Tredyffrin/Easttown School District / Overview



NAME ________________________________________________________ DATE ______ PER______CHAPTER 8 sTUDY GUIDE – From DNA to PRoteins8.2 Structure of DNAnucleotidebase pairing rulesdouble helixKey Concept: DNA structure is the same in all organisms.DNA is a chain of nucleotides. In DNA, each nucleotide is made of a phosphate group, a sugar called deoxyribose, and one of four nitrogen-containing bases. These four bases are cytosine (C), thymine (T), adenine (A), and guanine (G). Two of the bases, C and T, have a single-ring structure. The other two bases, A and G, have a double-ring structure.Although scientists had a good understanding of the chemical structure of DNA by the 1950s, they did not understand its three-dimensional structure. The contributions of several scientists helped lead to this important discovery.?Erwin Chargaff analyzed the DNA from many different organisms and realized that the amount of A is equal to the amount of T, and the amount of C is equal to the amount of G. This A = T and C = G relationship became known as Chargaff’s rules.?Rosalind Franklin and Maurice Wilkins studied DNA structure using x-ray crystallography. Franklin’s data suggested that DNA is a helix consisting of two strands that are a regular, consistent width apart.James Watson and Francis Crick applied Franklin’s and Chargaff’s data in building a three-dimensional model of DNA. They confirmed that DNA is a double helix in which two strands of DNA wind around each other like a twisted ladder. The sugar and phosphate molecules form the outside strands of the helix, and the bases pair together in the middle, forming hydrogen bonds that hold the two sides of the helix together. A base with a double ring pairs with a base with a single ring. Thus, in accordance with Chargaff’s rules, they realized that A pairs with T, and C pairs with G. The bases always pair this way, which is called the base pairing rules.1.What did Chargaff’s rules state?A only pairs with T and C only pairs with G; the amount of A and T will be equal and the amount of G and C will be equal2.What did Franklin’s data show about the three-dimensional structure of DNA?That it was of uniform width3.What forms the backbone strands of the DNA double helix? What connects these strands in the middle?The backbone is made up of sugar and phosphatesThe backbone is connected in the middle by nitrogen base pairs bonded by hydrogen bondsMain Idea: DNA is composed of four types of nucleotides.4238625307340001.In the space below, draw a nucleotide and label the phosphate group, the nitrogen-containing base, and the deoxyribose sugar.Fill in the blank with the word or phrase that best completes the sentence.2.How many types of nucleotides are present in DNA? 43.All nucleotides have two parts that are the same: the deoxyribose sugar and phosphate. The third part, nitrogen base, is different.MAIN IDEA: Watson and Crick developed an accurate model of DNA’s three-dimensional structure.Circle the word or phrase that best completes the statement.4.Franklin’s data revealed that the structure of DNA is uniform / variable in width.5.Watson and Crick determined the three-dimensional shape of DNA by building models / building genomes.6.DNA base pairing results in a molecule that has a uniform width. A sugar-phosphate backbone is on the inside / outside. Inside the structure, a base with two rings always pairs with a base with one / two ring(s).MAIN IDEA: Nucleotides always pair in the same way.7.The T nucleotide pairs with the A nucleotide, and the C nucleotide pairs with the G nucleotide.2959100120015008.See figure 2.4. In the space to the right, draw a DNA double helix. Label the sugar-phosphate backbone, the nitrogen-containing bases, and the hydrogen bonds.Vocabulary CheckFill in the blank with the word or phrase that best completes the sentence. 9.The DNA double helix is similar to a spiral staircase: the sugar-phosphate backbone is like the twisting handrails of the staircase, and the nitrogen-containing bases are like the steps that connect the railings to each other.Select from the lettered list to fill in the blanks in the sentence below. 10.The base pairing rules of DNA relate to Chargaff’s rules. The base pairing rules state that A only pairs with T and C only pairs with G. Therefore, the amount of A will be equal to the amount of T, and the amount of C will be equal to the amount of G.a.less thanb.more thanc.equal toreplicationDNA polymerase8.3 DNA REPLICATIONKEY CONCEPT: DNA replication copies the genetic information of a cell. Every cell needs its own complete set of DNA, and the discovery of the three-dimensional structure of DNA immediately suggested a mechanism by which the copying of DNA, or DNA replication, could occur. Because the DNA bases pair in only one way, both strands of DNA act as templates that direct the production of a new, complementary strand. DNA replication takes place during the S stage of the cell cycle.The process of DNA replication is very similar in both eukaryotes and prokaryotes, but we will focus on eukaryotes.?During the S stage of the cell cycle, the DNA is loosely organized in the nucleus. Certain enzymes start to unzip the double helix at places called origins of replication. The double helix unzips in both directions along the strand. Eukaryotic chromosomes are very long, so they have many origins of replication to help speed the process. Other proteins hold the two strands apart.?The unzipping exposes the bases on the DNA strands and enables free-floating nucleotides to pair up with their complementary bases. DNA polymerases bond the nucleotides together to form new strands that are complementary to the original template strands.?The result is two identical strands of DNA. DNA replication is described as semiconservative because each DNA molecule has one new strand and one original strand.DNA polymerase not only bonds nucleotides together. It also has a proofreading function. It can detect incorrectly paired nucleotides, clip them out, and replace them with the correct nucleotides. Uncorrected errors are limited to about one per 1 billion nucleotides.1.Why is DNA replication described as semiconservative?Because each molecule consists of one old strand and one new strand2.What are two major functions that DNA polymerase performs?1) Bonds new nucleotides to the exposed nitrogen bases; 2) detects incorrectly paired nucleotides and fixes them Main Idea: Replication copies the genetic information.Fill in the blank or circle the word or phrase that best completes the statement.1.DNA replication is the process by which DNA is copied / observed during the cell cycle.2.DNA replication takes place in the centrosome / nucleus of a eukaryotic cell.3.DNA is replicated during the M stage / S stage of the cell cycle.4.DNA replication needs to occur so that every cell / organism will have a complete set of DNA following cell division.5.A template is something that serves as a pattern.6.Suppose that one strand of DNA has the sequence TAGGTAC. Write down the sequence of the complementary DNA strand. A T C C A T GMain Idea: Proteins carry out the process of replication.7.Circle all of the roles that proteins play during DNA replication.a.They help unzip the DNA strand.b.They hold the DNA strands apart.c.They attach nucleotides to the nucleus.d.They remove nucleotides from the DNA strands. e.They bond nucleotides together.Fill in the blank with the word or phrase that best completes the sentence.8.In order for the DNA strands to separate, the hydrogen bonds connecting base pairs must be broken.9.DNA replication is called semiconservative because each molecule consists of one old strand and one new strand.Place the following sentences in the correct order to summarize the steps of replication. Draw a diagram showing each step.a.Enzymes unzip the helix.b.Two identical DNA molecules result.2984552387512.11.10.ACB0012.11.10.ACBc.DNA polymerase binds nucleotides together to form new strands that are complementary to the original strands.40265355715000220281598425004222759715500Main Idea: Replication is fast and accurate. Circle the word or phrase that best completes the statement.13.Human chromosomes have only one / hundreds of origin(s) of replication, where the DNA is unzipped so replication can begin.14.DNA polymerase has a proofreading function that enables it to detect errors / enzymes and correct them.Vocabulary CheckFill in the blank with the word or phrase that best completes the sentence. 15.The suffix -ase indicates an enzyme. A polymer is a string of repeating structural units. DNA polymerase is an enzyme that makes DNA by forming bonds between nucleotides. ................
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