about genome of mitochondria, dharacteristics, differences between nuclear and mitochondrial dna.

1. MITOCHONDRIAL DNA
MUZAFFAR KHAN ALAM KHAN MD.,
GROUP-3 STUDENT OF TSMU

2. OBJECTIVES:
 WHAT IS MITOCHONDRIAL GENOME?
 CHARACTERISTICS.
 NUCLEAR DNA VS MITOCHONDRIAL DNA.
 MATERNAL INHERITANCE
 INTERACTIONS BETWEEN MITOCHONDRIAL AND
NUCLEAR GENOMES
 MUTATIONS IN MTDNA AND DISEASE
 MITOCHONDRIAL GENETIC BOTTLENECK

3. MITOCHONDRIAL GENOME:
 This genome consists of a circular chromosome,16.5kb in size that is located inside
the mitochondrial organelle,not in the nucleus.
 Most cells contain at least 1000 mtDNA molecules distributed among hundreds of
individual mitochondria.
 Not all the RNA and protein synthesized in a cell are encoded in the DNA of the
nucleus.
 It contains 37 genes, and encodes 2 types of rRNA and 22 tRNAs
 Genes encode 13 proteins that are subunits of enzymes of oxidative
phosphorylation
 The remaining 74 polypeptides of the oxidative phosphorylation complex are
encoded by the nuclear genome.

4. NUCLEAR DNA VS MITOCHONDRIAL DNA
0%
20%
40%
60%
80%
100%
1%
99%
DNA

5.  Nuclear DNA
 found in nucleus of the cell
 2 sets of 23 chromosomes
 maternal and paternal
 can "discriminate between
individuals of the same
maternal lineage“
 double helix
 bounded by a nuclear
envelope
 DNA packed into chromatin
 Mitochondrial DNA
 found in mitochondria of the cell
 each mitochondria may have
several copies of the single
mtDNA molecule
 maternal only
 cannot "discriminate between
individuals of the same maternal
lineage“
 Circular
 free of a nuclear envelope
 DNA is not packed into chromatin
Nuclear DNA vs. Mitochondrial DNA

6. CHARACTERISTICS
 Is inherited exclusively from the mother!
mtDNA is a circular shape single chromosome
 It is only 16 kb in length - contains 16,600 bp
 Codes for 37 genes
 Contains 22 tRNA and 2 rRNA coding genes
 Encodes 13 proteins that are subunits of oxidative phosphorilation
 Contains only exons, no introns
 Has no reparation system – high mutation rate especially in D-loop!
 No crossing over
 Replicative segregation, homoplasmy & heteroplasmy

7. Myoclonic epilepsy with ragged-red fibers
 More than 100 different rearrangements and 100 different point
mutations have been identified in mtDNA that can cause human
disease,often involving the CNS and musculoskeletal system
 The diseases that result from these mutations show distinctive pattern
of inheritance because of 3 unusual features of mitochondria.
1.Replicative Segregation
2.Homoplasmy and Heteroplasmy
3.Maternal Inheritance

8. Replicative segregation
 At cell division, multiple copies of mtDNA in each of
the mitochondria in a cell replicate and sort randomly
among newly synthesized mitochondria.
 The mitochondria in turn are distributed randomly
between the 2 daughter cells. This is called as
replicative segregation.
 The first unique feature of mitochondria is the
absence of tightly controlled segregation seen during
mitosis and meiosis of the 46 nuclear chromosomes.

9. Homoplasmy and Heterolasmy
 One daughter cell may by chance receive mitochondria that contain only a
pure population of normal mtDNA or a pure population of mutant
mtDNA(Homoplasmy)
 The daughter cell may receive a mixture of mitochondria some with and
some without mutation(Heteroplasmy)

11. Maternal Inheritance of mtDNA
 Sperm mitochondria are generally eliminated from the
embryo so that mtDNA is inherited from the mother.
 All children of a female who is homoplasmic for a
mtDNA mutation will inherit the mutation
 None of the offspring of a male carrying the same
mutation will inherit the defective DNA
 Maternal inheritance of a homoplasmic mtDNA
mutation causing Leber Hereditary optic neuropathy is
known.

12. Features of Maternal Inheritance
 1.Number of mtDNA molecules within the developing
oocyte is reduced before being amplified to the huge
total seen in mature oocytes.This restriction and
subsequent amplification of mtDNA during oogenesis is
termed Mitochondrial genetic Bottleneck.
 2.Variablity in the percentage of mutant mtDNA
molecules seen in the offspring of a mother with
heteroplasmy for a mtDNA mutation arises from the
sampling of only a subset of mtDNAs during oogenesis.

