Glossary of Scientific Terms

G

Gene
A gene is an hereditary unit of an organism that cannot be partitioned any further into smaller units; it is made of DNA. Functionally, a gene consists of regulatory and coding sequences. The regulatory sequences allow a cell to control when and how a gene is expressed its gene product (= RNA or protein) encoded by the coding sequence is synthesized. Often, gene products are only functional as groups (protein complexes) that require the expression of more than one gene (heteromeric complexes) or of a single gene in high copy numbers (homomeric complexes).

Genetic Information

Refers to the information content of genes or genomes and is organized in sequences of nucleotides, structures of genes, and arrangement of genes within genomes. Genetic information is the information that is inherited from generation to generation and can be accessed by the cellular machinery with the help of proteins to synthesize all necessary components for the growth maintenance of an organism.

Genetic code see Code (Note: genetic code is often used inappropriately in the news media when in fact the topic is the genome or genetic information of an organism.)

Genome
The genome denotes the full set of genes or genetic information of an organism. It included both coding and non-coding sequences and is physically partitioned into chromosomes. The importance of coding sequences is for protein synthesis and RNA synthesis, while non-coding sequences contain regulatory sequences, sequences of old, inactive genes, repeat sequences that allow recombination of genetic information (DNA pieces) from different chromosomes, locations, or even foreign DNA that is introduces by microbial or viral infection. Many non-coding sequences are transposable elements meaning that they can copy and insert themselves at many different sites within chromosomes. These rearrangement of physical location of DNA strands affects number, location, and sequence of genes coding for proteins and RNA and thus are vital for generating mutations important for evolutionary fitness of an organism. The human genome has been found to contain only 5% coding sequences (genes that make proteins), while half of all non-coding portions are made of transposable elements reminiscent of viral DNA. This similarity between human and viral DNA indicates that human evolution cannot be thought of as independent but is closely related to the evolution of viruses. The modern existence of pathogenic viruses is an indication of the importance of this co-evolution that likely has helped humans to maintain a heterogeneous genepool important for rapid adaptation to environmental changes.

Genotype
The genetic description of an organism; often only one or two genes out of thousands are of interest in a genetic comparison between individuals or the analysis of genealogical traits, family history etc..  The genotype is the genetic information underlying a phenotype, the exterior expression of characteristics or traits (e.g. eye color). Most phenotypes that are really physical or functional attributes of an organism are multifactorial, meaning that several genes contribute to its expression. Even at the level of cellular mechanism and metabolism, phenotypes (e.g. photosynthesis) are multifactorial because of the particular composition of enzymes as protein complexes, where individual proteins are coded for by different genes. Photosynthesis, for example, is the concerted action of dozens of proteins (genes) with copy numbers in the hundreds to enable a simple chemical equation:  carbon dioxide + water =  sugar. In fact this simple overall equation is really performed in many different subsets of reactions.

Genotyping
Genotyping is the process of comparing various strains of microorganisms including viruses and bacteria to distinguish pathogenic from non-pathogenic strains (infectious versus non-infectious types). The technique used for genotyping are DNA microarrays.

Glucose
The major carbohydrate in starch and fruit sugar. The latter is also known as succrose and contains fructose with every glucose molecule.

Glycemic index
A measure of how rapidly glucose of various forms of carbohydrates are absorbed into the blood circulation.

Glycogen
The major complex carbohydrate in animal cells made of glucose. Glycogen is for animals what starch is for plants. Although glycogen is an important long term storage of energy in muscle and liver cells, it is of little nutritional significance, because most glycogen in muscle spontaneously degrades during slaughtering. Thus meats, except liver, have little or no carbohydrate content.

Glycolysis
A metabolic pathway found in all organisms. This pathway consists of ten chemical reactions catalyzed by proteins (enzymes) and is responsible for the degradation and synthesis of carbohydrates. Glycolysis does not depend on the presence of oxygen and is able to provide the cell with the universal energy currency called ATP, short for adenosine triophosphate. This pathway can degrade glucose only partially and will produce waste products such as lactate (in mammalian muscle causing sour muscle under anaerobic exercise conditions) or ethanol in microorganisms (used for fermentation of wine or beer). In the presence of oxygen, no waste products are formed and instead further degraded to carbon dioxide and water. The latter processes are known as Krebs cycle and oxidative phosphorylation.