chromosomes

Examples of chromosomes in the following topics:

• Chromosomes and DNA Replication in the Archaea

  • The cell division process is controlled by the cell cycle; the chromosomes within the Archaea are replicated to produce two daughter chromosomes.
  • Archaea typically have a single circular chromosome.
  • The two daughter chromosomes are then separated and the cell divides.
  • The circular chromosomes contain multiple origins of replication, using DNA polymerases that resemble eukaryotic enzymes.
  • The replication of DNA, beginning at the origins of replication present on the circular chromosomes, requires initiator proteins.

• Introduction to Plasmids

  • A plasmid is a small DNA molecule that is physically separate from, and can replicate independently of, chromosomal DNA within a cell.
  • In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of the chromosomal DNA.They are double-stranded and, in many cases, circular.
  • The upper half of the image shows a bacterium with its chromosomal DNA and plasmids dividing into two identical bacteria, each with their chromosomal DNA and plasmids.
  • The lower half of the image shows a bacterium with its chromosomal DNA, but with an episome.
  • Next to this bacterium, we see the same bacterium, but after the episome has integrated into the chromosomal DNA and has become a part of it.

• Bacterial Transduction

  • If the lysogenic cycle is adopted, the phage chromosome is integrated (by covalent bonds) into the bacterial chromosome, where it can remain dormant for thousands of generations.
  • At the same time, some phage genes are left behind in the bacterial chromosome.
  • If by chance bacterial chromosomal DNA is inserted into the viral capsid which is usually used to encapsulate the viral DNA, the mistake will lead to generalized transduction.
  • The genes that get transferred (donor genes) depend on where the phage genome is located on the chromosome.
  • Specialized transduction occurs when the prophage excises imprecisely from the chromosome so that bacterial genes lying adjacent to the prophage are included in the excised DNA.

• Bacterial Chromosomes in the Nucleoid

  • It is commonly referred to as a prokaryotic chromosome.
  • The term "chromosome" is misleading, because the genophore lacks chromatin.
  • The genophore is compacted through a mechanism known as supercoiling, but a chromosome is additionally compacted through the use of chromatin.
  • Genophores are generally of a much smaller size than Eukaryotic chromosomes.

• Bacteriophage Lambda as a Cloning Vector

  • However, under certain conditions, the phage DNA may integrate itself into the host cell chromosome in the lysogenic pathway.
  • The genes that get transferred (donor genes) depend on where the phage genome is located on the chromosome.
  • Specialized transduction occurs when the prophage excises imprecisely from the chromosome so that bacterial genes lying adjacent to the prophage are included in the excised DNA.
  • The excised DNA is then packaged into a new virus particle, which delivers the DNA to a new bacterium where the donor genes can be inserted into the recipient chromosome or remain in the cytoplasm, depending on the nature of the bacteriophage.
  • When the partially encapsulated phage material infects another cell and becomes a "prophage" (is covalently bonded into the infected cell's chromosome), the partially coded prophage DNA is called a "heterogenote. "

• Caulobacter Differentiation

  • Chromosome replication and cell division only occurs in the stalked cell stage.
  • An essential feature of the Caulobacter cell cycle is that the chromosome is replicated once and only once per cell cycle.
  • This is in contrast to the E. coli cell cycle where there can be overlapping rounds of chromosome replication simultaneously underway.
  • The opposing roles of the Caulobacter DnaA and CtrA proteins are essential to the tight control of Caulobacter chromosome replication.
  • The DnaA protein acts at the origin of replication to initiate the replication of the chromosome.

• Genetic Analysis

  • Bacterial chromosomes contain double stranded molecules of DNA arranged in a circular form called plasmids .
  • Bacteria possess extra chromosomal genetic elements that encode for antibiotic resistance, toxins, virulence determining genes, and reduced sensitivity to mutagens such as heavy metals.
  • PFGE is essential for estimating the sizes of whole genomes/chromosomes prior to sequencing and is necessary for preparing large DNA fragments for large insert DNA cloning and analysis of subsequent clones.

• The Cell Wall of Bacteria

  • The term "nucleoid" refers to the region of the cytoplasm where chromosomal DNA is located, usually a singular, circular chromosome.

• Annotating Genomes

  • The genome sequence of an organism includes the collective DNA sequences of each chromosome in the organism.
  • For a bacterium containing a single chromosome, a genome project will aim to map the sequence of that chromosome.

• Hosts for Cloning Vectors

  • If the DNA to be cloned is exceptionally large (hundreds of thousands to millions of base pairs), then a bacterial artificial chromosome or yeast artificial chromosome vector is often chosen.