Tag: Mitochondrial DNA

Mitochondrial DNA

Mitochondrial DNA


Mitochondrial DNA (mtDNA)

  • It is a separate genome located in the cytoplasm of nearly all eukaryotic cells
  • Is closede circular, double-stranded, and composed of heavy (H) and light (L) chains or strands.
  • Contains 16,569 bp.
  • Encodes 13 protein subunits of the respiratory chain (of a total of about 67) –
  1. Seven subunits of NADH dehydrogenase (complex I) and Cytochrome b of complex III
  2. Three subunits of cytochrome oxidase (complex IV)
  3. Two subunits of ATP synthase
  • Encodes large (16S) and (12S) mt ribosomal RNAs
  • Encodes 22 mt tRNA molecules
  • Genetic code differs slightly from the standard code –
  1. UGA (standard stop codon) is read as Trp.
  2. AGP and AGG (standard codons for Arg) are read as stop codons,
  • Contains very few untranslated sequences.
  • Nemaline myopathy results due to mutations in mt- DNA
  • Heteroplasmy is the presence of mixture of more than one type of an organelle genome (mt- DNA) within a cell or individual.
  • High mutation rate (5 to 10 times that of nuclear DNA).
  • Comparisons of mtDNA sequences provide evidence about evolutionary origins of primates and other species.
  • High mutation rate occurs due to point mutation and large scale rearrangements.
  • mitochondrial DNA contains no (or very few) introns (i.e. untraslated sequences).

Mitochondrial DNA is always maternally inherited.

  1. Important mitochondrial diseases are mitochondrial encephalomyopathy with lactic aciilosis and stroke like episodes (MELAS),
  2. leber hereditary optic neuropathy, myoclonic epilepsy with ragged-red fibers, leigh syndrome, Pearson syndrome, kearns-sajre syndrome,
  3. chronic progressive external ophthalmoplegia and NARP (neurogenic weakness with ataxia & retinitis pigmentosa).
  • All children from affected mother will inherit the disease but it will not be transmitted from an afiected father to his children

Exam Important

  • Is closede circular, double-stranded, and composed of heavy (H) and light (L) chains or strands.
  • Contains 16,569 bp.
  • Encodes 13 protein subunits of the respiratory chain (of a total of about 67)
  • Nemaline myopathy results due to mutations in mt- DNA
  • Heteroplasmy is the presence of mixture of more than one type of an organelle genome (mt- DNA) within a cell or individual.
  • High mutation rate (5 to 10 times that of nuclear DNA).
  • Comparisons of mtDNA sequences provide evidence about evolutionary origins of primates and other species.
  • High mutation rate occurs due to point mutation and large scale rearrangements.
  • mitochondrial DNA contains no (or very few) introns (i.e. untraslated sequences).
  • Mitochondrial DNA is always maternally inherited.
  • All children from affected mother will inherit the disease but it will not be transmitted from an afiected father to his children
Don’t Forget to Solve all the previous Year Question asked on Mitochondrial DNA

Module Below Start Quiz

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

Mitochondrial genome is maternally transmitted

 D

Heteroplasmy is a feature of mtDNA

Q. 2

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

Cause Leber hereditary optic neuropathy

 A

mtDNA contains only 37 genes

 B
 C

Mitochondrial genome is maternally transmitted

 D

Heteroplasmy is a feature of mtDNA

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 a 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 has a maternally inherited mtDNA mutation.
 
Ref: Ethics of mitochondrial gene replacement: from bench to bedside, Annelien L Bredenoord ; BMJ 2010;341:c6021

Q. 3 True about mitochondrial DNA

 A

UGA codes for tryptophan

 B

Codes for 13 protein

 C

Circular double stranded DNA

 D

All

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:

A, B,C i.e. UGA codes for tryptophan, Codes for 13 protein, Circular double stranded DNA, Mitrochondrial disease occur due to Point Mutations and Large-Scale Rearrangements

Quiz In Between


Q. 4

Mitochondrial DNA is:

 A

Paternally inherited

 B

Maternally inherited

 C

Horizontal inheritance

 D

Vertical inheritance

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- DN(A) is known for all except –

 A

Maternal inheritance

 B

Heteroplasmy

 C

Leber hereditary optic neuropathy is the prototype

 D

Nemaline myopathy results due to mutations in mt- DNA

Q. 5

Mitochondrial DNA (mt- DN(A) is known for all 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 mitochondria] disorder.

o Mitochondrial DNA is always maternally inherited.

o Heteroplasmy is the presence of mixture of more than one type of an organelle genome (mt- DNA) within a cell or individual. It is a factor for the severity of 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 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

Q. 6

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.
The majority of the peptides in mitochondria (about 54 out of 67) are coded by nuclear genes.
The rest are coded by genes found in mitochondrial (mt) DNA
This mtDNA codes for mt ribosomal and transfer RNAs and for 13 proteins that play key roles in the respiratory chain.

Quiz In Between



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