Mitochondrial DNA

Mitochondrial DNA

Q. 1 Mitochondrial DNA is:

 A Closed circular

 B

Nicked circular

 C

Linear

 D

Open circular

Q. 1

Mitochondrial DNA is:

 A

Closed circular

 B

Nicked circular

 C

Linear

 D

Open circular

Ans. A

Explanation:

Mitochondrial DNA is a closed circular double helix molecule which is transmitted maternally and is found within cells in multiple copies.

It contains 37 genes. All of these genes are essential.

Ref: Ganong’s Review of Medical Physiology, 22nd Edition, Page 10

 


Q. 2

All of the following states are TRUE regarding mitochondrial DNA (mtDNA) disease, EXCEPT:

 A

mtDNA contains only 37 genes

 B

Cause Leber hereditary optic neuropathy

 C

The mitochondrial genome is maternally transmitted

 D

Mitochondrial disease occurs only with Heteroplasmy 

Ans. D

Explanation:

All human cells contain two genomes: one in the nucleus and one in the mitochondria. 

  • The mitochondrial genome contains only 37 genes
  • Genome is maternally transmitted. 

The ratio of genetically aberrant to normal mitochondria transmitted can vary during mitosis and through generations—a situation known as heteroplasmy. People with entirely faulty mitochondria (homoplasmy) or a large proportion of faulty mitochondria may develop the mtDNA disease. 

 

These are clinically heterogeneous but usually severe diseases resulting from defects in energy production and include deafness, blindness, diabetes, loss of skills, and heart and liver failure. About 1 in 400 people have a maternally inherited mtDNA mutation.

Heteroplasmy:

– Heteroplasmy is defined as the presence of normal and mutant DNA in different proportions in different cells

Mitochondrial disease with homoplasmy:

– Leber’s hereditary optic neuropathy

– Sensorineural deafness 


Q. 3

True about mitochondrial DNA-

 A

UGA codes for tryptophan

 B

Codes for 13 protein

 C

Circular double stranded DNA

 D

All

Ans. D

Explanation:

Major Features of Human Mitochondrial DNA

– It is circular double-stranded, composed of heavy and light strands.

– It encodes 13 protein subunits of the respiratory chain-

  • Seven sub-units of NADH dehydrogenase 
  • Cytochrome b of complex III
  • 3 subunits of cytochrome oxidase
  • 2 subunits of ATP synthase

– Encodes tRNA molecules and Ribosomal RNAs

– Genetic code is slightly different from the standard code-

  • UGA(stop codon) is read as Trp.
  • AGA and AGG (code for arginine) is read as the stop codon

– High mutation rate


Q. 4

Mitochondrial DNA is:

 A

Paternally inherited

 B

Maternally inherited

 C

Horizontal inheritance

 D

Vertical inheritance

Ans. B

Explanation:

B i.e. Maternally inherited


Q. 5

Mitochondrial DNA (mt- DNA) is known for all of the following except –

 A

Maternal inheritance

 B

Heteroplasmy

 C

Leber hereditary optic neuropathy is the prototype

 D

Nemaline myopathy results due to mutations in mt- DNA

Ans. D

Explanation:

Ans. is ‘d’ i.e., Nemaline myopathy results due to mutations in mt- DNA

o Nemaline myopathy is not a mitochondrial disorder.

it results from mutations in genes providing instructions for producing proteins that play important roles in skeletal muscles. Mutations in any of the genes associated with nemaline myopathy lead to disorganization of the proteins found in the sarcomeres of skeletal muscles. The disorganized proteins cannot interact normally, which disrupts muscle contraction. Inefficient muscle contraction leads to muscle weakness and the other features of nemaline myopathy.

o Mitochondrial DNA is always maternally inherited.

o Heteroplasmy is the presence of a mixture of more than one type of organelle genome (mt- DNA) within a cell or individual. It is a factor for the severity of the mitochondrial disease since every eukaryotic cell contains many hundreds of copies of mt- DNA; it is possible and indeed very frequent for mutations to affect only some of the copies, while the remaining ones are unaffected.


Q. 6 The function of mitochondrial DNA‑

 A

Encodes proteins of cell membrane

 B

Encodes proteins of respiratory chain

 C

Helps in cell replication

 D

Formation of rRNA

Ans. B

Explanation:

  • Human mitochondria contain two to ten copies of a small circular double-stranded DNA molecule that makes up approximately 1% of total cellular DNA.
  • Encodes 13 protein subunits of the respiratory chain.
  • Encodes large (16S) and small (12S) mt ribosomal RNAs.
  • High Mutation rate.
  • Encodes 22 mt tRNA molecules.


Leave a Reply

%d bloggers like this:
Malcare WordPress Security