Following statements were made about mitochondria: A. The D loop of the mitochondrial genome is required for replication, but not for the regulation of transcription. B. The L strand of mitochondrial genome possesses more cytosine. C. In plants, most mitochondrial tRNAs are encoded by the nuclear genome and then imported into the mitochondrion. D. Cycloheximide inhibits protein synthesis by mitochondrial ribosomes, but does not affect eukaryotic cytosolic ribosomes. E. Some organisms have been found to carry linear mitochondrial DNA. Which one of the following options represents a combination of the correct statements?
B, C, E
Understanding Mitochondrial Statements
The question asks us to identify the correct statements among the given options regarding mitochondria and their components or functions. Let's analyze each statement.
Analyzing Statement A: D Loop Function
Statement A claims that the D loop of the mitochondrial genome is required for replication but not for the regulation of transcription. This statement is incorrect. The D loop region in mitochondrial DNA is crucial for initiating replication (specifically the synthesis of the H strand) and also plays a significant role in regulating the transcription of mitochondrial genes. It contains promoters for both the heavy (H) and light (L) strands.
Analyzing Statement B: L Strand Composition
Statement B states that the L strand of the mitochondrial genome possesses more cytosine. Mitochondrial DNA consists of a heavy strand (H strand) and a light strand (L strand). The H strand is rich in purines (Adenine and Guanine), making it denser. The L strand is complementary to the H strand and is consequently rich in pyrimidines (Cytosine and Thymine). Therefore, the L strand indeed has a higher proportion of cytosine compared to the H strand. This statement is correct.
Analyzing Statement C: Plant Mitochondrial tRNAs
Statement C says that in plants, most mitochondrial tRNAs are encoded by the nuclear genome and then imported into the mitochondrion. This is a well-established fact in plant mitochondrial biology. While animal and fungal mitochondria encode most of their tRNAs within their own genome, plant mitochondria have lost many tRNA genes and rely heavily on importing tRNAs that are transcribed from nuclear genes in the cytosol. This statement is correct.
Analyzing Statement D: Cycloheximide Effect
Statement D claims that Cycloheximide inhibits protein synthesis by mitochondrial ribosomes but does not affect eukaryotic cytosolic ribosomes. This statement is incorrect. Cycloheximide is a metabolic inhibitor used in molecular biology research that specifically inhibits protein synthesis on eukaryotic cytosolic ribosomes (80S type). Protein synthesis on mitochondrial and prokaryotic ribosomes (70S type) is typically inhibited by drugs like Chloramphenicol or Erythromycin. Therefore, Cycloheximide affects cytosolic ribosomes, not mitochondrial ones.
Analyzing Statement E: Linear Mitochondrial DNA
Statement E suggests that some organisms have been found to carry linear mitochondrial DNA. While the mitochondrial DNA of most vertebrates and many other organisms is circular, linear mitochondrial DNA exists in various eukaryotes, including some protists, algae, fungi (like Neurospora crassa and certain yeasts), and even in some metazoans. This statement is correct.
Identifying the Correct Combination
Based on the analysis:
- Statement A is incorrect.
- Statement B is correct.
- Statement C is correct.
- Statement D is incorrect.
- Statement E is correct.
The combination of correct statements is B, C, and E.
Let's check the options provided:
- Option 1: A, B, C (Incorrect, A is false)
- Option 2: B, D, E (Incorrect, D is false)
- Option 3: A, C, D (Incorrect, A and D are false)
- Option 4: B, C, E (Correct, B, C, and E are true)
Therefore, the correct option is the one containing statements B, C, and E.
Important Questions from Molecular Biology Techniques
Which one of the following does NOT use RNA-sequencing?
Which one of the following statements related to molecular cloning procedures is INCORRECT?
Amongst the following, which one is the most appropriate strategy to sequence and assemble highly repeated regions of a genome?
Given below are statements related to various molecular techniques
A. During molecular cloning of DNA fragments, a vector and insert molecule digested with two different enzymes can never be ligated with each other.
B. Only 3' → 5' exonucleases and not 5' → 3' exonucleases can be used for digesting nucleic acids to generate blunt-ended fragments for cloning.
C. In Sanger's dideoxy sequencing method, each reaction consists of a mixture of three dNTPs and one ddNTP.
D. Self-ligation of a vector with compatible ends can be prevented by treatment with alkaline phosphatase.
Which one of the following options represents a combination of correct statements?
Given below are four DNA sequences and a set of forward and reverse primers for PCR amplification.
In the absence of any other factors such as (but not restricted to) Tm, length, percent GC, etc., which one of the above template-primers combinations would produce an amplified fragment?Sequence Primes A 5' ACAATCGT.....ACTAGTAC-3' FP: 5'-TGTTAG-3'
RP: 5'-TAGTAC-3'B 5' AGTCTTAG.....ATGCCAGT - 3' FP: 5'-AAGACT-3'
RP: 5'-ACTGGC-3'C 5' CTTGACTA.....GTACAGTCA-3' FP: 5'-CTTGAC-3'
RP: 5'-TGACTG-3'D D 5' GATCTAGC.....TCAAGCAGAC-3' FP: 5'-GATCTA-3'
RP: 5'-CAGACG-3'
