Name____________________________
ALE #6 DNA replication, transcription, translation
DNA Structure
1. a. What is a nucleotide? Why are nucleotides important, that is, what do your cells use them for?
b.
Label the three main components (phosphate, sugar, nitrogen base) of the simplified representation of a nucleotide
below.
c.
Indicate the nitrogen bases found in DNA and RNA by completing the table below.
Nitrogen Bases Found in DNA
Nitrogen Bases found in RNA
DNA Replication
2. a. Why is it DNA replication necessary for all organisms on earth today?
b. When during the cell cycle does DNA replication occur?
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3.
DNA Replication. Use the hypothetical representation of a double stranded DNA molecule, below, to complete the
following tasks.
a. Complete the base sequence of the complementary strand of the hypothetical DNA molecule diagrammed below.
b. Use dashed lines to indicate hydrogen bonding between paired bases.
c. Show how this molecule would be replicated:
o Draw the molecule partially “unzipped” while undergoing replication, followed by the resulting daughter
molecules with their correct nucleotide sequences and base pairing.
o Use two colors, one for the template (or parent) strands, and another for the newly synthesized daughter
strands.
4. a. Name the enzyme responsible for lengthening each strand during DNA replication by repeatedly adding
nucleotides to the end of each strand.
b.
How does this enzyme “know” which nucleotide to use during DNA replication—that is, what “rules” does the
enzyme follow?
c.
Name the enzyme that proofreads and corrects any errors it finds in the DNA strands after the completion of DNA
replication.
d.
What is a mutation? What are the four causes?
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Relating DNA Replication to the Cell Cycle
5. a. As in mitosis, the chromosomes are duplicated prior to the start of meiosis I. How many duplicated chromosomes
will there be in a human “pregamete” cell just before the start of meiosis I?
6.
b.
How many DNA molecules are in a human “pre-gamete” cell just before the start of meiosis I?
c.
Just after meiosis II and cytokinesis (the division of the cytoplasm) how many chromosomes are there in each
gamete?
d.
Just after meiosis II and cytokinesis how many DNA molecules are there in each gamete?
Diploid “pregamete” cells from a hypothetical mammal were examined under a microscope and found to contain 4
chromosomes (2 homologous pairs).
a.
Draw one of these cells in metaphase I of
meiosis. Consider the size and shape of your
chromosomes.
Plasma
Membrane
b.
A drug is given to this animal so that the S phase
(DNA replication) does not occur. Draw one of
these cells in metaphase I of meiosis. Draw your
chromosomes so that the size and shape is
consistent with the cell you drew in part a.
Plasma
Membrane
7. Explain why AZT prevents another nucleotide from being added to a growing DNA strand and then explain how AZT
will affect DNA replication.
8. Most nerve cells do not replicate their DNA upon reaching maturity. Suppose that a cell biologist measured the amount
of DNA in several different types of human cells:
1) Nerve cells
2) Sperm cells
3) Bone cells just starting interphase
4) Skin cells in the S phase
5) Intestinal cells just beginning mitosis
She found x amount of DNA in the nerve cells. Use this fact and the information in the table below to identify
Cells A - D.
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Cell Type
Nerve Cell
Cell A
Cell B
Cell C
Cell D
9.
Amount of DNA in Cell
x
2x
1.6x
0.5x
x
Identity of Cell
Nerve Cell
Fill in the following spaces concerning the “central dogma” of biology. Use the following terms only once:
(phenotype, nucleotides, DNA, amino acids, protein, shape ) A gene is a section of _______________ that contains
the code for the synthesis of one particular ___________________. The order of ____________________________ in
a gene determines the order of nucelotides in mRNA, which determines the order of __________________________
in the protein the gene codes for. This order controls the ______________________ of the protein, which in turn
determines the function of that protein. An organism’s genotype determines the kind of proteins an organism can make.
These proteins determine an organism’s _________________________________.
10. Compare the differences in RNA and DNA by completing the table below.
DNA
RNA
Number of Strands
Name of sugar in
nucleotides
Bases present
Where produced in cell
mRNA:
Where found in cell
tRNA:
rRNA:
Name of process that
makes it
11. Here is a hypothetical gene showing the sequence of DNA nucleotides for the coding strand (i.e. the coding strand is
the strand that is transcribed). IMPORTANT!! This sequence includes the regions that code for start and stop in
translation—that is, locate both the start codon and stop codon in the mRNA before you translate it into protein!!
Coding strand of DNA:
3’ T A G G T A C T G G G G C A T T A A 5’
a.
What would be the sequence of bases in the resulting mRNA if this strand of DNA was transcribed?
mRNA:
b.
What is the amino acid sequence of the protein that this gene codes for? (You will need the table of codons in your
textbook to answer this question.)
The amino acid sequence is:
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12. Outline the basic steps from DNA to the formation of proteins: DNA  RNA  Protein. For each step indicate where
it takes place in the cell, the name of each process involved, what is needed for each process to occur, the names of the
major enzymes involved, etc. Be sure to include the major events of each process.
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13. Hemoglobin is a protein in your red blood cells that is responsible for carrying oxygen. A mutation in the gene that
codes for hemoglobin leads to a disease called sickle cell anemia. Sickle cell hemoglobin is unable to carry oxygen
effectively, resulting in weakness in individuals who inherit one copy of this gene, death in results if the faulty gene is
inherited by from both parents. There are over 300 known mutations in the hemoglobin genes. One of these mutations
causes a condition called Hemoglobin C disease, which is not as serious as sickle cell anemia. You will need the table
of codons in your book to answer some of these questions.)
a.
b.
Below is the part of the sequence from the coding strand of DNA for three variants of the hemoglobin gene. Circle
the mutation in the sickle cell sequence and the hemoglobin C sequence.

sickle cell anemia:

hemoglobin C disease: 3’...T G A G G A C A C C T C...5’

normal hemoglobin:
3’...T G A G G A T T C C T C...5’
3’...T G A G G A C T C C T C...5’
What is the mRNA sequence of the normal hemoglobin gene?
mRNA of normal hemoglobin:
c.
What is the amino acid sequence of the normal hemoglobin gene?
The amino acid of normal hemoglobin:
d.
e.
Exactly what is the difference between the normal hemoglobin protein and the hemoglobin protein in a person
with sickle cell anemia and a person with hemoglobin C disease?

normal hemoglobin vs. sickle cell:

normal hemoglobin vs. hemoglobin C:
As mentioned above, there are over 300 known mutations in the hemoglobin genes. While many of these
mutations lead to diseases, some of these mutations do not change the ability of the hemoglobin protein to do its
job. Describe how it is possible that a mutation in the hemoglobin gene doesn't affect how the hemoglobin protein
works.
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14. Cystic fibrosis is due to the inheritance of two faulty CFTR genes. The normal CFTR gene codes for a membrane
protein found in cells involved with secretion, for example: mucous secreting cells in the respiratory tract, sweat
glands in the skin, digestive enzyme secreting cells of the pancreas, etc. The CFTR protein is actually a
glycoprotein, that is, it is a protein that has been modified to by the addition of several monosaccharides.
a. Trace the pathway of the normal CFTR protein from the organelle where CFTR is made to its final location in the
cell membrane.



 Plasma membrane
b.
The function CFTR protein is to pump chloride ions (i.e. salt) into the cells lining the lungs and cells lining various
ducts in the body. In cystic fibrosis, the protein never makes it to the plasma membrane of these cells. Use this
information to explain why people with CF experience the following symptoms:
 Salty sweat

Mucous collects in the lungs

Chronic respiratory infections

Problems digesting food

Reduced fertility in women

Sterility in males
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