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There were three suspects in an assault case - VCE - SSCE Biology - Question 5 - 2002 - Paper 1
Question 5
There were three suspects in an assault case. A forensic scientist found blood, other than the victim’s, at the site. DNA was extracted from five blood samples. - th... show full transcript
Worked Solution & Example Answer:There were three suspects in an assault case - VCE - SSCE Biology - Question 5 - 2002 - Paper 1
Step 1
a. Explain the role of the polymerase enzyme in PCR.
Answer
The DNA polymerase enzyme plays a crucial role in the Polymerase Chain Reaction (PCR) by catalyzing the synthesis of new DNA strands. It does this by incorporating nucleotides into a growing DNA strand, which is initiated by a primer that binds to the template DNA strand. This process occurs in three main stages: denaturation, annealing, and extension.
- Denaturation: The heat used in the PCR process separates the double-stranded DNA into two single strands.
- Annealing: The temperature is lowered to allow primers to bind to their complementary sequences on the single-stranded DNA.
- Extension: The DNA polymerase enzyme extends the primers to synthesize a new daughter strand by adding nucleotides one by one, according to the template strand sequence.
In conclusion, the polymerase enzyme is essential for amplifying specific DNA sequences, allowing for sufficient quantities of DNA for analysis.
Step 2
b. Name two properties of the DNA fragments which allow them to be separated from each other during gel electrophoresis.
Answer
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Size: DNA fragments are separated based on their length. Smaller fragments move faster through the gel matrix and thus travel farther than larger fragments, which face more resistance.
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Charge: DNA molecules are negatively charged due to the phosphate backbone. When an electric current is applied, they migrate towards the positive electrode, allowing for separation based on size as they pass through the gel.