All Free Biology MCQs with Answers

• A. DNA replication
• B. Nucleotide
• C. Prokaryotes
• D. 2 nm

Explanation: Matthew Meselson, an American molecular biologist, contributed significantly to our understanding of DNA replication. In 1958, Meselson and Franklin Stahl conducted the famous Meselson-Stahl experiment, which provided evidence for the semi-conservative replication of DNA. This experiment involved labeling DNA with heavy nitrogen (^15N) and then switching to light nitrogen (^14N) and observing the distribution of the DNA strands in subsequent generations. Their findings supported the hypothesis that DNA replication occurs semi-conservatively, where each newly synthesized DNA molecule consists of one parental and one newly synthesized strand. Meselson's work thus laid the foundation for our understanding of how DNA replicates.

• A. Prokaryotes
• B. Nucleotide
• C. DNA replication
• D. 2 nm

Explanation: The lagging strand which elongates away from the replication fork, is synthesized discontinuously as a series of short segments that are later connected. These segments, called Okazaki fragments are about 100 - 200 nucleotides long in eukaryotes and 1000 - 2000 nucleotides long in prokaryotes.

• A. Transcription
• B. Nucleosomes
• C. Alkaptonuria
• D. Metacentric

Explanation: Homogentistic acid is an intermediate in the metabolism of tyrosine and phenylalanine. In individuals with alkaptonuria, a genetic disorder, homogentisic acid accumulates in the body due to a deficiency in the enzyme homogentisate 1,2-dioxygenase, leading to its excretion in urine and various health issues including dark pigmentation of connective tissues.

• A. Submetacentric
• B. Transcription
• C. Nucleosomes
• D. Metacentric

Explanation: Every 200 nucleotides, the DNA duplex is coiled around a core of eight histone proteins forming a complex known as a nucleosome.

• A. Alkaptonuria
• B. Nucleosomes
• C. Transcription
• D. Metacentric

Explanation: Metacentric refers to a chromosome in which the centromere is located approximately in the middle, resulting in two arms of roughly equal length.

• A. Metacentric
• B. Nucleosomes
• C. Submetacentric
• D. Transcription

Explanation: The interaction between RNA polymerase and the promoter region is pivotal in transcription, the process by which genetic information encoded in DNA is transcribed into RNA. RNA polymerase, the enzyme responsible for this process, recognizes and binds to specific sequences within the promoter region of a gene. Once bound, RNA polymerase initiates transcription by unwinding the DNA double helix and synthesizing an RNA molecule complementary to one of the DNA strands. Promoters serve as regulatory regions that dictate when and where transcription occurs, as they contain sequences recognized by RNA polymerase and other transcription factors. Together, RNA polymerase and the promoter coordinate the initiation of transcription, ensuring the accurate and timely synthesis of RNA molecules necessary for gene expression and protein synthesis within cells.

• A. tRNA
• B. Human cell
• C. mRNA
• D. Promotor sequence

Explanation: The genetic code is directly related to messenger RNA (mRNA) because mRNA serves as the intermediary molecule that carries the genetic information from the DNA to the ribosome during protein synthesis. The sequence of nucleotides on the mRNA molecule is transcribed from the DNA template and represents the genetic code. Each sequence of three nucleotides on the mRNA molecule, called a codon, corresponds to a specific amino acid or a start/stop signal, according to the rules of the genetic code. Thus, the genetic code dictates the sequence of codons on the mRNA, which in turn determines the sequence of amino acids in the resulting protein during translation. Therefore, mRNA acts as the messenger that faithfully transmits the genetic information encoded in the DNA to the ribosome, where it is translated into a functional protein according to the genetic code.

• A. tRNA
• B. mRNA
• C. Human cell
• D. Sense strand

Explanation: The coding strand, also known as the sense strand, is the strand of DNA that has the same sequence as the mRNA transcript (except for T's in DNA being replaced by U's in RNA). It serves as the template for mRNA synthesis during transcription. The other DNA strand, the template strand, is complementary to the coding/sense strand and is used as the template for mRNA synthesis.

• A. Sigma factor
• B. GC + AT base pairs
• C. U ribonucleotide
• D. Core enzyme

Explanation: It is a protein in prokaryotic organisms (such as bacteria) that assists RNA polymerase in recognizing the promoter region of a gene, thereby initiating transcription.

• A. GC + AT base pairs
• B. 3' end
• C. U ribonucleotide
• D. Core enzyme

Explanation: Uridine (U) ribonucleotide, when found in messenger RNA (mRNA), can be related to a stop signal through the presence of a specific sequence known as a stop codon. In the genetic code, there are three stop codons: UAG, UAA, and UGA. When the ribosome encounters one of these stop codons during translation, it signals the termination of protein synthesis. Uridine (U) ribonucleotide is involved in the formation of these stop codons within the mRNA molecule, thus playing a crucial role in the regulation of protein synthesis.