Download L2 Prokaryote vs Eukaryote Cells Prokaryotic Cells Prokaryotes

Archaea (very old life forms) L2 Prokaryote vs Eukaryote Cells 
Prokaryotic Cells: (pro: before, karyon: nucleus) are cells in which the double stranded DNA lies free within the cell (in an area ‐ the nucleoid)  Ribosomes can attach directly to mRNA, even while being synthesised in the cytoplasm Eukaryotic Cells: (eu: proper, karyon: nucleus) are more complex cells that arose from, bacterial ancestors. DNA is enclosed within a nucleus 
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Prokaryotic Cells 
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Have a smaller in simpler structure that eukaryotes Morphologically identical to bacteria (no internal compartments Over half of Archaean genes were new to science ► Discovered by the testing of nucleic acid Biochemically, Archaea are nearly as different from bacteria as they are from Eukarya ► Making them a separate domain ► Archaean transcription & translation are more similar to Eukaryotes Lack a peptidoglycan wall Most were believed to be EXTREMOPHILES ‐ found in extreme environments None have been found to produce resting spores No clear examples of Archaean pathogens known Comparison of Structural + Biochemical Features 
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Prokaryotes are the smallest cellular like on earth and differ structurally and functionally from eukaryotes. They are Earth's first inhabitants (dating back ~3.6 billion years), thus have evolved with high diversity, and have adapted to almost every climate CYANOBACTERIA (photosynthetic) produces O2 for the previously oxygen less atmosphere (The Great Oxygenation Event) ► Caused the extinction of many anaerobic organisms ► The first billions of years saw no change ‐> O2 bound to iron ► O2 was split by the radiation of the sun ‐> created the ozone layer Produce resting spores that can lay dormant for >250 million years Split every 20 mins (BINARY FISSION) Feature Bacteria Archaea Eukarya Membrane‐bound nucleus absent absent Present Introns in genes absent absent Present Plasmids present present Rare RNA polymers single multiple Multiple Protein synthesis ‐
initiation RNA Formyl Methionine Methionine methionine Peptidoglycan Yes No No Membrane lipids Esters Ethers Esters Methane‐generating No Yes (some) No Nitrification Yes (some) No Nitrogen fixing Yes (some) Yes (some) No Photosynthesis Yes (some) No Yes (some) No Yes No Yes No No Protein synthesis sensitive to:  Diphtheria toxin
 Streptomycin
 Cycloheximide
Yes No No No Prokaryotes Functions and Features 
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Three Domains of Life 
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The bacteria The Archaea The Eukarya Ubiquitous and metabolically diverse Cause of many diseases Decomposers and recyclers ► Removes dead organic matter, recycling carbon, nitrogen in water to safe levels Agents in industrial and agricultural processes ► In fermented foods e.g. salami, soy sauce Nitrogen fixation ► Fixes atmospheric (unusable) nitrogen to organic compounds ‐ can then be accessed by other organisms Biotech applications ► GM bacteria make pharmaceuticals e.g. harvesting pathogen free hormones ► GM plants 
Cyanobacteria ‐ major primary producer 
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Contain chlorophyll A, plus phycocyanin and phycoerythin as accessory pigments Resemble algae and plants 
Eukaryotes have almost equal numbers of genes from both Archaeans and Bacteria 
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Possess internal, membrane‐bound organelles Has a semi‐permeable cellular membrane Accessory pigments ‐ captures other wavelengths (photons) that chlorophyll A might miss, then passes it to chlorophyll A ► Makes the organism appear in various shades of brown or red L3 Eukaryotic Cell The Nucleus Complex Organelles Derived from Relict 
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Surrounded by the nuclear envelope ► Double membrane ► Separated by 50um, but joined at the pores ~30 proteins surround each pore acting as filters ► Substances need proteins (NLS, NES) to enter and exit the pores DNA in the nucleolus are covered with histones to form chromosomes ► Histones are used to compact the DNA ► They are +vely charged and balance out the ‐
ve charge of DNA RNA transcribes from DNA leaves the nucleus via pores and is translated in the cytoplasm The nucleolus contains rRNA, proteins, DNA and ribosomes in various stages of synthesis. Mitochondria 
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Cellular respiration occurs in the mitochondria in all eukaryotes Cells may contain several, or have a single large one They have two membranes ► An outer membrane ‐ highly permeable ► And a highly convoluted inner membrane ‐ highly permeable Symbionts (Endosymbiont) 
An organism living (operating) inside another organism where they both benefit each other ► MITOCHONDRIA are believed to be derived from PURPLE BACTERIA ► CHLOROPLASTS are believed to be derived from CYANOBACTERIA Primary Endosymbiosis (plastids with two membranes)  99% of the time, objects absorbed my phagocytosis become dissolved  There may have been a mutation in the cyanobacteria cell wall that made it unrecognisable as food  Over time, the cyanobacteria became a plastid ► Lost its autonomy ‐ controlled by the nucleus ► Food vacuole disappears and becomes a chloroplast Secondary / Eukaryotic Endosymbiosis 
Chloroplasts 
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Have: ► An outer membrane ► A complex internal network of lamellae or thylakoids  Form stacks called grana  Where pigments are and photosynthetic reactions take place Stroma ‐ liquid surrounding thylakoids (high pH) Lumen ‐ liquid within thylakoids (low pH) When a chloroplast is believed to be derived from a symbiotic, eukaryotic cell rather than a prokaryote. Protists: have chloroplasts taken from other eukaryotes ► Single celled ► Produce ~60% of the world's oxygen Evidence for the Endosymbiotic origin 1.
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These organelles appear morphologically similar to bacteria They are surrounded by a membrane similar to a cell membrane, while their inner membrane invaginates to form thylakoids / cristae Mitochondria & chloroplasts are semi‐autonomous ► Retains their own genome They also retain their own machinery for synthesising proteins, including ribosomes Their metabolism are like existing prokaryotic organisms (CYANOBACTERA/PURPLE BACTERIA) Some chloroplast still have the bacterial peptidoglycan wall between inner and outer membranes (e.g. cyanophora) ► Evidence that it was a domain bacteria Chloroplast metabolism is like that of existing prokaryotic cyanobacteria CRYPTOMONADS: flagellates with secondary plastids (has 4 genomes)  Cryptomonad plastids have chlorophyll and a phycobilin pigment ► Products of photosynthesis is stored outside the plastid as starch  Reproduce asexually, are unicellular  Have a nucleomorph, a second vestigial nucleus ► Proof that the endosymbiont was a photosynthetic eukaryote  Mitochondria & chloroplasts contain genetic material themselves  Ribosomes, cytoplasm, DNA. Plasma membrane; are features that prokaryotes and eukaryotes share.