The Structure of DNA Pre-AP Biology 11/10/2018

Bellwork Examine the organisms on the next slide and list 5 characteristics that make them unique. 11/10/2018 Property of CTE Joint Venture

Different Biological Organisms found on Planet Earth 11/10/2018 Property of CTE Joint Venture

Objectives Describe the structure of DNA. List the components that make up a nucleotide. Distinguish between a purine and pyrimidine. Explain complementary base pairing Identify the proteins involved in DNA replication. 11/10/2018 Property of CTE Joint Venture

Key Terminology Nucleotide Deoxyribose sugar Purine Pyrimidine Complementary base pairing Antiparallel Hydrogen bonding Helicase DNA Polymerase 11/10/2018 Property of CTE Joint Venture

DNA DNA stands for deoxyribonucleic acid Function of DNA Storage of genetic information that determines the characteristics of the organism Structure of DNA Made of two strands Each strand is a polymer of nucleotides 11/10/2018 Property of CTE Joint Venture

Composition of a Nucleotide A nucleotide has three components: 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 nucleotide can be further classified as Pyrimidines-single ring structure (T) Thymine (C) Cytosine Purines – double ring structure (A) Adenine (G) Guanine 11/10/2018 Property of CTE Joint Venture 8

DNA molecule is a double helix Two strands of nucleotides are twisted in a helical shape The two strands are antiparallel meaning they run in opposite directions The strands are held together by hydrogen bonds a weak bond between the strands 11/10/2018 Property of CTE Joint Venture

PROPERTY OF PIMA COUNTY JTED, 2010 Think-Pair-Share Give an everyday analogy that would illustrate the term antiparallel. Explain how this everyday analogy is related to the antiparallel nature of the two strands of DNA. 3. Think-pair-share teacher presents a question teacher gives wait time for student to form answer teacher instructs students to share their answer with a partner teacher calls on non-volunteers to share with the class PROPERTY OF PIMA COUNTY JTED, 2010 3 10

Chargoff’s Observations Edwin Chargoff, an American Biochemist examined the % composition of nitrogenous bases (adenine, guanine, thymine, and cytosine) in different organisms. www.sciencephoto.com/images/download_lo_res.html?id72403113 11/10/2018

PROPERTY OF PIMA COUNTY JTED, 2010 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. 3. Think-pair-share teacher presents a question teacher gives wait time for student to form answer teacher instructs students to share their answer with a partner teacher calls on non-volunteers to share with the class PROPERTY OF PIMA COUNTY JTED, 2010 3

Chargoff’s Data Human 31.0 31.5 19.1 18.4 Fruit Fly 27.3 27.6 22.5 Species Adenine (%) Thymine (%) Guanine (%) Cytosine (%) Human 31.0 31.5 19.1 18.4 Fruit Fly 27.3 27.6 22.5 Corn 25.6 25.3 24.5 24.6 Yeast 23.0 23.3 27.1 26.6 Bacteria 24.3 25.5 11/10/2018 Property of CTE Joint Venture

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 In other words, a purine always pairs with a pyrimidine These pairs are referred to as complementary base pairs 11/10/2018 Property of CTE Joint Venture

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. 11/10/2018 Property of CTE Joint Venture

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: 11/10/2018 Property of CTE Joint Venture

DNA synthesis New copies of DNA are made by a biochemical process known DNA replication 11/10/2018

DNA replication involves a complex of proteins These proteins are: DNA Helicase – opens the double helix Single-stranded binding protein – keeps the two strands separated DNA polymerase – adds nucleotides that are complementary to the DNA template

DNA Replication New DNA made by the enzyme DNA polymerase During DNA replication, each strand of the original DNA is used as the template DNA polymerase synthesizes the complementary new strand DNA replication is considered semi-conservative. Why? Keeps one original strand and makes one new strand

DNA replication

Closure Activity: Rope Ladder analogy: Explain how DNA is like/different from a rope ladder.