 12 hours after the last meal. It is the energy requirement for the maintenance of metabolic integrity, nerve and muscle tone, circulation and respiration (see Figure 1.2 for the contribution Table 5.2 Definitions in energy metabolism Table 5.2 Definitions in energy metabolism Energy expenditure in the post-absorptive state measured under...

Problem Measurement of urine glucose

As discussed in section 4.2.1.4, glucose in plasma and urine can be determined in two ways, using an alkaline copper reagent or using glucose oxidase linked to a dyestuff. Both methods were used to determine urine glucose in six people A a person with hitherto undiagnosed diabetes mellitus (section 10.7) B a known diabetic patient, with poor glycaemic control, taking supplements of 500 mg of vitamin C per day C a non-diabetic subject taking supplements of 500 mg of vitamin C per day D a person...

Additional resources

Self-assessment quiz 5 on the CD. Winston is a 75-kg man who takes part in a 100 m sprint. His plasma lactate was 0.5 mmol L before the race and 11.5 mmol L immediately after the race. Thirty minutes later, when his breathing had returned to normal, it was 1.0 mmol L. Assuming that extracellular fluid is 20 of body weight, what is the total amount of lactate that he metabolizes during this 30 minutes Most of this lactate will be metabolized in the liver,...

Problem an experiment with C and Nlabelled urea

The first enzyme to be crystallized and hence the first evidence that enzymes are proteins was urease, which catalyses the hydrolysis of urea to ammonium and carbon dioxide. The original preparation of urease was from plant material, but the enzyme is also known to occur in a number of bacteria. In this study, a group of volunteers were given an intravenous infusion of 20 mmol urea labelled with both 13C and 15N and their urinary excretion of label was measured over 24 hours. Complete recovery...

Experimental determination of K and V

Plotting the graph of rate of reaction against substrate concentration, as in Figure 2.8, permits only an approximate determination of the values of K and V , and a ' J m max' number of methods have been developed to convert this hyperbolic relationship into a linear relationship, to permit more precise fitting of a line to the experimental points, and hence more precise estimation of K and V . The most widely used such linearization of the data is the Lineweaver Burk double-reciprocal plot of...

Synthesis of fatty acids and triacylglycerols

From Oxaloacetate Pyruvate

Fatty acids are synthesized by the successive addition of two-carbon units from acetyl CoA, followed by reduction. Like -oxidation, fatty acid synthesis is a spiral sequence of reactions, with different enzymes catalysing the reaction sequence for synthesis of short, medium- and long-chain fatty acids. Unlike -oxidation, which occurs in the mitochondrial matrix, fatty acid synthesis occurs in the cytosol. The enzymes required for fatty acid synthesis form a multienzyme complex, arranged in a...

The gastrointestinal tract

Water Digestion And Absorption

The gastrointestinal tract is shown in Figure 4.1. The major functions of each region are starch hydrolysis catalysed by amylase, secreted by the salivary glands fat hydrolysis catalysed by lingual lipase, secreted by the tongue absorption of small amounts of vitamin C and a variety of non-nutrients including nicotine . denaturation of dietary proteins section 4.4.2 and the release of vitamin B, iron and other minerals from protein binding, for which gastric acid is important protein hydrolysis...

The fasting state

Ketone Bodies Starvation

In the fasting state sometimes known as the post-absorptive state, as it begins about 4 5 hours after a meal, when the products of digestion have been absorbed metabolic fuels enter the circulation from the reserves of glycogen, triacylglycerol and protein laid down in the fed state Figure 5.7 . As the concentration of glucose and amino acids in the portal blood falls, so the secretion of insulin by the P-cells of the pancreas decreases and the secretion of glucagon by the a-cells increases....

Digestion and absorption of carbohydrates

What Ch2oh Called

Carbohydrates are compounds of carbon, hydrogen and oxygen in the ratio Cn H 'O . The basic unit of the carbohydrates is the sugar molecule or monosaccharide. Note that sugar is used here in a chemical sense, and includes a variety of simple carbohydrates that are collectively known as sugars. Ordinary table sugar cane sugar or beet sugar is correctly known as sucrose as discussed in section 4.2.1.3, it is a disaccharide. It is just one of a number of different sugars found in the diet. 4.2.1...

