Structure of DNA

Units of inheritance Chromosomes: in nucleus, made of DNA and proteins (histones) – carry GENES Chromosomes: in nucleus, made of DNA and proteins (histones) – carry GENES Genes – segments of DNA that contain instructions for a protein Genes – segments of DNA that contain instructions for a protein –Unit of heredity, made up of a unique sequence of DNA –Controls the growth, development and function of organism

Genome (all genes within an individual) Gene (segment of DNA coding for one particular protein) Polypeptide gene product (protein built from genetic code) Protein (remember secondary, tertiary and quaternary organisation?) DNA interactive animation: How DNA is packaged

DNA structure DNA = deoxyribonucleic acid DNA = deoxyribonucleic acid Made of nucleotide subunits (which include the base: A, C, G or T) Made of nucleotide subunits (which include the base: A, C, G or T) Sugar molecule Phosphate molecule Nitrogen base (adenosine, guanine, cytosine or thymine)

Bonding in the DNA molecule Sugar bonds to phosphate of the next nucleotide (base sticks out) Sugar bonds to phosphate of the next nucleotide (base sticks out) Hydrogen bonds between base pairs (weak) Hydrogen bonds between base pairs (weak) Segments of DNA “start” and “finish”. The end with an exposed phosphate is called the 5’ end, and the end with an exposed sugar is the 3’ end. ssets/images/gem4s1_1.jpg

The double helix One DNA molecule = 2 nucleotide chains One DNA molecule = 2 nucleotide chains 3’ end of one chain is matched with 5’ of the other chain 3’ end of one chain is matched with 5’ of the other chain DNA-5-3.jpg The 3’ Carbon of one sugar is attached via a phosphate to the 5’ Carbon of the next sugar. DNA is read from 5’ to 3’.

Base pairing A pair of bases is also called a “complementary pair” A pair of bases is also called a “complementary pair” A bonds with T, C bonds with G A bonds with T, C bonds with G Two types of nucleotide: A/G = purines (2 rings), T/C = pyramidines (1 ring) Two types of nucleotide: A/G = purines (2 rings), T/C = pyramidines (1 ring) If one strand code is known, the complementary can be inferred… If one strand code is known, the complementary can be inferred… What is the complementary strand to: What is the complementary strand to: 5’ ATTACGCGCGCCTAGTAC 3’ ? DNA interactive animation: DNA molecule, base pairing