Nucleotide structure and DNA sequence labeling worksheet.

Let's go through each question and provide a clear explanation and solution.

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Question 10: Draw the basic structure of a nucleotide with its three parts.

Solution:
A nucleotide consists of three components:
1. Phosphate group – attached to the 5' carbon of the sugar.
2. Pentose sugar – in DNA, this is deoxyribose; in RNA, it’s ribose.
3. Nitrogenous base – either a purine (adenine or guanine) or pyrimidine (thymine, cytosine, or uracil in RNA).

The image you provided already shows a correct diagram of a nucleotide with these labeled parts:
- Phosphate (left side)
- Ribose (pentagon-shaped sugar)
- Nitrogenous base (attached to the ribose)

✔ Note: The label says "ribose base" — this might be a typo. It should be just ribose, as the sugar is ribose (in RNA), not a "base." But since this is likely meant for RNA, the structure is correct.

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Question 11: Write the complementary sequence to the following DNA strand:

Given DNA strand:
```
A A T T C G C C G G T A T T A G A C G T T
```

We need to write the complementary strand using base pairing rules:

- A (Adenine) pairs with T (Thymine)
- T (Thymine) pairs with A (Adenine)
- C (Cytosine) pairs with G (Guanine)
- G (Guanine) pairs with C (Cytosine)

Now let's pair each base:

Original:
`A A T T C G C C G G T A T T A G A C G T T`
Complement:
`T T A A G C G G C C A T A A T C T G C A A`

So, the complementary sequence is:

👉 T T A A G C G G C C A T A A T C T G C A A

> ✔ Note: The answer below the line appears to have lowercase letters and may be incorrect. The correct complement should be written in uppercase and properly paired.

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Question 12: Use the image at the right to complete the following:

#### Instructions:
1. Circle a nucleotide.
2. Label the sugar and phosphate.
3. Label the bases that are not already labeled.

From the image:
- You've already circled a nucleotide (correctly).
- You've labeled one phosphate and ribose (though “ribose” is a bit misleading here — in DNA, it's deoxyribose).

Let’s fix and clarify:

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#### Step-by-step corrections and additions:

1. Nucleotide: A single unit consisting of:
- One phosphate group (black circle),
- One deoxyribose sugar (pentagon),
- One nitrogenous base (rectangle: A, T, G, C).

✔ Your blue circle includes all three — good!

2. Label the sugar and phosphate:
- The sugar is the pentagon shape → label it deoxyribose (since this is DNA).
- The phosphate is the black circle attached to the sugar → already labeled as "phospahte" (typo: should be phosphate).

✔️ Fix the spelling: phosphate.

3. Label the bases not already labeled:
- Already labeled: A, T, G, C
- Look at the bases on the opposite strands:
- Top strand has: A, T, G, ...
- Bottom strand has: T, A, C, ...

Let's identify missing labels:

From top to bottom:
- First base pair: A-T → both labeled
- Second: T-A → both labeled
- Third: G-C → G is labeled, but C is not clearly labeled on the bottom strand.

So, we need to label:
- The C (cytosine) on the bottom strand where it pairs with G.

Also, check if other bases are unlabeled:
- Next base: T-A → both labeled
- Then: A-T → both labeled
- Then: C-G → C is on top, G on bottom → C needs labeling?

Wait — looking at the image:

The top strand from left to right:
- A (top), T (bottom)
- T (top), A (bottom)
- G (top), C (bottom) ← C is not labeled
- Then: G (top), C (bottom) ← C not labeled
- T (top), A (bottom)
- A (top), T (bottom)
- G (top), C (bottom) ← C not labeled
- A (top), T (bottom)
- C (top), G (bottom) ← G not labeled?
- G (top), C (bottom)
- T (top), A (bottom)
- T (top), A (bottom)

So, many bases are unlabeled.

Let’s assume the goal is to label any unmarked bases.

For example:
- The C in the third base pair (under G) → label it C
- The C under next G → label C
- The G under C → label G
- etc.

But since the image is blurry, I’ll guide you:

✔ Action Steps:
- Label each unlabeled nitrogenous base with the correct letter:
- If it pairs with A, label it T
- If it pairs with T, label it A
- If it pairs with G, label it C
- If it pairs with C, label it G

So:
- Where there’s an A on one strand, the opposite base must be T
- Where there’s a T, the opposite is A
- Where there’s a G, opposite is C
- Where there’s a C, opposite is G

Therefore, label the missing ones accordingly.

Example:
- In the third row: G (top) → bottom base is C → label it C
- Fourth row: G (top) → bottom base is C → label C
- Fifth row: T (top) → bottom is A → label A
- Sixth row: A (top) → bottom is T → label T
- Seventh row: G (top) → bottom is C → label C
- Eighth row: A (top) → bottom is T → label T
- Ninth row: C (top) → bottom is G → label G
- Tenth row: G (top) → bottom is C → label C
- Eleventh row: T (top) → bottom is A → label A
- Twelfth row: T (top) → bottom is A → label A

So, add:
- C, C, A, T, C, T, G, C, A, A

And make sure all bases are labeled.

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✔ Summary of Corrections and Answers:

#### Q10: Correct — nucleotide shown with:
- Phosphate
- Sugar (ribose/deoxyribose)
- Nitrogenous base

(If this is DNA, use deoxyribose, not ribose.)

#### Q11: Complementary DNA strand:
```
Original: A A T T C G C C G G T A T T A G A C G T T
Complement: T T A A G C G G C C A T A A T C T G C A A
```

✔ Answer: T T A A G C G G C C A T A A T C T G C A A

#### Q12:
- ✔ Circle a nucleotide: Done (correct).
- ✔ Label sugar: Change “ribose” to deoxyribose (since it's DNA).
- ✔ Label phosphate: Corrected spelling to phosphate.
- ✔ Label missing bases: Add labels like C, G, A, T where needed based on base pairing.

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Final Notes:

- This is a DNA double helix model.
- The sugar is deoxyribose, not ribose.
- Base pairing: A-T, G-C.
- Always ensure spelling and accuracy in labels.

Let me know if you'd like a cleaned-up version of the image or help drawing it!