13.  Both the nuclear and mitochondrial genomes produce
polypeptides of oxidative phosphorylation, thus the
phenotypes associated with mutations in the nuclear
genes are often indistinguishable from those due to
mtDNA mutations
 The nuclear genome encodes approximately 200 factors
required for the maintenance and expression of mtDNA
or for the assembly of proteins, involved in oxidative
phosphorylation
Interactions between mitochondrial and nuclear
genomes

14.  This is why often mtDNA is referred to as the “slave”
of the nuclear DNA, because mtDNA depends on many
nuclear genome-encoded proteins for its replication and
the maintenance of its integrity.
 Thus, diseases of oxidative phosphorylation arise not
only from mutations in the mitochondrial genome but also
from mutations in nuclear genes that encode oxidative
phosphorylation components.
 Mutations in many of these nuclear genes can lead to
disorders with phenotype similar to that of the mtDNA
diseases.

15.  The mitochondrial genome has a very high mutation rate, 10- to
17-fold higher than that observed in nuclear DNA. Although
mtDNA repair systems do exist and , they are not sufficient to
counteract the oxidative damage sustained by the mitochondrial
genome.
 Protective histones are also lacking.
 Oxygenation process is high percentage.
 The mtDNA mutation rate can be increased by environmental
agents or by mutation of nuclear genes involved in mtDNA
maintenance
Why is mitochondrial mutation so high?

16.  About 1 in 4,000 children in the US develop mitochondrial disease by the
age of 10 years
 mtDNA genome mutates 10 times more frequently than does nuclear DNA
 More than 100 different rearrangements and about 100 different point
mutations that are disease-causing have been identified in mtDNA.
 The clinical phenotype resulting from mtDNA mutations is diverse, however
the diseases of central-nervous or muscular-skeletal systems are most
common.
 Pleiotropy and variable expressivity is common in different affected family
members (due to heteroplasmy).
 Pleiotropy – multiple phenotipic effects of a single allele or pair of alleles.
Mutations in mtDNA and disease

17.  It has been identified in mtDNA:
 (1) missense mutations in the coding regions of genes that
alter the activity of an oxidative phosphorylation protein;
 (2) point mutations in tRNA or rRNA genes that impair
mitochondrial protein synthesis;
 (3) Deletions or duplications of the mtDNA molecule. They
are generally somatic in origin, although a small proportion is
inherited, in some diseases.
THREE TYPES OF MUTATIONS

18.  All the children of a female who is homoplasmic for a
mtDNA mutation will inherit the mutation, whereas
none of the offspring of a male carrying the same
mutation will inherit the defective DNA.
Mitochondrial Genetic Bottleneck

19.  The number of mtDNA molecules within developing oocytes is reduced before
being subsequently amplified to the huge total seen in mature oocytes.
 This restriction and subsequent amplification of mtDNA during oogenesis is
termed the mitochondrial genetic bottleneck.
 Thus, mothers with a high proportion of mutant mtDNA molecules are more
likely to produce eggs with a higher proportion of mutant mtDNA and
therefore are more likely to have clinically affected offspring than are
mothers with a lower proportion.
 Also, for reasons unknown, deleted mtDNA molecules are generally not
transmitted from clinically affected mothers to their children.

20.  MERRF (Myoclonic Epilepsy with Ragged Red Fibres)
 MELAS (Myopathy, Epilepsy, Lactic acidosis, Stroke-
like episodes)
 LHON (Leber’s Hereditary Optic atrophy)
 Kearn-Sayre (eye problems, heart block, ataxia and
loss of coordination)
 Leigh syndrome (rare severe brain disease in infancy,
also heart problems)
Some diseases associated with mtDNA

21. References
 Ibrahim Okumus and Y. Çiftci / Turk. Turkish Journal of Fisheries and Aquatic Sciences 3: 51-
79 (2003)
 ARIAGNA LARA,* JOSE´ LUIS PONCE DE, Molecular Ecology Resources (2010) 10,
421–430
 Vallone, P.M., Just, R.S., Coble, M.D., Butler, J.M., Parsons, T.J. (2004) A multiplex allele-
specific primer extension assay for forensically informative SNPs distributed throughout the
mitochondrial genome. Int. J. Legal Med., 118: 147-157. [Protocol for 11plex SNP assay
developed at NIST] [Genotyper macro for mtSNP 11plex]
 Coble, M.D., Just, R.S., O'Callaghan, J.E., Letmanyi, I.H., Peterson, C.T., Irwin, J.A.,
Parsons, T.J. (2004) Single nucleotide polymorphisms over the entire mtDNA genome that
increase the power of forensic testing in Caucasians. Int. J. Legal Med., 118: 137-146.
 Coble, M.D. (2004) The identification of single nucleotide polymorphisms in the entire
mitochondrial genome to increase the forensic discrimination of common HV1/HV2 types in
the Caucasian population. PhD dissertation, George Washington University, 206 pp.
 www.google.co.in/mtdna/wikipedia/in