The Double Helix. DNA and RNA, part 2. Part A. Hint 1. The difference between purines and pyrimidines. Hint 2. Distinguish purines from pyrimidines

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1 DNA and RNA, part 2 Due: 3:00pm on Wednesday, September 24, 2014 You will receive no credit for items you complete after the assignment is due. Grading Policy The Double Helix DNA, or deoxyribonucleic acid, contains the genetic information that is used by all living things to produce their biomolecules essential for life. DNA is a double helix, with two strands. The two strands are held together by hydrogen bonds between complementary nitrogenous bases. The two strands are always complementary, ensuring that the DNA can be replicated accurately. The two complementary DNA strands always run in opposite directions: One runs from 5' to 3', and the other runs from 3' to 5', if you are looking along the strand, as seen in the image. Part A Pair up the nucleotide bases with their complementary partners. Drag each item to the appropriate bin. Hint 1. The difference between purines and pyrimidines The complementary partners in a DNA base pair are always made up of one purine and one pyrimidine, never two purines or two pyrimidines. Purines are the nucleotides that have the double-ring structures. Pyrimidines are the nucleotides that have the single-ring structures. An easy way to think of it is that the longer names (pyrimidines) have the smaller rings, and the shorter name (purines) have the bigger rings. Hint 2. Distinguish purines from pyrimidines Distinguish the purines from the pyrimidines. Drag each item to the appropriate bin. 第 1 页 ( 共 15 页 )

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3 In a DNA sequence, the purine adenine always pairs with the pyrimidine thymine, and the purine guanine always pairs with the pyrimidine cytosine. Part B Write the complementary sequence for the following DNA sequence, in order from 3' to 5': Use all capital letters to write the DNA sequence. 5 CGATATTGAGCTAAGCTT 3 Hint 1. The definition of a complementary sequence Each of the four nucleotides found in DNA has one complementary partner. Adenine ( ) always pairs with thymine ( T) and guanine ( G) always pairs with cytosine ( C) on the complementary DNA strand. The two complementary strands always pair up, each strand running in opposite directions. Below is an example of a DNA sequence and its complement. A Sequence Complement 5 ATGCTACG 3 3 TACGATGC 5 Hint 2. Select the complementary sequence As an example, select the complementary sequence for the following: 5 ATGC 3 第 3 页 ( 共 15 页 )

4 3 ATGC 5 3 CGTA 5 3 TACG 5 3 GCAT 5 3 GCTATAACTCGATTCGAA 5 Part C Rank the following base pairs according to their stability. Rank from most to least stable. To rank items as equivalent, overlap them. Hint 1. Hydrogen bonds and base-pair stability In general, the stability of a base pair is determined by the number of hydrogen bonds between the two bases. The more hydrogen bonds between the bases, the more stable the base pair is. Hint 2. Determine the number of hydrogen bonds between bases Which of the three base pairs has the largest number of hydrogen bonds between the bases? 第 4 页 ( 共 15 页 )

5 adenine-thymine adenine-cytosine guanine-cytosine 第 5 页 ( 共 15 页 )

6 The base pair adenine-cytosine occurs very rarely in nature. It only happens during a mutation event. When the DNA is replicated, one of the two daughters will contain a guanine-cytosine base pair in the location of the mutation, and the other daughter will contain an adenine-thymine base pair. Chemistry Review - Nucleic Acids: Structure Review the Structure tutorial. Then answer the questions. Part A RNA nucleotides contain than DNA nucleotides. 第 6 页 ( 共 15 页 )

7 more oxygen less phosphorus less oxygen different purines None of the above. Good thinking! RNA uses the sugar ribose, which has one more oxygen atom than the sugar used in DNA (deoxyribose). Part B The orange unit with two linked rings in this diagram represents... a nucleotide. a pyrimidine. a sugar. a purine. an amino acid. Yes! Purines have two linked rings. Part C How likely is it that the next base, out of sight at the top of this polymer, is uracil? 第 7 页 ( 共 15 页 )

