The Structure The Structure of DNAof DNA

Bioscience

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BellworkBellworkExamine the following organisms

on the next slide and list 5 characteristics that make them unique.

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Different Biological Different Biological Organisms found on Planet Organisms found on Planet EarthEarth

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ObjectivesObjectivesStudents 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.

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Terminology- the following Terminology- the following terms will be defined in the terms will be defined in the lessonlessonNucleotideDeoxyribose sugarPurinePyrimidineComplementary base pairingAntiparallelHydrogen bonding

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DNADNADNA stands for deoxyribonucleic

acidFunction of DNA

◦Storage of genetic information that determines the characteristics of the organism

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Overview of DNA structureOverview 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

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Overview of DNA Overview of DNA StructureStructure

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http://www.biologycorner.com/resources/dna.gif&imgrefurl=http://www.biologycorner.com/APbiology/pathology/virus.html&usg

DNA is composed of two strands DNA is composed of two strands that run parallel with nitrogen bases that run parallel with nitrogen bases as the backbone and sugar as the backbone and sugar phosphate as the stepsphosphate as the steps

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Composition of a NucleotideA nucleotide is

composed of three components. The three components are◦ A phosphate

group◦ Deoxyribose sugar

- a 5 carbon sugar◦ Nitrogenous base

http://www.biology.iupui.edu/biocourses/N100/images/3nucleotide.gif

Nitrogenous bases in a Nitrogenous bases in a nucleotide can be further nucleotide can be further classified asclassified asPyrimidines-

single ring structure◦ (T) Thymine◦ (C) Cytosine

Purines – double ring structure◦ (A) Adenine◦ (G) Guanine

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http://archive.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/Hadfield/Images/Purines%2520Pyrimidines%2520fig2.jpg

A nucleotide is composed of a phosphate A nucleotide is composed of a phosphate group, a deoxyribose sugar and a group, a deoxyribose sugar and a nitrogenous basenitrogenous base

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Chargoff’s ObservationsChargoff’s ObservationsEdwin Chargoff,

an American Biochemist examined the % composition of nitrogenous bases (adenine, guanine, thymine, and cytosine) in different organisms.

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www.sciencephoto.com/images/download_lo_res.html?id72403113

TThinkhink-P-Pairair-S-Sharehare 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

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Chargoff’s DataChargoff’s Data

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Species Adenine (%)

Thymine (%)

Guanine (%)

Cytosine (%)

Human 31.0 31.5 19.1 18.4

Fruit Fly

27.3 27.6 22.5 22.5

Corn 25.6 25.3 24.5 24.6

Yeast 23.0 23.3 27.1 26.6

Bacteria

24.6 24.3 25.5 25.6

Key ObservationsKey ObservationsGuanine 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

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Significance of Complementary Significance of Complementary Base PairsBase PairsBased on complementary base

pair rules, the sequence of nucleotides on one strand determines the sequence of nucleotides on the other strand.

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Student Sample ProblemStudent Sample ProblemFor 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 AStrand 2:

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Closure: Summary of DNA Closure: Summary of DNA StructureStructureFill 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

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