Glossary of Scientific Terms

C

Carbohydrates
Biochemical name for sugar containing molecules including single sugar (monosaccharides) like glucose and galactose, but also polysaccharides (complex carbohydrates) like starch (poly-glucose), cellulose (plant fiber material, also poly-glucose with a different chemical bond structure linking glucose units than those found in starch/glycogen and enzymatically indigestible by humans), chitin (hard shells of insects), and more complex carbohydrate components part of lipids and proteins such as blood serum glycoproteins (antibodies and blood group determinants A, O, B, rhesus positive or negative). All microorganisms (bacteria, viruses) contain carbohydrate surfaces (glycolipids) being the major determinants of immunogenic reactions during infections.

Carbon
The element that defines the chemical properties of all life. All molecules that contain carbon are known as organic molecules and studies by organic chemistry. Carbon is the third most common element in cells, after hydrogen and oxygen, which are the most common biological elements because they are found in water. Also water makes up to 70% of a cells weight, it is not an organic molecule, since it lacks carbon.

Calorie (Cal)
Chemical energy in foods is expressed in calories (Cal). The scientific definition of a calorie is the amount of energy needed to raise the temperature of 1 gram of water by one degree Celsius from 15° to 16° at atmospheric pressure. This is the true calorie, sometimes referred to as a "small calorie". A kilocalorie is equal to 1000 calories. In reference to food energy, the term "calorie" is actually a 1,000 calories or 1 kilocalorie. The USDA Nutrient Database for Standard Reference contains values for both kilocalories and kilojoules (1 kcal equals 4.184 kJ).

Capacitance
An element (capacitor) in an electrical circuit capable of separating charges and storing electrical energy. In cells, membranes have capacitor properties contributing to the storage of electrochemical energy (ion gradients).

Catabolism
The part of metabolism responsible for degradation of nutrients and energy extraction for the benefit of ATP production.

Cell
Smallest unit of life (single cell organism or bacteria) or unit of higher organisms, i.e., multicellular organisms. Cells are surrounded by a cell membrane (and cell wall in bacteria and plants = a membrane plus some chemically more stable structures, often mixtures of proteins and polysaccharides) and contain all necessary elements to sustain life; proteins, nucleic acids, lipids, minerals, and a diverse class of metabolites. Cells of higher organisms (known as eukaryotes) are subdivided into subcellular compartments called organelles such as the mitochondrion, the cell nucleus, the endoplasmatic reticulum, the Golgi apparatus and many smaller organelles with highly specialized functions. While all these organelles are found in animal cells, plant cells in addition contain a central vacuole that controls pressure to stabilize the cell and chloroplasts, the site of photosynthesis or light depended biosynthesis of sugars (carbohydrates).

Cellular automaton
A program the applies a simple rule of what to do repeatedly. Depending on the rule of what to do next, the pattern or behavior generated can look (i) repetitive, simple, and symmetric, (ii) nested (fractal), (iii) random and without any symmetry or repetition whatsoever, or (iv) complex with local patterns but overall broken symmetry (see also complexity).

Channel (Ion Channel)
A membrane protein that allows the passive flow of ions across a cell membrane. Ion channels are usually selective for a specific ion type (e.g. Na, or K, or Cl, or Ca) and or either open or closed. These are two structural states of the protein and the change from the open to the closed state (gating) is regulated by the cell. Several regulatory mechanisms have been described including voltage-gating, ligand-gating, heat, and mechano-sensation (touch sensitive). Channels are a category of transporters.

Cholesterol
Important lipid found only in animals. Cholesterol is important as cell membrane component, but also serves as a biosynthetic precursor for steroid hormones (e.g. sex hormones) and the active gall bladder ingredients bile acids (= detergents). The human liver can synthesize all the necessary levels of cholesterol and will reduce its own synthesis if cholesterol is taken in during a meal (only from animal sources). 'Bad' and 'Good' cholesterol refers to special transport particles of lipids in our blood serum called lipoprotein particles. The low density form or LDL is high in cholesterol and chronically high concentration of LDL in blood results in insoluble deposits that can clog arteries and restrict blood flow contributing to heart problems.

Chromosome
The physical unit of genetic material in a cell. Prokaryotes have usually one large circular chromosome and one or more small circular extra-chromosomal DNA (plasmids). Eukaryotic cells have often several to several dozen chromosomes. Humans have 46 chromosomes comprising two sets of 23 chromosomes. Each set constitutes the complete human Genome carrying approximately 35,000 genes. Each chromosome carries between 1,000 to 2,000 genes. Eukaryotic chromosomes are linear, long DNA molecules tightly packed with proteins that control their structure and activities of genes.

