Model 1 - The Structure of DNA: This educational diagram explains the components of a nucleotide and the double helix structure of DNA, highlighting the ladder and helix models.

Let’s go step by step to answer each question based on Model 1 – The Structure of DNA.

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

Looking at the diagram labeled “Nucleotide” in Model 1, we can see it is made up of:
- A circle labeled Phosphate
- A pentagon (5-sided shape) labeled Deoxyribose sugar
- A rectangle or other shape attached to the sugar, labeled Nitrogen-containing base

So, the three parts are:
→ Phosphate
→ Deoxyribose sugar
→ Nitrogen-containing base

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

In the same nucleotide diagram, the sugar part is clearly labeled as Deoxyribose sugar.

So, the answer is:
→ Deoxyribose

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Question 1c: Which nucleotide component contains nitrogen?

Again, looking at the nucleotide diagram, one part is called “Nitrogen-containing base.” That tells us directly which part has nitrogen.

Also, under “Nitrogen Bases,” they list Adenine, Thymine, Guanine, Cytosine — all of these contain nitrogen.

So, the answer is:
→ The nitrogen-containing base (or just “the base”)

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

Under the section “Nitrogen Bases,” there are four shapes with labels next to them:

- Arrowhead shape → Adenine
- Striped rectangle → Thymine
- Gray rectangle → Guanine
- Half-circle/oval → Cytosine

So, the four bases are:
→ Adenine, Thymine, Guanine, Cytosine

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Question 2a: Circle a single nucleotide on each side of the ladder model of DNA.

The “Ladder Model of DNA” shows two vertical strands (like the sides of a ladder). Each rung is made of two bases connected together. But each *side* of the ladder is made of repeating units — each unit is a nucleotide.

Each nucleotide on the side includes:
- One phosphate (circle)
- One deoxyribose sugar (pentagon)
- One nitrogen base (attached to the sugar, pointing inward toward the center of the ladder)

To circle one nucleotide on each side:
→ On the left strand, pick any one set of: circle + pentagon + base attached to that pentagon.
→ Do the same on the right strand.

Since you’re doing this on paper, you’d draw a circle around one complete nucleotide unit on the left and one on the right. For example:
- Left side: circle the topmost phosphate, its attached sugar, and the base sticking out from that sugar.
- Right side: do the same for any matching unit on the right.

(Note: Since this is text-based, I can’t actually circle anything, but if you’re working on the worksheet, just find one full nucleotide on each side and circle it.)

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Final Answer:

1a. Phosphate, deoxyribose sugar, nitrogen-containing base
1b. Deoxyribose
1c. The nitrogen-containing base
1d. Adenine, Thymine, Guanine, Cytosine
2a. [On your worksheet, circle one complete nucleotide unit — phosphate + sugar + base — on the left side of the ladder, and another on the right side.]