DNA Intro. & Replication (S phase) DNA = deoxyribonucleic acid Objective: D3 - Identify the components of DNA and describe…DNA replication

I. History of DNA A. Avery, Oswald (1944)  Discovered that the nucleic acid, DNA, stores and transmits the genetic information from one generation of an organism to the next B. HERSHEY & CHASE (1952)  CONCLUDED THAT THE GENETIC MATERIAL OF THE BACTERIOPHAGE WAS DNA, NOT PROTEIN

C. Chargaff, Erwin  Discovered a relationship in the nitrogenous bases  ADENINE (A) = THYMINE (T) GUANINE (G) = CYTOSINE (C) D. Rosalind Franklin (1952) TOOK AN X-RAY OF THE DNA STRUCTURE SO THE PATTERNS COULD BE SEEN THE X-RAYS SHOW THAT DNA IS TWISTED AROUND EACH OTHER LIKE A HELIX AND HAS 2 STRANDS

E. Watson and Crick (1953) Studied the structure of the DNA by building a 3-D model AFTER using clues from Franklin’s x-ray of DNA proposed that DNA is made up of 2 chains of nucleotides & that the 2 strands are twisted together in a shape called a double helix

Nucleus II. Overview of DNA

*Chromosomes are made up of super coiled DNA* Histone Proteins DNA (double helix) Base pairs Sugar- phosphate backbone

Structure of DNA  Made up of nucleotides  Nucleotides have 3 parts: o Phosphate o Sugar o Nitrogen base  Traits are carried in the sequence of nitrogen bases  Common to all organisms

Adenine always pairs with Thymine Cytosine always pairs with Guanine DNA Base Pairing Rules

Copying process by which a cell duplicates its DNA DNA molecule separates into two strands, then produces two new complementary strands following the rules of base pairing Each strand of the double helix of DNA serves as a template for the new strand DNA – Genetic Information DNA – Deoxyribonucleic acid III. DNA Replication (S phase)

How Replication Occurs Enzymes unzip DNA by breaking the weak hydrogen bonds between the base pairs, which produces two replication forks DNA polymerase Joins individual nucleotides to make a new strand Proofreads each new strand

Chromosome Number The number of chromosomes are the same at the end of mitosis

Practice: If one strand of DNA looks like this, ATC GTA CCG, what will the complementary side look like? TAG CAT GGC If the number of chromosomes in a human skin cell is 46, how many chromosomes will there be in a skin cell after mitosis? 46 ATC GTA CCG ___________