All Free Biology MCQs with Answers

• A. Transcription
• B. Replication
• C. Translation
• D. None

Explanation: Transcription is the process by which an RNA molecule is synthesized from a DNA template. During transcription, the enzyme RNA polymerase binds to a specific region of DNA called a promoter and unwinds the DNA double helix. Then, RNA polymerase reads the DNA sequence and synthesizes a complementary RNA molecule, following the rules of base pairing (A-U, G-C). This RNA molecule is called messenger RNA (mRNA) and serves as the template for protein synthesis during translation.

• A. Non-sense codon
• B. Stop codon
• C. Both (A) and (B)
• D. Promoters

Explanation: Non-sense codons, also known as stop codons, are specific sequences of three nucleotides (in DNA or mRNA) that signal the termination of protein synthesis during translation. When a ribosome encounters a non-sense codon (such as UAA), it does not correspond to any amino acid, but instead signals the end of the polypeptide chain being synthesized.

• A. None
• B. Ligases
• C. Nucleases and phosphatases
• D. Polymerases

Explanation: Nucleases are enzymes that degrade nucleic acids, while phosphatases remove phosphate groups from molecules. The caps and tails on mRNA protect it from nucleases and phosphatases by providing structural stability and preventing enzymatic degradation. This protection ensures that the mRNA remains intact for longer periods, allowing it to carry out its functions such as translation into proteins.

• A. Cancer
• B. Phenylketonuria
• C. Sickle cell anemia
• D. All

Explanation: In 1956, Vernon Ingram's discovery focused specifically on the molecular basis of sickle cell anemia. He found that a single amino acid substitution in the hemoglobin protein caused the characteristic sickling of red blood cells in individuals with the disease. This substitution involves the replacement of a glutamic acid residue with a valine residue at position 6 of the beta-globin chain. This discovery significantly advanced our understanding of the genetic basis of sickle cell disease.

• A. Antisense
• B. Sense
• C. Both (A) and (B)
• D. Coding

Explanation: This term refers to the non-coding DNA strand also called template strand that serves as the template for RNA synthesis during transcription. It is complementary to the RNA transcript and serves as the template for RNA polymerase to synthesize the RNA molecule.

• A. Point mutation
• B. Line mutation
• C. Stop mutation
• D. None

Explanation: This occurs when a single nucleotide base is changed, inserted, or deleted from a DNA or RNA sequence. It's called a "point" mutation because it affects only one point in the genetic sequence.

• A. Polymerase III
• B. Primase
• C. DNA ligase
• D. Synthatase

Explanation: Primase is an enzyme responsible for synthesizing RNA primers during DNA replication. It initiates the synthesis of a short RNA primer complementary to a template DNA strand. This RNA primer provides a starting point for DNA polymerase III to begin synthesizing the new DNA strand.

• A. Ionic bond
• B. Hydrophobic interaction
• C. Phosphodiester bond
• D. None

Explanation: The overall stability of DNA is primarily due to the phosphodiester bond. This bond forms between the phosphate group of one nucleotide and the sugar group of the adjacent nucleotide in the DNA strand, creating the backbone of the DNA molecule.

• A. P.A. Levene
• B. Watson and Crick
• C. F. Miescher
• D. Franklin

Explanation: Friedrich Miescher, a Swiss biologist, is credited with the first isolation of DNA in 1869. He discovered a substance he called "nuclein" in the nuclei of white blood cells, which we now know to be DNA. However, the significance of his discovery was not fully recognized until later.

• A. Lysine, serine
• B. Lysine, glutamine
• C. Arginine, lysine
• D. Arginine, proline

Explanation: Both arginine and lysine have positively charged side chains, making this option correct. Arginine contains a guanidinium group, and lysine contains an amino group.