Question

name: zahra urey class: 4th date: 9/30/15 the components and structure of dna

1. identify the components of a nucleotide in the diagram below. label the bases as purines or pyrimidines.
2. is the following sentence true or false? adenine and guanine are larger molecules than cytosine and thymine because they have two rings in their structure.
3. what forms the backbone of a dna chain?
4. is the following sentence true or false? the nucleotides must be joined together in a specific order.
5. according to chargaff’s rules, the percentages of __ are equal to thymine and the percentages of __ are equal to guanine in the dna molecule.
6. rosalind franklin’s work with x - ray diffraction showed that the dna molecule is shaped like a(an) __ and contains __ strands.
7. how did francis crick and james watson try to understand the structure of dna?
8. how did watson and crick describe the structure of dna?
9. is the following sentence true or false? according to the principle of base pairing, hydrogen bonds could form only between adenine and cytosine.
10. adenine, guanine, cytosine, and thymine are four kinds of ____ bases in dna.

Explanation:

1. A nucleotide has a sugar, a phosphate group, and a nitrogen - containing base. Adenine and guanine are purines (double - ring structures), cytosine and thymine are pyrimidines (single - ring structures).
2. Adenine and guanine are purines with two rings, making them larger than cytosine and thymine (pyrimidines with one ring), so the statement is true.
3. The backbone of a DNA chain is formed by alternating sugar (deoxyribose) and phosphate groups.
4. Nucleotides must be joined in a specific order to code for genetic information, so the statement is true.
5. According to Chargaff's rules, the percentages of adenine are equal to thymine and the percentages of cytosine are equal to guanine in the DNA molecule.
6. Rosalind Franklin's X - ray diffraction work showed that the DNA molecule is shaped like a double - helix and contains two strands.
7. Francis Crick and James Watson built physical models to try to understand the structure of DNA.
8. Watson and Crick described DNA as a double - helix structure with two strands held together by hydrogen bonds between complementary base pairs.
9. According to base - pairing rules, hydrogen bonds form between adenine and thymine, and between cytosine and guanine, not between adenine and cytosine, so the statement is false.
10. Adenine, guanine, cytosine, and thymine are four kinds of nitrogen - containing bases in DNA.

Answer:

1. Sugar, phosphate group, nitrogen - containing base. Adenine and guanine are purines, cytosine and thymine are pyrimidines.
2. True
3. Alternating sugar (deoxyribose) and phosphate groups
4. True
5. Adenine; cytosine
6. Double - helix; two
7. They built physical models.
8. A double - helix structure with two strands held together by hydrogen bonds between complementary base pairs.
9. False
10. Nitrogen - containing