11.1 DNA DNA and Genes

What is DNA? Instructions for building proteins Living things contain proteins in skin, muscles, bones Proteins called enzymes are important for functions like eating, running, thinking

What is DNA? DNA is the code that tells how to make proteins

The structure of DNA DNA is a polymer Made of nucleotides Sugar Phosphate group Nitrogen base Deoxyribonucleic acid

The structure of DNA nucleotides Sugar Phosphate group Nitrogen base Adenine Guanine Cytosine Thymine

The structure of DNA Nucleotides join together to form long chains

The structure of DNA In 1953 James Watson and Francis Crick proposed DNA is two chains joined by bonds between nitrogen bases After seeing Rosalind Franklin’s x-ray diffraction image of DNA

The structure of DNA Four nucleotides code for everything The sequence or order is important Just like order of letters in a word Different nucleotide sequence carries different meaning – codes for different protein

Replication of DNA Before a cell divides by mitosis or meiosis a copy of the chromosomes is made

Replication of DNA 1. strand separates – an enzyme breaks the hydrogen bonds holding nucleotides together

Replication of DNA 1. strand separates 2. nucleotides that are floating free nearby bond to the single strands 3. another enzyme bonds nucleotides into a new chain

Get two identical DNA so when cell divides, each daughter cell has a copy

Coming up: more on how DNA is like a library of books and how the information is used to make proteins