2. Molecular Biology – 2.7 DNA replication, transcription, & translation
Name:
2.7 Essential Idea: Genetic information in DNA can be accurately copied and can be
translated to make the proteins needed by the cell.
Understandings, Applications and Skills (This is what you maybe assessed on)
Statement
Guidance
2.7.U1
The replication of DNA is semi-conservative and depends
on complementary base pairing.
2.7.U2
Helicase unwinds the double helix and separates the two
strands by breaking hydrogen bonds.
2.7.U3
DNA polymerase links nucleotides together to form a new The different types of DNA polymerase do
strand, using the pre-existing strand as a template.
not need to be distinguished.
2.7.U4
Transcription is the synthesis of mRNA copied from the
DNA base sequences by RNA polymerase.
2.7.U5
Translation is the synthesis of polypeptides on ribosomes.
2.7.U6
The amino acid sequence of polypeptides is determined by
mRNA according to the genetic code.
2.7.U7
Codons of three bases on mRNA correspond to one amino
acid in a polypeptide.
2.7.U8
Translation depends on complementary base pairing
between codons on mRNA and anticodons on tRNA.
2.7.A1
Use of Taq DNA polymerase to produce multiple copies of
DNA rapidly by the polymerase chain reaction (PCR).
2.7.A2
Production of human insulin in bacteria as an example of
the universality of the genetic code allowing gene transfer
between species.
2.7.S1
Use a table of the genetic code to deduce which codon(s)
corresponds to which amino acid.
2.7.S2
Analysis of Meselson and Stahl’s results to obtain support
for the theory of semi-conservative replication of DNA.
2.7.S3
Use a table of mRNA codons and their corresponding
amino acids to deduce the sequence of amino acids coded
by a short mRNA strand of known base sequence.
2.7.S4
Deducing the DNA base sequence for the mRNA strand.
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Review questions
1. State during which phase of the cell cycle DNA replication occurs.
2. State the function of DNA replication.
3. Which of the following is the end product of DNA replication in a human somatic cell?
a. 23 chromosomes
b. 46 chromosomes
c. 23 pairs of chromosomes
d. 23 pairs of sister chromatids
2.7.U2 Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds.
4. Outline the molecular structure of Helicase.
5. Label and annotate the diagram below to describe the function of helicase.
2.7.U3 DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a
template.
6. State the groups that DNA polymerase joins the bond formed.
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7. Label and annotate the diagram below to describe the function of DNA Polymerase.
8. Explain why the free nucleotides used in DNA replication are deoxynucleoside triphosphates not
deoxynucleoside (mono) phosphates.
9.
State the direction in which DNA polymerase catalyses the formation of the new strand.
2.7.U1 The replication of DNA is semi-conservative and depends on complementary base pairing.
10. Explain the importance of complementary base pairing in conserving the base-sequence during DNA
Replication.
11. Explain why DNA replication of this kind of referred to as being semi-conservative.
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2.7.A1 Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain
reaction (PCR).
12. polymerase chain reaction (PCR) is a key technique in DNA manipulation and analysis.
a. State the main uses of PCR.
b.
State the name of the specialised apparatus needed to support this process.
c.
Complete outline of the three keys steps in the process of PCR.
d.

Denaturation:

Annealing:

Elongation:
If one cycle of PCR yields two identical copies of the DNA sequence. Calculate how many copies
20 cycles would yield.
2.7.S2 SL ONLY Analysis of Meselson and Stahl’s results to obtain support for the theory of semiconservative replication of DNA.
The image to the right details the three possible methods of DNA replication.
Review your understanding of Meselson and
Stahl’s experiments by using using the
presentation, the McGraw and Hill animation
(clear and accessible) or the Scitable article
(Nature education) (more detailed).
https://upload.wikimedia.org/wikipedia/commons/a/a2/DNAreplicationModes.png
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13. SL ONLY At the start of a Meselson and Stahl experiment (generation 0) a single band of DNA with a
density of 1.730 g cm-3 was found. After 4 generations two bands were found, but the main band had a
density of 1.700 g cm-3.
a. Explain why the density of the main band changed over four generations. (2)
b. After one generation only one DNA band appeared, but the density had changed.
i.
Estimate the density of the band. (1)
ii.
Which (if any) mechanisms of DNA replication are falsified by this result? (1)
iii.
Explain why the identified mechanism(s) are falsified. (1)
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c. Describe the results after two generations and which mechanisms and explain the identified
mechanism(s) (if any) are falsified as a consequence. (3)
d. Describe and explain the result found by centrifuging a mixture of DNA from generation 0 and 2. (2)
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Review questions
14. Transcription and translation is also known as protein synthesis, and is the expression of genes. The
genetic code determines the amino acid sequence of a polypeptide, and the properties of the amino
acids give the final structure and function of the protein. Other than membrane proteins, state four
functions of proteins in the cell.




