Answer Key
From Gene to Protein Answer Key
-
University:
Campbell University -
Course:
BIOL 342 | Genetics Academic year:
2023
-
Views:
118
Pages:
10
Author:
Fletcher Wallace
From Gene to Protein - Transcription and Translation'
How do genes influence our characteristics ?
A gene is a segment of DNA that provides the instructions for making a protein. Proteins have many
different functions that influence our characteristics. This chart shows an example.
Gene in DNA
-»
Protein
-»
Another version of the gene provides
instructions to make defective protein
enzyme.
-»
JIBE
Si
->
One version of a gene provides
instructions to make normal protein
enzyme.
Characteristic
*fmJ
Kwr
—>
*
Normal enzyme makes the
pigment molecule in skin
and hair.
Defective enzyme does not
make this pigment
F
.
Normal skin and hair
-> color
-»
molecule.
.
:!
Albinism ( very pale
skin and hair)
1 How can a gene determine whether a person has albinism? (Give a molecular explanation.)
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How does a gene provide the instructions for making a protein?
A two-step process:
: DNA
The first step is transcription of the gene in the DNA.
Transcription produces messenger RNA (mRNA).
i
TRANSCRIPTION
/
^
mRNA
The second step is translation of the mRNA molecule.
Translation produces proteins.
TRANSLATION
"
—^iud.^.
,5
Cytoplasm
i
Protein
2a . Fill in the blanks in this figure to label the DNA,
mRNA and protein molecules.
2b. DNA and RNA are polymers of nucleotides. The
four nucleotides in DNA are A, T,
four nucleotides in RNA are A, lv\
OAIA
Transcription
tp W
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C . and (~7 . The
. ( and (A
2c. A protein is a polymer of amino acids. Draw a
circle around the amino acid Gly ( glycine ) in the
protein.
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Translation
i-
3a. During transcription, the sequence of nucleotides in a gene in the DNA is copied to a corresponding
- C cfjLQ in mRNA.
sequence of 1WC: (
;
\ TcA
3b. During translation, the sequence of nucleotides in mRNA determines the sequence of Q. WVl AD CLC,i
in the protein. The sequence of amino acids determines the structure and function of the protein.
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4a Which process takes place in the nucleus ?
.
translation
transcription
4b Explain why this process must occur in the nucleus.
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Transcription
.
5 Why does a cell need to carry out transcription in order to make a protein?
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6. In this activity, you will model how a cell carries out transcription and translation to make the
,
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beginning of the hemoglobin molecule. What type of molecule is hemoglobin?
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During transcription, the enzyme RNA polymerase:
• separates the two strands of a DNA
•
double helix * ‘ ncorr ck
^
•
.
do&i U‘s
uses a gene in one DNA strand as a guide
to make an mRNA molecule.
*
r
RNA
polymerase
jf % 1 1 jg I I I
.
7 In the figure:
- Write enzyme next to the name of the enzyme.
- Trace the outlines of the DNA molecule.
RNA polymerase adds one nucleotide at a time to
the growing mRNA molecule. Each DNA
nucleotide in the gene is matched with a
complementary RNA nucleotide which has a
matching shape and charge distribution.
RNA nucleotides
•i •
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rum
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To model the process of transcription, your group will need a page showing an RNA polymerase
molecule inside a nucleus, a paper strip showing a single strand of DNA labeled "Beginning of
Hemoglobin Gene", RNA nucleotides and tape.
One of you will be the RNA polymerase. Another group member will be the cytoplasm which
surrounds the nucleus and supplies the ' nucleotides which are used to make the mRNA molecule.
'
>
RNA polymerase: Insert the "Beginning of
Hemoglobin Gene" DNA molecule through
the slot in the RNA polymerase diagram so
the first two nucleotides of the gene are
on the dashes labeled DNA.
Your RNA polymerase should look like this
figure. ( Note: A real RNA polymerase
molecule and DNA and RNA nucleotides
are much smaller than the nucleus.)
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Nucleus
SF
i k polymerase
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w ere e syme forms
Vcovalentbond
^ between
^ nucleotides
vv
ww
II
>
Cytoplasm: Use the base-pairing rules to choose
>
an RNA nucleotide that is complementary to the
first DNA nucleotide. Give this nucleotide to the RNA polymerase person.
RNA polymerase: Put the first RNA nucleotide in the box labeled RNA nucleotide.
