Educational worksheet covering DNA, RNA, and protein synthesis with fill-in-the-blank questions and a DNA helix illustration.

Let’s go through each question one by one. I’ll explain the answers clearly so you can understand and remember them for your test or homework.

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1. The letters “DNA” stand for
→ Deoxyribonucleic Acid

2. DNA is composed of smaller subunits known as
→ Nucleotides

3. The three parts of a nucleotide are
→ A sugar (deoxyribose), a phosphate group, and a nitrogen base

4. The four nitrogen bases that are found in DNA are
→ Adenine, Thymine, Guanine, Cytosine

5. Two of the nitrogen bases are single ring structures known as
→ Pyrimidines. These two bases are Cytosine and Thymine

6. The other two bases are double ring structures known as
→ Purines. These two bases are Adenine and Guanine

7. _______ and _______ are the two scientists that discovered the structure of the DNA molecule
→ James Watson and Francis Crick
*(Note: Rosalind Franklin also contributed greatly with her X-ray images, but the question asks for the two who are most commonly credited with discovering the double helix structure.)*

8. DNA looks like a ladder twisted into a shape known as a
→ Double helix

9. The two molecules that make up the sides of the ladder or the side portion of a DNA molecule are
→ Sugar (deoxyribose) and Phosphate

10. The molecules that meet across the middle, forming the steps of the “ladder” are known as
→ Nitrogen bases (or base pairs)

11. Which nitrogen bases always pair with one another?
→ Adenine pairs with Thymine
→ Guanine pairs with Cytosine

12. According to Chargaff’s rules, the percentages of _______ are equal to those of thymine and the percentages of _______ are equal to those of guanine in the DNA molecule.
→ Adenine; Cytosine
*(Because A=T and G=C in DNA)*

13. The nitrogen bases are held together in the center of the molecule by
→ Hydrogen bonds

14. True or False? According to the principle of base pairing, hydrogen bonds could form only between adenine and cytosine.
→ False
*(Adenine pairs with Thymine, not Cytosine. Cytosine pairs with Guanine.)*

15. The type of sugar found in DNA is
→ Deoxyribose

16. If the sequence on the right hand side of the DNA molecule was TAGGCTCA, the complimentary side would have a sequence of
→ Let’s match each base:
- T → A
- A → T
- G → C
- G → C
- C → G
- T → A
- C → G
- A → T

So, complementary strand = ATCCGAGT

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Final Answer:

1. Deoxyribonucleic Acid
2. Nucleotides
3. Sugar, phosphate, nitrogen base
4. Adenine, Thymine, Guanine, Cytosine
5. Pyrimidines; Cytosine, Thymine
6. Purines; Adenine, Guanine
7. Watson, Crick
8. Double helix
9. Sugar, phosphate
10. Nitrogen bases (or base pairs)
11. Adenine with Thymine; Guanine with Cytosine
12. Adenine; Cytosine
13. Hydrogen bonds
14. False
15. Deoxyribose
16. ATCCGAGT