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Carbohydrates

Terms

Monosaccharide - A simple sugar with the general formula (CH?O)n, where n represents the number of times the ratio is repeated. Dietary monosaccharides are 6 carbon structures in the form of five or six-sided rings and include fructose, glucose, and galactose.

Disaccharides - A class of sugars formed via a glycosidic bond between two monosaccharides. Dietary disaccharides include maltose, sucrose, and lactose.

Oligosaccharides - Carbohydrates consisting of three to ten monosaccharide units joined by glycosidic linkages.

Polysaccharides - Carbohydrates containing thousands of glucose units joined by alpha or beta glycosidic bonds. Common polysaccharides include glycogen and starch (amylose or amylopectin).

Nucleotide - A structural unit containing a nitrogenous base, a sugar and one or more phosphate groups. The sugar is a five-sided ring consisting of two hydroxyl groups, as in ribonucleic acid (RNA), or one hydroxyl group as in deoxyribonucleic acid (DNA).

Glucose - A six-carbon monosaccharide composed of hydroxyl groups in its cyclic form and an aldehyde group in its linear form. In solution, the sugar exists mostly in its cyclic form and is the primary source of energy in the body.

Fructose - A six-carbon monosaccharide consisting of hydroxyl groups in its cyclic form and a ketone group in its linear form. In solution, it exists as a five- membered cyclic structure and is metabolized to a derivative of glucose by the liver after absorption into the blood.

Galactose - A six-carbon sugar identical to glucose except that it differs in the three- dimensional arrangement of one hydroxyl group. Because of this unique difference, it is known as an epimer of glucose.

Hydroxyl group - A chemical group consisting of an oxygen atom covalently bonded to a hydrogen atom. Since its electron density is greatest around the oxygen atom, the group has a polar character to its bond and is therefore either very hydrophilic or water soluble.

Epimer - A sugar or other compound differing in three-dimensional configuration about a single asymmetric center.

Chair conformation - A three-dimensional configuration consisting of a six-membered ring in which all hydroxyl groups face away from the ring in an equatorial position. The chair conformation is the most energetically stable of all different forms of the ring. Bonding angles appear in the shape of a chair. For an Organic Chemistry explanation of chair conformations, see Carbocycles.

Boat conformation - Slightly less stable than the chair conformation, the boat conformation consists of a six-membered ring in which some of the hydroxyl groups face toward the ring. Bonding angles appear in the shape of a boat. For an Organic Chemistry explanation of chair conformations, see Carbocycles.

Steric hindrance - An organic chemistry term that helps describes how molecular groups interfere with other groups in the structure. For an Organic Chemistry explanation of chair conformations, see Conformations.

Isomers - Molecules that have the same chemical formula but different structures.

Ketone - Compounds containing a carbon-oxygen double bond where two chemical groups surround the carbon atom. Neither of these chemical groups which are bonded to the carbon atom can be a hydrogen atom.

Aldehyde - Compounds contain a carbon-oxygen double bond where one of the chemical groups surrounding the carbon atom is a hydrogen atom.

Glycosidic bond - A type of covalent chemical bond that joins two simple sugars via an oxygen atom. The bond may be either above the plane of the ring as in a beta glycosidic bond or below the plane as in an alpha glycosidic linkage.

Fermentation - Fermentation is the conversion of carbohydrates to form alcohol, acids, or carbon dioxide without the use of oxygen.

Lactic acid - Lactic acid is the product of an oxidation-reduction reaction between the reduced form of nicotinamide adenine dinucleotide (NADH) and pyruvate. It can cause muscle cramping and fatigue during exercise.

Anaerobic - Coming from the words "without oxygen," anaerobic conditions persist when the body cannot use oxygen to obtain energy because energy is required at a faster pace than the electron transport chain can provide.

Starch - Starch is the storage form of glucose in plants. It comes in two different forms: amylose and amylopectin.

Amylose - One of the two different forms of starch, amylose is a linear polymer of glucose joined by repeating alpha glycosidic bonds. Amylose is easily digested and degraded to glucose by the enzymes in the small intestine.

Amylopectin - Similar to amylose, this form of starch is a polymer of glucose joined by alpha glycosidic linkages. Unlike its cousin, amylopectin is a highly branched structure due to the fact it contains alpha glycosidic bonds that are joined at different locations in the glucose polymer. It is easily digested by the enzymes in the small intestine.

Cellulose - An indigestible polysaccharide, cellulose is an important form of dietary fiber and is present in many different plants. Due to its glycosidic linkages and its intramolecular hydrogen bonding, cellulose is very strong polymer of glucose.

