All Free Biology MCQs with Answers

• A. Leading strand
• B. Antisense strand
• C. Sense strand
• D. Lagging strand

Explanation: The coding strand, also known as the sense strand or non-template strand, is the strand of DNA that has the same sequence as the RNA transcript produced during transcription, except it contains thymine (T) instead of uracil (U). Unlike the template strand, the coding strand is not directly involved in RNA synthesis.

• A. RNA Polymerase I
• B. RNA Polymerase II
• C. RNA Polymerase III
• D. None of the above

Explanation: mRNA (messenger RNA) is synthesized by RNA polymerase II in eukaryotic cells. RNA polymerase II is responsible for transcribing protein-coding genes into pre-mRNA molecules, which undergo further processing (such as splicing and polyadenylation) to become mature mRNA molecules.

• A. RNA Polymerase I
• B. RNA Polymerase II
• C. RNA Polymerase III
• D. None of the above

Explanation: tRNA (transfer RNA) is synthesized by RNA polymerase III in eukaryotic cells. RNA polymerase III is responsible for transcribing genes that encode tRNA molecules from specific regions of the DNA. These transcribed tRNA precursor molecules undergo further processing, including trimming and modification, to become mature tRNA molecules.

• A. Operator
• B. Promoter
• C. Enhancer
• D. None of the above

Explanation: Transcription typically starts at a specific DNA sequence called the promoter region. In eukaryotic cells, RNA polymerase, along with various transcription factors, binds to the promoter region to initiate transcription.

• A. TTGGC
• B. TTGACA
• C. TTGCAA
• D. TTGAAC

Explanation: The binding site "TTGACA" corresponds to the consensus sequence of the -35 region of the promoter in bacterial DNA. In prokaryotes, such as bacteria, RNA polymerase binds to specific DNA sequences known as promoter regions to initiate transcription.

• A. Alpha factor
• B. Sigma factor
• C. Beta factor
• D. Gama factor

Explanation: In bacterial RNA polymerase, the sigma (σ) factor is indeed an essential subunit. The sigma factor associates with the core enzyme to form the holoenzyme, which is responsible for recognizing and binding to specific promoter sequences on DNA to initiate transcription.

• A. CA
• B. GA
• C. GC
• D. TA

Explanation: The stop sequences at the end of the gene terminate the synthesis of mRNA. The simplest stop signal is a series of GC base pairs followed by a series of AT base pairs. The RNA formed in this region forms a GC hairpin followed by four or more U ribonucleotides. The hairpin causes RNA polymerase to stop synthesis.

• A. Poly A
• B. Poly C
• C. Methyl GTP
• D. Methyl ATP

Explanation: Explanation for this question will be added soon!

• A. Poly A
• B. Poly C
• C. Methyl GTP
• D. Methyl ATP

Explanation: The tail of mRNA is called the poly(A) tail. It consists of a string of adenine nucleotides added to the 3' end of the mRNA molecule after transcription. This poly(A) tail plays roles in mRNA stability, export from the nucleus, and translation efficiency.

• A. Two nucleotides
• B. Three nucleotides
• C. Four nucleotides
• D. All of the above

Explanation: The genetic code is a combination of nucleotide triplets called codons, which are sequences of three adjacent nucleotides along the mRNA molecule. Each codon encodes a specific amino acid or a start or stop signal, forming the basis of the genetic instructions for protein synthesis.