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Answer either A or B in the space below and on pages 31 and 32 - Scottish Highers Biology - Question 14 - 2018
Question 14
Answer either A or B in the space below and on pages 31 and 32. A Write notes on DNA under the following headings. (i) Organisation of DNA in prokaryotic and eukar... show full transcript
Worked Solution & Example Answer:Answer either A or B in the space below and on pages 31 and 32 - Scottish Highers Biology - Question 14 - 2018
Step 1
Organisation of DNA in prokaryotic and eukaryotic cells;
Answer
In prokaryotic cells, DNA is organized in circular chromosomes and often includes plasmids, which are small circular DNA molecules that can replicate independently. Examples include bacteria and archaea.
In eukaryotic cells, such as plant and animal cells, DNA exists as linear chromosomes located within the nucleus. Eukaryotic DNA is tightly coiled around histone proteins, forming nucleosomes, which further pack into higher-order structures.
Additionally, eukaryotic cells contain circular DNA in organelles like mitochondria and chloroplasts.
In summary, the structure of DNA reflects the complexity of the organism, with prokaryotes exhibiting simpler arrangements compared to the highly organized structures of eukaryotes.
Step 2
The polymerase chain reaction (PCR).
Answer
The polymerase chain reaction (PCR) is a technique used to amplify specific DNA sequences.
The process involves several steps:
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Denaturation: The reaction is heated to temperatures between 90°C and 98°C to separate the DNA strands by breaking hydrogen bonds.
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Annealing: The temperature is then lowered to around 50°C to 65°C, allowing primers to bind to the complementary sequences on the single-stranded DNA templates.
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Extension: The temperature is adjusted to approximately 70°C to 80°C, where DNA polymerase synthesizes new DNA strands by adding nucleotides to the 3' ends of the primers. Heat-tolerant polymerases, such as Taq polymerase, are used for this purpose.
This cycle is repeated multiple times, resulting in exponential amplification of the target DNA sequence, making PCR a powerful tool in genetics for applications such as forensic analysis and paternity testing.