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Nucleotide A subunit of DNA or RNA consisting of a nitrogenous base (purine in adenine and guanine, pyrimidine in thymine, or cytosine for DNA and uracil cytosine for RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). Depending on the sugar the nucleotides are called deoxyribonucleotides or ribonucleotides. Thousands of nucleotides are linked to form a DNA or RNA molecule. See also base pair.
Related Terms:
Deoxyribonucleic acid (DNA) The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner.
Ribonucleic acid (RNA) A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell. The structure of RNA is similar to that of DNA. There are several classes of RNA molecules, including messenger RNA, transfer RNA, ribosomal RNA, and other small RNAs, each serving a different purpose.
Nitrogenous base A nitrogen-containing molecule having the chemical properties of a base. See purine and pyrimidine.
Purine A nitrogen-containing, double-ring, basic compound (cf. nitrogenous base) that occurs in nucleic acids. The purines in DNA and RNA are adenine and guanine.

purine structure 7 H-Purine

Adenine (A) Adenin is a purine base (nitrogenous base) and constituent of nulceotides and as such one member of the base pair A-T (adenine-thymine) in DNA and A-U (adenine-uracil) in RNA.

adenine structure

Guanine (G) Guanine is a purine base (nitrogenous base) and constituent of nucleotides and as such one member of the base pair G-C (guanine and cytosine).

guanine structure

Pyrimidine A nitrogen-containing, single-ring, basic compound (cf. nitrogenous base) that occurs in nucleic acids. The pyrimidines in DNA are cytosine and thymine. The pyrimidines in RNA are cytosine and uracil.

pyrimidine structure

Thymine (T) Thymine is a pyrimidine base (nitrogenous base) and constituent of nulceotides and as such one member of the base pair A-T (adenine-thymine) in DNA.

thymine structure

Cytosine (C) Cytosine is a pyrimidne base (nitrogenous base) and constituent of nulceotides and as such one member of the base pair G-C (guanine and cytosine) .

cytosine structure

Uracil (U) Uracil is a pyrimidine base (nitrogenous base) and constituent of nucleotides and as such one member of the base pair A-U (adenine-uracil). It is normally found in RNA but not DNA.

uracil structure

Base pair (bp) Two nitrogenous (purine or pyrimidine) bases (adenine and thymine or guanine and cytosine) held together by weak hydrogen bonds. Two strands of DNA are held together in the shape of a double helix by the bonds between base pairs. The number of base pairs is often used as a measure of length of a DNA segment, eg 500 bp.

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Database: Birgid Schlindwein. Please contact me if you encounter any mistakes or if you are missing anything
© Dr. Birgid B. Schlindwein
last update of the database 10/01/2006