Eukaryotes, prokaryotes and viruses
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Eukaryotes DNA: Linear bound to protein DNA, Introns. Organelles: Nucleus, membrane bound, 80S/70S ribosome. Reproduction: Mitosis and meiosis, paired chromosomes (diploid). Average size 10-100 μm. Extras: Mitotic spindle, sterols in plasma membrane, internal membranes (in organelles), ER, mitochondria, lysosomes, golgi, peroxisomes, cytoskeleton, cell wall only in some fungi.
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Prokaryotes DNA: Naked circular DNA, No introns. Organelles: No nucleus, No membrane-bound, 70s ribosomes. Reproduction: Binary fission, single chromosome (haploid). Average size: 1-5 μm. Extras: Internal membranes only in photosynthetic organisms, cell wall.
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Viruses Nucleic acid + protein coat. Needs host to replicate.
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Sizes (copy)
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Cytoskeleton Actin = thinnest (muscle). Microtubules = thickest (pull daughter cells apart). Intermediate filaments = mechanical strength of cell.
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Cytoplasm cytosol + organelles
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Nucleus Only organelle visible by light microscopy. Contains packaged genetic material. Covered by nuclear envelope (double membrane) which has nuclear pores.
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Plasma membrane Phospholipid bilayer. Contains cholesterol, proteins (integral, transmembrane and peripheral) and carbs.
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Lysosome Electron dense. Membrane bound. >50 hydrolytic enzymes for all major macromolecules. All require low pH. Organelle turnover/autophagy.
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Peroxisome Detoxification. Phospholipid synthesis. Oxidation of VLCFA (Very Long Chain Fatty Acids). Enzymes which generate & degrade H2O2. Large. Not very electron dense.
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Smooth endoplasmic reticulum Making lipids and steriods. Start of N-linked glycosylation. Detoxification of Xenobiotics.
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Rough endoplasmic reticulum Coated with ribosome (translation, proteins for secretion or insertion in cell membrane). Proteins folded (Cys-Cys brdges form). Vesicles bud off and go to golgi. RER and SER are continuous set of endosomes.
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Golgi 4-8 closely-stacked, membrane-bound channels (cisterna). Modifies proteins from RER vesicles (modifying N-linked carbs and Glycosylation of O-linked carbs and lipids). Synthesis/package materials for secreted. Direct new proteins in vesicles to their correct compartments. Transport membrane lipids around cell. Create lysosomes.
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Mitochondrion Double membrane. Contain DNA & enconde some of their proteins (~1%). Sugars oxidised to generate ATP (krebs). Cristae (inner membrane folds) to increase surface area for ETC.
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Chromatin Complex of DNA with histone and non-histone proteins
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Nucleolus Where rDNA is transcribed and ribosome subunits assembled.
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Structure and function of cellular organelles
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Cytoplasm |
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Nucleus |
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Plasma membrane |
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Lysosome |
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Peroxisome |
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Smooth endoplasmic reticulum |
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Rough endoplasmic reticulum |
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Golgi |
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Cytoskeleton |
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Mitchondrion |
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Chromatin |
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Nucleolus |
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Sizes
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Cytoskeleton Actin = 7nm diameter. Intermediate filaments = 8-10nm. Microtubules =25nm.
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Cytoplasm |
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Nucleus diam 3 - 10 μm
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Plasma membrane 5 - 10 nm thick
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Lysosome 0.2 - 0.5 μm
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Peroxisome 0.5 - 1.5 μm
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Smooth endoplasmic reticulum 50nm diam
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Rough endoplasmic reticulum |
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Golgi |
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Mitochondrion 0.5 - 3 μm
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Chromatin |
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Nucleolus 0.2 to 3.5 μm
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Extra lecture info
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Electron microscopy Involves elaborate prep & can only evaluate dead cells
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Transmission Electron microscope To look inside cell, electrons through specimen
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Scanning Electron Microsope To see cell surface, electrons scattered off surface by heavy metal coating e.g Au
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Max size of cell is determined by diffusion reduced >50 μm. As cell increases vol increases more than SA. Being too large influcnes movement of intermediates, waste products and nutrients.
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Cells specialized for diffusion Thin processes. Giant multinucleate cells: gene expression occurs in multiple places. Gap junctions: allow movement between cells.
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Cellular organelles pros allows for specialised enviroments within them
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DNA DNA packed as chromosomes. Chromosomes made up of chromatin. Chromatin made up of nucleosomes. Unless cell is dividing, chromatin is decondensed.
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DNA sizes Naked human DNA = 1.8m. DNA packaged in nucleosomes: 9.5mm. Condensed as chromosomes in mitosis 120 μm.
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Secretory vesicles Bud off golgi & fuse with inner surface of plasma membrane for exocytosis.
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Mitochondria membrane lengths 0.5 - 2 μm
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