Lecture 14: Uniparental inheritance of organelle DNA

I.Importance

-explain deviation from mendelian inheritance

-reveal evolutionary relationships among organisms

-interesting origin of important cellular organelles

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Uniparental inheritance- traits are inherited only from one parent (usually the mother)

II. History

Correns (1909)

chloroplasts and mitochondria are mostly inherited via mother (some exceptions)= uniparental inheritance

III. Brief introduction to mitochondria and chloroplast organelles

A.Mitochondria

Site of the Krebs Cycle and an Electron Transport Chain that carries out oxidative phosphorylation of ADP to ATP

Food into energy:

pyruvate and fatty acids (breakdown products of carbohydrates and fats) to produce high-energy

electron carriers- NADH and FADH₂ then transport of high energy electrons to ATP via Oxygen

B. Chloroplast

The light absorbing protiens capture energy from sun light and transfer solar energy to photonsynthetic electron transport chain

During light-trapping phase solar energy is used to boost electron in pigment molecules (chlorophyll) to

higher energy levels

Energized electrons are transferred to an electron

transport system converts water to oxygen and H⁺ and then forms NADPH and then ATP.

ATP is used to make sugars in stroma

IV. Genomes of Mitochondria and Chloroplasts

Both organelles have their own DNA

**maintenance and assembly of both require gene

products from both organelle and nuclear genomes

**some proteins have subunits encoded by organelle

and nuclear genomes

A. A.DNA of Mitochondria

found in nucleoids and each mt has a number of nucleoids

DNA is circular, proteins associated with making ATP tRNA and rRNA

variation in genetic code

B. The Chloroplast Genome

like genes of mt, the genes are closely packed, many more genes than mt

protein, tRNA and rRNA genes (same as found in eubacteria)

C. Origin and Evolution of Organelle Genomes

Genomes of both resemble bactieria (also morphologically similar to aerobic and living

photosynthetic bacteria)

Endosymbiont Theory:

Ancestors to Eukaryotes had mutualism with some bacteira

Evidence:

both organelles have their own DNA which replicates independently of nuclear gemome

do not have histones, inhibitors of translation work for bacteria and organelle genomes, but not nuclear

genome, genes are similar in sequence to bacteria

Gene transfer

some plant mtDNA carry large fragments of cpDNA suggests that DNA can be transferred between organelles

nonfunctional, intact or partial copies of organelle genes are found in Eukaryotic genomes

V. Use of mtDNA and cpDNA to reconstruct evolutionary history

mtDNA has higher mutation rate, thus good molecule to distinguish groups that are closely related

(like different ethnic groups)

neither genome is recombining, thus can infer maternal lineage through time

VI. Summary

Organellar DNA explains uniparental inheritance has an interesting evolutionary history due to endosymbiosis and can be used to infer evolutionary history

Terms and Concepts to know:

uniparental inheritance, chloroplast, mitochondria, aspects of the chloroplast and mitochondria genomes, origin of organelle genomes, use of organelle genomes to infer evolutionary relationships

Figs/Tables: fig 14.2, 14.3, T14.1, T14.2, Fig 14.5, Table 14.3, Table 14.4, Fig 14.7, 14.8 Fig on page 513, and first figure not in book