DNA

What is DNA? DNA stands for.. –D: Deoxyribose –N: Nucleic –A : Acid DNA contains the genetic information that ultimately determines an organism’s traits. Found in the chromosomes of ALL living things, including bacteria, viruses, mushrooms, pine trees, and zebras!

Why is it important? Everything that is living contains proteins. All actions that we do, such as eating, running, and even thinking, depends on proteins called enzymes. Your DNA determines the structure of these enzymes.

Who discovered that DNA was the genetic molecule? Alfred Hershey and Martha Chase

Who discovered it? Alfred Hershey and Martha Chase – in 1952, performed an experiment using radioactive viruses that infect bacteria. These viruses were made of only protein and DNA. They saw that it was the DNA, that entered the cells and caused the bacteria to produce new viruses.

Rosalind Franklin

The first scientist to ever take a "picture" of the DNA molecule using X-ray crystallography. She saw that.. 1)DNA molecule was long and thin 2)helical and twisted

Watson and Crick

James Watson and Francis Crick 1953: Watson and Crick Proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases. It is shaped like a long zipper that is twisted into a coil like a spring, looks like a twisted ladder. They called it a double helix.

Watson and Crick

Chain #1 Chain #2 Nitrogenous bases

Components of DNA DNA is made of repeating subunits called nucleotides. Nucleotides have three parts: 1. A nitrogenous base 2. A deoxyribose sugar 3. A phosphate group.

A Nucleotide Phosphate group Sugar (deoxyribose ) Nitrogenous base

Four Nitrogenous Bases In DNA, there are four different nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine (A) Guanine (G) Thymine (T) Cytosine (C )

Simplified

Components of DNA Nucleotides with different bases, are strung together in chains Chains are held together by hydrogen bonds between the bases Attached chains form a twisted ladder, in the shape of a double helix. The phosphates and sugars make up the “backbone” of the molecule and the bases stick out like prongs of a zipper.

Chain #1 Chain #2 Nitrogenous bases Hydrogen bonds

Chargoff’s Rule For each strand, there is a complimentary strand with matching base pairs. The amount of adenine is always equal to the amount of thymine The amount of guanine is always equal to the amount of cytosine. Adenine ALWAYS bonds with Thymine Cytosine ALWAYS bonds with Guanine

On the strands.. –“A” = Adenine –“T” = Thymine –“C” = Cytosine –“G” = Guanine A=T (double bond) C≡G (triple bond)

Example of Base-Pairing Example strand of DNA (Find each complimentary base pair for the strand of DNA) A—C—T—A—G—A—C—C—T—A—G—T | | | | | | | | | | | | T—G—A—T—C—T—G—G—A—T—C—AT—G—A—T—C—T—G—G—A—T—C—A

Life on earth All organisms, from bacteria to humans are made up of the same bases, just in a different order.

DNA Replication Replication is DNA making a copy of itself. Replication occurs before cell division (during interphase) so each new daughter cell has the same genetic information. Replication results in two strands of DNA IDENTICAL to the original. Each original strand serves as a template for the new one. Without DNA replication, new cells would have only half the DNA of their parents

Steps of Replication 1. Enzymes break the H+ bonds, holding the bases together. 2. The DNA molecule “unzips” and new nucleotides are attached by their base pair to each original strand. 3. Results in two identical DNA molecules, each has one strand from the original and one new.

Original DNA molecule New strand (red) Original strand (blue) New strand (red) Original strand (red) Original strand (blue)

Example of DNA Replication (Unzip the following strand of DNA, and write the two strands of DNA that would result from the replication) C—G—T—C—A—T—C—G—C—A—A—T—G | | | | | | | | | | | | | G—C—A—G—T—A—G—C—G—T—T—A—C Strand #1 C—G—T—C—A—T—C—G—C—A—A—T—G | | | | | | | | | | | | | G—C—A—G—T—A—G—C—G—T—T—A—C Strand #2 | | | | | | | | | | | | | G—C—A—G—T—A—G—C—G—T—T—A—C C—G—T—C—A—T—C—G—C—A—A—T—G 

Sooo, DNA is a CODE! 1. What is a code? **symbols used to store info. (ex. *Morse, computers, DNA, alphabet ) 2. How is DNA a code? **it stores genetic information (traits, cell function) We’ll talk more about what this Code does next time