DNA The Secret Code

Genes Genes, which are sections of DNA, are known to: Carry information from one generation to the next. Put that information to work by determining the heritable characteristics of organisms. Be easily copied, because all of a cell’s genetic information is replicated (copied) every time a cell divides.

How do we know that all of our genetic information comes from DNA? Thanks to many scientists and many experiments over the last ≈ 80 years. Griffith Hershey and Chase Franklin Watson and Crick

DNA Nucleic Acid: Deoxyribonucleic Acid (polymer) Made up of units (monomers) called nucleotides. Three components: 5-carbon sugar: Deoxyribose A phosphate group A nitrogenous base DNA Nucleotide

DNA Structure Called a double helix Twisted Ladder Backbone (sides) : 5-carbon sugar and phosphate groups Rungs: nitrogenous bases

Nitrogenous bases Our alphabet has 26 letters Can create many different words  many different sentences  billions of different books of information. DNA’s alphabet has 4 letters A, T, C, and G Create 3 letter words  Amino acids  proteins  billions of different organisms

Nitrogenous bases Purines: Pyrimidines: Adenine Guanine Thymine Cytosine

DNA Replication Replication: The process of making a copy of DNA The “parent” molecule has two complementary strands of DNA. Each is base paired by hydrogen bonding with its specific partner: A with T and G with C

DNA Unzips The first step in replication is the separation of the two strands. An enzyme called DNA helicase unzips DNA

New nucleotides added Each parental strand now serves as a template that determines the order of the bases along a new complementary strand. an enzyme called DNA polymerase adds the bases

Gaps are closed (zipped closed) The nucleotides are connected to form the sugar-phosphate backbones of the new strands. DNA ligase Each “daughter” DNA molecule consists of one parental strand and one new strand….semi-conservative

Reviewing DNA Replication Replication #3 and more