Chapter 4 - Section 4.1 - DNA and RNA-The Nucleic Acids - Apply What You Know - Page 115: 1

To find the base sequence of the DNA strand that is complementary to ATTGACTCG, you need to use the complementary base pairing rules: - Adenine (A) pairs with Thymine (T). - Thymine (T) pairs with Adenine (A). - Cytosine (C) pairs with Guanine (G). - Guanine (G) pairs with Cytosine (C). So, for the given sequence ATTGACTCG, its complementary sequence would be: TAACGACTGA Now, let's address the second part of your question regarding the percentage of cytosine (C) in a DNA molecule known to be 20% adenine (A). In a DNA molecule, the total percentage of adenine (A) is always equal to the total percentage of thymine (T), and the total percentage of cytosine (C) is always equal to the total percentage of guanine (G). This is due to the complementary base pairing mentioned above. If adenine (A) makes up 20% of the DNA, then thymine (T) also makes up 20%, as they pair with each other. Therefore, the remaining 60% of the DNA must be divided between cytosine (C) and guanine (G). Since they pair with each other, they must also be equal, so each of them accounts for half of the remaining 60%. Percentage of cytosine (C) = Percentage of guanine (G) = (60% / 2) = 30% So, in a DNA molecule known to be 20% adenine (A), the percentage of cytosine (C) would be 30%, and the percentage of thymine (T) would also be 30%.

To find the base sequence of the DNA strand that is complementary to ATTGACTCG, you need to use the complementary base pairing rules: - Adenine (A) pairs with Thymine (T). - Thymine (T) pairs with Adenine (A). - Cytosine (C) pairs with Guanine (G). - Guanine (G) pairs with Cytosine (C). So, for the given sequence ATTGACTCG, its complementary sequence would be: TAACGACTGA Now, let's address the second part of your question regarding the percentage of cytosine (C) in a DNA molecule known to be 20% adenine (A). In a DNA molecule, the total percentage of adenine (A) is always equal to the total percentage of thymine (T), and the total percentage of cytosine (C) is always equal to the total percentage of guanine (G). This is due to the complementary base pairing mentioned above. If adenine (A) makes up 20% of the DNA, then thymine (T) also makes up 20%, as they pair with each other. Therefore, the remaining 60% of the DNA must be divided between cytosine (C) and guanine (G). Since they pair with each other, they must also be equal, so each of them accounts for half of the remaining 60%. Percentage of cytosine (C) = Percentage of guanine (G) = (60% / 2) = 30% So, in a DNA molecule known to be 20% adenine (A), the percentage of cytosine (C) would be 30%, and the percentage of thymine (T) would also be 30%.