DNA is the basis of life - it means deoxyribose nucleic acid. DNA codes for proteins; the building blocks our bodies.
In these AQA AS Biology: Biol2 notes, we will focus on DNA structure, nucleotide structure, the function of DNA, genes, the triplet code, chromosomes and homologous chromosomes, alleles, meiosis, and recombination by crossing over.
DNA: The Structure
DNA - Heriditary material responsible for passing on genetic information from cell to cell and down generations
Nucleotide - The structure of DNA, containing deoxyribose sugar, a phosphate group, and an organic base
- DNA is made up of nucleotides
- Nucleotides contain three components: deoxyribose sugar (pentagon), phosphate molecule (circle), and an organic base (rectangle)
- The three molecules are bonded together by condensation reactions
- Nucleotides join together to make dinucleotides or polynucleotides
- So how is DNA formed through this? Quite simply. Two nucleotides, or strands, are combined by hydrogen bonds between bases.
- Theory: 1953 - Watson and Crick took credit for Rosalind Franklin's work on DNA by figuring out structure on X-ray diffraction patterns
Pairing of bases
Complementary base pairs - two DNA bases which pair up due to their ring structures
- There are four bases, made up of nitrogen
- These are Adenine, Thymine, Guanine, and Cytosine
- The two bases Adenine and Guanine have double ring structures, so they are considered purine bases
- The two bases Thymine and Cytosine have single ring structures so they are considered pyrimidine bases
- One purine pairs up with one pyrimidine
- A + T with two hydrogen…