Worksheet Chapter 13: Human biochemistry glossary

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1 Worksheet 13.1 Chapter 13: Human biochemistry glossary α-helix Refers to a secondary structure of a protein where the chain is twisted to form a regular helix, held by hydrogen bonds between peptide bonds four amino acids apart. It is characteristic of the protein keratin, found in hair, claws, etc. Amino acid The monomer from which proteins are built. Amino acids contain an amino NH 2 group and a carboxylic acid COOH group attached to the same carbon atom. They join together by a condensation reaction forming a peptide bond. Amphoteric Having the properties of both an acid and a base. Amino acids are amphoteric due to the presence of both the carboxylic acid and amino groups. Anabolic steroid Hormones which contain androgens, most notably testosterone. Anaemia A condition characterized by a diminished capacity to supply oxygen to the cells from the blood. It is a symptom of iron deficiency. Artherosclerosis A medical condition where lipids are deposited in the walls of the main blood vessels, thus restricting blood flow. Bomb calorimeter An instrument used to measure the enthalpy of combustion of a reaction. It is commonly used to determine the energy value of food substances. β-pleated sheet Refers to a secondary structure of a protein where the polypeptide chains are in a more extended form, held by inter-chain hydrogen bonds. It is characteristic of the protein silk fibroin. Buffer A substance which is able to resist significant change in ph on the addition of small amounts of acid or alkali. Amino acids act as buffers in solution. Cellulase An enzyme that is used in the digestion of cellulose. It is not produced by humans. Cellulose A polymer of beta-glucose. It is a rigid structure due to inter-chain hydrogen bonds and is abundant in the cell walls of plants. Condensation A reaction in which water is released. Condensation reactions occur during the buildup of large molecules from smaller molecules, such as during protein synthesis. Conformation The specific three-dimensional shape of a globular protein. It is determined by the tertiary structure, the most stable arrangement of all the interactions between the R groups. Changes to the conformation have a significant effect on the activity of the protein, especially in the case of enzymes. Deactivation The process where enzyme activity is halted by a very low temperature. Denaturation Loss of the tertiary structure of a globular protein as the result of disruption of the forces and bonds between the R groups. Denaturation may be caused by changes in temperature or ph. 1

2 Dietary fibre Substances, such as cellulose, which cannot be digested in the human body and so contribute to the bulk of faeces. Digestion The breakdown of large macromolecules into smaller soluble molecules, catalyzed by enzymes. It is a series of hydrolysis reactions. Dipeptide Two amino acids joined together by a peptide bond. It has an N-terminal (free amino group) and a C-terminal (free carboxlic acid group) end. Disaccharide Two monosaccharides joined together by a glycosidic link. Common examples include maltose, sucrose and lactose. Endocrine gland having no duct. A gland that releases hormones directly into the blood. It is characterized by Enzymes Biological catalysts that are involved in every metabolic reaction. Enzymes are made from proteins. They speed up reactions by forming a complex with their substrate(s), which lowers the activation energy of the reaction. Essential amino acid Amino acids that cannot be synthesized by the body and so must be included in the diet. Essential fatty acid Fatty acids that cannot be synthesized by the body and so must be included in the diet. Fibrous proteins Proteins that have a well-defined secondary structure. They are physically tough, insoluble in water and include structural proteins, such as keratin. Globular proteins Proteins that have a well-defined tertiary structure. They are compact, soluble molecules and include enzymes, hormones and carrier molecules. Glycogen A polymer of alpha glucose with a large number of 1 6 as well as 1 4 glycosidic links. Glycosidic link The bond formed as monosaccharides join together in condensation reactions. Goitre A swelling of the thyroid gland in the neck. It is a response to iodine deficiency. Hexose sugar A sugar that contains six carbon atoms. Glucose, fructose and galactose are common examples. Hormone A chemical messenger in the body, transported in the blood from the endocrine gland where it is produced to its target cells. Hydrolysis A reaction in which water is used and becomes split. Hydrolysis reactions occur during breakdown of macromolecules into smaller molecules, such as occurs during digestion. Iodine number A measure of the amount of unsaturation in a fat or oil. It is expressed as the number of grams of iodine which reacts with 100 grams of fat. 2

