DP Topic 2.
6:
Structure of
DNA & RNA
DNA Nucleotide Structure
Exercise 1: Fill in the blanks
Nucleotides are the subunits that strands are built from,
in the same way that starch or glycogen are built from
subunits. Polynucleotide strands are used to form nucleic acids: and .
DNA Nucleotides are formed by joining a group and a
base to a sugar. This is a 5 carbon (pentose) sugar and the
phosphate and nitrogenous bases are joined to opposite ends of this molecule via
reactions.
DNA Polynucleotide strand
Exercise 2: Use your knowledge of condensation and hydrolysis reactions and the
diagram below to outline in your own words how DNA nucleotides are linked together
by covalent bonds into a single strand (Use extra paper if necessary).
DNA double helix
Exercise 3: Use your knowledge of hydrogen bonding and the diagram below to
explain in your own words how a DNA double helix is formed using complementary
base pairing and hydrogen bonds (Use extra paper if necessary)
A simple diagram of the molecular structure of DNA
Exercise 4: Use this space to complete a simple diagram of the molecular structure of
DNA.
RNA and DNA
Exercise 5: Use the table to compare the structure of RNA and DNA
RNA DNA
The Structure of DNA and RNA
Aim: To learn the basic differences between DNA and RNA structure.
Questions
1. Complete the table to identify differences and similarities between the two molecules.
Feature DNA Molecules RNA Molecule
The number of strands
The type of sugar
The names of the bases
2. Explain how the bases of DNA will pair to bases of RNA.
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© David Faure, InThinking www.biology-inthinking.co.uk
1
DNA Structure – IB Style Questions
Multiple Choice Questions
1. Double Helix is best described as …
A. The specific pairing of bases in DNA: A to T and C to G
B. The name of the twisted shape of the DNA molecule, as it contians two strands.
C. The weak bonds that hold the two strands of DNA together.
D. Guanine - the base that pairs with Cytosine
2. Which of these shapes most commonly represents deoxyribose sugar in a DNA diagram?
A.
B.
C.
D.
3. “A” is used to represent which nitrogenous base?
A. the base that pairs with Thymine
B. - the base that pairs with Cytosine
C. - the base that pairs with Guanine
D. - the base that pairs with Adenine
4. Hydrogen Bonds
A. The weak bonds that hold the two strands of DNA together.
B. The bases that pairs with Adenine
C. The specific pairing of bases in DNA: A to T and C to G
D. Forces that together with the sugar make the backbone of DNA
© David Faure, InThinking www.biology-inthinking.co.uk 1
DNA Structure – IB Style Questions
5. The base ‘Cytosine’ is best described as
A. - the base that pairs with Thymine
B. - the base that pairs with Guanine
C. - the base that pairs with Adenine
D. - the base that pairs with Cytosine
6. The letter “T” is used instead of which base in DNA?
A. Thyroxin
B. Thyroid
C. Triose phosphate
D. Thymine
7. Which of the descriptions best represents the Phosphate group in a DNA diagram?
A. Together with the phosphate molecules makes the DNA backbone
B. T- the base that pairs with Guanine
C. Together with the sugar it makes the backbone of DNA
D. One of four different bases. The order of these bases makes the genetic code.
8. Complementary base pairing
A. The specific pairing of bases in DNA: A to T and C to G
B. Cytosine - the base that pairs with Guanine
C. Adenine - the base that pairs with Thymine
D. The specific pairing of bases in DNA: A to G and C to T
9. The best description for the letter “G” in a DNA diagram is …
A. - the base that pairs with Cytosine
B. - the base that pairs with Thymine
C. - the base that pairs with Guanine
D. - the base that pairs with Adenine
© David Faure, InThinking www.biology-inthinking.co.uk 2
Essential idea: The structure of DNA allows efficient storage of genetic information.
Biology guide
2.6 Structure of DNA and RNA
Nature of science:
Using models as representation of the real world—Crick and Watson used model making to discover the structure of DNA. (1.10)
Understandings: Theory of knowledge:
t The nucleic acids DNA and RNA are polymers of nucleotides. t The story of the elucidation of the structure of DNA illustrates that
t DNA differs from RNA in the number of strands present, the base cooperation and collaboration among scientists exists alongside competition
composition and the type of pentose. between research groups. To what extent is research in secret ‘anti-scientific’?
What is the relationship between shared and personal knowledge in the
t DNA is a double helix made of two antiparallel strands of nucleotides linked
natural sciences?
by hydrogen bonding between complementary base pairs.
Utilization:
Applications and skills:
Syllabus and cross-curricular links:
t Application: Crick and Watson’s elucidation of the structure of DNA using
Biology
model making.
Topic 2.2 Water
t Skill: Drawing simple diagrams of the structure of single nucleotides of DNA Topic 3.5 Genetic modification and biotechnology
and RNA, using circles, pentagons and rectangles to represent phosphates, Topic 7 Nucleic acids
pentoses and bases.
Guidance:
t In diagrams of DNA structure, the helical shape does not need to be shown,
but the two strands should be shown antiparallel. Adenine should be shown
paired with thymine and guanine with cytosine, but the relative lengths of
Topic 2: Molecular biology
the purine and pyrimidine bases do not need to be recalled, nor the numbers
of hydrogen bonds between the base pairs.
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