Essential Question: What is the overall structure of DNA

Where is DNA located in the Cell?

3 DNA DNA.DNA is often called the blueprint of life. DNA contains the instructions for making proteins within the cell.

DNA ( deoxyribonucleic acid) Functions 1. Storage of genetic information 2. Expression of the genetic message (information). 3. Self-duplicate (replicates itself) DNA’s major function is to code for proteins.

By the early 1900’s it was known that the chromosomes carry the genetic information Chromosomes consist of DNA (deoxyribonucleic acid) Discovery of DNA

- Watson & Crick proposed a model of DNA shape - won Nobel Prize in 1962

Discovery of DNA - Rosalind Franklin produced X ray photographs of DNA - helped Watson and Crick develop their model - Did NOT win Nobel Prize for her work

Watson and Crick’s Double Helix Model explained: 1.How replication of DNA during mitosis produces exact copies for the daughter cells. 2.The double helix structure, two nucleotide strands are antiparallel (complementary). 3.How DNA acts as a code, specifying how proteins are made by the cell.

Structure of DNA

DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix. A molecule of DNA is made up of millions of tiny subunits (monomers) called Nucleotides. Each nucleotide consists of: 1.Phosphate group 2.Pentose sugar 3.Nitrogenous base

Nucleotides Phosphate Deoxy- Ribose sugar Nitrogen Base

12 The Double Helix Molecule The DNA double helix has two strands twisted together.

Four Nucleotides A Adenine T Thymine G Guanine C Cytosine

Structure of DNA - 4 different nucleotides are used to make the DNA molecule - Adenine (A) - Guanine (G) - Cytosine (C) - Thymine (T)

15 Types of Bases Double ring PURINES Adenine (A) Guanine (G) Single ring PYRIMIDINES Thymine (T) Cytosine (C) T or C A or G copyright cmassengale

Structure of DNA - held together by hydrogen bonds - pairing rules: A binds with T G binds with C

Chargaff’s Rule: Adenine and Thymine always join together, base pairing A T Cytosine and Guanine always join together, base pairing C G

Base-Pairings Purines only pair with Pyrimidines Guanine & Cytosine CG 3 H-bonds

T A Adenine & Thymine

20 One Strand of DNA The backbone of the molecule is alternating phosphates and deoxyribose sugars The nitrogenous bases are inside of the double helix. phosphate deoxyribose bases

G G A T T A A C T G C A T C

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23 Complementary Base Pairing the order of the bases in one strand determines the order of the bases in the other strand. DNA has two strands that fit together like a zipper.