Chyme
Digested content of the stomach released for further digestion in the small intestine.

Clone, cloning
A clone is a genetic copy of a parent cell or organism. Cloning is the process of producing a genetically identical offspring or copy. Cloning is a natural process that underlies asexual reproduction that include the binary fission of prokaryotic cells (bacteria and archaea) and mitotic cell division of eukaryotic cells. Mitosis occurs continuously in the human body due to growth and tissue repair (wound healing) and maintenance (skin regeneration, hair growth). Cloning can also refer to the technical process of duplicating genetic material in the laboratory, for instance through the polymerase chain reaction (PCR).

Co-Enzymes or Co-Factors
Non-protein substances necessary for the function of some enzymes. Essential coenzymes are also known as vitamins.

Code (genetic)
The genetic code is the information needed to translate a nucleic acid (gene) sequence into an amino acid (protein) sequence. The code consists of triplet structures called codons such as UUG meaning two uracil and one guanine base along the messenger RNA template. This codon is recognized through base pairing by an anti-codon (triplet) on a transfer RNA. The transfer RNA is a specialized small ribonucleic acid that identifies genetic sequences on messenger RNAs (with the help of ribosomes) and carries one specific amino acid. An amino acid always matches one particular anti-codon. There are twenty amino acids to choose from for protein synthesis, and a total of 64 triplet codons (four bases in triplet sequence = 4x4x4 combinations). Thus there are 64 codons to match 20 amino acids, which means that some amino acids are coded by more than one codon. Which codons are responsible for which amino acid is evolutionarily conserved and most organisms have the same code or translation table. There are some alternate assignments found in mitochondrial genomes, viral genomes and some bacterial genomes. Yet, the fact that most organisms, bacteria, archaea and eukarya use the same genetic code explains the ability for recombinant DNA technology, i.e., to cut and past genetic elements from one organism into an other organism, since the assign amino acids to the same codons. Thus a human gene can be expressed in bacteria or yeast or jelly fish, and jelly fish genes can be expressed in bacteria, plants, fungi, animals and protists. There are almost limitless combinations possible. Read more about genetic codes at the National Center for Biotechnology Information and see the standard genetic code for humans and most organisms.

Cognitive, cognition
Cognition refers to the physical recognition of external stimuli that lead to conscious experiences.

Complexity
Complexity is the measure of the number and strength of interactions of its components. The components are organized not in a linear chain, but a network with specific connectivity, branches and loops. Network components affect each other through their interactions (molecular interactions). Complexity in biology is the result of dynamic interactions that follow each other in time and with both forward and feedback loops. Because of loops, the output of a network will affect a future input, thus continuously adjusting the physical output value of the system. Biological networks have evolved as stable systems. Stability means that biological systems are in homeostatic equilibrium, with information constantly flowing through the system and the output kept within a narrow range.

Conductance
Conductance refers to the flow of ions (charges molecules and elements and measured in 'Siemens') such as sodium, potassium, and chloride and is the proportionality factor relating current to a voltage difference. In electricity theory conductance is the inverse of the resistance as defined by Ohm's law V = RI, where V is the voltage, R the resistance, and I the current).

Covalent
The chemical bond between atoms.

Crystal
In biology refers to large, regular assembly of macromolecules such as proteins and nucleic acids. It is possible to isolate and purify proteins or DNA in large quantity and let them crystallize in saturated solution. These protein or DNA crystals contain millions of regularly aligned units that allow the determination of the electron distribution from X-ray diffraction studies. Since atoms are distinguished by their specific numbers of electrons, their distribution allows an analysis of the atomic composition of proteins or DNA. This electron distribution is then used to calculate the so called high resolution structure of molecules.

Cytoskeleton
A fibrous network made of proteins that contributes to the structure and internal organization of eukaryotic cells. The cytoskeleton is found in the cytoplasm of cells and has three major fiber types: microfilaments made of actin protein, intermediate filaments made of various kinds of proteins (e.g. keratin), and microtubules made of tubulin. The three fiber types serve different functions; actin filaments are often associated to changes in cell size and structure, contractility such as in muscle cells, and cell division, growth and motility. Microtubules are major filaments for internal transport and movement of chromosomes and organelles during cell division. Intermediate filaments contribute to flexibility, elasticity, and stiffness of cells and tissues.