8 It's sure to be uracil, since A, C, and G are already present. The chances are very good, since the bases are equally common. Not a chance, since this is a DNA molecule, not an RNA molecule. It's as likely as any of the bases; about one chance in four. Since RNA has five bases, there is one chance in five. Good thinking! The sugars tell you this is DNA, which doesn't have uracil. Part D Which statement helps to explain how DNA stores hereditary information? DNA is a self-replicating type of protein. DNA binds a master copy of each kind of protein. DNA contains 20 kinds of amino acids. DNA contains four kinds of nitrogenous bases. DNA is made from thousands of kinds of monomers.! Information is stored in the sequence of nitrogenous bases along the DNA polymer. The bases include two kinds of pyrimidines and two kinds of purines. Part E DNA and mrna differ with respect to... 第 8 页 ( 共 15 页 )

9 Both (a) and (b). (c) how many kinds of nucleotides are used to make the polymer. (b) the kinds of purines they contain. (a) the kind of sugar they contain. (d) the ability to make a double helix. Right! RNA uses ribose; DNA uses deoxyribose. The polymer names reflect this difference: RNA is short for Ribonucleic acid; DNA is short for deoxyribonucleic acid. Chapter 4 Blue Thread Question 2 Part A 第 9 页 ( 共 15 页 )

10 When double-stranded DNA is heated to 95 C, the bonds between complementary base pairs break to produce single-stranded DNA. Considering this observation, is the strand separation step required for replication of the double helix spontaneous? Why or why not? Hint 1. Review Chapter 2, Section 3 on spontaneous reactions. Yes. A continuous input of energy is required. No. A continuous input of energy is required. Yes. Energy is released. No. Energy is released. 第 10 页 ( 共 15 页 )

11 . Chemical reactions are spontaneous if they can proceed on their own, without any continuous external influence such as added energy (in this case heat). Chapter 4 Blue Thread Question 3 Part A Complementary base pairing is possible only if two DNA strands align in antiparallel instead of parallel fashion. Which statement best explains why? Hint 1. Review Figure 4.6b and the interactions responsible for complementary base pairing. Only antiparallel strands create the geometry that allows complementary base pairs to form via van der Waals interactions. Only antiparallel strands contain unusual backbone atoms which allow complementary base pairing Only antiparallel strands create the geometry that allows complementary base pairs to form via hydrogen bonding. Only antiparallel strands contain the nitrogenous bases necessary to form complementary base pairs.. Given the bond angles and distances in nucleotides, a DNA double helix anchored by complementary base pairing is possible only with antiparallel polynucleotide strands. 第 11 页 ( 共 15 页 )

12 Chemistry Review - Nucleic Acids: Functions of Nucleic Acids Review the Functions tutorial. Then answer the questions. Part A Which statement is true of nucleic acids? (a) rrna positions amino acids along mrna. (b) mrna binds amino acids together to make proteins. (c) mrna is part of the ribosome. (d) DNA carries information for making RNA. Both (b) and (d).! All RNA is made by copying segments of DNA. Part B The information in DNA tells a cell how to make... (a) proteins. (b) DNA. (c) trna. Both (a) and (b). (a), (b), and (c). 第 12 页 ( 共 15 页 )

13 Excellent! The information in DNA tells how to make every nucleic acid and protein that the cell's parent could make. Part C The green molecules in the diagram... (a) contain the base uracil. (b) contain the sugar deoxyribose. (c) are made by copying RNA. Both (a) and (c). (a), (b), and (c). Great! All kinds of RNA contain uracil. Part D Which statement is true of the process in the animation below? 第 13 页 ( 共 15 页 )

14 (a) It's called DNA replication. (b) Cells do it to produce proteins. (c) Its product contains the nitrogenous base thymine. Both (a) and (b). Both (b) and (c).! All the information stored in DNA is concerned, directly or indirectly, with making proteins. The process you see here is called transcription. Its products help to build proteins. Chapter 4 Blue Thread Question 5 Part A 第 14 页 ( 共 15 页 )

15 DNA molecules with a high percentage of guanine (G) and cytosine (C) are particularly stable. Why? Hint 1. Review Figure 4.6b and think about the interactions that stabilize complementary base pairs. G-C base pairs stack more tightly than A-T base pairs in the interior of the double helix. G and C form more hydrogen bonds with water, making the DNA more hydrophilic. A G-C base pair has three hydrogen bonds, while an A-T base pair has two. Bases are closer together in a G-C pair than an A-T pair.. G-C base pairs are more stable than A-T base pairs. Score Summary: Your score on this assignment is 90.4%. You received 5.42 out of a possible total of 6 points. 第 15 页 ( 共 15 页 )