NAME ____________________________________________
DNA REPLICATION WORKSHEETS
1. What is the name given to the enzyme that unwinds the two strands of DNA when replication starts
on a DNA molecule? ______________________________________________________________
2. What does Chargaff’s Rule state? _____________________________________________________
3. Who were the two men responsible for making the first model of DNA out of tin & wire?
_________________________________________________________________________________
5-6. Write the name of the appropriate Nitrogen base beside each letter:
A: _______________________
T: _______________________
G: ___________________________
C: ___________________________
7. Which two nitrogen bases are classified as Purines? _____________________________________
8. Which two nitrogen bases are classified as Pyrimidines? _________________________________
9. What 3 things make up a nucleotide in DNA?
a. __________________________________________________________________________
b. __________________________________________________________________________
c. __________________________________________________________________________
10. What 3 things make up a nucleotide in RNA?
a. __________________________________________________________________________
b. __________________________________________________________________________
c. __________________________________________________________________________
11. What is the process of making new strands of DNA called? ________________________________
12. Using your answer to #10, where in the cell is this taking place? ____________________________
13. Name the 2 molecules which alternate to form the upright or side portion of a DNA molecule.
___________________________________________________________
14. If 4 guanine bases appear in a DNA model, how many cytosine bases should there be?
_______________________________________________________________________
15. Your DNA model has 4 guanine bases. Does the number of cytosine bases in your model agree with
your prediction from questions #13? __________________________________
16.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 DNA molecule.
Thymine
Adenine
_____________________
_____________________
17.
Guanine
_____________________
Guanine
_____________________
Cytosine
_____________________
Thymine
_____________________
Cytosine
_____________________
Adenine
_____________________
How many molecules of adenine are in each DNA molecule? __________________________
18.
How many molecules of thymine? _______________________________________________
19.
Do the numbers agree? ________________________________________________________
20.
Explain how the pairing of the nitrogen bases in a DNA molecule allows the DNA to replicate
itself. _______________________________________________________________________
____________________________________________________________________________
RNA is similar to DNA in that its molecules also form nucleotides. However, deoxyribose and
thymine are not found in RNA. Ribose replaces deoxyribose and uracil replaces thymine.
Phosphoric acid, guanine, adenine, and cytosine are present in RNA.
21.
Knowing the shapes of purine & pyrimidine groups, what group would uracil belong in?
_____________________________________________________________________________
22.
Is the sequence or order of bases in RNA different from the unused left side of the original DNA
molecule above? (Do not consider uracil replacing thymine as a change in sequence)
____________________________________________________________________________
23.
Do the RNA half rung bases pair exactly as they would if this were DNA replication? (Once
again, do not consider uracil replacing thymine as a change.) ___________________________
Scientists believe that RNA is only a single stranded molecule. Thus, the series of RNA
nucleotides formed from DNA represents an RNA molecule. After its formation, RNA leaves
the nucleus of the cell and goes to the ribosomes. It carries the DNA message of base sequences
(in complementary form) to the cell’s ribosomes.
Complete Table 1 by using check marks to indicate to which molecule each item applies.
TABLE 1 – Similarities and Differences Between DNA & RNA
DNA
RNA
Ribose present
Deoxyribose present
Phosphoric acid present
Adenine present
Thymine present
Uracil present
Guanine present
Cytosine present
Double stranded
Single strand
Remains in nucleus
Moves out of nucleus
tRNA & Protein Building
RNA produced in the nucleus of a cell moves out of the nucleus toward the cell’s ribosomes. It
carries with it a specific sequence of bases copied from the DNA. RNA carries the genetic
message of the chromosomes into the cell. Thus, it is called messenger RNA, or simply mRNA.
At the ribosomes, mRNA directs the building of proteins. How can mRNA secure the proper
amino acids to construct protein molecules? How does mRNA decode the base sequence of the
DNA?
The answer to the first question involves another molecule. The molecule is transfer RNA or
tRNA. This molecule brings amino acids to the mRNA
1.
To join tRNA molecules to the mRNA pattern, which sequence of tRNA molecules will match
base pairs of the U, U, A sequence in mRNA? _______________________________________
Which tRNA sequence of bases can join the U, C, A sequence of bases in mRNA? __________
2.