Problem Arthur N

Arthur is a 75-year-old man, 170 cm tall and weighing 50 kg. He has advanced cancer, and has lost 2 kg body weight over the last 4 weeks. What is his body mass index Is it within the desirable range His mean skinfold thickness is 1.9 mm, suggesting that he has negligible reserves of adipose tissue, and he shows considerable wasting of muscle, so we can assume that most of his weight loss is muscle. The composition of muscle is 79 water, 17 protein at 17 kJ g and 3 fat at 37 kJ g . What was his...

Enzymes with two substrates

Ordered Ping Pong Lineweaver Burk Graph

Most enzyme-catalysed reactions involve two substrates it is only enzymes catalysing lysis of a molecule or an isomerization reaction section 2.5 that have only a single substrate. Figure 2.9 The Lineweaver Burk double-reciprocal plot to determine K and V . For a reaction involving two substrates and two products A B C D the enzyme may act by either an ordered mechanism, in which each substrate binds in turn A Enz A-Enz A-Enz B A-Enz-B C-Enz-D C-Enz D C-Enz Enz C a ping-pong mechanism in which...

Functions of ATP

Dephosphorylation Atp H2o

Under normal conditions, the processes shown in Figure 3.2 are tightly coupled, so that the oxidation of metabolic fuels is controlled by the availability of ADP, which, in turn is controlled by the rate at which ATP is being utilized in performing physical and chemical work. Work output, or energy expenditure, thus controls the rate at which metabolic fuels are oxidized, and hence the amount of food that must be eaten to meet energy requirements. As discussed in section 5.3.1, metabolic fuels...

Glutathione peroxidase

Tocopheroxyl Radical

Lipid peroxides formed by radical action on unsaturated fatty acids in membranes and LDL can be reduced to unreactive alcohols by the enzyme glutathione peroxidase, with the oxidation of the tripeptide glutathione y-glutamyl-cysteinyl-glycine, GSH to the disulphide-linked GSSG. In turn, oxidized glutathione is reduced back to the active peptide by glutathione reductase, as shown in Figure 5.15. Glutathione reductase has selenium at the catalytic site, as a selenocysteine residue section...

Digestion and absorption of proteins

Quaternary Structure Protein Bonds

Unlike starch and glycogen, which are polymers of only a single type of monomer unit glucose , proteins consist of a variety of amino acids. There is an almost infinite variety of proteins, composed of different numbers of the different amino acids between 50 and 1,000 amino acids in a single protein molecule , in different order. There are some 30 50,000 different proteins and polypeptides in the human body. Each protein has a specific sequence of amino acids....

Desirable body weight

Figure 6.1 shows the relationship between body weight and premature death. It is based on a study of 750,000 people, who were classified according to their percentage of the average weight of the study group, then followed for 15 years. There is a steady lt 80 85 95 105 115 125 135 gt 140 weight as percent of mean Figure 6.1 Excess mortality with obesity. From data reported by Garfinkel L 1986 Cancer 58 1826-1829. increase in mortality with increasing body weight above average, so that people...

Chemical reactions breaking and making covalent bonds

Breaking covalent bonds requires an initial input of energy in some form normally as heat, but in some cases also light or other radiation. This is the activation energy of the reaction. The process of breaking a bond requires activation of the electrons forming the bond a temporary shift of electrons from orbitals in which they have a stable configuration to other orbitals, further from the nucleus. Electrons that have been excited in this way have an unstable configuration, and the covalent...

Protein synthesis

Dna Protein Metabolism

The information for the amino acid sequence of each of the 30 50,000 different proteins in the body is contained in the DNA in the nucleus of each cell. As required, a working copy of the information for an individual protein the gene for that protein is transcribed, as messenger RNA mRNA , and this is then translated during protein synthesis on the ribosomes. Both DNA and RNA are linear polymers of nucleotides. In RNA the sugar is ribose, whereas in DNA it is deoxyribose. 9.2.1 The structure...

Riboflavin and flavoproteins

Vitamin B2 riboflavin section 11.7 is important in a wide variety of oxidation and reduction reactions. A few enzymes contain riboflavin itself, while others contain a riboflavin derivative either riboflavin phosphate sometimes called flavin mononucleotide or flavin adenine dinucleotide FAD Figure 2.14 . When an enzyme contains riboflavin, it is usually covalently bound at the active site. Although riboflavin phosphate and FAD are not normally covalently bound to the enzyme, they are very...

