expressed in groups rather than in separate genes. The groups are called “operons”. They are later divided into separate proteins. Prokaryotes also have a larger surface area to volume ratio. This means that they are more highly metabolically active when compared to eukaryotes. They divide faster and have a shorter generation time (which is the time from cell division to another cell division). Prokaryotes are “haploid”, meaning they have just one copy of the genes. On the contrary, eukaryotes are diploid, having two copies of a particular gene. They do not have histones, which are the proteins that condense the genetic material. They have their own condensing proteins and supercoil the circular piece of DNA in order to condense it. Transcription and translation into proteins happen at the same time in prokaryotes but not in eukaryotes.
PROKARYOTE STRUCTURE There are many different structures of bacteria. These are small cells—only about a tenth of the size of most eukaryotic cells, being less than 5 micrometers in length. The main shapes of bacteria include spherical, called “cocci” bacteria, rod-shaped, called bacilli, comma-shaped, called vibrio, and spiral-shaped, called spirochetes. There are very rarely other shapes, including star-shaped bacteria. The cell wall and the intracellular cytoskeleton determine what the shape of bacterial species is. The shape of the bacterial organism determines many things, including the mobility of the organism. While bacteria are essentially single-celled organisms, they often form multicellular shapes. Streptococcus bacteria form chains of varying lengths, while Neisseria species form pairs or diploid configurations. Staphylococcus species are rarely singular and come in bunches, looking like spherical bunches of grapes. Myxobacteria, Actinobacteria, and Streptomyces form aggregates, filaments, and hyphae, respectively. Figure 12 shows what different bacterial shapes look like:
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