DNA Structure and Replication 8.2 and 8.3 Chapter 8 DNA Structure and Replication 8.2 and 8.3

What is DNA? Deoxyribonucleic acid (DNA) is a long molecule made up of units called nucleotides. Nucleotides are made up of: 5-carbon sugar (deoxyribose) Phosphate group Nitrogenous base (adenine, guanine, cytosine, or thymine) All the genetic information for an organism is carried on its DNA.

Nucleotides Form DNA Nucleotide Structure

History of DNA DNA winds around itself, forming a twisted ladder (double helix) Chargaff discovered the rules of base pairs in 1950 Rosalind Franklin took a picture of DNA in 1952 using X-ray diffraction Watson and Crick coined the term “Double Helix” in 1953

Groups of Bases Purines (two ring) Pyrimidines (one ring) Adenine Guanine Pyrimidines (one ring) Cytosine Thymine

Structure of DNA Cont’d Chargaff’s Rules: The four bases (adenine, guanine, thymine, cytosine) pair up in a certain way A = T C = G The bases are held together by hydrogen bonds (hydrogen bonds are weak bonds)

A C T G Chargaff’s Rules G A T C

Storage of DNA Prokaryotes – DNA is found in the cytoplasm Most have single circular DNA molecule Eukaryotes – Much more DNA than in prokaryotes (up to 1000x as much!) Condensed into chromosomes Chromosome number varies wildly from one species to the next. (humans have 46)

DNA Replication Before a cell divides, it must copy its DNA in a process called replication. During DNA replication: DNA unwinds using an enzyme called topoisomerase DNA then unzips into two strands using helicase DNA polymerase makes complimentary strands using base pairing. Each strand of the original DNA molecule is used as a template for the new DNA.

The area where DNA unwinds is called a replication fork.