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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 typically organized in a circular form, existing as a chromosomal structure along with plasmids. Notably, prokaryotes do not contain a defined nucleus. In contrast, eukaryotic cells possess linear chromosomes housed within the nucleus. Eukaryotic DNA is associated with proteins named histones that help in packaging the DNA into a more compact form. This distinction is crucial, as prokaryotic DNA can be viewed as more simplistic compared to the organized structure found in eukaryotic cells.
Step 2
The polymerase chain reaction (PCR).
Answer
The polymerase chain reaction (PCR) is a method utilized to amplify a specific segment of DNA, producing multiple copies of the target sequence. The process begins with heating the sample to a temperature between 90°C and 98°C to denature the DNA, subsequently separating the strands. The temperature is then lowered to about 50°C to 65°C, allowing primers to anneal to the single-stranded DNA.
Following this, the temperature is raised to approximately 70°C to 80°C, enabling DNA polymerase to extend the primers by adding complementary nucleotides to the growing strand. This enzyme is often a heat-tolerant variant like Taq polymerase, which withstands the initial high temperatures.
The PCR cycle involves repeated processes of heating and cooling, leading to exponential duplication of the target DNA segment, which is widely applied in various fields such as forensics and paternity testing.