GENETICS Recap & Basics

DNA Structure Function Replication

Structure of DNA Deoxyribose sugars joined by Phosphate bonds Bases – A, T, C, G bonded to sugars Two corresponding strands are joined together by weak bonds between bases (A & T; C & G) Twisted into a double helix

Function of DNA Carries the genetic code for functioning of an organism The sequence of bases on one strand contains the genetic code for all proteins needed by an organism Three bases = a triplet; one triplet codes for one amino acid (protein is made up of chains of amino acids). Groups of triplets code for a protein = a gene. (gene is section of DNA that codes for a protein)

Packaging of DNA There is a lot of DNA in cells, especially in eukaryotes. It has to be wound around proteins to make it fit into the cell. Usually DNA occurs as chromatin fibres within cells. Before replication, chromatin fibres condense to form chromosomes.

Replication of DNA DNA in cells replicates itself before cell division. Mitosis: cell division for growth and repair Meiosis: cell division for sexual reproduction Cell division

Chromosomes In somatic cells, chromosomes exist in homologous pairs (one from father and one from mother). Humans have 23 pairs – so 46 chromosomes. One half of the pairs is a set called the haploid number, n. Two sets are diploid, 2n. In gametes (egg & sperm) there is only a haploid number of chromosomes.

Genes Genome is the total amount of genetic material an individual has. One gene codes for one protein. It is possible to have variations of the same protein. These arise from variation of the same gene. Different varieties of the same gene are called alleles.