Chapter 12 DNA and GENES

Structure and Function of DNA Deoxyribonucleic Acid -- Complex polymer called a nucleic acid Serves as master copy of information code Passed with each cell division Passed from one generation to the next Composed of repeating nucleotides Subunit of a nucleic acid

Nucleotide Structure Three parts: Simple sugar called deoxyribose Phosphate group One of four nitrogen bases: Adenine (A) Thymine (T) Guanine (G) Cytosine (C)

Nucleotide Structure A purine joins with a pyrimidine: Adenine always joins with Thymine Cytosine always joins with Guanine

Nucleotide Chains Nucleotides combine to form a long chain Two chains joined together at the bases by hydrogen bonds (looks like ladder) Ladder twists, giving a “double helix” shape

Importance of Sequence ALL DNA has similar structure and function Four bases offer thousands of possible combinations= COUNTLESS POSSIBILITIES!!!

Replication of DNA DNA must be “copied” every time a cell divides HOW? Enzymes break down the hydrogen bonds and “unzip” the DNA Free-floating nucleotides join in to make new pairs Enzymes reform hydrogen bonds