This definitions covers Key Definitions within DNA Genome for GCSE Biology. DNA structure, function, and the human genome It is section 6 of 13 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Topic position
Section 6 of 13
Practice
25 questions
Recall
25 flashcards
Key Definitions
DNA (deoxyribonucleic acid): A double-stranded molecule wound into a double helix, made of nucleotides containing the bases A, T, C, and G, which carries the genetic code of an organism.
Gene: A section of DNA on a chromosome that codes for a specific sequence of amino acids and therefore a specific protein.
Genome: The entire genetic material (all of the DNA) of an organism. In humans, this consists of approximately 20,000 genes on 23 pairs of chromosomes.
Chromosome: A long, coiled molecule of DNA found in the nucleus of a cell. Humans have 46 chromosomes (23 pairs), each containing thousands of genes.
Allele: One of two or more alternative versions of a gene that can occupy the same position (locus) on a chromosome. For example, the gene for eye colour has alleles for brown and blue.
Double helix: The three-dimensional shape of a DNA molecule — two polynucleotide strands wound around each other like a twisted ladder, held together by complementary base pairing.
Complementary base pairing: The rule that governs which bases bond together in DNA: adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G).
Genotype: The genetic makeup of an organism — the specific alleles it carries for a given characteristic (e.g., Bb).
Phenotype: The physical or observable characteristic that results from an organism's genotype and its interaction with the environment (e.g., brown eyes).
Transcription: The process by which a section of DNA is copied into a complementary strand of mRNA in the nucleus. The enzyme unzips the DNA and builds the mRNA strand using complementary base pairing.
Translation: The process by which the sequence of codons on mRNA is read at the ribosome to produce a chain of amino acids (a polypeptide / protein).
mRNA (messenger RNA): A single-stranded molecule that carries a copy of the genetic code from the nucleus to the ribosome. Uses uracil (U) instead of thymine (T).
Codon: A sequence of three consecutive bases on mRNA that codes for one specific amino acid (or a start/stop signal).
Mutation: A change in the DNA base sequence of a gene. Mutations can be neutral, harmful, or (rarely) beneficial depending on how they affect the protein produced.