Educational worksheet on DNA and genetic transformation featuring diagrams and questions.

Let’s go through each question one by one and fill in the blanks with the correct answers.

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1. A nucleotide is made of three parts: a ______________ group, a five carbon ______________, and a nitrogen containing ______________.

A nucleotide = phosphate group + sugar (5-carbon) + nitrogenous base
→ So: phosphate, sugar, base

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2. The sides of the DNA ladder consist of alternating ______________ and phosphates.

DNA backbone = sugar-phosphate-sugar-phosphate...
→ So: sugars

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3. The 5’ end of a single DNA strand contains a free ______________, while the 3’ end contains a free ______________.

In DNA strands:
- 5’ end has a free phosphate group
- 3’ end has a free hydroxyl group (-OH) — but often just called “hydroxyl” or “OH group”

But in many basic biology classes, they say:
→ 5’ end: phosphate
→ 3’ end: sugar (because the OH is attached to the sugar)

Actually, more precisely:
The 5’ carbon of the sugar has a phosphate attached (free if at end), and the 3’ carbon has an OH group (free if at end).

So standard answer:
→ 5’ end: phosphate group
→ 3’ end: hydroxyl group

But sometimes simplified to:
→ 5’: phosphate
→ 3’: sugar

Wait — let’s check common textbook phrasing.

Most textbooks say:
“The 5’ end has a free phosphate group; the 3’ end has a free hydroxyl group.”

But since this is likely for high school level, and the blank says “a free ________”, we can use:

→ 5’ end: phosphate
→ 3’ end: hydroxyl

However, some curricula simplify it as:

→ 5’ end: phosphate group
→ 3’ end: sugar group — but that’s not accurate.

Actually, looking at common worksheet answers:

Many sources say:
“5’ end has a free phosphate; 3’ end has a free sugar” — which is misleading.

Better to be precise:

Correct scientific answer:
→ 5’ end: phosphate group
→ 3’ end: hydroxyl group

But since the question says “a free ________”, and in context of DNA structure, it’s acceptable to say:

→ 5’: phosphate
→ 3’: hydroxyl

I’ll go with that.

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4. Chromosomes consist of DNA wrapped around ______________.

DNA wraps around proteins called histones to form chromatin → chromosomes.

→ Answer: histones

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5. DNA was not thought to be the genetic blueprint originally; instead many scientists believed ______________ contained the genetic code and blueprint of life.

Before Avery-MacLeod-McCarty and Hershey-Chase experiments, many thought proteins were the genetic material because they are more complex.

→ Answer: proteins

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6. Purines have ______________ rings, and pyrimidines have ______________ ring.

Purines (adenine, guanine) = double-ring structures
Pyrimidines (cytosine, thymine, uracil) = single-ring structures

→ So: two, one

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7. Check each of the following statements that are true with regard to Griffith’s experiment:

Griffith’s experiment (1928) with Streptococcus pneumoniae:

- He used two strains: Smooth (S, virulent, encapsulated) and Rough (R, non-virulent, no capsule)
- Injecting live S → mouse dies
- Injecting live R → mouse lives
- Injecting heat-killed S → mouse lives
- Injecting heat-killed S + live R → mouse dies, and he found live S bacteria in the dead mouse → transformation occurred

Now evaluate:

a. Griffith discovered transformation in bacteria. → TRUE. He observed that something from dead S bacteria transformed live R into S.

b. Mice injected with smooth bacteria quickly became sick and died. → TRUE. Smooth strain is virulent.

c. Encapsulated bacteria can become "naked" bacteria. → This is tricky. In Griffith’s experiment, the reverse happened: naked (rough) bacteria became encapsulated (smooth) after taking up DNA from dead smooth bacteria. There’s no evidence in his experiment that encapsulated bacteria lost their capsule naturally. So this statement is NOT supported by Griffith’s work.

Actually, “encapsulated bacteria can become ‘naked’” — meaning lose capsule? That might happen under certain conditions, but Griffith didn’t observe or report that. His key finding was transformation FROM rough TO smooth.

So c is FALSE in the context of Griffith’s experiment.

Thus, only a and b are true.

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Final Answers:

1. phosphate, sugar, base
2. sugars
3. phosphate group, hydroxyl group
4. histones
5. proteins
6. two, one
7. a. ✓, b. ✓, c. ✗

But since the question says “Check each... that are true”, we should mark only the true ones.

For part 7, we need to indicate which are true. Since it’s a checklist, we can write:

a. True
b. True
c. False

Or if they want boxes checked, but since it’s text, we’ll state which are true.

Looking back at the format: “Check each...” — so probably expect to list which letters are correct.

Common way: “a and b”

But to match the blank style, perhaps write:

a. yes
b. yes
c. no

But the original has blanks like “_______ Griffith discovered...”

So likely, they want you to put a checkmark or write “true” etc.

Since it’s fill-in, I think for 7, we should specify which statements are true.

But the instruction says “solve the problem accurately”, so for 7, we need to identify which are true.

Perhaps best to write:

7. a. true, b. true, c. false

But let’s see the exact wording: “Check each of the following statements that are true”

So in answer, we can say: Statements a and b are true.

But to fit the format, maybe:

For 7: a. ✓, b. ✓, c. (leave blank or mark X)

Since it’s text-based, I’ll write:

7. a. true, b. true, c. false

Now compiling all:

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Final Answer:
1. phosphate, sugar, base
2. sugars
3. phosphate group, hydroxyl group
4. histones
5. proteins
6. two, one
7. a. true, b. true, c. false