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Chapter 26 The Tree of Life: - page 13 / 18





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The proposed ancestors of plastids were photosynthetic prokaryotes.

The prokaryotic ancestors of mitochondria and plastids probably gained entry to the host cell as undigested prey or internal parasites.

The symbiosis became mutually beneficial.

A heterotrophic host could use nutrients released from photosynthesis.

An anaerobic host would have benefited from an aerobic endosymbiont.

As they became increasingly interdependent, the host and endosymbionts became a single organism.

All eukaryotes have mitochondria or their genetic remnants.

The theory of serial endosymbiosis supposes that mitochondria evolved before plastids.

Overwhelming evidence supports an endosymbiotic origin of plastids and mitochondria.

The inner membranes of both organelles have enzymes and transport systems that are homologous to those in the plasma membranes of modern prokaryotes.

Mitochondria and plastids replicate by a splitting process similar to prokaryotic binary fission.

Like prokaryotes, each organelle has a single, circular DNA molecule that is not associated with histone.

These organelles contain tRNAs, ribosomes, and other molecules needed to transcribe and translate their DNA into protein.

Ribosomes of mitochondria and plastids are similar to prokaryotic ribosomes in terms of size, nucleotide sequence, and sensitivity to antibiotics.

Which prokaryotic lineages gave rise to mitochondria and plastids?

Comparisons of small-subunit ribosomal RNA from mitochondria, plastids, and various living prokaryotes suggest that a group of bacteria called the alpha proteobacteria are the closest relatives to mitochondria and that cyanobacteria are the closest relatives to plastids.

Over time, genes have been transferred from mitochondria and plastids to the nucleus.

This process may have been accomplished by transposable elements.

Some mitochondrial and plastic proteins are encoded by the organelle’s DNA, while others are encoded by nuclear genes.

Some proteins are combinations of polypeptides encoded by genes in both locations.

Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 26-13

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