All Free Biology MCQs with Answers

• A. E site
• B. P site
• C. A site
• D. C site

Explanation: In protein synthesis, the initiator tRNA molecule carrying chemically modified initial amino acid, methionine (known as N-formyl methionine) binds to a small ribosomal subunit at P-site (peptidyl site) where a peptide bond will form. This binding is controlled by an enzyme called initiation factors (IF1 and IF2).

• A. 5 - 2' direction
• B. 5'- 3' direction
• C. 3'- 5 direction
• D. 2 - 5 direction

Explanation: DNA polymerase can only make DNA in the 5' to 3' direction.

• A. tRNA synthetase
• B. Amino tRNA synthetase
• C. tRNA ligase
• D. Aminoacyl tRNA synthetase

Explanation: The enzyme associated with the binding of amino acids and RNA molecules is called "Aminoacyl tRNA synthetase".

• A. RNA polymerase
• B. DNA polymerase
• C. Primase
• D. Ligase

Explanation: The synthesis of a primer is necessary because DNA polymerases, can only attach new DNA nucleotides to an existing strand of nucleotides. The primer therefore serves to prime and lay a foundation for DNA synthesis.

• A. H1
• B. H2A
• C. H2B
• D. H3

Explanation: A nucleosome is the basic structural unit of DNA packaging in eukaryotes. The structure of a nucleosome consists of a segment of DNA wound around eight histone proteins. The nucleosome is the fundamental subunit of chromatin. Each nucleosome is composed of a little less than two turns of DNA wrapped around a set of eight proteins called histones, which are known as a histone octamer. Each histone octamer is composed of two copies each of the histone proteins H2A, H2B, H3, and H4.

• A. 5' to 3'
• B. 3' to 5'
• C. 3' end of the primer to 3' end of template strand
• D. 3' end of the template strand to the 3' end of the primer

Explanation: DNA polymerase is able to add nucleotides only in the 5′ to 3′ direction (a new DNA strand can be extended only in this direction). It also requires a free 3′-OH group to which it can add nucleotides by forming a phosphodiester bond between the 3′-OH end and the 5′ phosphate of the next nucleotide.

• A. Radioactive phage were found in the pellet
• B. Radioactive cells were found in the supernatant
• C. Radioactive sulfur was found inside the cell
• D. Radioactive phosphorus was found in the cell

Explanation: The experiments by Hershey and Chase helped confirm that DNA was the hereditary material as radioactive phosphorus was found in the cell.The Hershey-Chase experiments were not the first studies to oppose the prevailing theory in the early 1900s that genetic material was composed of proteins. In 1944, nearly a decade before Hershey and Chase's work, scientists published sound evidence that genes were made of DNA rather than protein so it was confirmed by presence of phosphorus.

• A. 12
• B. 24
• C. 36
• D. 48

Explanation: 12 mRna codons there are 36 nucleotides. As 3 nucleotide cob]combine to form one codon so 3 multiply by 12 gives 36.

• A. UGA
• B. UAU
• C. CAU
• D. GAU

Explanation: Stop codons are also called nonsense codons because they do not code for an amino acid and instead signal the end of protein synthesis. Thus, nonsense mutations occur when a premature nonsense or stop codon is introduced in the DNA sequence.Stop codons (UAA, UAG or UGA) are recognized by release factors which bind into the A-site and use an activated water molecule to hydrolyze the ester linkage between the completed polypeptide and tRNA.

• A. Somatic Mutation
• B. Hereditary mutation
• C. Germ line mutation
• D. De novo mutation

Explanation: De navo mutation is A genetic alteration that is present for the first time in one family member as a result of a variant (or mutation) in a germ cell (egg or sperm) of one of the parents, or a variant that arises in the fertilized egg itself during early embryogenesis.De novo gene birth is the process by which new genes evolve from DNA sequences that were ancestrally non-genic.