Chap 9: Molecular Structure of DNA and RNA

molecular genetics

the study of DNA structure and function at the molecular level.

DNA

the genetic material. It is a double-stranded structure, with each strand composed of repeating units of deoxyribonucleotides.

RNA

a nucleic acid that is composed of ribonucleotides. In living cells, —- is synthesized via the transcription of DNA.

nucleic acid

RNA or DNA. A macromolecule that is composed of repeating nucleotide units.

nucleotide

the repeating structural unit of nucleic acids, composed of a sugar, one to three phosphates, and a nitrogen-containing base.

strand

in DNA or RNA, a long linear polymer formed of nucleotides covalently linked together.

double helix

the structure that results when two strands of DNA (or sometimes strands of RNA) interact with each other to form a double-stranded helical structure.

deoxyribose

the sugar found in DNA.

ribose

the sugar found in RNA

purine

a type of nitrogenous base that has a double-ring structure. Examples are adenine and guanine.

pyrimidine

a type of nitrogenous base that has a single-ring structure. Examples are cytosine, thymine, and uracil.

adenine (A)

a purine base found in DNA and RNA. It base-pairs with thymine in DNA.

guanine (G)

a purine base found in DNA and RNA. It base-pairs with cytosine in DNA

thymine (T)

a pyrimidine base found in DNA. It base-pairs with adenine in DNA.

cytosine (C)

a pyrimidine base found in DNA and RNA. It base-pairs with guanine in DNA.

uracil (U)

a pyrimidine base found in RNA.

nucleoside

structure in which a base is attached to a sugar, but no phosphate is attached to the sugar.

phosphodiester linkage

in a DNA or RNA strand, a linkage in which a phosphate group connects two sugar molecules.

directionality

in DNA and RNA, refers to the 5′ to 3′ orientation of nucleotides in a strand; in proteins, refers to the linear arrangement of amino acids from the N-terminus to the C-terminus.

Chargaff’s rule

the observation that in DNA the amounts of A and T are equal, as are the amounts of G and C

base pair (bp)

the structure in which two nucleotides in opposite strands of DNA hydrogen bond with each other.

AT/GC rule

in DNA, the phenomenon in which an adenine base in one strand always hydrogen bonds with a thymine base in the opposite strand, and a guanine always hydrogen bonds with a cytosine.

complementary

describes sequences in two DNA strands that match each other according to the AT/GC rule

antiparallel

refers to an arrangement in a double helix in which one strand is running in the 5′ to 3′ direction, while the other strand runs in the 3′ to 5′ direction.

base stacking

In DNA, the orientation of base pairs in which the flat sides of the bases are facing each other.

grooves

in DNA, the indentations where the atoms of the bases are in contact with the water in the surrounding cellular fluid

minor groove

a narrow indentation in the DNA double helix in which the bases have access to water.

major groove

a wide indentation in the DNA double helix in which the bases have access to water.