DNA Structure, DNA Replication, Protein Synthesis Review
1. What are some difference between RNA and DNA?
RNA
DNA
Single strand
Double strand
Ribose sugar
Deoxyribose sugar
2. Describe some structural features of DNA.
a. Double helix
b. Complimentary base pairing
c. Anti-parallel
3. What are the 5 different bases?
a. Adenine
b. Thymine
c. Guanine
d. Cytosine
e. Uracil
4. Purine=2rings and Pyrimidine=1 ring
5. A to T = 2 bonds
6. What is a nucleotide made of?
a. Deoxyribose sugar (5 carbon sugar)
b. Nitrogeneous base
c. Phosphate
7. Draw and # the carbons of a deoxyribose sugar.
8. What is a phosphodiester bond?
a. A phosphodiester bond is a group of strong covalent bonds between a phosphate group
and two 5-carbon ring carbohydrates (pentoses) over two ester bonds.
9. How do the bases bond? How many bonds are between each?
a. Through H-bonding; 2 between A&T and 3 between G & C
10. Draw out the basic structure of DNA nucleotides linked together. Indicate the bonds present.
11. How does the DNA double helix form based on complimentary base pairing?
a. A-T; G-C
12. What is meant by 5’? 3’?
a. The end of DNA where the 5’ carbon is exposed
b. The end of DNA where the 3’ carbon is exposed
13. What does RNA primase do?
RNA primase lays the RNA primer that allows DNA polymerase to add nucleotides. One on
leading and several on lagging.
14. What does gyrase do?
a. Relieves tension in DNA double helix
15. What unwinds DNA?
a. Helicase
16. What are nucleotides?
a. A ribose/deoxyribose sugar, phosphate and a nitrogenous base
17. What is the purpose of an RNA primer?
a. Is laid as a starting point for DNA polymerase to add nucleotides
18. Describe who discovered and how the structure of DNA was discovered.
a. Rosalind franklin- xray crystallography
b. Watson and Crick awarded with structure.
19. Draw, and annotate the structure of nucleosomes.
20. What is the purpose of a nucleosome?
a. To keep DNA organized
b. Prevent transcription
21. Do prokaryotes have nucleosomes
a. No
22. Describe the relationship between nucleosomes and transcription?
a. When in a nucleosome, DNA transcription is inhibited
23. What is the difference between unique or single copy genes and highly repetitive sequences?
a. Single copy=coding
b. Repetitive=non-coding; protective;contain gene switches; repetitive centromere
sequence
24. What are exons? Introns?
a. Exons coding
b. Introns non-coding
25. What is the difference between prokaryote and eukaryote genetic info in terms of exons and
introns?
a. Prokaryotes lack introns
26. What is meant by junk DNA?
a. Dark matter or non-coding portion of DNA. Makes up most of DNA
27. What direction does replication occur in?
a. 5’-3’
28. Where does replication occur?
a. In the nucleus
29. Make a chart outlining the function of each of the enzymes that take part in DNA replication.
Enzyme/Protein
Function
Helicase
•
Cleaves and unwinds short section of DNA ahead
of the replication fork
Single stranded binding
proteins SSBs
•
Keep DNA from re-annealing
DNA polymerase III
•
•
•
Attaches nucleotide to 3’ end of parent strand
Synthesis 5’ to 3’
Proofreads base pairing
DNA polymerase I
•
Removes RNA primers, proofread
DNA ligase
•
Catalyzes formation of phosphate bridges to join
Okazaki fragments
Primase
•
Synthesizes RNA primer to begin elongation
Telomerase
•
Replenishes telomeres
30. Explain the steps involved in DNA replication.
a. The enzyme gyrase relieves tension
b. Helicase breaks h-bonds
c. SSBP’s prevent re-annealing
d. RNA primase lays primer
e. DNA polym III lays new nucleotides 5’-3’. Continuously on leading strand and
discontinuously on lagging strand resulting in okazaki fragments.
f. DNA polym I excises primer and lays missing nucleotides.
g. Ligase joins the gaps from the okazaki fragments by creating a phosphodiester bond
h. DNA polym I and III proofread
31. What is a deoxyribonucleoside triphosphate?
a. ATP, GTP, CTP, TTP- free floating nucleosides are used for synthesizing new strand of
DNA once excess phosphates are removed
32. What is the difference between ribonucleoside triphosphates and deoxyribonucleoside
triphosphate?
a. One used to make RNA, deoxy- to make DNA
33. Where do nucleotides come from?
a. Free floating nucleosides triphospahtes modified
34. What are okazaki fragments?
a. Short segments on lagging strand
35. What is a replication fork?
a. The point at which helicase opens DNA and site of replication
36. What is a replication bubble?
a. Openings within DNA strands where replication occurs. There can be many along DNA
simultaneously.
37. What is the significance of multiple replication bubbles?
a. speed
38. Explain the significance of base pairing in conservation of the base sequence of DNA.
a. Simple and sure way of getting the correct sequence time and again. Using a template
reduces possible errors
39. By what theory is DNA replicated?
a. Semi-conservative
40. What joins okazaki fragments?
a. Ligase
41. What proofreads?
a. Polymerase I and III
42. What is the difference between leading and lagging strands?
a. Leading continuous/ lagging discontinuous
b. No fragments/okazaki fragments
c. No ligase/ligase
d. One primer/many primers laid
e. Fast/slower
f. Both occur 5’ to 3’
43. It is important to have weak h-bonds for the quick and efficient separating of strands. They
easily re-anneal without input of energy. Since helicase only cleaves the H-bonds the other
covalent bonds on the DNA remain intact.
44. What are the ends of chromosomes called?
a. Telomeres
45. What happens to these ends as replication continues? What is this related to?
a. Telomeres shorten. Related to aging.
46. What helps regenerate these ends?
a. telomerase