DNA is a polymer made of repeating units called nucleotides. Each nucleotide has a sugar, a phosphate and one of four bases: A, T, C or G. Two strands twist into a double helix, held by complementary base pairs: A always pairs with T, and C with G. The genome is all of an organism's DNA.
A gene is a sequence of bases that codes for a particular protein. Every three bases (a triplet) code for one amino acid. In protein synthesis, a copy of the gene is carried out of the nucleus to a ribosome, where amino acids are joined in the order the code dictates. The chain folds into a specific shape, which decides what the protein does, for example as an enzyme or a hormone. A mutation changes the base sequence and may change the protein's shape.
Worked example
One strand of DNA reads ATTGC. What is the complementary strand?
- A pairs with T and T pairs with A.
- C pairs with G and G pairs with C.
Answer:The complementary strand is TAACG.
Key words
- nucleotide
- a sugar, a phosphate and a base
- complementary base pairs
- A with T, C with G
- triplet
- three bases coding for one amino acid
- genome
- all the DNA of an organism
New questions every time.
NGSS-referenced: HS-LS1-1