Biology

Molecular Genetics

917 Questions

Molecular genetics explores the mechanisms of genetic information transfer, including DNA replication, transcription, and translation. It is a core component of biology syllabi. These concepts frequently appear in general science sections of major competitive exams.

DNA replicationTranscription processTranslation processRNA typesCentral dogma

Molecular Genetics Questions

Multiple choice

Ribozymes consist of

  1. RNA and protein

  2. RNA and DNA

  3. only RNA

  4. RNA and a prosthetic group
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Ribozymes are RNA molecules that possess catalytic activity, functioning like enzymes but made entirely of RNA rather than protein. They were discovered in the 1980s and changed our understanding of biological catalysis. Some ribozymes can even cleave or ligate other RNA molecules.

Multiple choice

cDNA is known to be synthesised, or manufactured from an mRNA or messenger RNA template. Which of the following statements regarding the synthesis of complementary DNA (cDNA) is incorrect?

  1. It is likely that the ssDNA forms a hairpin loop at the 3' end.

  2. DNA polymerase is added along with deoxynucleotide triphosphates.

  3. A poly-T oligonucleotide primer is hybridised onto the poly-A tail of the mature mRNA template.

  4. The mixture of mature mRNA strands is extracted from the cell.

  5. A eukaryotic cell transcribes the DNA into RNA.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Reverse transcriptase is added along with deoxynucleotide triphosphates (A, T, G, C). This synthesises one complementary strand of DNA hybridised to the original mRNA strand.

Multiple choice

The mutation leading to the formation of a premature stop codon is

  1. Frameshift mutation

  2. Nonsense mutation

  3. Missense mutations

  4. Silent mutations

  5. Neutral mutation
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon or a nonsense codon in the transcribed mRNA, and possibly a truncated and often non functional protein product.

Multiple choice

Premature translation termination mediates triosephosphate isomerase mRNA degradation. Which one of the following types of mutations is most likely to lead to premature termination of translation?

  1. Exon skip

  2. Single base change in a promoter

  3. Deletion of an entire gene

  4. Deletion of three bases from DNA

  5. Insertion of a single base into DNA
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Insertion of one base will alter the reading frame and usually leads to a stop codon eventually.

Multiple choice

A spliceosome is a large and complex molecular machine found primarily within the splicing speckles of the cell nucleus of eukaryotic cells. Which one of the following types of RNA is included in the splicosome?

  1. snRNA

  2. miRNA

  3. tRNA

  4. siRNA

  5. rRNA
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The spliceosome is assembled from snRNAs and protein complexes. The spliceosome removes introns from a transcribed pre-mRNA, a kind of primary transcript. snRNA (small nuclear RNA) is a component of the splicosome.

Multiple choice

_____ is the centre of protein synthesis for bacteria.

  1. Centrosome

  2. Ribosome

  3. Nucleus

  4. Cell wall

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ribosomes are the centre of protein synthesis in bacteria (and all cells). They are the molecular machines that read messenger RNA (mRNA) and assemble amino acids into polypeptide chains according to the genetic code. Bacteria have 70S ribosomes.

Multiple choice

Which among the following statements is/are not correct?

  1. The start codon always codes for methionine in eukaryotes.
  2. The most common start codon is AUG.
  3. The anticodon is a sequence of three base pairs of the tRNA that is complementary to the matching three base pairs on the mRNA.
  4. The termination codon is a nucleotide triplet within tRNA that signals the termination of translation.

  1. Only 1

  2. Only 2

  3. 1 and 2

  4. 1, 2 and 3

  5. Only 4
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

This option is correct because the stop codon or termination codon is a nucleotide triplet within mRNA that signals a termination of translation.

Multiple choice

Translation of mRNA into a ribosome proceeds _______.

  1. from the 3' end to the 5' end

  2. from the 5' end to the 3' end

  3. from the middle to the 3' end and then from the middle to the 5' end

  4. from either the 5' or 3' end, depending on the enzymes present

  5. from the middle simultaneously toward the 3' and 5' ends
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ribosomes read mRNA in the 5' to 3' direction during translation. As the ribosome moves along the mRNA, it reads codons sequentially and adds amino acids to the growing polypeptide chain. The 3' to 5' option describes the template strand direction during DNA replication, not translation.

Multiple choice

The shift of mRNA by 3 nucleotides in order to bring another codon into position in the ribosome is called ______.

  1. translocation

  2. transformation

  3. packaging

  4. transcription

  5. transport
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Translocation is the process where the ribosome moves exactly 3 nucleotides (one codon) along the mRNA after peptide bond formation. This shifts the tRNAs: the deacylated tRNA moves to the E site, the peptidyl-tRNA moves to the P site, and a new codon enters the A site for decoding.