Question
During semi-conservative replication of DNA in eukaryotic cells, the following processes occur.
1 Free nucleotides are hydrogen bonded to those on the exposed strand.
2 Hydrogen bonds are broken between the complementary base pairs.
3 The cell receives the signal to begin to divide.
4 Covalent bonds form between adjacent nucleotides on the same strand.
5 The DNA double helix is unwound.
Which shows the correct order of some of the processes?
A 3 → 1 → 2 → 4
B 3 → 2 → 4 → 5
C 5 → 2 → 1 → 4
D 5 → 2 → 3 → 1
▶️Answer/Explanation
Answer C
During semi-conservative replication of DNA in eukaryotic cells, the first step is the unwinding of the DNA double helix (5). This is necessary to expose the nucleotide bases for replication. The second step is the breaking of hydrogen bonds between the complementary base pairs (2). This allows for the separation of the two strands of DNA.
The third step is the addition of free nucleotides to the exposed strand. Free nucleotides are hydrogen bonded to those on the exposed strand (1). This step is important because it allows for the formation of new complementary base pairs with the exposed nucleotides.
The fourth step is the formation of covalent bonds between adjacent nucleotides on the same strand (4). This process is catalyzed by enzymes and results in the formation of a new phosphodiester bond between the 3′ end of the new nucleotide and the 5′ end of the previous nucleotide.
Option C is the correct answer because it includes all of the steps in the correct order. Option A is incorrect because it includes the process of cell division, which is not a step in DNA replication. Option B is incorrect because it does not include the unwinding of the DNA double helix. Option D is incorrect because it includes the addition of free nucleotides before the separation of the two strands of DNA.
Question
A length of double-stranded DNA contains 120 nucleotides and codes for polypeptide X.
What is the maximum length of polypeptide X?
A 20 amino acids
B 40 amino acids
C 60 amino acids
D 120 amino acids
Answer/Explanation
Answer A
The genetic code specifies that each set of three nucleotides, known as a codon, codes for a specific amino acid. Therefore, the maximum length of the polypeptide would depend on the number of amino acids that can be coded for by the 120 nucleotides in the DNA.
DNA is double-stranded. Each would have 60 nucleotides.
The maximum length of this section of a polypeptide amino acids.
Hence, the correct option is A.
Question
What is the maximum number of hydrogen bonds in a length of DNA containing 700 base pairs?
A 350 B 700 C 1400 D 2100
Answer/Explanation
Ans:
D
The hydrogen bonds between A-T is double, and between G-C, it’s triple.
The maximum number would be if the entire length of DNA would contain G-C. This means 700 pairs of G-C.
Therefore:
700 (total nucleotides) 3 (total hydrogen bonds) = 2100.
2100 Hydrogen bonds is the maximum number.
Hence , the correct option is is D.
Question
Which type of molecule is always the end product of transcription?
A. amino acid
B. functional protein
C. mRNA
D. polypeptide
▶️Answer/Explanation
Ans:
C
The end product of transcription is the formation of a single-stranded RNA molecule, called messenger RNA (mRNA), which is synthesized from a DNA template.
Therefore, the correct answer is option C: mRNA.
After transcription, the mRNA molecule is transported out of the nucleus and into the cytoplasm of the cell, where it serves as a template for protein synthesis. During translation, the mRNA is read by ribosomes, which use the genetic code to synthesize a specific sequence of amino acids, which are assembled into a polypeptide chain.
However, the final product of transcription is mRNA, not a functional protein or polypeptide. The mRNA molecule must undergo additional processing and translation before it can be used to synthesize a functional protein.
Question
A short piece of DNA 19 base pairs long was analysed to find the number of nucleotide bases in each of the polynucleotide strands. Some of the results are shown below.
How many nucleotides containing C were present in strand 1?
A 2 B 3 C 5 D 7
Answer/Explanation
Ans:
B
In strand 1, 4 T are present, so in strand 2, 4 A will be present.
In strand 2, 5 T are present, so in strand 1, 5 A will be present.
In strand 2, 7 C are present, so in strand 1, 7 G will be present.
Total in strand 1 = =
Total C in strand 1 = =
In strand 1, there will be 3 nucleotide bases containing C.
Thus the correct answer is B.