DNA: The Genetic Material The Structure of DNA DNA Replication

Review: All living things must have genetic material –Species must be able to pass on that genetic material to future generations.

DNA is short for Deoxyribonucleic acid It is located in the nucleus of cells in eukaryotes. In the Cytoplasm of prokaryotes It is the Blueprint that makes you who you are. It is a double helix.

The Structure of DNA

Building Blocks of DNA Nucleotides: subunits that make up the extraordinarily long thin molecule of DNA –Each nucleotide is constructed of three parts: A phosphate group A five-carbon sugar molecule A nitrogen base

Building Blocks of DNA Five-carbon sugar molecule: is called deoxyribose Phosphate group: is attached to the sugar and is the same for all moecules of DNA

Building Blocks of DNA Nitrogen group- has four possible configurations: –Adenine (A) –Guanine (G) –Thymine (T) –Cytosine (C)

Building Blocks of DNA Purines: a class of organic molecules that have a double ring of carbon and nitrogen atoms –Adenine –Guanine

Building Blocks of DNA Pyrimidines: a class of organic molecules that have a single ring of carbon and nitrogen –Thymine –Cytosine

Chargarff’s Rules Base pairing rules: for the DNA in each Organism –The amount of guanine always equals the amount of cytosine (number of G = number of C) –The amount of adenine always equals the amount of thymine (number of A = number of T)

Why are the bases so picky?

DNA looks like a Helix  1952: Rosalind Franklin  Studied DNA using x-rays and discovered that DNA looks like coiled spring. This spring shape is called a helix.

DNA is a Double Helix 1953: Watson and Crick Using the base pairing rule and X-ray photos from 1950 made a 3-D model using tin and wire –The result was the double helix, a “spiral staircase” configuration

DNA is a Double Helix Double Helix: –Has a sugar and phosphate backbone –The back bone is held together by purine and pyrimidine bonded by hydrogen Adenine pairs with Thymine Guanine pairs with Cytosine Due to the base pairing the two strand are complementary to each other

DNA is a Double Helix Write the complementary strand for the following sequence AGTCCTGAAATCGG TCAGGACTTTAGCC

Replication After Watson and Crick proposed the double helix model of DNA, three models for DNA replication were proposed: conservative, semiconservative, and dispersive. The semiconservative model was proved to be the correct one.

How DNA is Copied Replication: the process of synthesizing (making) a new strand of DNA –First: the DNA strand is unwound by enzymes called helicases Replication fork: The point at which the double helix separates –Second: DNA polymerase at the replication fork add nucleotides to the exposed strands to both the leading and lagging strand

How DNA is Copied –Third: leading strand is synthesized continuously and the lagging strand is synthesized in Okazaki fragments –Fourth: DNA ligase anneals bases together and seals the ends

Draw the process

DNA Replication

DNA double helix unwinds DNA helicase divides strand DNA polymerase brings together nucleotides to form new DNA strand After chromosomes are copied, polymerase falls off. Two copies of DNA are formed. DNA re-twists The cell divides, each containing one copy of DNA

Questions 1. Using the DNA below as a template, write the nucleotides that would be replicated on the other DNA strand. 5' - agg ctt gtt aga cta aaa atg acc - 3‘ 2. Where is DNA found in eukaryotic Cells? 3. What is the structure of DNA? 4. DNA is the Polymer of ? 5. Which of the following are pyrimidines?