Chromosome Structure and DNA Sequence Organization

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Chapter 11

• Chromosome Structure and DNA Sequence
  Organization

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Viral and Bacterial Chromosomes

• Relatively simple DNA molecules
• less complex than eukaryotes
• Single nucleic acid molecule, no associated
  proteins like histones
• Little genetic information

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Viral Chromosomes

• Either DNA or RNA
• Single or double stranded
• Usually contained in a protein head structure
• Circular dsDNA in bacteriophage ?

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Phage T2

• DNA and viral protein
• Most of the space in the head is occupied by
  nucleic acid
• Nucleic acids of viruses are functionally inert
  until introduced back into a host cell

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Bacterial DNA

• ds DNA packed into a nucleoid region
• Relatively simple and doesnt take up the whole
  cell
• Several DNA binding proteins involved HU and H1
• positively charged AA bind to the negatively
  charged DNA
• similar to histones but do not function in
  packaging
• DNA is active and transcribed and replicated

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Mitochondria and Chloroplasts

• DNA similar to bacteria and viruses, different
  than the nuclear DNA in the cell
• Have own DNA and genetic system to express the
  information
• remember can influence the phenotype and cause
  disease (Chapter 4)
• Arose from free-living prokaryotes that did
  aerobic respiration and photosynthesis
• endosymbiotic theory prokaryotes are engulfed
  by primitive large cell without bioenergetic
  functions, symbiotic relationship occurs and
  eventually loose the ability to live independently

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mtDNA

• dsDNA, replicates semiconservatively, no
  chromosomal proteins
• Size of DNA varies on organism and copies
• Appear to have no introns or repetitive sequences
  
• Use several modification of genetic code
• Requires nuclear DNA gene products to replicate
  mtDNA

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Human mtDNA

• Contains 2 rRNA, 22 tRNA and numerous polypeptide
  genes for cellular respiration remainder comes
  from nuclear DNA
• Ribosomes are different from cytoplasmic ones,
  usually in S close to bacterial ribosomes
• Nuclear coded genes for DNA replication and
  transcription
• DNA/RNA pol, initiation/elongation factors,
  ribosomal proteins, aminoacyl tRNA synthetase
• distinct from cytoplasmic things
• pol is sensitive to antibiotics like bacteria

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Mitochondrial and Cellular Components
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cpDNA

• Autonomous genetic system DNA and complete
  protein synthesis apparatus jointly form
  chloroplast and nuclear DNA
• Much larger than mtDNA, similar in DNA in
  bacteria
• Circular dsDNA, semiconservative, free of
  associated proteins
• Many copies in the chloroplast
• Some gene products function during translation

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Higher Plant Chloroplasts

• 2 copies of genes encoding 5S, 16S and 23S rRNA,
  25 tRNA genes, number of ribosome proteins
  specific to cp-ribosomes
• ribosomes are part cp and nuclear gene products
• cpDNA has genes for photosynthesis process
  small subunit of ribulose-1-5-bisphosphate
  carboxylase by nuclear DNA and large subunit by
  cpDNA
• cpDNA has non-coding regions and duplications of
  sequences independent addition of chloroplasts
  and mitochondria