- Which of the following correctly explains the difference between euchromatin and heterochromatin?
a) Euchromatin is transcriptionally active, while heterochromatin is transcriptionally inactive
b) Euchromatin consists of repetitive DNA, while heterochromatin consists of coding DNA
c) Heterochromatin is found in the nucleus, while euchromatin is in the cytoplasm
d) Euchromatin contains tightly packed DNA, while heterochromatin is loosely packed
Answer: a) Euchromatin is transcriptionally active, while heterochromatin is transcriptionally inactive
Explanation: Euchromatin is a less condensed form of chromatin that is accessible for transcription, making it transcriptionally active. Heterochromatin, on the other hand, is more tightly packed and transcriptionally inactive.
- Which of the following statements about the genetic code is false?
a) The genetic code is degenerate, meaning multiple codons can code for the same amino acid
b) The genetic code is nearly universal among all organisms
c) A single codon can code for multiple amino acids
d) The genetic code includes start and stop codons to signal the beginning and end of translation
Answer: c) A single codon can code for multiple amino acids
Explanation: A single codon cannot code for multiple amino acids. Each codon specifies only one amino acid, but multiple codons can code for the same amino acid, which is known as the degeneracy of the genetic code.
- Which of the following processes does not contribute to genetic variation?
a) Crossing over during meiosis
b) Independent assortment of chromosomes
c) Mitosis
d) Mutation
Answer: c) Mitosis
Explanation: Mitosis is a process of cell division that produces genetically identical daughter cells, so it does not contribute to genetic variation. Genetic variation is generated by processes like mutation, crossing over, and independent assortment during meiosis.
- Which of the following statements best describes an inducible operon?
a) It is always active unless repressed by a repressor protein
b) It is turned on by the presence of a specific substance
c) It is turned off by the presence of a specific substrate
d) It regulates genes responsible for amino acid synthesis
Answer: b) It is turned on by the presence of a specific substance
Explanation: An inducible operon, such as the lac operon, is normally inactive but becomes activated in the presence of a specific inducer, such as lactose, which binds to the repressor and allows transcription of the operon.
- Which of the following statements is true regarding RNA interference (RNAi)?
a) RNAi leads to the degradation of mRNA, preventing translation
b) RNAi enhances the translation of specific mRNAs
c) RNAi increases the stability of mRNA
d) RNAi promotes DNA replication in eukaryotes
Answer: a) RNAi leads to the degradation of mRNA, preventing translation
Explanation: RNA interference (RNAi) is a biological process in which small RNA molecules, such as siRNA or miRNA, bind to complementary mRNA and trigger its degradation, thus preventing translation and gene expression.
- In prokaryotes, which of the following proteins binds to the promoter region to initiate transcription?
a) RNA polymerase
b) Sigma factor
c) DNA polymerase
d) Helicase
Answer: b) Sigma factor
Explanation: In prokaryotes, the sigma factor is a subunit of RNA polymerase that recognizes and binds to the promoter region of a gene to initiate transcription. Once transcription begins, the sigma factor is released.
- Which of the following is true about histones?
a) Histones are proteins that help in the packaging of DNA into chromatin
b) Histones bind to RNA to stabilize its structure
c) Histones are enzymes that synthesize DNA during replication
d) Histones are non-protein coding regions of DNA
Answer: a) Histones are proteins that help in the packaging of DNA into chromatin
Explanation: Histones are positively charged proteins that package negatively charged DNA into nucleosomes, forming chromatin. This packaging allows DNA to be efficiently organized and condensed within the nucleus.
- The A site, P site, and E site are part of which of the following structures?
a) RNA polymerase
b) Ribosome
c) Spliceosome
d) DNA polymerase
Answer: b) Ribosome
Explanation: The A site (aminoacyl site), P site (peptidyl site), and E site (exit site) are the three key functional sites on a ribosome involved in the translation of mRNA into protein. These sites facilitate the binding of tRNA and the addition of amino acids to the growing polypeptide chain.
- What is the function of the TATA box in eukaryotic transcription?
a) It is a start codon in mRNA
b) It is a promoter sequence that helps RNA polymerase bind to the DNA
c) It is a region where translation terminates
d) It is a sequence that signals the addition of a poly-A tail
Answer: b) It is a promoter sequence that helps RNA polymerase bind to the DNA
Explanation: The TATA box is a conserved DNA sequence found in the promoter region of many eukaryotic genes. It helps RNA polymerase bind to the promoter, initiating the process of transcription.
- Which of the following is an outcome of DNA methylation?
a) Increased gene expression
b) Decreased gene expression
c) Increased rate of DNA replication
d) Promotion of mRNA stability
Answer: b) Decreased gene expression
Explanation: DNA methylation typically results in the repression of gene expression. When methyl groups are added to cytosine residues in DNA, it can prevent transcription factors from binding, leading to decreased transcriptional activity.
- The initiation codon for protein synthesis in both prokaryotes and eukaryotes is:
a) UAA
b) UAG
c) AUG
d) UGA
Answer: c) AUG
Explanation: AUG is the initiation codon that signals the start of translation and codes for the amino acid methionine in eukaryotes and formylmethionine in prokaryotes. It sets the reading frame for protein synthesis.
- Which of the following molecules is involved in post-transcriptional gene silencing?
a) miRNA
b) rRNA
c) tRNA
d) mRNA
Answer: a) miRNA
Explanation: MicroRNA (miRNA) is involved in post-transcriptional gene silencing by binding to complementary mRNA sequences, either degrading the mRNA or preventing its translation into protein.
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