Chapter 11 DNA and GENES

DNA: The Molecule of Heredity

• DNA, the genetic material of organisms, is composed of four kinds nucleotides.

• A DNA molecule consist of two strands of nucleotides with sugar and phosphates on the outside and bases paired by hydrogen bonding on the inside.

• The paired strands form a twisted-Zipper shape called a double helix.

From DNA to Protein

• Because adenine can pair only with thymine, and guanine can pair only with cytosine, DNA can replicate itself with great accuracy.

• This process keeps the genetic information constant through cell division and during reproduction.

• Genes are small sections of DNA.• Most sequences of three bases in the DNA of

gene code for a single amino acid in a protein.

Genetic Changes

• The order of nucleotides in DNA determines the order if the nucleotides in messenger RNA in a process called transcription.

• Translation is a process through which the order of bases in a messenger RNA codes for the order of amino acids in a protein.

• A mutation is a change in the base sequence of DNA.

• Mutations may affect only one gene, or they may affect whole chromosomes.

• Mutations in a egg or sperm affect future generation by producing offspring with new characteristics.