Overview of Metabolism & Carbohydrate Significance PDF

Overview of Metabolism Carbohydrate Significance  Overview of Metabolism & the Provision of Metabolic Fuels Metabolic pathways fall into three categories: (1) Anabolic pathways, which are those involved in the synthesis of larger and more complex compounds from smaller prec...

Overview of Metabolism Carbohydrate Significance  Overview of Metabolism & the Provision of Metabolic Fuels Metabolic pathways fall into three categories: (1) Anabolic pathways, which are those involved in the synthesis of larger and more complex compounds from smaller precursors. (2) Catabolic pathways, which are involved in the breakdown of larger molecules, commonly involving oxidative reactions;  Overview of Metabolism & the Provision of Metabolic Fuels A 70-kg adult human being requires about 8 to 12 MJ from metabolic fuels each day. This energy requirement is met from carbohydrates (40%-60%), lipids (30%-40%), and protein (10%-15%), depending on physical activity. Growing children have a proportionally higher requirement to allow for the energy cost of growth. Average physical activity increases metabolic rate. Abnormal metabolism may result from nutritional deficiency, enzyme deficiency, abnormal secretion of hormones, or the actions of drugs and toxins.  Overview of Metabolism & the Provision of Metabolic Fuels In the fed state, after a meal, there is an ample supply of carbohydrate, and the metabolic fuel for most tissues is glucose. In the fasting state, glucose must be spared for use by the central nervous system and the red blood cells. Therefore, tissues that can use fuels other than glucose do so; muscle and liver oxidize fatty acids and the liver synthesizes ketone bodies from fatty acids to export to muscle and other tissues. These processes are controlled by hormones of fed and fasted states.  CLINICAL ASPECTS Diabetes (diabetes mellitus) is a health condition where your body has trouble managing glucose. Body breaks down sugars and starches into glucose, which is a type of sugar that fuels your cells. Normally, a hormone called insulin helps your body use glucose for energy. But in diabetes, either body doesn't produce enough insulin or can't use it effectively. This leads to high levels of glucose in your blood, which can cause various health problems over time if not managed properly. Coma results from both the acidosis (because of ketone bodies production) and also the considerably increased osmolality of extracellular fluid (mainly as a result of the hyperglycemia, and diuresis resulting from the excretion of glucose and ketone bodies in the urine).  CLASSIFICATION AND STRUCTURE OF CARBOHYDRATES Carbohydrates are the most abundant organic molecules in nature. They have a wide range of functions, including providing a significant fraction of the dietary calories; acting as a storage form of energy in the body; serving as cell membrane components that mediate some forms of intercellular communication; The empiric formula for many of the simpler carbo - hydrates is (CH2O)n, hence the name “hydrate of carbon.” Glucose is the most important carbohydrate.  CARBOHYDRATES ARE ALDEHYDE OR KETONE DERIVATIVES OF POLYHYDRIC ALCOHOLS Carbohydrates are classified as follows: 1. Monosaccharides are those sugars that cannot be hydrolyzed into simpler carbohydrates. They may be classified as trioses, tetroses, pentoses, hexoses, or heptoses, depending upon the number of carbon atoms and as aldoses or ketoses, depending on whether they have an aldehyde or ketone group. 2. Disaccharides are condensation products of two monosaccharide units, for example, lactose, maltose, sucrose. 3. Oligosaccharides are condensation products of three to ten monosaccharides. Most are not digested by human enzymes. 4. Polysaccharides are condensation products of more than ten monosaccharide units.  ISOMERS AND EPIMERS D and L isomerism: The orientation of the —H and —OH groups around the carbon atom adjacent to the terminal alcohol carbon (carbon 5 in glucose) determines whether the sugar belongs to the D or L series. Most of the naturally occurring monosaccharides are D sugars, and the enzymes responsible for their metabolism are specific for this configuration. Fischer Projection Formulas Pyranose and Furanose ring structures: The ring structures of monosaccharides are similar to the ring structures of either pyran (a six-membered ring) or furan (a five membered ring). For glucose in solution, more than 99% is in the pyranose form. Epimers: are like sugar molecules but have one small difference. Imagine glucose as the original when we slightly change the position of some parts of glucose, we get mannose and galactose, which are its epimers. For example, mannose changes at carbon 2, and galactose changes at carbon 4. Aldose-ketose isomerism: Both fructose and glucose have the same molecular formula, C6H12O6. Despite having the same atoms (carbon, hydrogen, and oxygen) in the same proportion, the arrangement of these atoms differs in fructose and glucose. In glucose, the carbonyl group is an aldehyde (at the end of the chain), whereas in fructose, it's a ketone (within the chain). This structural difference gives them distinct chemical and biological properties.  Disaccharides α and β Maltose are two distinct forms of maltose, which is a disaccharide composed of two glucose molecules. In α maltose, the glycosidic bond between the two glucose molecules is formed with the alpha configuration. This means that the oxygen atom in the first glucose molecule is below the plane of the ring, and in the second glucose molecule, it's above the plane.  Disaccharides In β maltose, the glycosidic bond between the two glucose molecules is formed with the beta configuration. This means that the oxygen atoms in both glucose molecules are above the plane of the ring. Alpha maltose is the more common form found in nature and is the primary form produced during starch digestion. Beta maltose is less common in nature and typically arises from enzymatic or chemical processes that specifically generate the beta form. Disaccharides  Polysaccharides Starch and Glycogen are both storage forms of glucose in plants and animals, respectively. Amylose is a linear polymer of glucose units joined by alpha-1,4- glycosidic bonds. Amylopectin is a branched polymer with both alpha- 1,4 and alpha-1,6 glycosidic bonds.  Glycoproteins Glycoproteins (also known as mucoproteins) are proteins containing branched or unbranched oligosaccharide chains including fucose. They occur in cell membranes and many proteins are glycosylated. The sialic acids are N- or O-acyl derivatives of neuraminic acid. Neuraminic acid same as Sialic acid is a ninecarbon sugar. Sialic acids are constituents of both glycoproteins and gangliosides. Ser or Thr residues (O-linked glycosylation) or Asn residues (N-linked glycosylation). Cell recognition and signaling: Immune response: Structural support: Enzymatic activity: Cell adhesion: Hormone function: