11.2 Notes DNA STRUCTURE

What is DNA? Deoxyribonucleic acid = DNA Deoxyribonucleic acid = DNA Heritable genetic information Heritable genetic information Information passed down to you from parents Information passed down to you from parents Genome: the complete set of genetic material from your parents Genome: the complete set of genetic material from your parents Human Genome Project: Scientists tackling the challenge of sequencing the entire human genome (2000) Human Genome Project: Scientists tackling the challenge of sequencing the entire human genome (2000)

Nucleotides Nucleotides ARE the building blocks (monomers) of nucleic acids (polymers). Nucleotides ARE the building blocks (monomers) of nucleic acids (polymers). DNA IS a kind of nucleic acid DNA IS a kind of nucleic acid Each nucleotide is made up of: Each nucleotide is made up of: 1. A ring-shaped sugar called deoxyribose 2. A phosphate group 3. A nitrogenous base (a single or double ring of carbon and nitrogen atoms)

There are FOUR types of nucleotides found in DNA There are FOUR types of nucleotides found in DNA They only differ by their nitrogenous bases or ring structure. They only differ by their nitrogenous bases or ring structure. 1. Thymine (T) single ring=Pyrimadine 2. Cytosine (C) single ring=Pyrimadine 3. Adenine (A) double ring=Purine 4. Guanine (G) double ring=Purine HINT: CUT PY (cut pie) = (Cytosine, Uracil, Thymine = PYrimidine!

How do the nucleotides pair? Cytosine and Guanine pair with 3 hydrogen bonds Cytosine and Guanine pair with 3 hydrogen bonds Thymine and Adenine pair with 2 hydrogen bonds Thymine and Adenine pair with 2 hydrogen bonds A=T and C=G A=T and C=G

Quick Quiz… If Guanine always pairs with Cytosine & Adenine always pairs with Thymine...then they are always found in set or equal amounts. If Guanine always pairs with Cytosine & Adenine always pairs with Thymine...then they are always found in set or equal amounts. If one strand of DNA has 20% Guanines, how many Cytosines? If one strand of DNA has 20% Guanines, how many Cytosines? And Adenines? And Thymines? And Adenines? And Thymines? 20%G + 20%C = 40% G&C ; 20%G + 20%C = 40% G&C ; that leaves 60%... 30% A and 30% T that leaves 60%... 30% A and 30% T

Formation of the DNA strand Each nucleotide (A,T,G,C) is joined together by covalent bonds Each nucleotide (A,T,G,C) is joined together by covalent bonds The phosphate group on one nucleotide will join with the sugar group of another nucleotide The phosphate group on one nucleotide will join with the sugar group of another nucleotide Nucleotides will be strung together by sugar-phosphate-sugar- phosphate forming what is known as a backbone. Nucleotides will be strung together by sugar-phosphate-sugar- phosphate forming what is known as a backbone.

The nitrogenous base pairs are lined up along the backbone. The nitrogenous base pairs are lined up along the backbone. They meet in the middle of the Sugar- Phosphate backbone. They meet in the middle of the Sugar- Phosphate backbone. Are like rungs on a ladder. Are like rungs on a ladder.

The Backbone and Base Pairs

A one ring structure pairs with a two ring structure. A one ring structure pairs with a two ring structure. Must be a purine+ a pyrimidine Must be a purine+ a pyrimidine Must have three rings TOTAL to make a “ rung ” of the DNA “ ladder ” Must have three rings TOTAL to make a “ rung ” of the DNA “ ladder ”

1952: X-Ray Evidence… Rosalind Franklin and Wilkins Using X-ray crystallography she was able to take a picture of DNA Using X-ray crystallography she was able to take a picture of DNA X shaped pattern = DNA twisted around itself like a tightly coiled spring X shaped pattern = DNA twisted around itself like a tightly coiled spring X shape pattern had to be a helix so DNA was an Alpha Helicase. X shape pattern had to be a helix so DNA was an Alpha Helicase.

1953: Watson & Crick They were able to take all information from the work of scientists before them… They were able to take all information from the work of scientists before them… Proposed a 3-D model of the DNA molecule capable of: Proposed a 3-D model of the DNA molecule capable of: copying itself accurately copying itself accurately being translated into a living organism being translated into a living organism It was a double helix! It was a double helix!

Complimentary Bases Pairs Two strands on the double helix. Run in opposite directions of each other. (you ’ ll see this in the activity today!!) Two strands on the double helix. Run in opposite directions of each other. (you ’ ll see this in the activity today!!) The 2 strands are held together by base pairs that are complimentary to each other. The 2 strands are held together by base pairs that are complimentary to each other. A pairs with T A pairs with T G pairs with C. G pairs with C. These combinations on both strings of DNA can be passed down from generation to generation on chromosomes. These combinations on both strings of DNA can be passed down from generation to generation on chromosomes.

Each cell of yours, whether blood cell or brain cell has 3 billion nucleotides, or 6 feet of DNA. Each cell of yours, whether blood cell or brain cell has 3 billion nucleotides, or 6 feet of DNA. DNA supercoils around histones (proteins) to form chromosomes … remember where they ’ re located?? DNA supercoils around histones (proteins) to form chromosomes … remember where they ’ re located?? In the nucleus! In the nucleus! How does all that DNA fit into one cell?