Question 1: DNA (Deoxyribonucleic acid) is the molecule that carries genetic information in living organisms. It is made up of two strands forming a double helix, with each strand composed of nucleotide units containing a sugar, a phosphate group, and a nitrogenous base.

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

Question 2: Explain the role of hydrogen bonds in maintaining the structure of DNA.

Answer: Hydrogen bonds hold the nitrogenous bases together in the double helix, stabilizing the DNA structure by pairing complementary bases.

Question 1: Calculate the percentage of adenine (A) in a DNA molecule if the total content of guanine (G) is 20%. Assume the DNA has equal amounts of adenine and thymine, and equal amounts of cytosine and guanine.

Answer: Adenine = 30%

Question 2: If a DNA strand contains 15,000 nucleotides, how many of these are thymine (T)?

Answer: Thymine = 3750 nucleotides

Question 1: Describe a basic experiment to extract DNA from a fruit. Include the main steps and safety precautions.

Answer: To extract DNA, mash the fruit, add a solution of soap and salt to break cell membranes and release DNA, filter the mixture, then add alcohol to precipitate the DNA. Safety precautions include wearing gloves, goggles, and handling chemicals carefully.

Question 2: Identify the independent and dependent variables in an experiment testing the effect of temperature on DNA stability.

Answer: Independent variable: Temperature; Dependent variable: DNA stability or integrity.

Question 1: A study reports that a certain mutation results in the substitution of thymine with cytosine in a DNA segment. Explain how this mutation might affect the structure and function of the DNA.

Answer: The substitution may alter base pairing, potentially affecting the stability of the DNA double helix and possibly leading to changes in gene expression or protein synthesis.

Question 2: In a laboratory setting, how is the size of a DNA molecule measured? Describe the method briefly.

Answer: DNA size is measured using techniques like gel electrophoresis, where DNA fragments are separated based on size, and their length is compared to a known standard.