The phosphorylation of ADP to ATP

Muscle Metabolism And Atp

A small number of metabolic reactions involve direct transfer of phosphate from a phosphorylated substrate onto ADP, forming ATP substrate-level phosphorylation. Two such reactions are shown in Figure 3.13 both are reactions in the glycolytic pathway of glucose metabolism section 5.4.1 . Substrate-level phosphorylation is of Figure 3.13 Formation of ATP by substrate level phosphorylation see also Figure 5.10 . Figure 3.13 Formation of ATP by substrate level phosphorylation see also Figure 5.10...

Indirect calorimetry and the respiratory quotient

Energy expenditure can be determined from the rate of consumption of oxygen. This is known as indirect calorimetry, as there is no direct measurement of the heat produced. As shown in Table 5.1, there is an output or expenditure of 20 kJ per litre of oxygen consumed, regardless of whether the fuel being metabolized is carbohydrate, fat or protein. Measurement of oxygen consumption is quite simple using a spirometer. Such instruments are portable, so people can carry on more or less normal...

Luxury status of scarce and expensive foods

Foods that are scarce or expensive have a certain appeal of fashion or style they are rightly regarded as luxuries for special occasions rather than everyday meals. Conversely, foods that are widespread and cheap have less appeal. In the nineteenth century, salmon and oysters were so cheap that the Articles of apprentices in London specified that they should not be given salmon more than three times a week, while oysters were eaten by the poor. Through much of the twentieth century, salmon was...

The citric acid cycle as pathway for metabolic interconversion

Citric Cycle Metabolism

In addition to its role in oxidation of acetyl CoA, the citric acid cycle is an important central metabolic pathway, providing the link between carbohydrate, fat and amino Figure 5.19 The GABA shunt an alternative to a-ketoglutarate dehydrogenase in the citric acid cycle. Figure 5.19 The GABA shunt an alternative to a-ketoglutarate dehydrogenase in the citric acid cycle. acid metabolism. Many of the intermediates can be used for the synthesis of other compounds a-Ketoglutarate and oxaloacetate...

Hunger and satiety shortterm control of feeding

Lateral Hypothalamus Hunger

As shown in Figure 1.3, there are hunger and satiety centres in the brain, which stimulate us to begin eating the hunger centres in the lateral hypothalamus and to to stop eating when hunger has been satisfied the satiety centres in the ventromedial hypothalamus . A great deal is known about the role of these brain centres in controlling food intake, and there are a number of drugs which modify responses to hunger and satiety. Such drugs can be used to reduce appetite in the treatment of...

Carnitine and the transport of fatty acids into the mitochondrion

Carnitine Structure

As shown in Figure 5.21, fatty acids are esterified with coenzyme A, forming acyl CoA, as they enter the cell. This is necessary to protect the cell membranes against the lytic action of free fatty acids. Fatty acyl CoA cannot cross the mitochondrial membranes to enter the matrix, where the enzymes for -oxidation are. On the outer face of the outer mitochondrial membrane, the fatty acid is transferred from CoA onto carnitine, forming acylcarnitine, which enters the inter-membrane space through...

Glycolysis the anaerobic metabolism of glucose

Glycolysis Ch2oh Atp Adp

Overall, the pathway of glycolysis is cleavage of the six-carbon glucose molecule into two three-carbon units. The key steps in the pathway are two phosphorylation reactions to form fructose bisphosphate cleavage of fructose bisphosphate to yield two molecules of triose three-carbon sugar phosphate two steps in which phosphate is transferred from a substrate onto ADP, forming ATP and hence a yield of 4 X ATP per mole of glucose metabolized one step in which NAD is reduced to NADH equivalent to...

The pentose phosphate pathway an alternative to glycolysis

Pentose Phosphate Pathway

There is an alternative pathway for the conversion of glucose 6-phosphate to fructose 6-phosphate, the pentose phosphate pathway sometimes known as the hexose monophosphate shunt , shown in Figure 5.14. Overall, the pentose phosphate pathway produces 2 mol of fructose 6-phosphate, 1 mol of glyceraldehyde 3-phosphate and 3 mol of carbon dioxide from 3 mol of glucose 6-phosphate, linked to the reduction of 6 mol of NADP to NADPH. The sequence of reactions is as follows Three mol of glucose are...

