Deck 20: Organelle DNA

Question 1

In most organisms, genes encoded by mtDNA and cpDNA are inherited from a single parent. A gamete may contain more than one distinct type of mtDNA or cpDNA; in these cases, random segregation of the organelle DNA may produce phenotypic variation within a single organism or it may produce different degrees of phenotypic expression among progeny.

-In a few organisms, traits encoded by mtDNA can be inherited from either parent. This observation indicates that, in these organisms,

A) mitochondria do not exhibit replicative segregation.
B) heteroplasmy is present.
C) both sperm and eggs contribute cytoplasm to the zygote.
D) there are multiple copies of mtDNA in each cell.

Answer 1

both sperm and eggs contribute cytoplasm to the zygote.

Question 2

Mitochondria and chloroplasts are membrane-bounded organelles of eukaryotic cells that generally possess their own DNA. The well-supported endosymbiotic theory proposes that these organelles began as free-living eubacteria that developed stable endosymbiotic relations with early eukaryotic cells.
-What evidence supports the endosymbiotic theory?

Answer 2

Many modern protists are host to endosymbiotic bacteria. Mitochondria and chloroplasts are similar in size to eubacteria and have their own DNA, as well as ribosomes that are similar in size and shape to eubacterial ribosomes. Antibiotics that inhibit protein synthesis in eubacteria also inhibit protein synthesis in mitochondria and chloroplasts. Gene sequences in mtDNA and cpDNA are most similar to eubacterial DNA sequences.

Question 3

The mitochondrial genome consists of circular DNA with no associated histone proteins, although it is complexed with other proteins that have some histonelike properties. The sizes and structures of mtDNA differ greatly among organisms. Human mtDNA exhibits extreme economy, but mtDNAs found in yeast and flowering plants contain many noncoding nucleotides and repetitive sequences. Mitochondrial DNA in most flowering plants is large and typically has one or more large direct repeats that can recombine to generate smaller or larger molecules.

-Which of the following characteristics applies to ancestral mitochondrial genomes?

A) Have genes with many introns
B) Contain more genes than derived genomes do
C) Possess much noncoding DNA between genes
D) Have nonuniversal codons

Answer 3

Contain more genes than derived genomes do

Question 4

The processes of replication, transcription, and translation vary widely among mitochondrial genomes and exhibit a curious mix of eubacterial, eukaryotic, and unique characteristics.

-Which of the following statements applies to mitochondrial translation?

A) Elongation factors are similar to those in eukaryotic translation.
B) There is no wobble.
C) Antibiotics that inhibit bacterial translation have no effect on mitochondrial translation.
D) The initiation codon specifies N-formylmethionine.

Question 5

Most chloroplast genomes consist of a single circular DNA molecule not complexed with histone proteins. Although there is considerable size variation among species, the cpDNAs found in most vascular plants are about 150,000 bp. Genes are scattered in the circular chloroplast genome, and many contain introns. Most cpDNAs contain a large inverted repeat.

-In its organization, chloroplast DNA is most similar to

A) eubacteria.
B) archaea.
C) nuclear DNA of plants.
D) nuclear DNA of primitive eukaryotes.

Question 6

Many aspects of the transcription and translation of cpDNA are similar to those of eubacteria. Chloroplast DNA sequences are most similar to DNA sequences in cyanobacteria, which supports the endosymbiotic theory. Most cpDNA evolves slowly in sequence and structure.

-Which characteristic does not apply to chloroplast DNA or mRNA?

A) Promoters are similar to eubacterial promoters.
B) Genes in cpDNA are transcribed in groups.
C) Many chloroplast mRNAs have Shine-Dalgarno sequences.
D) Poly(A) tails are added to chloroplast mRNAs