Nucleic acids

1. What is the universal genetic material in all living organisms?

DNA.

2. What is the exception to DNA as genetic material?

Viruses — some use RNA.

3. Why aren’t viruses considered living?

They require a host cell to replicate.

4. What are the three parts of a nucleotide?

Pentose sugar + nitrogenous base + phosphate group.

5. What sugar does DNA contain?

Deoxyribose.

6. What sugar does RNA contain?

Ribose.

7. What bonds link nucleotides together?

Covalent bonds between sugar and phosphate.

8. What extends outward from the backbone?

Nitrogenous bases.

9. Why is the backbone strong?

Covalent bonds share electrons → high stability.

10. Which bases are found in DNA?

A, T, G, C.

11. Which bases are found in RNA?

A, U, G, C.

12. Which bases are purines?

Adenine, Guanine (double‑ring).

13. Which bases are pyrimidines?

Thymine, Cytosine, Uracil (single‑ring).

14. Is RNA single‑stranded or double‑stranded?

Single‑stranded.

15. What reaction links RNA nucleotides?

Condensation (releases water).

16. What does antiparallel mean?

One strand runs 5’→3’, the other 3’→5’.

17. What bonds hold the sugar‑phosphate backbone together?

Covalent bonds.

18. What bonds hold the two DNA strands together?

Hydrogen bonds between bases.

19. How many hydrogen bonds are in A–T pairs?

2

20. How many hydrogen bonds are in G–C pairs?

3

21. Why does a purine always pair with a pyrimidine?

Maintains uniform helix width → structural stability.

22. Which base pair is more stable?

G–C (3 H‑bonds).

23. What is the formula for possible DNA sequences?

4ⁿ (n = number of nucleotides).

This formula represents the total combinations of sequences that can be formed from four nucleotides in DNA.

24. Why does this matter?

Allows massive genetic diversity.

25. What does universal DNA usage suggest?

All life shares a common ancestor.

26. What is the 5’ end of a nucleic acid?

Phosphate group.

27. What is the 3’ end?

Hydroxyl group on sugar.

28. In what direction do replication, transcription, and translation occur?

5’ → 3’.

29. Why must DNA be packaged?

It’s too long to fit freely in the nucleus.

30. What proteins does DNA wrap around?

Histones.

31. How many histones form the nucleosome core?

8 (octamer).

32. What does H1 histone do?

Clamps linker DNA → stabilizes structure.

33. What is the “beads on a string” model?

Nucleosomes connected by linker DNA.

34. What question did Hershey–Chase investigate?

Is DNA or protein the genetic material?

35. What radioactive label was used for DNA?

Phosphorus.

36. What radioactive label was used for protein?

Sulfur

37. Where was radioactive phosphorus found after infection?

Inside bacterial pellet → DNA enters cells.

38. What was the conclusion?

DNA is the genetic material.

39. What did Chargaff discover?

A = T and G = C.

40. Why was this important?

Supported base‑pairing and disproved equal base hypothesis.