Bioflavonoids

The bioflavonoids are a variety of compounds gt 4000 are known in all plants most occur as glycosides with a variety of sugars and are hydrolysed to aglycones by digestive enzymes. They serve both to protect plants against attack and also as the pigments of many plants. They were at one time considered to be vitamins vitamin P , although there is no evidence that they are dietary essentials, then during the 1970s were considered to be mutagens and carcinogens, because, as shown in Figure 7.21,...

Effect of substrate concentration

In a simple chemical reaction involving a single substrate, the rate at which product is formed increases linearly as the concentration of the substrate increases. When more substrate is available, more will undergo reaction. With enzyme-catalysed reactions, the change in the rate of formation of product with increasing concentration of substrate is not linear, but hyperbolic, as shown in Figure 2.8. At relatively low concentrations of substrate region A in Figure 2.8 , the catalytic site of...

Synthesis of triacylglycerols

Synthesis Triacylglycerols

The storage lipids in adipose tissue are triacylglycerols glycerol esterified with three molecules of fatty acids. As discussed in section 4.3.1, the three fatty acids in a triacylglycerol molecule are not always the same, and the fatty acid at carbon-2 is usually unsaturated. Triacylglycerols are synthesized mainly in the liver, adipose tissue and small intestinal mucosa, as well as lactating mammary gland. As shown in Figure 5.29, the substrates for triacylglycerol synthesis are fatty acyl...

Oxidation of acetyl CoA THE citric acid CYCLE

Simple Krebs Cycle

The acetate of acetyl CoA undergoes a stepwise oxidation to carbon dioxide and water in a cyclic pathway, the citric acid cycle, shown in Figures 5.17 and 5.18. This pathway is sometimes known as the Krebs cycle, after its discoverer, Sir Hans Krebs. For each mole of acetyl CoA oxidized in this pathway, there is a yield of Figure 5.17 An overview of the citric acid cycle also known as the Krebs cycle or tricarboxylic acid cycle . Figure 5.17 An overview of the citric acid cycle also known as...

Coenzymes and metals in oxidation and reduction reactions

In its simplest form, oxidation is the combination of a molecule with oxygen. Thus, if a carbohydrate, such as glucose C6H12O6 , is burned in air or metabolized in the body , it is oxidized to carbon dioxide and at the same time oxygen is reduced to water Oxidation reactions need not involve the addition of oxygen oxidation is the removal of electrons from a molecule. Thus, the conversion of the iron Fe2 ion to Fe3 is also an oxidation, although in this case there is no direct involvement of...

Complete oxidation of four and fivecarbon compounds

Although the citric acid cycle is generally regarded as a pathway for the oxidation of four- and five-carbon compounds arising from amino acids, such as fumarate, oxaloacetate, a-ketoglutarate and succinate see Figure 5.20 , it does not, alone, permit complete oxidation of these compounds. Four-carbon intermediates are not overall consumed in the cycle, as oxaloacetate is reformed. Addition of four- and five-carbon intermediates will increase the rate of cycle activity subject to control by the...

Ketone bodies

Most tissues have a limited capacity for fatty acid oxidation and in the fasting state cannot meet their energy requirements from fatty acid oxidation alone. By contrast, the liver is capable of forming considerably more acetyl CoA from fatty acids than is required for its own metabolism. It takes up fatty acids from the circulation and oxidizes them to acetyl CoA, then synthesizes and exports the four-carbon ketone Figure 5.24 -Oxidation offatty acids. bodies formed from acetyl CoA to other...

Cooperative allosteric enzymes

Allosteric Enzyme Sigmoid

Not all enzymes show the simple hyperbolic dependence of rate of reaction on substrate concentration shown in Figure 2.8. Some enzymes consist of several separate protein chains, each with an active site. In many such enzymes, the binding of substrate to one active site causes changes in the conformation not only of that active site, but of the whole multi-subunit array. This change in conformation affects the other active sites, altering the ease with which substrate can bind to the other...

Gluconeogenesis the synthesis of glucose from

To a considerable extent the plasma concentration of glucose is maintained in short-term fasting by the use of glycogen, and by releasing free fatty acids from adipose tissues and ketone bodies from the liver, which are preferentially used by muscle, so sparing such glucose as is available for use by the brain and red blood cells. However, the total body content of glycogen would be exhausted within 12 18 hours of fasting if there were no other source of glucose. This is the process of...

