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Cells A Comparison of Eukaryotes and Prokaryotes What is a Prokaryote Cell? • Most prokaryote cells are small, very small (less than 5 micrometers), with a simple internal stucture. • They are surrounded by a simple membrane to protect the bacterial cell • This is the point of attack for antibiotics (they affect cell wall synthesis) A Prokaryotic Cell • Some bacteria can move, propelled by flagella (different from those in Eukaryotes) • Surface projections called pili (pilus sing.) are used to attach bacteria to surfaces or for genetic exchange. A Prokaryotic Cell • Capsules or slime layers are polysaccharide or protein coatings that some diseasecausing bacteria secrete outside their cell wall helping cells attach to their host. A Prokaryotic Cell • Studies have been done with mutants lacking this coating or shell and they seem to have no harmful effects without it. • Unlike the elaborate cytoplasm of Eukaryote cells Prokaryote cytoplasm is generally very simple. A Prokaryotic Cell • Prokaryote cells generally have a single circular strand of DNA which is coiled and attache to the plasma membrane and concentrated in the region of the cell called the nucleoid. A Prokaryotic Cell • The nucleoid is not however physically separated from the cytoplasm. • This is a key difference, prokaryotic cells lack nulei as well as the other membrane-enclosed organelles that eukaryotic cells posses. • Though this is not a strict rule, some photosynthetic bacterial cells posses membrane bound lightcapturing proteins and enzymes. A Prokaryotic Cell • One of the last structure to be mentioned about prokaryotic cells is the existence of ribosomes. • These are structures composed of proteins and ribonucleic acid (RNA) on which proteins are synthesis occurs A Prokaryotic Cell • Finally there may be the existence of food granules that store engery-rich materials such as glycogen. Comparison of Prokaryote and Eukaryote