How does the sequence of bases on mRNA control the type of mRNA joining with it?
_____________________________________________________________________________
_____________________________________________________________________________
3.
A base sequence of A, A, A in mRNA could only join with what sequence of bases in tRNA?
_____________________________________________________________________________
4.
What specific amino acid is brought to the mRNA by a tRNA molecule with a terminal sequence
of A, A, U? (Look at the genetic code for the answer) ___________________________________
5.
What amino acid is brought to the mRNA by a tRNA terminal sequence of A, G, U? (Look at the
genetic code for the answer) ________________________________________________________
6. How many base of mRNA are responsible for the coding of one amino acid? ___________
When many amino acid molecules are brought to the mRNA by tRNA, the amino acids join
together to form a protein molecule. Thus, joining tRNA molecules with their attached amino
acids to the bases of the mRNA simulates the beginning of a protein molecule.
Depending on the type and order of amino acids, an almost endless variety of proteins can be
produced. Because of the repeated matching of base sequence, the sequence of bases in the
DNA of chromosomes codes and controls the formation of protein molecules at ribosomes.
7. A protein molecule consists of the following amino acid sequence: leucine, glutamine, tyrosine,
leucine, serine, serine. What would be the sequence of tRNA molecules responsible for forming this
protein? (Use Table 2 below) __________________________________________________
______________________________________________________________________________
8. A ribosome receives the following mRNA message: AAA, CGA, GAA, GUU. What will be the
sequence of tRNA bases joining the mRNA molecule? (Use Table 2 below)
______________________________________________________________________________
9. What will be the sequence of amino acids formed from this code? (Use Table 2 below)_______
________________________________________________________________________
TABLE 2 – TRNA TRIPLET CODES OF SOME AMINO ACIDS
AMINO ACIDS
tRNA Code
Serine
AGU
Proline
GGG
Leucine
AAU
Glutamin Acid
CUU
Tyrosine
AUA
Arginine
GCU
Glutamine
GUU
Phenylalanine
AAA
Valine
CAA
Lysine
UUU
A portion of DNA on a chromosome has the sequence of bases along one strand of DNA as indicated in
Table 3.
Complete the 2nd column with the sequence of bases of an mRNA molecule formed from the DNA strand.
Complete the 3rd column with the sequence of bases of the tRNA molecules that would join the mRNA
strand.
Complete the 4th column with the sequence of amino acids that results from the mRNA strand.
TABLE 3 – BASE SEQUENCE CHANGES DURING AMINO ACID FORMATION
Chromosome (DNA)
mRNA
tRNA
Amino Acid
A
A
T
G
G
G
A
T
A
A
A
A
G
T
T
Mutations and Base Sequence
Rarely does the DNA code of instructions make an error in directing cells to form a protein.
When it does, however, the error is called a mutation and will result in formation of a different
type of protein.
Hemoglobin is a protein in red blood cells. Hemoglobin results from the proper arrangement of
almost 600 amino acids. Most humans have the correct type of hemoglobin. However, in some
people the arrangement is incorrect. These people have a disease called sickle-cell anemia.
Their red blood cells are sickle-shaped rather than round. As a result, the red blood cells cannot
transport oxygen efficiently.
The following amino acid sequence represents a portion of the normal hemoglobin molecule:
proline, glutamic acid, glatamic acid, lysine. In sicle-cell anemia, the first glutamic acid is
replaced by the amino acid valine.
9.
List the sequence of amino acids that represent the same area of a sickle-shaped hemoglobin
molecule.
10.
Using the list of tRNA bases in Table 2, what is the sequence of bases of the segment of normal
hemoglobin? ______________________________________________________
sickled hemoglobin? ______________________________________________________
11.
What is the sequence of mRNA bases that determine the amino acid sequence of the segment of
normal hemoglobin? _____________________________________________
sickled hemoglobin? ______________________________________________________
12.
What is the sequence of bases in this segment of DNA of a person who has
normal hemoglobin? ______________________________________________________
sickled hemoglobin? ______________________________________________________
13.
Why do persons having a mutation pass this condition on to their offspring? __________
_______________________________________________________________________