3 Isoelectric point The ph at which an amino acid or a protein is electrically neutral. Due to the influence of different R groups, the value of the isoelectric point is specific for each amino acid. These values are given along with the structures of the R groups in the IB Data booklet. Kwashiorkor A condition effecting young children resulting from protein deficiency. Lactose A disaccharide consisting of beta glucose and beta galactose. Lipase An enzyme that digests lipids into fatty acids and glycerol. Locating reagent A chemical used to dye the spots left on a chromatogram or following electrophoresis, so that their position can be clearly identified. A common example is ninhydrin, which stains amino acids purple. Macronutrient Nutrients needed in relatively large amounts. They are used for the structure of the body as well as to provide energy. Malnutrition Occurs when the diet does not include a regular balanced supply of the diverse nutrients needed. Maltose A disaccharide consisting of two alpha glucose molecules. Marasmus A condition found in infants resulting from protein deficiency. Metabolism The sum of the chemical reactions that occur in a living organism. Micronutrient Nutrients needed in very small amounts, less than 0.005% of body mass per day. They are used to enable the body to produce enzymes and hormones. Monosaccharide Simple sugar with the formula C n H 2n O n. They are soluble molecules. Examples include glucose and fructose. Monounsaturated fat Fat containing fatty acids which have one carbon carbon double bond. Ninhydrin A locating reagent used in chromatography and electrophoresis to detect the position of amino acids. Most amino acids turn purple in the presence of ninhydrin. Non-competitive inhibitors Chemicals that bind to the enzyme at a position other than the active site. Their binding causes a conformation change in the enzyme which reduces the ability of the substrate to bind. Nucleotide Monomers which link together to form nucleic acids. Obesity A medical condition characterized by increased body weight as a result of accumulation of excess fat. Oil A lipid which is liquid at room temperature. Oils typically contain a high proportion of unsaturated fatty acids. 3

4 Optimum temperature The temperature at which an enzyme-catalyzed reaction achieves the maximum rate. Pentose sugar A sugar that contains five carbon atoms. Ribose and deoxyribose, found in RNA and DNA respectively, are pentose sugars. Peptide bond The bond that forms between amino acids as they react together to form peptides and proteins. It is an amide link. Phospholipid A lipid consisting of two fatty acids condensed with a glycerol molecule and a phosphate group. These molecules have distinct hydrophobic and hydrophilic parts and are important in membrane structures. Polypeptide A chain of amino acids held together by peptide bonds. Folding of the polypeptide chain gives rise to the secondary and tertiary structures of the protein. Polysaccharide A large number of monosaccharide units held together by glycosidic links. Polysaccharides are insoluble. Examples include starch, cellulose and glycogen. Polyunsaturated fat Fats containing fatty acids that have several carbon carbon double bonds. Primary structure of protein The sequence of amino acids in a protein. This is determined by the base sequence in the DNA and in turn determines the specific conformation of the protein and so its function. Prosthetic group A non-protein part of a protein molecule. The heme group in hemoglobin is an example. Quaternary structure of protein Occurs where a protein is comprised of more than one polypeptide, and refers to the associations between these chains. Respiration A complex series of oxidation reactions that make energy available to cells from the breakdown of energy-rich molecules such as glucose. R f values Retention factor. Used to identify a component from a mixture in chromatography. It is defined as the distance moved by the component divided by the distance moved by the solvent. Ribose A monosaccharide that contains five carbon atoms and is found in RNA. Secondary structure of protein The pattern of regular hydrogen bonds in a protein, which are the result of interactions between atoms of the peptide bonds along its length. Solvent front The furthest distance moved by the solvent during chromatography. Starch A polymer of alpha-glucose containing mostly 1 4 and some 1 6 glycosidic linkages. It is used as a storage carbohydrate in plants. Substrate The reactant in an enzyme-catalyzed reaction. Sucrose A disaccharide consisting of alpha glucose and beta fructose. 4

5 Tertiary structure of protein The twisting, coiling and folding of the polypeptide chain as a result of interactions between the R groups. It results in a specific conformation, characteristic of globular proteins. Trace minerals Inorganic micronutrients, such as Fe, Cu, Zn and I. Trans fat Fats that are formed by the partial hydrogenation of oils. They are present in many processed foods and are linked with increasing incidence of heart disease. Triglyceride A lipid consisting of a glycerol molecule which has condensed with three fatty acids. Triose sugar A sugar containing three carbon atoms. Pyruvate, formed during glycolysis in the first part of respiration, is a triose sugar. Tripeptide Three amino acids joined together by peptide bonds. It has an N-terminal (free amino group) and a C-terminal (free carboxlic acid group) end. Unsaturated fat Vitamins Fat which contains fatty acids with at least one carbon carbon double bond. Organic micronutrients. Their absence from the diet leads to deficiency diseases. Xerophthalmia A condition characterized by dry eyes and night blindness as a result of vitamin A deficiency. Zwitterion A form of an amino acid in which both the amino group and the acid group have been ionized to NH 3 + and COO respectively. This is the form in which amino acids commonly occur in solution. 5