2.7.U4 Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
15. Outline the process of transcription in the nucleus, including the roles of RNA polymerase,
ribonucleoside triphosphates and complementary base pairing.
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2.7.U5 Translation is the synthesis of polypeptides on ribosomes.
16. Complete the table to compare and contrast the processes of transcription and translation.
Transcription
Translation
Begins with…
mRNA
Ends with…
Location
Uses…
RNA polymerase
17. SL ONLY Ribosomes are the cell
components that carry out the process
of translation. Outline the structure of
the ribosome and explain how it is
adapted to carry out translation.
http://www.hartnell.edu/tutorials/biology/translation.html
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2.7.U6 The amino acid sequence of polypeptides is determined by mRNA according to the genetic code.
2.7.U7 Codons of three bases on mRNA correspond to one amino acid in a polypeptide.
18. Define mRNA in terms of it’s function
19. Suggest why the length of mRNA molecules varies.
20. Describe what is meant by the term ‘genetic code’.
21. Define the term codon.
22. Calculate the number of different codons combinations.
23. State the number of amino acids that can be translated by ribosomes.
24. Explain what is meant by the term degenerate. Refer to the last two questions in your answer.
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2.7.U8 Translation depends on complementary base pairing between codons on mRNA and anticodons on
tRNA.
25. State the molecule on which anti-codons, which are complementary to codons, can be found.
26. Complete the steps to outline the process of translation.
a. mRNA binds to the ________________ of the ribosome.
b. The mRNA contains a series of ___________________ each of which codes for an amino acid.
c. tRNA molecules contain ____________which are complementary to the ________ on the
_______.
d. tRNA molecules bind to a _____________________ that corresponds to the anticodon
e. The _____________ binds to the small subunit of the ribosome.
f.
There are ____ binding sites on the ________________ of the ribosome, but only _____ can
contain tRNA molecules at a time
g. The _____________ moves along the mRNA and presents codons in the first two
________________.
h. ______ with anticodons ________________ to the codons bind (the bases are linked by the
formation of ________________ )
i.
A ________________ is formed between the two amino acids (carried by the tRNAs)
j.
As the ________________ moves along ______ a tRNA moves to the ______ binding site and
________________.
k. Another ______ carrying an amino acid binds to the ______ site and a second
________________ is formed.
l.
The process (i.e. the last two steps) repeats forming a ________________.
Extension: sketch diagrams below to show translation and use the steps above as annotations.
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2.7.S1 Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid.
2.7.S3 Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of
amino acids coded by a short mRNA strand of known base sequence.
2.7.S4 Deducing the DNA base sequence for the mRNA strand.
The genetic code – how mRNA codons translate to amino acids
Use the genetic code table to help
answer the questions below.
http://www.ib.bioninja.com.au/_Media/genetic_code.jpeg
27. Deduce the codon(s) that
translate for Aspartate.
28. If mRNA contains the base sequence CUGACUAGGUCCGGA
a. deduce the amino acid sequence of the polypeptide translated.
b.
deduce the base sequence of the DNA antisense strand from which the mRNA was transcribed.
c.
If mRNA contains the base sequence ACUAAC deduce the base sequence of the DNA sense
strand.
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29. Transcribe and translate this DNA sequence.
DNA T
A
C
G G G C
C
C
G T
G A
C
A
G C
C
A
C
T
mRNA
Amino
acid
30. An mRNA strand has 76 codons. How many amino acids will be in the polypeptide?
31. A polypeptide contains 103 amino acids. What is the length of the gene (unit = base pairs)?
32. A gene is 105kbp (kilobase pairs). How many amino acids are in the polypeptide?
2.7.A2 Production of human insulin in bacteria as an example of the universality of the genetic code
allowing gene transfer between species.
33. Diabetes in some individuals is due to destruction of cells in the pancreas that secrete the hormone
insulin. It can be treated by injecting insulin into the blood. Despite the differences in the amino acid
sequence between animal and human insulin, they all bind to the human insulin receptor and cause
lowering of blood glucose concentration. However, some diabetics develop an allergy to animal insulins,
so it is preferable to use human insulin. In 1982 human insulin became commercially available for the
first time. It was produced using genetically modified E. coli bacteria. Since then methods of production
have been developed using yeast cells and more recently safflower plants.
a.
Describe what is meant by the term ‘universality of the genetic code’
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b.
Complete the table to outline the keys steps in the process of gene transfer.
Diagrams
Notes
Citations:
Allott, Andrew. Biology: Course Companion. S.l.: Oxford UP, 2014. Print.
Taylor, Stephen. "Essential Biology 03.4 DNA Replication.docx." Web. 1 Oct. 2014.
<http://www.slideshare.net/gurustip/essential-biology-34-dna-replication-core>.
Taylor, Stephen. "Essential Biology 03.5 DNA Transcription and Translation.docx." Web. 1 Oct. 2014.
<http://www.slideshare.net/gurustip/essential-biology-35-transcription-translation-core>.
Taylor, Stephen. "4.4 Genetic Engineering and Biotechnology.pptx" Web. 1 Oct. 2014.
<http://www.slideshare.net/gurustip/genetic-engineering-and-biotechnology-presentation>.
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(Chris Paine)