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Worksheet 13.1
Chapter 13: Human biochemistry – glossary
Active site The region of an enzyme where the substrate binds to form the enzyme substrate
complex. This is where the substrate is converted into product and released from the enzyme.
Aerobic respiration Respiration that occurs in the presence of oxygen. It enables glucose to be
oxidized fully to carbon dioxide and water with the release of much more energy than anaerobic
respiration.
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 –NH2
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.
Anaerobic respiration Respiration that takes place in the absence of oxygen. No energy can be
released beyond the breakdown of glucose in glycolysis, and the products are either lactate or
ethanol and carbon dioxide. Anaerobic respiration releases significantly less energy then aerobic.
Anticodon
RNA.
A triplet of bases in transfer RNA which is complementary to the codon in messenger
Anti-parallel DNA Refers to the fact that the two polynucleotide strands in the double helix run
in opposite directions: one is 5 primed to 3 primed, the other 3 primed to 5 primed.
Artherosclerosis A medical condition where lipids are deposited in the walls of the main blood
vessels, thus restricting blood flow.
Autoradiogram The result following exposure of the electrophoresis plate used in DNA profiling
to X ray film. It shows the positions of the DNA fragments as dark bands.
Base pair Two bases in different polynucleotide strands held together by hydrogen bonds in the
centre of the DNA double helix.
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.
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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.
Codon
A sequence of three bases in mRNA which specifies a specific amino acid.
Competitive inhibitors Chemicals that bind reversibly at the active site of the enzyme and so
prevent the binding of substrate.
Condensation A reaction in which water is released. Condensation reactions occur during the
build-up 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.
Cytochrome Electron transport carriers containing a prosthetic group with Fe and also sometimes
Cu.
Cytochrome oxidase
to water.
Deactivation
The terminal electron carrier that passes its electrons to oxygen, reducing it
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.
Deoxyribose Monosaccharide sugar with five carbon atoms found in DNA.
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.
DNA
cells.
Deoxyribonucleic acid. The molecule which stores the genetic information in the nucleus of
DNA profiling
The process of using the unique nature of a person’s DNA to identify them.
Double helix The structure of DNA in which two polynucleotide chains are coiled around the
same axis and held together by hydrogen bonds between the stacked bases.
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Electron transport carriers These carriers are part of membrane structures and become
successively reduced then reoxidized as they accept electrons and pass them on to the next in the
chain. As electrons flow through the cytochrome chain, energy is made available to cells.
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
included in the diet.
Essential fatty acid
in the diet.
Amino acids that cannot be synthesized by the body and so must be
Fatty acids that cannot be synthesized by the body and so must be included
Fibrous proteins Proteins that have a well-defined secondary structure. They are physically
tough, insoluble in water and include structural proteins, such as keratin.
Genetic code The specific relationship between a triplet of bases in mRNA (codon) and the
amino acid which will be incorporated into the protein.
Genome
The entire set of DNA possessed by every cell of the body.
Globular proteins Proteins that have a well-defined tertiary structure. They are compact, soluble
molecules and include enzymes, hormones and carrier molecules.
Glycogen
Glycolysis
used.
A polymer of alpha glucose with a large number of 1–6 as well as 1–4 glycosidic links.
The first stage of respiration where glucose is oxidized to pyruvate. Oxygen is not
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.
Induced fit mechanism The mechanism where the conformation of the enzyme at the active site
is modified slightly in the presence of the substrate, in order to bind effectively with it.
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.
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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.
Km The Michaelis constant. This is derived from the Michaelis–Menten graph and is defined as
the substrate concentration at which the reaction rate is one half its maximum value.
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 CnH2nOn. 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.
Optimum temperature
maximum rate.
The temperature at which an enzyme-catalyzed reaction achieves the
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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.
Polymerase chain reaction (PCR) A technique used to amplify regions of DNA by making a
vast number of copies very quickly. It is used in DNA profiling.
Polynucleotide A chain of nucleotides which gives rise to nucleic acids. RNA is a single
polynucleotide chain, DNA is two polynucleotides coiled into a double helix.
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
example.
A non-protein part of a protein molecule. The heme group in hemoglobin is an
Purine A base found in nucleotides that consists of two fused heterocyclic rings (containing
carbon and nitrogen). Adenine and guanine are purine bases.
Pyrimidine A base found in nucleotides that consists of a single heterocyclic ring (contains
carbon and nitrogen). Cytosine, thymidine and uracil are pyrimidine bases.
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.
Restriction enzymes
Enzymes used to cut DNA into small pieces.
Rf 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.
RNA Ribonucleic acid. It exists in several forms including messenger RNA and transfer RNA,
and acts to transmit information between the DNA in the nucleus and the events leading to protein
synthesis in the cytoplasm.
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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.
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
Transcription
Inorganic micronutrients, such as Fe, Cu, Zn and I.
The synthesis of messenger RNA from a DNA template. It occurs in the nucleus.
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.
Translation The synthesis of a protein from a messenger RNA template. The sequence of bases
in mRNA is converted into a sequence of amino acids in the protein. It occurs at the ribosomes in
the cytoplasm.
Triglyceride
acids.
A lipid consisting of a glycerol molecule which has condensed with three fatty
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.
Triplet code The fact that the genetic code specifies each amino acid by a triplet of bases in
messenger RNA, known as a codon.
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.
Vmax The maximum velocity of an enzyme under the conditions of the experiment.
Xerophthalmia
A deficiency.
A condition characterized by dry eyes and night blindness as a result of vitamin
Zwitterion A form of an amino acid in which both the amino group and the acid group have been
ionized to –NH3 + and –COO– respectively. This is the form in which amino acids commonly occur
in solution.
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