Instructor’s Copy
Lab Worksheet:
1. Give the molecular formula for
(a) deoxyribose C5H10O4
(b) phosphoric acid H3P1O4
2. Of the four bases, which other base does
(a) adenine most resemble in shape? guanine
(b) thymine most resemble in shape? cytosine
A molecule of deoxyribose joins with phosphoric acid and any one of the four bases to form a
chemical compound called a nucleotide. A nucleotide is named for the base that joins with the
deoxyribose. For example, if thymine attaches to deoxyribose, the molecule is called a thymine
nucleotide.
3. List the four different nucleotides. Adenine nucleotide, thymine nucleotide, guanine
nucleotide and cytosine nucleotide.
4. (a) How is each nucleotide alike? All contain deoxyribose and phosphoric acid.
(b) How does each nucleotide differ? bases.
5. If DNA is “ladderlike,” which two molecules of a nucleotide form the sides, or upright portion of
the ladder? Deoxyribose and phosphoric acid.
6. To which molecule does each base attach? Deoxyribose.
7. Name the molecules of each nucleotide that form part of the ladder’s rungs. bases
8. Is the order of half-rung bases exactly the same from top to bottom of each side of your model?
No
9. Only two combinations of base pairings are possible for the rungs. Name these molecule
combinations or pairs. Adenine + Thymine and Guanine + Cytosine
10. If four guanine bases appear in a DNA model, how any cytosine bases should there be?
4
11. Your DNA model has four guanine bases.
(a) Does the number of cytosine bases in your model agree with your predication? Yes
(b) The following are the bases on the left side of a DNA molecule. List the bases that would
make up the right side of a DNA molecule.
Thymine
Adenine
Guanine
Guanine
Cytosine
Adenine
Thymine
Cytosine
Cytosine
Guanine
12. Do the two new molecules contain the same number of rungs? Yes
13. Is the order from top to bottom of base pairs (rungs) different or the same for each new
DNA molecule? same
14. How many molecules of adenine and thymine are in each DNA molecule? 2
15. Do the numbers agree? Yes
16. Are the two DNA molecules exact copies of each other? Yes
17. (a) Which base is replaced in RNA by uracil? Thymine
(b) What chemical replaces deoxyribose in RNA ? Ribose
18. To which base in DNA do the following RNA bases pair?
(a) guanine
cytosine
(b) adenine
thymine
(c) cytosine
guanine
(d) uracil
adenine
19. Do the RNA half-rung bases pair exactly as they would if this were DNA replication?
Yes, except that uracil replaces thymine
Complete the table by using check marks to indicate to which molecule each characteristic applies.
Similarities and Differences Between DNA and RNA
DNA
RNA
Deoxyribonucleic acid
X
Ribonucleic acid
X
Ribose present
X
Deoxyribose present
X
Phosphoric acid present
X
X
Adenine present
X
X
Thymine present
X
Uracil present
X
Guanine present
X
X
Cytosine present
X
X
Formed from nucleotides
X
X
Double stranded
X
Single stranded
X
Remains in nucleus
X
Moves out of nucleus
X
Contains a chemical message or code
X
X