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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 eukary... 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
Prokaryotes possess circular chromosomes that are typically located in the nucleoid region, along with plasmids. In contrast, eukaryotic cells, such as yeast, contain linear chromosomes enclosed within the nucleus. Additionally, eukaryotic cells house circular chromosomes within mitochondria and chloroplasts, highlighting the dual nature of genetic organization across cell types. Furthermore, the linear DNA of eukaryotes is tightly coiled around specific proteins called histones, which are crucial for DNA packaging and regulation.
Step 2
The polymerase chain reaction (PCR).
Answer
The polymerase chain reaction (PCR) is a method used to amplify specific DNA sequences, producing multiple copies of the target DNA. The process involves several key steps:
- Denaturation: Heating the reaction mixture to approximately 90°C - 98°C causes the double-stranded DNA to denature, breaking the hydrogen bonds between the strands.
- Annealing: The temperature is then lowered to around 50°C - 65°C, allowing primers to bind to their complementary sequences on the target DNA.
- Extension: The temperature increases to 70°C - 80°C, during which DNA polymerase synthesizes new DNA strands by adding nucleotides to the 3' end of the primers.
Heat-tolerant DNA polymerase, such as Taq polymerase, is used to withstand the high temperatures of the denaturation step. This cycle of heating and cooling is repeated multiple times, resulting in exponential amplification of the target sequence. PCR has applications in various fields, including forensics and paternity testing.