>
Cytoplasm: Give
>
>
the next RNA nucleotide ( complementary to the next DNA nucleotide) to the RNA
polymerase person.
RNA polymerase: Put this nucleotide in the box labeled "next RNA nucleotide". Join the two RNA
nucleotides together with transparent tape; the tape represents the covalent bond between these
two nucleotides in the growing mRNA molecule. Then, move the DNA molecule and the mRNA
molecule one space to the left.
these last two steps as often as needed to complete transcription of the beginning of the
hemoglobin gene, adding one nucleotide at a time to the mRNA molecule.
Repeat
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6
r 10. The first column of this table describes DNA replication. Fill in the blanks in the second column
to summarize the differences between DNA replication and transcription.
Transcription
DNA replication
1
The whole chromosome is replicated.
3ex
)&
is transcribed.
mRNA is made.
DNA is made.
DNA is double-stranded.
-stranded.
mRNAis
RAJA polymerase is the enzyme which carries
DNA polymerase is the enzyme which carries out
DNA replication.
out transcription.
T = thymine is replaced by _
so A in DNA pairs with
T = thymine is used in DNA,
so A pairs with T in DNA.
= uracil in RNA,
in mRNA.
.
11 Fill in the blanks to describe the similarities between transcription and DNA replication.
Both transcription and DNA replication produce nucleic acids which are polymers of
A.u/
ieoWlcs,
( C, G, A, and T or U). Both processes depend on a
1^ Vi dP
.
at a time To determine which nucleotide is added
enzyme which adds one Du ^, * 0
next, both transcription and DNA replication use the nucleotide sequence in a
bft.Se,- paAn AG
the
strand and
rules.
.
12a. Fill in the blanks to label each type of molecule in
the figure.
12b. Name the process shown in the figure and explain
how this process occurs. Include in your answer each of
the molecules shown and these words and phrases:
gene, base-pairing rules, one at a time
.
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4 Translation
.
13 To show how translation follows transcription,
fill in the blanks and box in this figure.
Sene fn DNA
m
i
How can four different types of nucleotide in mRNA
provide a different code for each of the 20 different
types of amino acids in proteins ?
The answer is that the mRNA code for each
type of amino acid is a sequence of three
nucleotides called a codon.
l
m
Transcription
:
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CoclM
14. In the figure, circle the mRNA codon that codes for
the amino acid Gly ( glycine ).
1
Jiis
i< A
Translation requires two types of RNA: mRNA and transfer RNA = tRNA . tRNA molecules bring the
correct amino acid for each codon in the mRNA.
There are multiple different types of tRNA, each with a different anticodon. Each tRNA anticodon has
three nucleotides that are matched by the base-pairing rules to the three nucleotides in the mRNA
codon for a specific amino acid.
.
15 What is the tRNA anticodon for the amino acid Gly (glycine) ?
16. For each type of tRNA, there is a specific enzyme that attaches the correct amino acid for the
anticodon in that tRNA. These enzymes are needed for step
^ in the figure below.
(1/2/3/4)
0
Translation takes place in
ribosomes ( tiny structures
inside cells ).
Inside the ribosome, a
codon in an mRNA
molecule is matched by
the base-pairing rules with
an anticodon in a tRNA
( step 3). This tRNA brings
the next amino acid to be
added to the growing
protein molecule.
Translation
.
1 tRNA and amino acids
float freely in cytoplasm
/o0
mmm
4. Amino acids are
joined together to
make a protein
.
.
17 In the ribosome, circle
a codon in the mRNA and
the complementary
anticodon in a tRNA
molecule.
2. Enzymes bind each tRNA
to the appropriate amino acid
for that tRNA‘s anticodon
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3. Using the base-pairing rules, each
mRNA codon is matched with the
anticodon in a tRNA The tRNA brings the
right amino acid for that mRNA codon.
mRNA
Each amino acid is joined
to the previous amino
acid in the growing protein molecule ( step 4).
.
.
^
ribosome
The ribosome moves along the mRNA,
adding one amino acid at a time to produce
the protein coded for by the mRNA.
18 Use an arrow to show where the next amino acid will be added to the growing protein molecule. .
19 What part of translation depends on the base-pairing rules ?
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Translation Modeling Procedure
In this section you will simulate the steps in translation to produce the beginning of a hemoglobin
protein.
One of you will be the ribosome, and another will be the cytoplasm.
>
Preparation
To model translation, you will need a page showing a ribosome, tRNA molecules, amino acids,
the mRNA you made during your simulation of transcription, and a strip labeled "Second Part
>
ofmRNA".
