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Given the millions of different phages in the environment, phage genomes come in a variety of forms and sizes. RNA phages such as MS2 have the smallest genomes, with only a few kilobases. However, some DNA phages such as T4 may have large genomes with hundreds of genes; the size and shape of the capsid varies along with the size of the genome. [72]
Phages can also impact abiotic factors via the encoding of exotoxins (a subset of which are capable of solubilizing the biological tissues of living animals). Phage ecosystem ecologists are primarily concerned with the phage impact on the global carbon cycle , especially within the context of a phenomenon known as the microbial loop .
Phages make up the majority of most viromes and are currently understood as being the most abundant organism. [5] Oftentimes scientists will look only at a phageome instead of a virome while conducting research. Variations due to many factors have also been explored such as diet, age, and geography.
Temperate phages (such as lambda phage) can reproduce using both the lytic and the lysogenic cycle. [4] How a phage decides which cycle to enter depends on a variety of factors. [5] For instance, if there are several other infecting phages (or if there is a high multiplicity), it is likely that the phage will use the lysogenic cycle.
Bacteria are classified by their shape. Bacteria have been on this planet for approximately 3.5 billion years, and are classified by their shape. [9] Bacterial genetics studies the mechanisms of their heritable information, their chromosomes, plasmids, transposons, and phages.
Superinfection exclusion, or protection against infection by multiple phages, can be conferred by prophage integration. [12] Additionally, phage-mediated recombination mechanisms may remodel the host chromosome and provide new ways for cells to regulate metabolism and gene expression, such as those involved in sporulation and competence.
Dating back to the 1940s and continuing today, T-even phages are considered the best studied model organisms. Model organisms are usually required to be simple with as few as five genes. Yet, T-even phages are in fact among the largest and highest complexity virus, in which these phage's genetic information is made up of around 300 genes.
The life cycle of lambda phages is controlled by cI and Cro proteins. The lambda phage will remain in the lysogenic state if cI proteins predominate, but will be transformed into the lytic cycle if cro proteins predominate. The cI dimer may bind to any of three operators, O R 1, O R 2, and O R 3, in the order O R 1 > O R 2 > O R 3.