The Structure of DNA Bioscience 10/22/20151

Bellwork Examine the following organisms on the next slide and list 5 characteristics that make them unique. 10/22/2015Property of CTE Joint Venture2

Different Biological Organisms found on Planet Earth 10/22/2015Property of CTE Joint Venture3

Objectives Students will be able to: 1.Describe the structure of DNA. 2.List the components that make up a nucleotide. 3.Distinguish between a purine and pyrimidine. 4.Explain complementary base pairing. 10/22/2015Property of CTE Joint Venture4

Terminology- the following terms will be defined in the lesson Nucleotide Deoxyribose sugar Purine Pyrimidine Complementary base pairing Antiparallel Hydrogen bonding 10/22/2015Property of CTE Joint Venture5

DNA DNA stands for deoxyribonucleic acid Function of DNA ◦ Storage of genetic information that determines the characteristics of the organism 10/22/2015Property of CTE Joint Venture6

Overview of DNA structure Characteristics of DNA structure  Two strands of nucleotides; the nucleotides are the building blocks of DNA  The strands are antiparallel meaning they run in opposite directions  The strands are held together by hydrogen bonds-a weak bond between a hydrogen atom of one molecule and another atom of another molecule  The two strands are twisted into a helical structure  The backbone of the helix is sugar phosphate and the steps represent the nitrogen bases 10/22/2015Property of CTE Joint Venture7

Overview of DNA Structure 10/22/2015Property of CTE Joint Venture8 ogy/pathology/virus.html&usg

DNA is composed of two strands that run parallel with nitrogen bases as the backbone and sugar phosphate as the steps Thumbs up / Thumbs down ? PROPERTY OF PIMA COUNTY JTED,

Composition of a Nucleotide A nucleotide is composed of three components. The three components are ◦ A phosphate group ◦ Deoxyribose sugar - a 5 carbon sugar ◦ Nitrogenous base otide.gif

Nitrogenous bases in a nucleotide can be further classified as Pyrimidines-single ring structure ◦ (T) Thymine ◦ (C) Cytosine Purines – double ring structure ◦ (A) Adenine ◦ (G) Guanine 10/22/2015Property of CTE Joint Venture11 adfield/Images/Purines%2520Pyrimidines%2520fig2.jpg

A nucleotide is composed of a phosphate group, a deoxyribose sugar and a nitrogenous base Thumbs up / Thumbs down ? PROPERTY OF PIMA COUNTY JTED,

Chargoff’s Observations Edwin Chargoff, an American Biochemist examined the % composition of nitrogenous bases (adenine, guanine, thymine, and cytosine) in different organisms. 10/22/

Think-Pair-Share Examine the numbers in the table on the next slide and write down trends you observe in your note-taker. Compare your observations with the person next to you PROPERTY OF PIMA COUNTY JTED,

Chargoff’s Data 10/22/2015Property of CTE Joint Venture15 SpeciesAdenine (%)Thymine (%) Guanine (%)Cytosine (%) Human Fruit Fly Corn Yeast Bacteria

Key Observations Guanine approximately equal to cytosine; adenine approximately equal to thymine Suggests that G always pairs with C and A always pairs with T These pairs are referred to as complementary base pairs 10/22/2015Property of CTE Joint Venture16

Significance of Complementary Base Pairs Based on complementary base pair rules, the sequence of nucleotides on one strand determines the sequence of nucleotides on the other strand. 10/22/2015Property of CTE Joint Venture17

Student Sample Problem For the nucleotide sequence of the DNA strand below, write on your note-taker the complementary strand. Remember A pairs with T and G pairs with C: Strand 1: A T G G C A C T A G C A A Strand 2: 10/22/2015Property of CTE Joint Venture18

Closure: Summary of DNA Structure Fill in the concept map in the note-taker using the following terms-DNA, helix, nucleotide, hydrogen bonds, nitrogenous base, pyrimidine, purine, cytosine, thymine, guanine, adenine 10/22/2015Property of CTE Joint Venture19