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Home »  Biology »  Genetics

Genetics of Mitochondria and Chloroplasts

Topic Review on "Title":

Mitochondrial DNA
Mitochondria have their own DNA molecules, usually multiple copies in one mitochondrion, in circular form, located in several nucleoid regions, with no histone association (naked).  Mitochondrial genome size varies, plants have mitochondrial average 150 -200 kb, but human mitochondria genome is only 16 kb.  It encodes enzymes required for oxidative phosphorylation and mitochondrial electron transfer.  A cell can have different types of mitochondria (heteroplasmy) or same type of mitochondria (homoplasmy).

Mitochondrial DNA replication
Mitochodnrial DNA has H (heavy) strand which is GC-rich and light (L) strand which is AT-rich.  A region of 1121 bp containing the replication origin is called D-loop, which is also the transcriptional start point for both H and L strand.  Mitochondrial gene transcrips are polycistrons, RNA are processed after transcription.  Translation is more similar to prokaryotes, with some unusual codon usage (non-universal).

Chloroplast DNA
Like mitochondria, chloroplast also contain circular double stranded DNA molecules.  They too do not associate with histones.  Chloroplast genome contain two inverted repeats called IRA and IRB, therefore many genes encoded by chloroplast genome have two copies.  Both transcription and translation procedure is similar to prokaryotes.

RNA editing
This is a feature unique to mitochondria and chloroplasts.  RNA editing means post-transcriptional modification of the primary sequence of RNA through nucleotide deletion, insertion, or base modification.

Origin of mitochondria and chloroplast –endosymbiont hypothesis
Mitochondria and chloroplast were free-living prokaryotes.  These organisms invaded primitive eukaryotes and established symbiotic relationship.  The evidence aree listed below: MtDNA and cpDNA are cicular, similar to bacteria, they have similar ribosomes with bacteria; they are similar in size; and they all have similar double membranes.

Extranuclear Inheritance
Both mitochondria and chloroplast genes are located in cytoplasm, therefore they are extranuclear genetic materials. They have distinct inheritance pattern as compared to Mendelian inheritance.  Usually they show maternal effect: the offsprings inherit the trait from their mother.   

Mutations in mitochondria
Mutation types include point mutations, deletion and duplication, or quantitatively loss of entire molecules. Mutation in mtDNA is a cause of aging and many other disorders.


Rapid Study Kit for "Title":
Flash Movie Flash Game Flash Card
Core Concept Tutorial Problem Solving Drill Review Cheat Sheet

"Title" Tutorial Summary :

Both mitochodnria and chloroplasts have their own genetic material, which are circular double stranded DNA.  They exist in nucleoid regions within the organelles, usually multiple copies, encode rRNA and some proteins for the organelle function.  For both organelles, the transcription and translation pattern are similar to prokaryotes, therefore it is hypothesized that these organelles have a symbiont origin. 


Tutorial Features:
  • Internal concept map to depict the relationship among
  • Diagrams describing mitochondrial and chloroplastic DNA
  • Electronic microscopic picture showing mtDNA
  • Color picture to describe extranuclear inheritance rules

"Title" Topic List:

Overview of mitochondrial genome

  • DNA structure
  • Gene
  • Heteroplasmy and homoplasmy
  • D-loop, H and L strand

Mitochondrial DNA replication, transcription and translation

  • DNA replication
  • Gene organization
  • Transcription
  • Translation

Chloroplast genome

  • Chloroplast DNA
  • Genome organization
  • Transcription and translation

For both mtDNA and ctDNA

  • RNA editing
  • Origin: symbiont hypothesis

Extranuclear inheritance

  • Rules
  • Example of leaf variegation
  • Poky mutant
  • Maternal effect
  • Nuclear-encoded maternal effect

Mitochondrial DNA mutation

  • Types of mutation
  • Consequence of mutation

See all 24 lessons in Genetics, including concept tutorials, problem drills and cheat sheets:
Teach Yourself Genetics Visually in 24 Hours

Home »  Biology »  Genetics
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