DNA and Protein Synthesis Review

1. What are nucleotides? Describe their structure.

2. Describe the work of Avery, et al. and explain how it implicated nucleic acids as the genetic material. (mouse and pneumococcus - the transforming material was heat stable)

3. Summarize the Hershey and Chase experiment and explain what their results suggested. (radioactive labels; showed that nucleic acid was used to infect)

4. Chargaff made an important contribution to uncovering the structure of DNA. What were his findings and what do they indicate? (complementary base pairing)

5. Who proposed the “double helix” model for the DNA molecule. (Watson and Crick)

6. Describe how DNA and RNA differ in their composition, structure, function, and location.

7. What is meant when we say that DNA replication is complementary? (A-T; C-G)

8. Why is DNA replication important for every cell? (each daughter needs full genome)

9. Compare the amount of DNA in a muscle cell with that in a brain cell. (same)

10. Whose work demonstrated that DNA replication is semi-conservative? (Meselson and Stahl)

11. What is meant by saying that DNA replication is semi-conservative? (each daughtermolecule has one parent strand and one daughter strand)

12. Briefly describe the steps in DNA replication.

13. Why is replication on one strand of DNA continuous, while on the other strand the replication must be discontinuous? (DNA polymerase works 5'-3' only and strands areantiparallel)

14. What functional group is at the 5' end of a DNA molecule? (phosphate)

15. Proofreading enzymes scan DNA to check for base pairing errors. Explain why these enzymes are important. (to minimize mutations)

16. A certain chemical is known to fuse thymine with adenine. Comment on the possible effects of exposure to this chemical. (same strands - dimer difficult to read; different strands - couldntseparate)

17. Why is the making of exact copies of DNA called replication rather than duplication? (because semi-conservative not original and duplicate)

18. If human DNA contains approximately 3x10⁹ base pairs, and DNA polymerase can work at the rate of about 50 nucleotides per second, how can our DNA be replicated so quickly? (manyorigins and proceeds both strands both directions)

19. If 27 percent of the bases in a certain segment of DNA were adenine, what would be the percentages of thymine (27%), cytosine (23%), and guanine (23%).

20. A segment of chromosomal DNA which contains instructions for one protein is a . (gene)

21. Describe the technique of DNA fingerprinting.

22. As a research biologist, you know of a bacterium that produces an antibiotic that is quite effective against a certain crop plant fungus. There would be great economic importance in enabling the plant to resist the fungus. How might you use DNA technology to accomplish this?

(insert antibiotic gene into plant)23. Name the two major steps in protein synthesis. Briefly, what is accomplished by each?

24. Where in the cell does each one occur? (transcription - copy gene - in nucleus; translation -decode mRNA instructions - make protein in cytosol)

25. Compare and contrast DNA replication and transcription. (replication - entire genome copied- makes DNA; transcription - one gene copied - makes mRNA)

26. How much of a molecule of DNA is untwisted during replication? During transcription? (short section at a time; one gene)

27. Name three types of RNA we described and explain the function of each. (mRNA - copy ofgene, tRNA - makes tRNA, rRNA - part of ribosome)

28. How many different DNA triplets are possible? (4³ = 64)

29.The DNA triplet “CGA” is transcribed into which RNA codon?

a) GUT (b) GUC *(c) GCU (d) AUG

30. Which enzyme “reads” the mRNA? (ribosome)

31. Explain the role played by each of the following in protein synthesis.

a) template strand of DNA (b) RNA codon (c) enzymes (d) rRNA (e) tRNA

32. During the process of translation what language change occurs? How is it possible to put together a polypeptide with the correct sequence of amino acids. (nucleic acid to amino acid;mRNA read one codon at a time)

33. What is the first codon in the mRNA of any polypeptide? (AUG)

34. How does a codon differ from a DNA triplet. How does an anticodon differ from a DNA triplet. (complementary, no T; same, no T)

35. Name the two important regions of a tRNA molecule. (anticodon, amino acid attachmentsite)

36. For the DNA triplet CGT, write the complementary mRNA codon and the tRNA anticodon. 39. What amino acid does the triplet GCA represent? (GCA, CGU, ala)

37. Explain the functions of start and stop codons. (signal begin and end of translation)

38. What would be the effect on translation if the termination codon were changed by mutation? (polypeptide too long)

39. If the start codon were mutated? (polypeptide not made at all)

40. What effect does the nucleotide sequence of DNA have on the cell? (determines whichproteins are made)

41. Suppose that during protein synthesis, a cell is starved of uracil and another base is supplied in its place. How will the proteins produced be affected by this substitution? (any codon with Uwould not be translated; possibly T used instead; effect probably catastrophic)

42. A molecular biologist discovers a drug that blocks the site of attachment of the ribosome to mRNA. How will the drug affect the functioning of the cell? (stop protein synthesis)

43.What kinds of factors act as mutagens? What effects could they have? Where or when might one be exposed to them? (VCR)