1[1 mark]
What joins the two strands of a DNA molecule together?
- Strong covalent bonds between sugar groups
- Weak hydrogen bonds between bases
- Strong covalent bonds between phosphate groups
- Weak hydrogen bonds between sugar groups
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Answer: B B: Weak hydrogen bonds between bases (1)
2[3 marks]
Describe the structure of a DNA molecule.
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- two strands coiled to form a double helix (1)
- strands linked by complementary base pairs joined by (weak) hydrogen bonds (1)
- made of nucleotides, each consisting of a sugar and phosphate group (1)
- with one of four different bases attached to the sugar (1)
- Max 3
3[2 marks]
A section of one strand of DNA has the base sequence A T G C C A. (a) Write the base sequence of the complementary strand. (1) (b) Name the type of bond that holds the two strands together. (1)
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- (a) T A C G G T (1)
- (b) hydrogen (bonds) (1)
4[2 marks]
State what is meant by (a) the genome of an organism (1) and (b) a gene (1).
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- (a) the entire DNA of an organism (1)
- (b) a section of a DNA molecule that codes for a specific protein (1)
5[4 marks]
Describe how DNA can be extracted from a strawberry.
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- mash / crush the strawberry (1)
- add detergent (and salt) to break down cell membranes / release DNA (1)
- filter to remove solid pieces (1)
- add ice-cold ethanol (1)
- DNA appears as white stringy strands / precipitate (1)
- Max 4