DNA Structure, DNA Replication, and Protein Synthesis Review worksheet featuring a labeled diagram of the DNA double helix.
Diagram illustrating DNA structure, showing a double helix with labeled nitrogenous bases (A, T, G, C), sugar-phosphate backbone, and instructions for labeling 3' and 5' ends, nucleotides, and base pairs.
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Show Answer Key & Explanations
Step-by-step solution for: DNA Structure Worksheet Answer Key
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Show Answer Key & Explanations
Step-by-step solution for: DNA Structure Worksheet Answer Key
Let's go through each question in the DNA Structure, DNA Replication, and Protein Synthesis Review worksheet and provide the correct answers with explanations.
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Answer:
A nucleotide is made of three parts: a phosphate group, a five-carbon sugar, and a nitrogen-containing base.
✔ Explanation:
Each nucleotide in DNA consists of:
- A phosphate group (attached to the 5' carbon of the sugar),
- A deoxyribose sugar (a five-carbon sugar),
- A nitrogenous base (either purine or pyrimidine).
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Answer:
In a single strand of DNA, the phosphate group binds to the 3' hydroxyl group of the next group.
✔ Explanation:
The sugar-phosphate backbone forms via phosphodiester bonds. The phosphate group of one nucleotide attaches to the 3' hydroxyl (-OH) group of the sugar in the next nucleotide, creating a 5' → 3' directionality.
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Answer:
The 5' end contains a free phosphate group, while the 3' end contains a free hydroxyl group.
✔ Explanation:
- The 5' end has a free phosphate group attached to the 5' carbon of the sugar.
- The 3' end has a free hydroxyl (-OH) group on the 3' carbon of the sugar.
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Answer:
Purines have two rings, and pyrimidines have one ring.
✔ Explanation:
- Purines (adenine and guanine) are double-ring structures (a six-membered ring fused to a five-membered ring).
- Pyrimidines (cytosine, thymine, uracil) are single six-membered rings.
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Answer:
Deoxyribonucleic acid
✔ Explanation:
DNA stands for Deoxyribonucleic Acid — "deoxy" refers to the sugar (deoxyribose), "nucleic" refers to its role in nucleic acids, and "acid" because it's acidic due to phosphate groups.
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We’ll describe how to label the diagram based on standard DNA structure.
#### Diagram Instructions:
- Label the 3' and 5' ends:
- The strand going from top to bottom (left side): the top end is 5', the bottom end is 3'.
- The opposite strand (right side): top is 3', bottom is 5'.
- So, antiparallel orientation.
- Circle a nucleotide:
- A nucleotide = one sugar + one phosphate + one base.
- Circle any single unit (e.g., the one with base A, T, G, or C).
- Label the sugar and phosphate:
- Sugar: the pentagon-shaped molecule (deoxyribose).
- Phosphate: the black circle (or dot) connected to the sugar’s 5' carbon.
- Label the bases not already labeled:
- Already labeled: A (adenine), T (thymine), G (guanine), C (cytosine).
- But in the diagram:
- A pairs with T (already labeled).
- G pairs with C (already labeled).
- So no additional labeling needed unless the complementary strands are unlabeled.
- If there's a base without a letter, label it accordingly.
- For example, if the base opposite G is missing, it should be C.
- Opposite C is G.
- Opposite T is A.
- Opposite A is T.
> So, if the diagram shows:
> - Top left: A → opposite base should be T
> - Second row: T → opposite base should be A
> - Third row: G → opposite base should be C
> - Bottom: C → opposite base should be G
But since A, T, G, C are already labeled, assume they're correct.
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Answer:
The two sides of the DNA helix are held together by hydrogen bonds between complementary nitrogenous bases.
✔ Explanation:
Hydrogen bonds form between:
- Adenine (A) and Thymine (T) → 2 hydrogen bonds
- Guanine (G) and Cytosine (C) → 3 hydrogen bonds
These weak bonds allow the strands to separate during replication.
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Answer:
The purines are adenine and guanine; the pyrimidines are cytosine and thymine.
✔ Explanation:
- Purines: A & G (double-ring)
- Pyrimidines: C & T (single-ring)
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Answer:
The term is antiparallel, which means the two strands run in opposite directions (one 5' to 3', the other 3' to 5').
✔ Explanation:
One strand runs 5' → 3' from top to bottom, the other runs 3' → 5' in the same direction, making them antiparallel.
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Adenine? _____ Thymine? _____**
Answer:
- Thymine (T): 30%
- Adenine (A): 30% (because A = T)
- Cytosine (C): 20%
- Guanine (G): 20% (because C = G)
✔ Explanation using Chargaff’s Rules:
- A = T
- G = C
- Total % = 100%
Given:
- T = 30% → A = 30%
- So A + T = 60%
- Remaining = 40% → G + C = 40%
- Since G = C → Each = 20%
So:
- Cytosine = 20%
- Adenine = 30%
- Thymine = 30%
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1. Phosphate, sugar, base
2. 3' hydroxyl group
3. Phosphate group, hydroxyl group
4. Two, one
5. Deoxyribonucleic acid
6. Hydrogen bonds between complementary nitrogenous bases
7. Adenine, Guanine; Cytosine, Thymine
8. Antiparallel, the two strands run in opposite directions (one 5'→3', the other 3'→5')
9. Cytosine: 20%, Adenine: 30%, Thymine: 30%
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Let me know if you'd like a labeled version of the diagram!
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1. A nucleotide is made of three parts: a ____________ group, a five-carbon ____________, and a nitrogen-containing ____________.
