DNA structure and Griffith's experiment on bacterial transformation.

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

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Question 1:
“A nucleotide is made of three parts: a ________ group, a five carbon ________, and a nitrogen containing ________.”

→ A nucleotide has:
- A phosphate group
- A five-carbon sugar (deoxyribose in DNA, ribose in RNA)
- A nitrogen-containing base (like adenine, thymine, etc.)

✔ Answer: phosphate, sugar, base

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Question 2:
“The sides of the DNA ladder consist of alternating ________ and phosphates.”

→ The backbone of DNA is made of alternating sugars and phosphates.

✔ Answer: sugars

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Question 3:
“The 5’ end of a single DNA strand contains a free ________, while the 3’ end contains a free ________.”

→ In DNA strands:
- The 5’ end has a free phosphate group attached to the 5th carbon of the sugar.
- The 3’ end has a free hydroxyl (-OH) group on the 3rd carbon of the sugar.

✔ Answer: phosphate, hydroxyl group (or OH group)

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Question 4:
“Chromosomes consist of DNA wrapped around ________.”

→ DNA wraps around proteins called histones to form chromatin, which condenses into chromosomes.

✔ Answer: histones

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Question 5:
“DNA was not thought to be the genetic blueprint originally; instead many scientists believed ________ contained the genetic code and blueprint of life.”

→ Before DNA was proven to be genetic material, scientists thought proteins were responsible because they are more complex.

✔ Answer: proteins

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Question 6:
“Purines have ________ rings, and pyrimidines have ________ ring.”

→ Purines (adenine and guanine) have two rings.
Pyrimidines (cytosine, thymine, uracil) have one ring.

✔ Answer: two, one

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Question 7:
Check true statements about Griffith’s experiment:

a. Griffith discovered transformation in bacteria. → ✔ TRUE — He showed that harmless bacteria could become harmful when mixed with heat-killed harmful bacteria.

b. Mice injected with smooth bacteria quickly became sick and died. → ✔ TRUE — Smooth bacteria have capsules and cause disease.

c. Encapsulated bacteria can become “naked” bacteria. → ✘ FALSE — In his experiment, it was the *non-encapsulated* (rough) bacteria that took up genetic material from dead encapsulated ones and became encapsulated — not the other way around. Also, “naked” usually means without capsule, but the process doesn’t involve losing the capsule — it involves gaining it.

So only a and b are true.

✔ Answers: a ✔️, b ✔️, c ✖️

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Final Answer:

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