All Free Biology MCQs with Answers

• A. Promoter
• B. Initiation complex
• C. Aminoacyl-tRNA
• D. Polysome

Explanation: In prokaryotes, polypeptide synthesis begins with the formation of the initiation complex. The initiation of polypeptide synthesis (translation) in prokaryotes involves the assembly of various components, including the small ribosomal subunit, mRNA, the initiation codon on the mRNA, and the initiator tRNA with the attached fMet (formylmethionine) amino acid. This complex forms the initiation complex, which is the starting point for protein synthesis in prokaryotes.

• A. Polymerase
• B. Elongation factor
• C. Initiation factor
• D. Release factor

Explanation: The translocation of ribosomes on mRNA during translation occurs due to elongation factors, not initiation factors, release factors, or polymerase. Elongation factors play a key role in moving the ribosome along the mRNA molecule in a 5' to 3' direction, allowing the ribosome to read the mRNA codons and facilitate the step-by-step addition of amino acids to the growing polypeptide chain during translation. The main elongation factor involved in this process in prokaryotes is known as EF-G (Elongation Factor G), which helps move the ribosome down the mRNA, facilitating the translation of the mRNA sequence.

• A. Condensation
• B. Polymerisation
• C. Replication
• D. Transcription

Explanation: DNA replication is the process by which a ds-DNA molecule is copied to produce two daughter DNA molecules. Transcription is the process by which the information in a strand of DNA is copied into a new molecule of mRNA. Both of these processes involve dehydration, condensation, and polymerisation of nucleotides. The process that does not occur during the formation of mRNA is replication. Replication is the process of making an exact copy of DNA, which is a separate process from transcription. During transcription, a complementary RNA molecule is synthesised based on a DNA template.

• A. Restriction endonuclease
• B. Primase
• C. DNA helicase
• D. DNA Ligase

Explanation: The enzyme that attaches the Okazaki fragments in the lagging strand during DNA replication is called DNA ligase. DNA ligase is responsible for sealing the nicks or gaps between the Okazaki fragments by catalysing the formation of phosphodiester bonds between adjacent nucleotides. This process results in a continuous and complete lagging strand.

• A. One place only without any specific sequence of DNA
• B. One or more places without any specific sequence of DNA
• C. Any place with the uncoiling of two strands of DNA
• D. One or more places where there is a specific sequence of nucleotides

Explanation: The process of DNA replication begins at one or more places where there is a specific sequence of nucleotides. These specific sequences where DNA replication initiates are known as the origins of replication. The DNA molecule is unwound, and the replication machinery assembles at these specific sites, allowing for the controlled and accurate duplication of the DNA. The presence of origins of replication ensures that DNA replication occurs at the right place and at the right time in the cell cycle. The exact locations of origins of replication vary between organisms, and the specific DNA sequence recognised at these origins can differ, but they are always specific and serve as starting points for DNA replication.

• A. DNA polymerase
• B. RNA polymerase
• C. DNA ligase
• D. Helicase

Explanation: The formation of a new strand of DNA from a template strand is the function of DNA polymerase. DNA polymerase is the enzyme responsible for synthesising the complementary strand of DNA during DNA replication. It adds nucleotides to the growing DNA strand, following the base-pairing rules (A with T and G with C), using the template strand as a guide.

• A. Conservative idea
• B. Dispersive idea
• C. Disruptive idea
• D. Semi-conservative idea

Explanation: The above context is about the dispersive model of DNA replication. In the dispersive model, it was proposed that parental DNA strands would become completely dispersed, and each strand of all the daughter molecules would be a mixture of old and new DNA.

• A. 50% hybrid duplex and 50% light duplex
• B. 60% hybrid duplex and 40% heavy duplex
• C. 100% heavy duplex
• D. 100% hybrid duplex

Explanation: When Meselson and Stahl conducted their famous experiment, they used bacteria grown in a heavy isotope of nitrogen (N-15) medium, and then they transferred these bacteria to a medium containing the lighter isotope of nitrogen (N-14) for replication. They were investigating the mode of DNA replication, specifically whether it followed a conservative or semi-conservative mechanism. The outcome of the experiment showed that after one round of replication, the DNA consisted of hybrid duplexes, with one strand being the original heavy strand (N-15) and one strand being the newly synthesised light strand (N-14). This result supported the semi-conservative model of DNA replication. After another round of replication, you would expect to see a mixture of DNA molecules. The result would be 50% hybrid duplex (one old heavy strand and one new light strand) and 50% light duplex (both strands containing the lighter isotope, N-14). The heavy duplex (both strands containing the heavier isotope, N-15) would not be present because the bacteria were no longer being cultured in the N-15 medium.

• A. 331
• B. 993
• C. 93
• D. 330

Explanation: To determine the number of amino acids in the polypeptide chain encoded by the mRNA sequence, divide the total number of nucleotides by 3 because each codon consists of 3 nucleotides. The mRNA sequence contains 993 nucleotides, which equate to 331 codons. However, among these, one is a stop codon that does not code for an amino acid, leaving 330 codons that do. Hence, 330 amino acids would be incorporated into the polypeptide chain. The incorrect options arise from either misunderstanding the role of the stop codon or miscalculating the division by 3.

• A. Telocentric
• B. Sub-metacentric
• C. Metacentric
• D. Acrocentric

Explanation: Chromosomes are classified according to the position of the centromere. If the centromere is present somewhere in between, but not exactly in the middle, of the chromosome, it is called a sub-metacentric chromosome. Chromosomes having centromere exactly in the middle are called metacentric. Acrocentric chromosomes have a centromere located very near their end. They appear as rod-shaped or "i" shaped chromosomes. The telocentric chromosomes have a centromere located at the end of the chromosome.