Question 1: DNA (Deoxyribonucleic acid) is a molecule that carries genetic information in living organisms. Its structure is a double helix composed of nucleotide units. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base.

Answer: DNA is a double helix made of nucleotides, each containing a sugar, phosphate group, and nitrogenous base.

Question 2: What are the four types of nitrogenous bases found in DNA?

Answer: Adenine, Thymine, Cytosine, Guanine

Question 1: Describe the complementary base pairing in DNA.

Answer: Adenine pairs with Thymine, and Cytosine pairs with Guanine via hydrogen bonds.

Question 2: Explain why the structure of DNA is described as a double helix.

Answer: Because the two strands of nucleotides twist around each other in a spiral shape, forming a helix.

Question 1: If a DNA molecule contains 15% Thymine, what percentage of Cytosine does it contain? (Assume equal amounts of Adenine and Thymine, and Cytosine and Guanine).

Answer: Cytosine 35%

Question 2: Calculate the number of hydrogen bonds between the base pairs in a DNA segment with 1000 base pairs, given that Adenine-Thymine pairs form 2 hydrogen bonds and Cytosine-Guanine pairs form 3 hydrogen bonds. Assume equal numbers of each pair.

Answer: 6000 hydrogen bonds

Question 1: Describe a basic experiment to extract DNA from onion cells. Include the key steps and safety precautions.

Answer: The experiment involves blending onion tissue with a detergent solution to break cell membranes, adding salt to precipitate DNA, and then filtering the mixture. Safety precautions include wearing gloves and goggles to handle chemicals and avoid contamination.

Question 1: A DNA sample shows a nitrogenous base composition of 30% Adenine, 20% Cytosine, 30% Thymine, and 20% Guanine. Does this data support the principles of complementary base pairing? Explain your reasoning.

Answer: Yes, because Adenine equals Thymine and Cytosine equals Guanine, consistent with base pairing rules.

Question 1: Explain the significance of the double helix structure of DNA in relation to its function in genetic inheritance. (6 marks)

Answer: The double helix structure allows for the stable storage of genetic information, with complementary base pairing enabling accurate replication. Its twisted shape facilitates compact packing within the nucleus and provides sites for enzymes involved in DNA replication and transcription.

Question 1: Describe how understanding DNA structure has contributed to advances in forensic science.

Answer: It enables DNA fingerprinting, allowing identification of individuals based on unique DNA profiles, which is useful in criminal investigations and paternity tests.

Question 2: Identify one ethical concern related to genetic analysis of DNA in humans.

Answer: Privacy issues and potential misuse of genetic information without consent.