DNA Structure and Replication: Model 1 - The Structure of DNA, including nucleotides, nitrogen bases, and the double helix.

Let’s go step by step to answer each question based on Model 1.

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Question 1: What are the three parts of a nucleotide?

Look at the “Nucleotide” diagram in Model 1. It shows:
- A circle labeled “Phosphate”
- A pentagon (5-sided shape) labeled “Deoxyribose sugar”
- A rectangle or other shape attached to the sugar, which is one of the nitrogen bases (like Adenine, Thymine, etc.)

So, every nucleotide has:
→ Phosphate group
→ Deoxyribose sugar
→ Nitrogen base (A, T, C, or G)

✔ Answer for 1a: phosphate, deoxyribose sugar, and a nitrogen base

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Question 1b: What kind of sugar is found in a nucleotide?

In the diagram, it clearly says “Deoxyribose sugar”.

✔ Answer for 1b: deoxyribose

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Question 1c: Which nucleotide component contains nitrogen?

The nitrogen bases — Adenine, Thymine, Guanine, Cytosine — all contain nitrogen. That’s why they’re called “nitrogen bases.” The sugar and phosphate do not contain nitrogen.

✔ Answer for 1c: the nitrogen base (Adenine, Thymine, Guanine, or Cytosine)

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Question 1d: Name the four nitrogen bases shown in Model 1.

Looking at the ladder model and key:
- Circle = Adenine
- Hexagon = Thymine
- Diamond = Guanine
- Rectangle = Cytosine

Also listed in the “Nitrogen Base” section with symbols.

✔ Answer for 1d: Adenine, Thymine, Guanine, Cytosine

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Question 2: DNA is often drawn as a “ladder model.” Locate this drawing in Model 1.

You can see the middle diagram labeled “Ladder Model of DNA” — it looks like a ladder with rungs made of paired bases.

Now, part a: Circle a single nucleotide on each side of the ladder model of DNA.

On the left side of the ladder, pick any one unit that includes:
- One phosphate (circle)
- One deoxyribose sugar (pentagon)
- One nitrogen base (attached to sugar)

Do the same on the right side — pick one complete nucleotide unit there too.

Since we can’t draw circles here, I’ll describe where to circle:

→ On the LEFT strand: Circle the topmost nucleotide — it has a phosphate at the top, connected to a sugar, connected to a base (say, Adenine).

→ On the RIGHT strand: Circle the bottommost nucleotide — it has a phosphate at the bottom, connected to a sugar, connected to a base (say, Thymine).

Each circled group should include all three parts: phosphate + sugar + base.

✔ Final Answers:

1.
a. phosphate, deoxyribose sugar, nitrogen base
b. deoxyribose
c. nitrogen base
d. Adenine, Thymine, Guanine, Cytosine

2.
a. [Circle one full nucleotide on left strand and one on right strand — each including phosphate, sugar, and base]

Final Answer:
1a. phosphate, deoxyribose sugar, nitrogen base
1b. deoxyribose
1c. nitrogen base
1d. Adenine, Thymine, Guanine, Cytosine
2a. Circle one complete nucleotide (phosphate + sugar + base) on each side of the ladder model — for example, top left and bottom right units.