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Chapter 21

BIOL 1000- PROKARYOTES (chap#21)

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BIOL 1000
Julie Clark

Tanya Sivamanoharan Thurs, Sept, 29/11 Biology- Chap# 21 Notes PROKARYOTES 21.1- The Full Extent of Prokaryotic Diversity is Unknown -everything derived about prokaryotes are from a few species (maybe 1%) -this is b/c most bacteria live in extreme conditions that we cannot provide 21.1a- Prokaryotes Make Up Two of the Three Domains of Life -there are two domains of prokaryote which are bacteria and Archaea -the more common one is bacteria b/c Archaea were only discovered about 40 yrs ago -archaea share some cellular features with eukaryotes and some with bacteria -many Archaea live under extreme environments that not even bacteria can survive in 21.2- Prokaryotic Structure and Function -prokaryotes are smallest organisms in world most less than 1-2um long -they are small but they dominate life on earth and their biomass is greater than animals and plants on earth -they were the only form of life for about 3 billion yrs. on earth so no surprise of being so diverse 21.2a- Prokaryotic Cells Appear Simple in Structure Compared with Eukaryotic Cells -there are three shapes of prokaryotes: -spiral spirilla -spherical cocci -bacilli rods -some Archaea are even square -typical prokaryotes may look simple than eukaryotes -prokaryotes have a cell wall and plasma membrane surrounding cytoplasm with DNA and scattered ribosomes -chromosome is not within a membrane-bound nucleus but is in a area called the nucleoid -prokaryotes cells have no cytoplasmic organelles -a recent discovery is that prokaryotes do have cytoskeletons although not similar to eukaryotes -internal structures: -a single, circular DNA molecule (few have a linear chromosome) -many prokaryotes also have small circle of DNA called plasmids -plasmids replicate independent of the cell’s chromosomes and can be transferred from cell to cell -prokaryotic cells contain ribosomes like eukaryotes, they are smaller but they still carry out protein synthesis -archaea also have ribosomes but have a diff. structure -prokaryotic cell walls: -most prokaryotes have a cell wall outside the plasma membrane -primary component of cell wall is peptidoglycanpolymer of sugars and amino acids, forming linear chains -peptide cross linkages give cell wall strength and rigidity -bacteria can be divided into 2 groups: -gram- positive describing bacteria that appear purple when stained using gram stain procedure -gram negative describing bacteria that do not retain the stain when stained using gram stain procedure -gram positive bacteria are composed of a single thick layer of peptidoglycan -gram negative bacteria have 2 layers: a thin peptidoglycan layer and an outer membrane outside the peptidoglycan layer -this outer membrane of gram negative bacteria have lipopolysaccharides, therefore diff. from the plasma membrane -archaea bacteria are built with a molecule from peptidoglycan but has diff. molecular components and structure -other Archaea have walls from proteins or other polysaccharides -many prokaryotic cell walls are covered by capsules -capsules sticky and protect cell -flagella and pili: -flagella extend from the cell wall and are diff. from eukaryotic flagella -prokaryotic flagella are made from rigid helical proteins and rotate like propeller of boat -archaen flagella is similar to bacteris flagella but are structurally diff. -some prokaryotes have proteins called pili enabling bacteria to bind to each other and animal cells -even though prokaryotes are simpler and less structurally diverse than eukaryotes, they are much more diverse metabolically 21.2b- Prokaryotes Have the Greatest Diversity of All Organisms -there are 2 modes of nutrition that exist only among prokaryotes: photoautotrophs and chemoautotrophs -photoautotrophs use light as energy to obtain carbon from organic molecules and not from inorganic CO2 -chemoautotrophs “lithotrophs” obtain energy by oxidizing inorganic substances such as hydrogen, iron, sulfur, ammonia, and nitrites and use CO2 as energy -chemolithotrophs live in deep-sea hydrothermal vents where inorganic compounds are abundant -some prokaryotes use oxygen as their final electron acceptor, and need oxygen to survive -some prokaryotes are anaerobic as in they use inorganic metals as the final electron acceptor -only prokaryotes are capable of anaerobic respiration -obligate anaerobes poisoned by oxygen and use fermentation in which organic molecules are the final electron acceptor 21.2c- Prokaryotes Play Key Roles in Biogeochemical Cycles -prokaryotes are a life-sustaining recycling of elements incl. carbon, oxygen, and nitrogen -biogeochemical cycle the pathway which
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