Answer:
A nucleotide is made of three parts: a phosphate group, a five-carbon sugar, and a nitrogen-containing base.
✔ Explanation:
Each nucleotide in DNA consists of:
- A phosphate group (attached to the 5' carbon of the sugar),
- A deoxyribose sugar (a five-carbon sugar),
- A nitrogenous base (either purine or pyrimidine).
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2. In a single strand of DNA, the phosphate group binds to the ____________ of the next group.
Answer:
In a single strand of DNA, the phosphate group binds to the 3' hydroxyl group of the next group.
✔ Explanation:
The sugar-phosphate backbone forms via phosphodiester bonds. The phosphate group of one nucleotide attaches to the 3' hydroxyl (-OH) group of the sugar in the next nucleotide, creating a 5' → 3' directionality.
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3. The 5' end of a single DNA strand contains a free ____________, while the 3' end contains a free ____________.
Answer:
The 5' end contains a free phosphate group, while the 3' end contains a free hydroxyl group.
✔ Explanation:
- The 5' end has a free phosphate group attached to the 5' carbon of the sugar.
- The 3' end has a free hydroxyl (-OH) group on the 3' carbon of the sugar.
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4. Purines have _______ rings, and pyrimidines have _______ ring.
Answer:
Purines have two rings, and pyrimidines have one ring.
✔ Explanation:
- Purines (adenine and guanine) are double-ring structures (a six-membered ring fused to a five-membered ring).
- Pyrimidines (cytosine, thymine, uracil) are single six-membered rings.
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5. Write out the complete name for DNA:
Answer:
Deoxyribonucleic acid
✔ Explanation:
DNA stands for Deoxyribonucleic Acid — "deoxy" refers to the sugar (deoxyribose), "nucleic" refers to its role in nucleic acids, and "acid" because it's acidic due to phosphate groups.
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On the diagram:
We’ll describe how to label the diagram based on standard DNA structure.
#### Diagram Instructions:
- Label the 3' and 5' ends:
- The strand going from top to bottom (left side): the top end is 5', the bottom end is 3'.
- The opposite strand (right side): top is 3', bottom is 5'.
- So, antiparallel orientation.
- Circle a nucleotide:
- A nucleotide = one sugar + one phosphate + one base.
- Circle any single unit (e.g., the one with base A, T, G, or C).
- Label the sugar and phosphate:
- Sugar: the pentagon-shaped molecule (deoxyribose).
- Phosphate: the black circle (or dot) connected to the sugar’s 5' carbon.
- Label the bases not already labeled:
- Already labeled: A (adenine), T (thymine), G (guanine), C (cytosine).
- But in the diagram:
- A pairs with T (already labeled).
- G pairs with C (already labeled).
- So no additional labeling needed unless the complementary strands are unlabeled.
- If there's a base without a letter, label it accordingly.
- For example, if the base opposite G is missing, it should be C.
- Opposite C is G.
- Opposite T is A.
- Opposite A is T.
> So, if the diagram shows:
> - Top left: A → opposite base should be T
> - Second row: T → opposite base should be A
> - Third row: G → opposite base should be C
> - Bottom: C → opposite base should be G
But since A, T, G, C are already labeled, assume they're correct.
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6. The two sides of the DNA helix are held together by _________________________.
Answer:
The two sides of the DNA helix are held together by hydrogen bonds between complementary nitrogenous bases.
✔ Explanation:
Hydrogen bonds form between:
- Adenine (A) and Thymine (T) → 2 hydrogen bonds
- Guanine (G) and Cytosine (C) → 3 hydrogen bonds
These weak bonds allow the strands to separate during replication.
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7. The purines are ______________ and ______________; the pyrimidines are ______________ and ______________.
Answer:
The purines are adenine and guanine; the pyrimidines are cytosine and thymine.
✔ Explanation:
- Purines: A & G (double-ring)
- Pyrimidines: C & T (single-ring)
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8. The term used to describe how the two strands of DNA are oriented is ______________, which means ______________.
Answer:
The term is antiparallel, which means the two strands run in opposite directions (one 5' to 3', the other 3' to 5').
✔ Explanation:
One strand runs 5' → 3' from top to bottom, the other runs 3' → 5' in the same direction, making them antiparallel.
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**9. In a strand of DNA, the percentage of thymine is 30%. What is the percentage of cytosine? _____
Adenine? _____ Thymine? _____**
Answer:
- Thymine (T): 30%
- Adenine (A): 30% (because A = T)
- Cytosine (C): 20%
- Guanine (G): 20% (because C = G)
✔ Explanation using Chargaff’s Rules:
- A = T
- G = C
- Total % = 100%
Given:
- T = 30% → A = 30%
- So A + T = 60%
- Remaining = 40% → G + C = 40%
- Since G = C → Each = 20%
So:
- Cytosine = 20%
- Adenine = 30%
- Thymine = 30%
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✔ Final Answers Summary:
1. Phosphate, sugar, base
2. 3' hydroxyl group
3. Phosphate group, hydroxyl group
4. Two, one
5. Deoxyribonucleic acid
6. Hydrogen bonds between complementary nitrogenous bases
7. Adenine, Guanine; Cytosine, Thymine
8. Antiparallel, the two strands run in opposite directions (one 5'→3', the other 3'→5')
9. Cytosine: 20%, Adenine: 30%, Thymine: 30%
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Let me know if you'd like a labeled version of the diagram!
Parent Tip: Review the logic above to help your child master the concept of dna structure labeling worksheet.
