DNA Structure and Replication

What is DNA? DNA: 1. molecule that has the instructions for all cell activity 2. molecule that is passed from generation to generation 3. located in the NUCLEUS

Structure of DNA Made of Nucleotides (monomer) Nucleotide consists of: Deoxyribose sugar (sugar) Phosphate group (phosphate) Nitrogen containing base (base) Each human cells contains millions and millions of nucleotides that stretch to over 6 feet in length!! DNA wraps tightly around proteins to fit inside cell DNA in nucleus= 1000 feet of rope in a backpack

Review Questions 1. What makes up DNA? 2. Where is DNA located? 3. What three parts make up a nucleotide? 4. What type of sugar is in DNA?

Sugar-Phosphate Backbone Sugar-Phosphate Backbone of DNA: Formed by the sugar and phosphate of each nucleotide bonded together Sides of the ladder

Nitrogeneous (Nitrogen) Bases Nitrogen Bases: Rungs or Steps of Ladder Adenine Thymine Cytosine Guanine Adenine ALWAYS pairs with Thymine Cytosine ALWAYS pairs with Guanine

Double Helix: The “Twisted Ladder” Discovered by Watson and Crick Double: Two strands of DNA connected by nitrogen bases (hydrogen bonds) Helix: Nucleotides twist together Always an equal number of A and T G and C

Review Questions 1. What two parts of a nucleotide make up the “backbone”? 2. How many different bases exist in DNA? What are they? 3. What bases bond together in DNA? 4. Why is DNA called a “double helix”?

How Does Replication Occur? The two strands of DNA must be “unzipped” “Unzipping” occurs when the hydrogen bonds between the nitrogen bases are broken DNA HELICASE: enzyme (protein) that breaks hydrogen bonds and unzips DNA DNA POLYMERASE: enzyme (protein) that brings new nucleotides and attaches them to old strand Each strand is duplicated separately New bases are brought in to complement the old (parent) strand New strand of DNA consists of an OLD, parent strand and a NEW, daughter strand

Replication Replication 2

Review Questions 1. What is the first step in DNA Replication? 2. What enzyme unzips the DNA? 3. What enzyme brings in new bases and attaches them to the old strand? 4. What are the strands called when the new bases are added and two strands of DNA now exist?