Responses to fastacting hormones by covalent modification of enzyme proteins

Glycogen Synthase

A number of regulatory enzymes have a serine or sometimes a tyrosine or threonine residue at a regulatory site. This can undergo phosphorylation catalysed by a protein kinase, as shown in Figure 10.5. Phosphorylation may increase or decrease the activity of the enzyme. Later, the phosphate group is removed from the enzyme by phosphoprotein phosphatase, thus restoring the enzyme to its original state. These responses are not instantaneous, but they are rapid, with a maximum response within a few...

Transfer of NADH from glycolysis into the mitochondria

Malate Aspartate Glycolysis

The mitochondrial inner membrane is impermeable to NAD, and therefore the NADH produced in the cytosol in glycolysis cannot enter the mitochondria for reoxidation. In order to transfer the reducing equivalents from cytosolic NADH into the mitochondria, two substrate shuttles are used The malate aspartate shuttle Figure 5.11 involves reduction of oxaloacetate in the cytosol to malate with the oxidation of cytosolic NADH to NAD . Malate enters the mitochondria and is reduced back to oxaloacetate,...

Cachexia

Patients with advanced cancer, human immunodeficiency virus HIV infection and acquired immune deficiency syndrome AIDS and a number of other chronic diseases are frequently undernourished. Physically they show all the signs of marasmus, but there is considerably more loss of body protein than occurs in starvation. The condition is called cachexia, from the Greek Ka e io for 'in a poor condition' . A number of factors contribute to the problem The patients are extremely sick, and because of this...

Effect of temperature

Chemical reactions proceed faster at higher temperatures, for two reasons Molecules move faster at higher temperatures, and hence have a greater chance of colliding to undergo reaction. At a higher temperature it is also easier for electrons to gain activation energy, and hence become excited into unstable orbitals to undergo reaction. With enzyme-catalysed reactions, although the rate at which the reaction comes to equilibrium increases with temperature, there is a second effect of temperature...

Problem Amelia Q

Amelia is the only child of non-consanguineous parents, born at term after an uneventful pregnancy. At 14 months of age she was admitted to hospital with a 1 day Table 10.6 Clinical chemistry results for plasma and urine samples from Amelia Q on admission and again 1 week later Glucose mmol L Sodium mmol L Chloride mmol L Glucose mmol L Sodium mmol L Chloride mmol L Lactate mg per g creatinine Ketone bodies, using Ketostix Lactate mg per g creatinine Ketone bodies, using Ketostix Table 10.7...

Time hours

Figure 4.22 The effect on plasma glucose of a 50 g test dose of lactose. The two solid lines show the range of results obtained for 10 of the subjects the dotted line marked with squares shows the results for one subject, Ahmed L. Table 4.3 Lactose intolerance in different population groups Population group or country of study Tuareg nomads of the central Sahara Singapore-born Chinese Canadian-born Chinese Papua New Guinea 4.7 7.5 12.7 15.0 23.0 25.0 26.2 71.2 72.5 75.0 75.0 78.0 89.0 92.4 97.9...

Hormonal control in the fed and fasting states

Hydrolysis Triacylglycerol

In the fed state see Figure 5.6 , when there is an ample supply of metabolic fuels from the gut, the main processes occurring are synthesis of reserves of triacylglycerol and glycogen glucose is in plentiful supply and is the main fuel for most tissues. By contrast, in the fasting state see Figure 5.7 the reserves of triacylglycerol and glycogen are mobilized for use, and glucose, which is now scarce, must be spared for use by the brain and red blood cells. As discussed in section 5.3, the...

Marasmus

Marasmus is a state of extreme emaciation the name is derived from the Greek iapao ioo for wasting. It is the predictable outcome of prolonged negative energy balance with severe depletion of all energy reserves in the body. Table 8.2 Classification of protein-energy malnutrition in children 60-80 of expected weight for lt 60 of expected weight for age Marasmus Marasmic kwashiorkor Not only have the body's fat reserves been exhausted, but there is wastage of muscle as well, and as the condition...

Intracellular regulation of enzyme activity

Activateur Reaction Enzymatique

As discussed in section 2.3.3, the rate at which an enzyme catalyses a reaction increases with increasing concentration of substrate, until the enzyme is more or less saturated. This means that an enzyme that has a high Km relative to the usual concentration of its substrate will be sensitive to changes in substrate availability. By contrast, an enzyme that has a low Km relative to the usual concentration of its substrate will act at a more or less constant rate regardless of changes in...

