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Lecture 5


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Biological Sciences

LECTURE 5 Chapter 21PROKARYOTESProkaryotes play a crucial role in ecosystems recycling nutrients and breaking down compounds that no other organism canMany live in very extreme environmentMake up tow of the three domains of life Bacteria and ArchaeaArchaea share some cellular features with eukaryotes and some with bacteriaMany of the Archaea live under very extreme conditions that no other organism can including bacteriaPROKARYOTES STRCTURE AND FUNCTIONprokaryotes are the smallest organisms in the worlddespite the size they dominate life on Earth they colonize every niche on Earth that support lifeProkaryotic cells appear simple in structure compared with Eukaryotic cells 3 cell shapes are common among prokaryotes SPIRAL spirilla SPHERICAL coccoid and CYLINDRICAL bacilliHave no cytoplasmic organelles equivalent to the mitochondria endoplasmic reticulum or Golgi complex of eukaryotic cellINTERNAL STRUCTUREThe genome of most prokaryotes consists of a single circular DNA molecule and contains small circles of DNA called PLASMIDPlasmids contain genes for beneficial functions such as antibiotic resistance they replicate independently of the cells chromosomes and can be transferred from one cell to another horizontal transferHorizontal transfer allows antibiotic resistance and other traits to spread very quickly in bacterial populationLike Eukaryotic cell Prokaryotes contain ribosomesBacterial ribosomes are smaller than eukaryotic ribosome but carry out protein synthesis like those of eukaryotesArchaea ribosomes are like bacterias ribosomes in size but different in structure Protein synthesis in Archaea is a combination of bacterial and eukaryotic processPROKARYOTIC CELL WALLSMost prokaryotes have a cell wall that lies outside their plasma membranePrimary component of bacterial cell walls is PEPTIDOGLYCAN a polymer of sugars and amino acids in a linear chain form
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