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Essential Biology 7.3 & 7.4: Transcription and Translation (AHL)
Resources: : Clegg pp 69-74 & 243-253, RG pp 38-41&122-128
You must also complete the Core (3.5) Essential Biology for this topic.
1.
Distinguish between sense and antisense strands in DNA.
The ______________ strand is complementary to the ___________ strand. The antisense strand
is also known as the ____________ strand, as it is used for _____________ , to make mRNA.
mRNA corresponds with the _____________ strand, with the exception of the base ___, which is
replaced with ____. mRNA is complementary to the ________________ strand.
2.
Describe the role of the antisense strand in transcription.
3.
State the direction of transcription and draw a simple diagram to show the addition of an RNA
molecule to a growing mRNA strand.
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Essential Biology 7.3 & 7.4: Transcription and Translation (AHL)
4.
Outline the roles of the following regions of DNA in transcription:
5.
Explain the process of transcription in prokaryotes, including the following: promoter region,
RNA polymerase, 5’-3’ direction, free nucleoside triphosphates, complementary base pairing,
terminator region.
6.
Distinguish between introns and exons in eukaryotic DNA (DNA structure revision).
7.
State one method of post-transcription modification of mRNA in eukaryotes.
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Essential Biology 7.3 & 7.4: Transcription and Translation (AHL)
8.
Label the following regions on this tRNA molecule, stating the function of each:
Acceptor stem, anticodon loop, hydrogen bonds.
9.
tRNA needs to be activated in order to pick up the corresponding amino acid. Explain how tRNA
is activated, including the role of a specific tRNA activating enzyme, ATP and amino acids.
10. Using a diagram, outline the structure of a ribosome, including protein and RNA composition,
large and small subunits, three tRNA binding sites and mRNA binding sites.
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Essential Biology 7.3 & 7.4: Transcription and Translation (AHL)
11. Describe polysomes and state their function.
12. State the direction of movement of the ribosome along the mRNA strand (the direction of
translation).
13. Explain the process of translation in four stages:
Keywords: mRNA, ribosome, small subunit, large subunit, start codon, AUG, tRNA
Explanation:
1. Initiation
Keywords: amino acids, peptide bond, transfer, anticodon, tRNA
Explanation:
2. Elongation
Keywords: tRNA, mRNA, codon, release
Explanation:
3. Translocation
4. Termination
Keywords: stop codon, release/ detachment
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Essential Biology 7.3 & 7.4: Transcription and Translation (AHL)
Explanation:
14. Draw and label the structure of a dipeptide.
15. Distinguish between polypeptides produced by free ribsomes and those produced by bound
ribosomes, such as in the RER. (Revision: exocytosis)
16. Data based question (from IB Questionbank):
It had always been assumed that eukaryotic genes were similar in organization to prokaryotic
genes. However, modern techniques of molecular analysis indicated that there are additional
DNA sequences that lie within the coding region of genes. Exons are the DNA sequences that
code for proteins while introns are the intervening sequences that have to be removed. The
graph shows the number of exons found in genes for three different groups of eukaryotes.
[Source: Benjamin Lewin, (1999) Genes VII, OUP, page 55]
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Essential Biology 7.3 & 7.4: Transcription and Translation (AHL)
Percentage of genes
100
80
Saccharomyces cerevisiae (a yeast)
60
40
20
0
40
30
Drosophila melanogaster (fruit fly)
20
10
0
20
15
Mammals
10
5
0
1
a)
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 <30<40<60>60
Number of exons
Calculate the percentage of genes that have five or less exons in mammals.
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(1)
(b)
Describe the distribution of the number of exons and the percentage of genes in
D. melanogaster.
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(2)
(c)
(i)
Compare the distributions of the number of exons found in genes of S.
cerevisiae and mammals.
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Essential Biology 7.3 & 7.4: Transcription and Translation (AHL)
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(2)
(ii)
Suggest one reason for the differences in the numbers of exons found in genes
of S. cerevisiae and mammals.
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(1)
Human DNA has been analysed and details of certain genes are shown in the table below.
Gene
Insulin
Gene size / kb*
mRNA size / kb
Number of introns
1.7
0.4
2
Collagen
38.0
5.0
50
Albumin
25.0
2.1
14
Phenylalanine hydroxylase
90.0
2.4
12
2 000.0
17.0
50
Dystrophin
*kilobase pairs
[Source: William S Klug and Michael R Cummings, (2002), Concepts of Genetics, 7th edition,
Prentice Hall, page 314]
(d)
Calculate the average size of the introns for the albumin gene.
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Essential Biology 7.3 & 7.4: Transcription and Translation (AHL)
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(2)
(e)
Analyse the relationship between gene size and the number of introns.
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(2)
(f)
Determine the maximum number of amino acids that could be produced by
translating the phenylalanine hydroxylase mRNA.
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(1)
Hemoglobin is a protein composed of two pairs of globin molecules. During the process of
development from conception to adulthood, human hemoglobin changes in composition. Adult
hemoglobin consists of two alpha- and two beta-globin molecules. Two globin genes occur on
chromosome 16: alpha- and zeta-globin. Four other globin genes are found on chromosome 11:
beta, delta, epsilon and gamma. The graph below illustrates the changes in expression of the
globin genes over time.
50
Key:
alpha-globin
gamma-globin
beta-globin
delta-globin
epsilon-globin
zeta-globin
40
Percentage of
hemoglobin 30
20
10
0
10
20
30
weeks of gestation
40
birth
2
6
4
month of age
[Source: adapted from M Cummings, Human Heredity, 4th edition, West/Wadsworth
Publishing Company]
(g)
State which globin genes are the first to be expressed after fertilization.
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Essential Biology 7.3 & 7.4: Transcription and Translation (AHL)
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(1)
(h)
Compare the expression of the gamma-globin gene with the beta-globin gene.
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(3)
(i)
Deduce the composition of the hemoglobin molecules
- at 10 weeks of gestation: .............................................................................
- 2 months after birth:
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(2)
(Total 17 marks)
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