>
Cytoplasm: Tape the CUG end of the mRNA you made to the ACU
end of the Second Part of
mRNA strip.
.
20 For tRNA to do its job, each tRNA molecule must be attached to the correct amino acid that
'
corresponds to the anticodon in that type of tRNA. To know which amino acid should be attached
to eacmtRNA molecule, use the base-pairing rules to complete this table
.
Amino acid
Anticodon in tRNA
molecule that carries
this amino acid
mRNA codon
amic acid
(Glu)
Valine
( Val)
GhC
GWC
CAc
CUG
GAG
GUG
Proline Leucine
(
(Pro)
Threonine
(Thr)
Histidine
(His)
UGA
6uA
A
A'
JSACT
ecu
Cytoplasm: Use this table to matplfeach model tRNA molecule with the correct amino acid for
>
that type of tRNA. Tape the fnino acidTothe tRNA very lightly, because they will only be
joined temporarily and wiffsoon separate.
^
Note: Each mod KRNA molecule only shows the three nucleotides of the anticodon and the
^
the amino acid. A real tRNA molecule has, many more nucleotides. Similarly, a
binding siteidr
s'
has.
real mRI A molecule has many more nucleotides than your strip
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.
.
A
n\
^
X
.
X
21 You.
arrange the amino acids in the correct sequence; then he tapes together all six amino acids.
carry out
Ex- lain why this would not be a good simulation of the actual sequence of steps used to
X
. (Hint: See page 5.)
-
^
Atranslation
1
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6 Modeling the Steps in Translation
>
>
>
Ribosome: Insert the mRNA through the slot in the model ribosome, with the first three
nucleotides of the mRNA in the " codon " position and the next three nucleotides in the "next
codon" position.
Cytoplasm: Use the base-pairing rules to supply the tRNA that has the
correct anticodon to match
the first codon in the mRNA.
Ribosome: Place this tRNA with its amino acid in position.
Your model ribosome should look like this:
Ribosome
place where ribosome forms
covalent bond between amino acids
o
-t
Valine
IliMJ
I
Ip
tRNA with next
amino acid
slot
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codon
next codon
In mRNA~
.
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mRNA
.
22 In the above diagram, put a rectangle around the anticodon in the tRNA. Use an arrow to indicate
the amino acid.
>
>
>
>
Cytoplasm: Supply the tRNA
position.
that has the correct anticodon to match the codon in the "next codon "
Ribosome: Place the tRNA in position. Tape the two amino acids together to represent the covalent
bond between these two amino acids. Detach the amino acid on the left from its tRNA.
Ribosome: Move the mRNA and matching tRNAs with amino acids one codon to the left. Release
the tRNA on the left to the cytoplasm.
Repeat
these three steps until you have attached all six amino acids to form the beginning portion
of the hemoglobin protein. u
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23. Why does axell need tRNA to
makers protein? Explain the function of tRNA and how tRNA and
mRNA work together to put the right amino acids in the right sequence as the protein is made.
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24 Explain why it makes sense to use the-word translation to describe protein synthesis and why it
would not make sense to use the word translation to describe mRNA synthesis.
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25 Why does a cell need to carry out transcription before translation?
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26a Fill in the blanks to label each type of
molecule in this figure
.
26b. Name the process shown in the figure and
explain each step in this process. Include in your
answer each of the molecules shown and these
words and phrases:
anticodon, base-pairing rules, codon,
ribosome, sequence of amino acids.
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Understanding How the Gene for Sickle Ceil Hemoglobin Results in Sickle Cell Anemia
Different versions of the same gene are called different alleles. These different alleles share the same
general sequence of nucleotides, but they differ in at least one nucleotide in the sequence.
27a. Complete this flowchart to show how different alleles can result in different characteristics.
In the DNA, different alleles of a gene have a different sequence of fW
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dnobl' Aj^
! franspripj-ioin
N/
different sequence of
AAAC-
si
/
different sequence of
OLmi A' sn
Ludieblb inmRNA
j-ra /isforfrfan
(3ooidJ
in a protein
\^
'
T
different structure and function of the protein
si'
different characteristics
27b. Label the arrow that represents transcription and the arrow that represents translation.
8 Next, you will analyze how different alleles of the hemoglobin gene can result in sickle cell anemia
vs. normal health.
