- Which of the following statements about telomeres is true?
a) Telomeres are found in prokaryotic chromosomes
b) Telomeres shorten with each round of DNA replication
c) Telomerase degrades telomeres to prevent cancer
d) Telomeres are synthesized during RNA splicing
Answer: b) Telomeres shorten with each round of DNA replication
Explanation: Telomeres are repetitive nucleotide sequences at the ends of eukaryotic chromosomes. They shorten with each round of DNA replication because DNA polymerase cannot fully replicate the ends of chromosomes. Telomerase helps restore telomere length in some cells.
- Which type of bond forms between nitrogenous bases in a DNA double helix?
a) Covalent bonds
b) Ionic bonds
c) Hydrogen bonds
d) Disulfide bonds
Answer: c) Hydrogen bonds
Explanation: Hydrogen bonds form between complementary nitrogenous bases in the DNA double helix. Adenine pairs with thymine via two hydrogen bonds, and cytosine pairs with guanine via three hydrogen bonds.
- Which of the following statements about the lac operon is false?
a) The lac operon is induced in the presence of lactose
b) The lac repressor binds to the operator when lactose is absent
c) The lac operon is an example of positive regulation
d) The genes of the lac operon are required for lactose metabolism
Answer: c) The lac operon is an example of positive regulation
Explanation: The lac operon is primarily regulated through negative regulation, where the lac repressor binds to the operator and prevents transcription in the absence of lactose. In the presence of lactose, the repressor is inactivated, allowing transcription.
- Which of the following is a feature of RNA but not DNA?
a) Double-stranded structure
b) Contains thymine instead of uracil
c) Ribose sugar in its backbone
d) Stable under alkaline conditions
Answer: c) Ribose sugar in its backbone
Explanation: RNA contains ribose sugar, while DNA contains deoxyribose sugar. Additionally, RNA contains uracil instead of thymine and is typically single-stranded. RNA is less stable than DNA under alkaline conditions.
- Which of the following processes does NOT occur in prokaryotes?
a) Transcription
b) Translation
c) RNA splicing
d) DNA replication
Answer: c) RNA splicing
Explanation: Prokaryotic genes do not contain introns, so RNA splicing does not occur in prokaryotes. RNA splicing is a feature of eukaryotic cells where introns are removed from pre-mRNA before translation.
- Which of the following mechanisms allows a single gene to encode multiple proteins?
a) DNA replication
b) Alternative splicing
c) RNA editing
d) RNA interference
Answer: b) Alternative splicing
Explanation: Alternative splicing allows a single gene to produce different mRNA transcripts by including or excluding certain exons, leading to the production of multiple proteins from the same gene.
- The process by which a bacterial cell takes up DNA from its surroundings and incorporates it into its own genome is called:
a) Conjugation
b) Transformation
c) Transduction
d) Transcription
Answer: b) Transformation
Explanation: Transformation is the process by which a bacterial cell takes up extracellular DNA and incorporates it into its genome. This can result in genetic changes. Conjugation and transduction are other mechanisms of genetic exchange in bacteria.
- Which of the following statements best describes the function of snRNPs (small nuclear ribonucleoproteins)?
a) They help in the degradation of mRNA
b) They assist in the assembly of ribosomes
c) They are involved in RNA splicing
d) They synthesize rRNA
Answer: c) They are involved in RNA splicing
Explanation: Small nuclear ribonucleoproteins (snRNPs) are part of the spliceosome, a complex responsible for removing introns from pre-mRNA during RNA splicing in eukaryotes.
- Which enzyme in prokaryotes is responsible for the synthesis of most of the new DNA during replication?
a) DNA polymerase I
b) DNA polymerase III
c) Primase
d) Ligase
Answer: b) DNA polymerase III
Explanation: DNA polymerase III is the main enzyme responsible for synthesizing new DNA strands during replication in prokaryotes. DNA polymerase I mainly functions in removing RNA primers and filling in the gaps with DNA.
- What is the consequence of a nonsense mutation?
a) It changes one amino acid in a protein
b) It introduces a stop codon, prematurely ending translation
c) It shifts the reading frame of the gene
d) It has no effect on the protein sequence
Answer: b) It introduces a stop codon, prematurely ending translation
Explanation: A nonsense mutation changes a codon to a stop codon, which leads to the premature termination of protein synthesis, often resulting in a truncated, nonfunctional protein.
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