DNA Structure and Replication
Answer each question using your notes and textbook. (sections 12.1 and 12.2)
1. What do genes do?
code for the making of proteins
2. What are the monomers that make up DNA?
nucleotides
3. What three parts is a nucleotide made up of?
phosphate group, nitrogen base, deoxyribose sugar
4. What are the four types of nitrogen bases?
adenine, thymine, cytosine, guanine
5. Draw a rough sketch of a DNA molecule. Use your diagram as a guide. Label the deoxyriboses, the phosphates and the nitrogen bases.
6. What did Erwin Chargaff discover about DNA?
A=T and G=C
7. What did Watson and Crick discover about DNA? How was Rosalind Franklin involved?
Made detailed model with placement of all atoms; Franklin determined that the overall shape of the molecule was a double helix
8. What types of cells have DNA? Where in a cell is DNA found?
All cells have DNA; nucleus
9. Only two combinations of base pairings are possible. Which bases pair with which other bases?
A-T and G-C
10. Differentiate between purines and pyrimidines.
purines – 2 rings; pyrimidines – 1 ring
11. How are the bases attached to each other?
hydrogen bonds
12. Why won’t thymine bond to cytosine?
thymine forms 2 bonds and cytosine forms 3 bonds
13. If a DNA molecule is found to be made up of 18% of adenine, what are the percentages of the three other bases ?
thymine = 18%; guanine = 32%; cytosine =32%
14. The following are the bases on the left side of a DNA molecule. List the bases that would make up the right side of the molecule.
5’ T –A
A –T
G –C
G –C
C –G
T –A
C –G
3’ A –T
15. What is the process of copying DNA called?
replication
16. Where in the cell does it occur?
nucleus
17. Why does it have to occur?
in order to make new cells
18. Describe in a few sentences how DNA is copied.
Hydrogen bonds between bases break and DNA molecule is separated. Free nucleotides floating in nucleus start attaching
to original strands forming new strands. New strands always
form from 5’ to 3’. There is a leading and a lagging strand.
19. After this copying process, like you did in the hands on activity, what do you end up with?
2 identical molecules of DNA
20. Complete the strands of DNA.
Original Strand -- New Strand New Strand --- Original Strand
5’ A T A T 3’
C G C G
C G C G
T A T A
A T A T
G C G C
3’ A T A T 5’
21. Describe the role of DNA helicase, DNA polymerase and DNA ligase in DNA replication.
All enzymes
DNA helicase – breaks H bonds joining N bases
DNA polymerase – adds nucleotides to original strands
DNA ligase – attaches pieces of new DNA strand called
Okazaki fragments
22. Describe how the leading and the lagging strands are made differently.
Leading strand- made in one continuous strand from the point
of origin to the replication fork
Lagging strand – made in fragments from the fork to the point of
origin. Must be joined together by enzyme ligase,