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1 Name: Date: Period: The Structure of DNA Mind Map Using the words from our class brainstorm, categorize these ideas into clusters and create a mind map displaying what you already know about DNA and its significance in society. DNA

2 We know that DNA is exceptionally well-suited to be the basic building block of genes. We hear DNA mentioned a lot in the media. For example, DNA fingerprints are often used to identify criminals and to settle questions of parenthood. We hear about geneticists modifying DNA to produce new traits in organisms used to fight diseases. Other genetically modified organisms are finding their way into our food supply. But what exactly is DNA? What does it look like? How was it discovered? And how is it that all life on Earth shares the same structure of DNA, but DNA codes for genetic information in ways that results in huge diversity of life? DNA = Deoxyribonucleic Acid DNA consists of three (3) chemical structures: 1. Phosphoric Acid (Phosphate Group) 2. Five Carbon Sugar (Deoxyribose) 3. Nitrogenous Base These three components make up the building blocks of DNA called nucleotides. The sugar and phosphate together is called the backbone of DNA.

3 Other things you should know about the DNA molecule: A nucleotide is made up of a deoxyribose sugar, a phosphate group, and a nitrogenous base. DNA strands are described as being a double-helix, which is often compared to a twisted ladder. a. The alternating deoxyribose sugar and phosphate group make the rails (sides) of the ladder. b. The pairs of nitrogenous bases connect through weak hydrogen bonds to make the rungs (steps) of the ladder. The sugar molecule in DNA is a monosaccharide (single sugar) called deoxyribose. This sugar has 5 carbon atoms (pentose sugar) and it lacks an oxygen atom, as its name suggests ( de-oxy ribose, meaning without an oxygen). The version of this sugar with the extra oxygen, called ribose, is found in RNA another structure that will be discussed later. Found in DNA Found in RNA

4 There are FIVE different nitrogenous bases that fall into two different categories (some that are part of the structure of DNA, and some that are part of the structure of RNA): Pyrimidines (one-carbon nitrogen ring bases) Thymine (T) *Found in DNA only! Cytosine (C) Uracil (U) *Found in RNA only! Purines (two-carbon nitrogen ring bases) Adenine (A) Guanine (G) Base Pairs The nitrogenous bases A and T are held together by TWO hydrogen bonds. The nitrogenous bases C and G are held together by THREE hydrogen bonds. Adenine ALWAYS pairs with Thymine. Guanine ALWAYS pairs with CYTOSINE.

5 Another unique feature of the DNA molecule is the direction, or orientation of the two strands. Carbon molecules can be numbered in organic molecules. Carbon 1 attaches to the nitrogenous base in its own nucleotide. Carbon 5 attaches to the phosphate in its own nucleotide. Carbon 3 attaches to the phosphate in the next nucleotide. On the left rail of the DNA ladder, the orientation of the sugar has the 5 (read five prime ) carbon on the top. On the end of that rail, the 3 (read three prime ) carbon is on the bottom. The strand is said to be orientated 5 to 3. The strand on the right runs in the opposite direction and is oriented 3 to 5. DNA is double stranded. Each strand is made up of nucleotides oriented in the opposite direction. This orientation of the two strands is called antiparallel.

6 Deoxyribose (Sugar) Nitrogenous Base Base Pairs (C and G) Hydrogen Bonds Nucleotide Phosphate Group Adenine (A) nitrogenous bases cytosine (C) bases (base pairs) replication double helix 12. Write the complimentary strand of DNA underneath the following sequence: 5 T A T G C A G 3 3 A T A C G T C If there is 20% cytosine in a molecule of DNA, how much thymine is there? 20% cytosine = 20% guanine 30% adenine and 30% thymine