Chapter 7: DNA structure and function

Deoxyribonucleic acid (DNA)

An information molecule that is the universal basis of an organism's genetic material; it contains instructions, in chemical code, for the operation of the cell

Nucleotide

The basic building block of nucleic acids (DNA and RNA) linked together by phosphodiester bonds; each nucleotide is made up of a five-carbon sugar molecule, a phosphate group and a nitrogenous base

Complementary bases

Nitrogenous bases that bind to each other in DNA (A-T and C-G) and in RNA (A-U and C-G)

Ribonucleic acid (RNA)

A short-lived molecule consisting of ribonucleotides; it plays an essential role in protein synthesis (as messenger RNA and transfer RNA) and as a structural component of ribosomes

Centromere

The waist-like constriction in a duplicated chromosome required for the movement of chromosomes during cell division

Chromosome

A structure composed of DNA and protein that contains, along its length linear arrays of genes carrying genetic information

Gene

A region of DNA that encompasses the coding and non-coding DNA for a particular protein or protein family

Gene locus

The specific physical location of a gene on a chromosome

Coding DNA

A section of DNA that specifically carries the code for direct translation into a polypeptide

Non-coding DNA

A section of DNA that carries information for when, where or how often its associated coding DNA is expressed

Promoter region

A region of DNA upstream of a gene that binds enzymes that initiate transcription

Intron

A section of DNA or mRNA that does not code for a polypeptide

Exon

A section of DNA or mRNA that codes for a polypeptide

Telomere

A region at the end of a chromosome, characterised by repeated sequences of non-coding DNA

Chromatin

The complex of proteins and DNA in eukaryotes

Heterochromatin

A tightly coiled complex of proteins and DNA that is characterised by few genes and limited transcription activity

Euchromatin

A loosely coiled complex of proteins and DNA that is characterised by many genes and high transcription activity

Histone

A protein that spools DNA in eukaryotic cells

Sister chromatids

The two identical copies of a single chromosome, formed by replication and connected by a centromere

Somatic

Of the body, as distinct from the sex cells or sex chromosomes

Homologous pair

A pair of unduplicated chromosomes that are the same size and shape, and have the same genes at the same locations; each member of the pair may carry a different allele for any particular gene

Alleles

Two or more alternative DNA sequences at the same gene locus on homologous chromosomes

Karyotype

A display of the number and appearance of the chromosomes of an organism or cell observed at metaphase

Plasmid

A small circular piece of DNA in bacteria that can replicate independently of the cell's chromosomes; plasmids carry antibiotic resistance markers

Endosymbiotic theory

A theory that suggests that chloroplasts and mitochondria arose from ancient prokaryotic cells that were ingested by other prokaryote host cells

Daughter cell

Either of the two cells formed when a cell undergoes cell division

DNA helicase

The enzyme that unwinds and separates the two strands of the DNA double helix in DNA replication

Parental DNA

The DNA of the original cell in cell division

Replication fork

The junction between the unwound single strands of DNA and the intact double helix during replication

DNA polymerase

The enzyme that forms the complementary strand in DNA replication

Leading strand

The DNA strand that is already in the 5' to 3' direction, so its complement cannot replicate continuously by DNA polymerase in the 5' to 3' direction because its parent strand is unzipped in the 3' to 5' direction

Lagging strand

The DNA strand that is already in the 5' to 3' direction, so its complement cannot be replicated continuously by DNA polymerase; replication forms Okazaki fragments that must be stitched together by DNA ligase

Okazaki fragments

The DNA fragments caused by the discontinuous replication of DNA on the lagging strand; they are stitched together to make a continuous strand by DNA ligase

Semiconservative replication

The production of two new DNA double helix molecules, each consisting of one parental strand and one daughter strand

Mutation

A permanent change in a sequence of DNA