Golgi complex cytoplasm mitochondria nucleolus nucleus lysosome endoplasmic reticulum cell membrane Each cell has a nucleus which is the cell’s control center Every nucleus carries all the information a living thing needs to grow live and reproduce This information is tightly packaged in a coil which looks like a wound up rope or hose The coil is made of long threadlike structures called chromosomes 6
Deoxyribonucleic acid or DNA forms the chromosomes DNA is at the very heart of genetics A DNA molecule is incredibly complex It looks like a twisted ladder Four bases or basic building blocks make up the rungs of the ladder Bases always come in pairs Each rung in the ladder is made of two out of the four bases base 1 base 3 base 2 base 4 The twisted ladder shape of DNA is called a double helix 7
DID YOU KNOW Inherited traits cannot explain everything about why living things look and act the way they do Environment and experience also play a part Traits that are not inherited are called acquired traits For example if an athlete lifts weights a lot his or her big muscles are an acquired trait The order of the rungs and the combination of the bases make up a kind of code The code carries instructions about how a living thing should grow change and operate DNA is the reason species are distinct Human babies are always born to humans kittens are born to cats and sunflowers make more sunflowers 8
The four DNA bases are adenine thymine guanine and cytosine Adenine only pairs with thymine Guanine only pairs with cytosine Scientists often refer to the bases by their first initials 9
