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Piatok, 24. mája 2024
Prokaryotic and eukaryotic cells compared
Dátum pridania: 27.12.2001 Oznámkuj: 12345
Autor referátu: kris_d
 
Jazyk: Angličtina Počet slov: 693
Referát vhodný pre: Stredná odborná škola Počet A4: 2.4
Priemerná známka: 3.00 Rýchle čítanie: 4m 0s
Pomalé čítanie: 6m 0s
 

Lysosomes contain digestive enzymes and help recycle worn – out cell parts. Some materials produced in the cell are modified and packaged in the Golgi complex. Finally, there is another very interesting structure that prokaryotes lack - the endoplasmic reticulum - “network within the cell”. There are two main types of ER: smooth ER (SER, detoxifies poisonous chemicals and also manufactures lipids) and rough ER (RER, it is loaded with ribosomes and involved in protein synthesis). As a whole, ER modifies and transports pre – made materials. It is the continue of the nuclear envelope and has cavities and ribosomes used for proteosynthesis.
It may also depend on the type of the eukaryotic cell whether it will or will not have some particular organelles. Chloroplasts, a special type of plastids, have two lipid bilayer membranes and tylakoids that contain green – colored pigments which harvest and trap sun’s energy in chemical form (ATP). They produce and store food and that is what we call photosynthesis. Chloroplasts and other plastids, like chromoplasts and leucoplasts, are only present in plant cells. The same does the vacuole, the big watery thing inside the plant cell that contains solution of various storage products. It provides cell’s nutrition (endocytosis – phagocytosis, pinocytosis) and excretion (exocytosis). On the other hand, animal cells have some “special” organelles, as well: cilia for outer and centrioles, with their nine microtubule triplets, for inner cell movement – they both are parts of the cytoskeleton. Although - evolutionally speaking - the prokaryotic cell is older, it is less developed than the eukaryotic, and that is why they are so different. Compared with eukaryotes’ membrane - bounded nucleus, DNA in several linear chromosomes and many specialized organelles, the prokaryotes with their no – membrane nucleus, circular strand of DNA and few organelles look very simple, but, and that the main difference, prokaryotic cells exist only like single celled, absolutely independent organisms (some eukaryotes do, as well, but in most cases they are specialized and work like subunits or multicellular organisms). .
 
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