28. Using the table below, compare the nucleotide sequence in the "Beginning of Normal
Hemoglobin Gene" vs. the "Beginning of Sickle Cell Hemoglobin Gene". What is the only
difference?
iitmeJl - T
5tMt Cell ~ A
Beginning of Normal Hemoglobin Gene
CACGTAGACTGAGGACTC
Transcription produces :
codonl
Translation produces:
amino
acid 2
acid 1
codon 4
amino
acid 3
codon 5
codon 6
amino
acid 4
acid 6
acid 5
nic
UforttM Mi /U bluhi
Aold
htshdt Ai
Beginning of Normal Hemoglobin Protein
/
'
CACGTAGACTGAGGACFC
6 Ub au CUG kOX CCU Gel 6
Beginning of Sickle Cell Hemoglobin Gene
Transcription produces :
Beginning of Sickle Cell Hemoglobin mRNA
Translation produces:
codon 1
codon 2
codon 3
codon 4
codon 5
codon 6
amino
amino
amino
acid 2
amino
acid 4
amino
acid 1
amino
acid 3
acid 5
acid 6
fodUkl hfrftot IOUOIM Jfauvwk
Beginning of Sickle Cell Hemoglobin Protein
29 Complete the above table. ('y
codon 3
CUG AGU CCU. bAG
GUG
OAU
amino
amino
amino
Beginning of Normal Hemoglobin mRNA
.
codon 2
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,
30 Compare the amino acid sequence for the beginning of sickle cell hemoglobin vs. the beginning
of normal hemoglobin. What difference do you observe ?
X
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Sickle cell hemoglobin and normal hemoglobin differ in only a single amino acid out of more than
100 amino acids in the complete hemoglobin protein. This difference in a single amino acid results
in the different properties of sickle cell hemoglobin compared to normal hemoglobin.
Hemoglobin is carried inside red blood cells. Normal hemoglobin dissolves in the watery cytosol of
red blood cells. Sickle cell hemoglobin is less soluble in the cytosol because:
Valine (Val) is much less water-soluble than glutamic acid (Glu).
Amino acid 6 is in a crucial location on the outer surface of the hemoglobin protein.
The chart on the next page shows how the lower solubility of sickle cell hemoglobin results in the
symptoms of sickle cell anemia.
•
•
A
r Genes in DNA
2 copies of the allele
that codes for
normal hemoglobin
(SS)
--
Protein
Normal hemoglobin dissolves in
the cytosol of red blood cells.
r\
»
m
I
Characteristics
Disk-shaped red blood cells can
squeeze through the smallest
blood vessels -> normal health
ft -# h
-I
A
a
If sickle cell hemoglobin clumps
in long rods
-» sickle-shaped red blood cells
-> clogged small blood vessels
+ fragile red blood cells
, damage to body organs
pain
->
+ anemia = sickle cell anemia
Sickle cell hemoglobin
can clump in long rods
in red blood cells.
2 copies of the allele
that codes for
sickle cell hemoglobin (ss)
.
31b. Use the letter for each of the following statements to label the box or boxes in the flowchart that
31a Circle the arrows in the chart that represent transcription + translation.
illustrate this statement.
A. Normal hemoglobin dissolves in the watery cytosol of red blood cells. The disk-shaped red
blood cells can squeeze through the smallest blood vessels so blood flow is normal.
B. If a person inherits two copies of the sickle cell hemoglobin allele and produces only sickle cell
hemoglobin, then the sickle cell hemoglobin molecules tend to clump together in long rods
inside red blood cells.
C. These hemoglobin rods can result in sickle-shaped red blood cells which can block blood flow in
smallblood vessels; this causes pain and damage to body organs. Sickle-shaped red blood cells
don't last as long as normal red blood cells; when the body can't produce enough replacement
red blood cells, this results in anemia.
.
32 Considering that we are all made up of the same 4 nucleotides in our DNA, the same 4 nucleotides
in our RNA, and the same 20 amino acids in our proteins, why are we so different from each other? For
example, why do some people have sickle cell anemia and others don't ?
i
.
icM' in
]
By Drs Ingrid Waldron and Jennifer Doherty, Department of Biology, University of Pennsylvania, Copyright, 2017. Teachers are encouraged to copy
this Student Handout for classroom use A Word file (which can be used to prepare a modified version if desired) arid Teacher Preparation Notes
with instructional suggestions and background biology are available at http:/ / serendipstudio ore/ sd edu/waldron/#trans
.
.
.
10
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