The pentose phosphate pathway in red blood cells favism

Pathway Production Red Blood Cells

The pentose phosphate pathway is also important in the red blood cell, where NADPH is required to maintain an adequate pool of reduced glutathione, which is used to remove hydrogen peroxide. As shown in Figure 5.15, the tripeptide glutathione y-glutamyl-cysteinyl-glycine is the reducing agent for glutathione peroxidase, which reduces H2O2 to H2O and O2. Glutathione peroxidase is a selenium-dependent enzyme section 11.15.2.5 , and this explains the antioxidant action of selenium. Oxidized...

The nicotinamide nucleotide coenzymes NAD and NADP

Nucleotide Coenzymes Coenzyme

The vitamin niacin section 11.8 is important for the formation of two closely related compounds, the nicotinamide nucleotide coenzymes - nicotinamide adenine dinucleotide NAD and nicotinamide adenine dinucleotide phosphate NADP . As shown in Figure 2.16, they differ only in that NADP has an additional phosphate group attached to the ribose. The whole of the coenzyme molecule is essential for binding to enzymes, and most enzymes can bind and use only one of these two coenzymes, either NAD or...

Problem A problem of bleeding cows and chickens rat poison and patients with thrombosis

During the 1920s a new disease of cattle involving fatal bleeding appeared over a wide area of prairie land in North America. It was eventually traced to feeding the animals on hay made from sweet clover Melilotus alba and M. officinalis , which had 'mysteriously gone bad'. After eating the hay, the animals suffered a gradual decline in the clotting power of the blood over about 15 days , followed by the development of internal haemorrhage which was generally fatal after 30 50 days. The disease...

Slowacting hormones changes in enzyme synthesis

Action Hormone

As discussed in section 9.1.1, there is continual turnover of proteins in the cell, and not all proteins are broken down and replaced at the same rate. Some are relatively stable, whereas others, and especially enzymes that are important in metabolic regulation, have short half-lives of the order of minutes or hours. This rapid turnover means that it is possible to control metabolic pathways by changing the rate at which a key enzyme is synthesized, and hence the total amount of that enzyme in...

Selection of fuel for muscle activity

Ketone Body Breakdown

its own reserves of glycogen triacylglycerol from plasma lipoproteins plasma non-esterified fatty acids triacylglycerol from adipose tissue reserves within the muscle. The selection of metabolic fuel depends on both the intensity of work being performed and also whether the individual is in the fed or fasting state. 10.6.1 The effect of work intensity on muscle fuel selection Skeletal muscle contains two types of fibres Type I red muscle fibres. These are also known as slow-twitch muscle...

The metabolism of amino acids

How Malate Converted Oxaloacetate

An adult has a requirement for a dietary intake of protein because there is continual oxidation of amino acids as a source of metabolic fuel and for gluconeogenesis in the fasting state. In the fed state, amino acids in excess of immediate requirements for protein synthesis are oxidized. Overall, for an adult in nitrogen balance, the total amount of amino acids being metabolized will be equal to the total intake of amino acids in dietary proteins. Amino acids are also required for the synthesis...

Kwashiorkor

Kwashiorkor was first described in Ghana, in west Africa, in 1932 the word is the Ghanaian name for the condition. In addition to the wasting of muscle tissue, loss of intestinal mucosa and impaired immune responses seen in marasmus, children with kwashiorkor show a number of characteristic features which distinguish this disease Fluid retention and hence severe oedema, associated with a decreased concentration of plasma proteins. The puffiness of the limbs, due to the oedema, masks the severe...

Problem Lucinda K

Lucinda is the second child of unrelated parents. She was born at term after an uneventful pregnancy, weighing 3.4 kg, and was breast fed, with gradual introduction of solids from 3 months of age. Her mother reported that, although Lucinda liked cheese, meat and fish, she frequently became irritable and grizzly after meals, and became lethargic, drowsy and 'floppy' after eating relatively large amounts of protein-rich foods. Her urine had a curious odour, described by her mother as being...

Problem Vitamin C and collagen synthesis

Clinically, scurvy section 11.14.3 is characterized by fragility of the blood vessel walls and small subcutaneous haemorrhages around hair follicles petechial haemorrhages , as well as inflammation of the gums and loss of the dental cement and hence loss of teeth and poor healing of wounds. In advanced cases there is intense deep bone pain, and there may be degenerative changes in the heart, leading to cardiac emergency. In some cases there are also mood changes indeed, scurvy is the old...