DNA Replication Goal: Students will be able to summarize the events of DNA replication.

Structure: DNA Length DNA molecules are very long. The nucleus of a human cell contains more than 1 meter (3 feet) of DNA. DNA must be folded and coiled in order to fit in such a small space.

Chromosome Supercoils Coils Nucleosome Histones DNA double helix

DNA Structure Chromosomes are made of DNA. The DNA is wound around proteins called Histones. (like thread around a spool) When chromosomes are unraveled, the DNA strands are called Chromatin.

Structure: DNA DNA is a double helix Two strands of nucleotides wound around each other like a twisted ladder Nitrogen bases of opposite strands held together by Hydrogen bonds. Sugar-Phosphate Backbone held together by Covalent bonds.

Sugar-phosphate backbone Covalent Bonds Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Covalent Bonds

Structure: Base Pairing DNA strands are made of nucleotides Phosphate group Deoxyribose sugar Nitrogen Base (G, C, A, or T) Purines bond to Pyrimidines A = T G = C

Structure: Nitrogenous Bases Double ring PURINES Adenine (A) Guanine (G) Single ring PYRIMIDINES Thymine (T) Cytosine (C) A or G T or C copyright cmassengale

DNA replication PURPOSE Every cell in your body has the SAME DNA DNA has to be copied before a cell divides DNA is copied during interphase New cells will need identical DNA strands

DNA replication PURPOSE DNA replication is SEMI-CONSERVATIVE. Each daughter molecule of DNA is made of ONE ORIGINAL strand and ONE NEW strand.

Summary of DNA Replication Helicase (an enzyme) breaks the Hydrogen bonds between the nitrogen bases and separates (unzips) the original strands of DNA. DNA polymerase (another enzyme) bonds complimentary DNA nucleotide bases to each original strand. (G=C, A=T) DNA polymerase then proofreads the DNA for mistakes (mutations).

DNA replication BIG IDEA Each strand serves as a template for the attachment of complimentary bases. G = C, A = T

DNA replication BIG IDEA Base Pairing ensures that when DNA is replicated, you get 2 identical copies of DNA each with ONE NEW STRAND and ONE ORIGINAL STRAND!