Deoxyribonucleic acid (DNA) - A long polymer of nucleotides joined by phosphate groups, DNA is the genetic material that provides the blueprint for the proteins that each different cell will produce in its lifetime. It consists of a five-sided sugar (deoxyribose) without a free hydroxyl group, a phosphate group linking the two nucleotides and a nitrogenous base. For more on the structure of DNA, see Structure of Nucleic Acids.

Ribonucleic acid (RNA) - RNA is a long polymer of ribose (a five-sided sugar with a free hydroxyl group) and nitrogenous bases linked via phosphate groups. It is complementary to one of the DNA strands and forms the proteins that are specified by the cell. For more on the structure of RNA, see Structure of Nucleic Acids.

Ketosis - Ketosis is a condition in which the incomplete breakdown of fatty acids due to the decline of glucose in the bloodstream causes the production of ketones.

Beta cells - A beta cell is a type of cell found in the pancreas that secretes insulin into circulation after sensing increasing concentrations of glucose in the bloodstream.

Insulin - Insulin is a type of hormone secreted into the bloodstream by pancreatic beta cells in response to increases in blood glucose. Upon binding to target cells, insulin allows various cell types to uptake glucose for use as an energy source.

Secrete - The process by which substances are produced and discharged from a cell into the bloodstream (endocrine secretion) or into a separate compartment (exocrine secretion).

Alpha cells - An alpha cell is a type of cell found in the pancreas that secretes the hormone glucagons in response to falling levels of glucose.

Gluconeogenesis - The process of synthesizing glucose from non-glucose precursors such as amino acids.

Pyruvate - Pyruvate is a three-carbon compound that is formed through the degradation of glucose via glycolysis. Two pyruvate molecules are formed per molecule of glucose that enters glycolysis.

Epinephrine - A hormone secreted from the adrenal medulla in response to sympathetic nervous system stimulation and low blood glucose. Its effects include causing the liver to degrade glycogen into glucose and decreasing the utilization of glucose by skeletal muscle.

Cortisol - A hormone secreted from the adrenal cortex in response to emotionally/physically stressful situations. Its effects include the ability to stimulate the production of new glucose (gluconeogenesis) and decreased utilization of glucose by cells.

Fatty acids - Fatty acids are long hydrocarbon chains that contain a carboxylic acid group at one end of the molecule. Three fatty acid units and one glycerol unit form a triglyceride.

Oxaloacetate - A four-carbon molecule found in the mitochondrion that condenses with acetyl CoA to form citrate in the first reaction of the Krebs cycle. Oxaloacetate must be constantly regenerated in order for the Krebs cycle and the electron transport chain to continue.

Krebs Cycle - Also known as the Citric Acid Cycle, the Krebs Cycle consists of a series of reactions that produce high-energy electron carriers to be used in the electron transport chain in the production of adenosine triphosphate (ATP). For more on the Krebs cycle, see Krebs Cycle

Acetyl CoA - A molecule produced in the mitochondrion upon the oxidation of pyruvate and the reduction of nicotinamide adenine dinucleotide (NAD+) to be used in the Krebs Cycle. It can also be formed via the degradation of fatty acids.

Diverticula - Diverticula are pouches that protrude through the exterior wall of the large intestine.

Hemorrhoids - A pronounced swelling of large veins, particularly those found in the anal region.

Diverticulitis - Diverticulitis is a disease in which the diverticula in the large intestine become inflamed.

Cholesterol - A multi-ring carbon structure containing one hydroxyl group that is found only in animal-derived food. It is thought to promote scarring of the arteries upon deposition along blood vessel endothelia, but it is also known to be a precursor in the production of steriods.

Carcinogens - Any molecule that enters the body through the lungs or gastrointestinal tract that causes the production of free radicals that can alter a cell's DNA. The mutation of a single base in DNA can lead to a non-functioning or overactive protein that may cause the cell to divide uncontrollably: cancer.

Glycolysis - Glycolysis is the sequence of reactions that converts glucose into pyruvate with the simultaneous net production of two molecules of adenosine triphosphate (ATP).

Oxidative Phosphorylation - Oxidative Phosphorylation is the process of converting adenosine diphosphate (ADP) to adenosine triphosphate (ATP) via the oxidation-reduction of a series of electron carriers in the mitochondrion membrane.

Cori Cycle - The Cori Cycle is a process through which lactic acid produced by working muscle is converted to glucose by the liver. The cycle shifts part of the metabolic burden to the liver.

Norepinephrine - A hormone secreted by the adrenal medulla that causes vasoconstriction in peripheral blood vessels as well as excitation of the heart and inhibition of the gastrointestinal tract.

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Types of Carbohydrates