Inside the Cell 1

Inside the Cell 1

Inside the Cell 1

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Prokarotes

Prokaryotes vs. Eukaryotes

  • Bacteria are the oldest and simplest prokaryote
  • Prokaryotes lack internal compartmentalisation seen in eukaryotes
  • Prokaryotic genome has less DNA
    • Can have diffuse location within cell compared to eukaryotes which have a true membrane-bound nucleus
  • Most prokaryotes have plasmids
    • small ring-shaped DNA molecules containing a few genes
  • Plasmid function:
    • Fertility -transfer of genetic material between two bacteria
    • Resistance - antibiotics
    • Degradative - digestion of organic substances
    • Virulence - turn the bacterium into a pathogen
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Bacterial Plasmids

  • Short, circular and double-stranded segment of DNA in the cytoplasm separate from main bacterial chromosome
  • Capable of autonomous replication
  • Can transfer genes from one cell to another
  • Acts as a vector in genetic engineering
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Prokaryotes vs. Eukaryotes

Eukaryotes

Organelles

  • Eukaryotic cells have an elaborate system of internal membrane-bound compartments (organelles)
    • Provide specialised environments
    • Facilitate processes with different chemical requirements
  • Each organelle has one or more compartments
  • Organelles act autonomously or cooperate to accomplish a given function
    • E.g.: protein trafficking involves the endoplasmic reticulum and Golgi apparatus
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Cytoplasm

  • Area contained by the plasma membrane
  • Contains many membrane-bound compartments
    • membranes facilitate distinct environments within organelles
  • Defined as everything excluding the nucleus
  • Contrast with cytosol - fluid elements of cytoplasm
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Cell Cytosol

  • Largest compartment of the cell
  • Composition
    • Densely-packed molecules
    • Aqueous gel, molecular soup
    • Site of many essential chemical reactions
  • Site of many essential chemical reactions
    • Early steps in nutrient breakdown
    • ATP generation (glycolysis)
    • Manufacture of proteins
    • Signalling transduction
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Mitochondria

  • Prsesent in all eukaryotic cells
  • Function: cellular respiration
    • Convert energy usable by cells
      • ATP
    • Cytosol: anaerobic glycolysis
    • Mitochondrion: pyruvate oxidation

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Mitochondria

  • Mitochondria remain fixed in some cells associated at sites requiring most energy
    • Muscle 
    • Brain
  • Number of mitochondria can very within a cell and between cell types
    • Liver ~1000-2000 per cell; 20% of cell volume
    • Numbers/size can increase in muscle cells
    • Exercise can increase mitochondria numbers in muscle cells as cells adapt to higher energy requirements
  • Mitochondria are made up of four separate components
    • Outer membrane, intermembrane space, inner membrane, matrix
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Outer Membrane and Intermembrane Space

  • Outer membrane
  • Structure: similar to plasma membrane
  • Functions
    • Separation of internal and external environments
    • Role in cell death
      • disruption of outer membrane allows proteins from intermembrane space to leak into cytosol
  • Intermembrane space
    • Cytochrome C
      • essential component of the electron transport chain
      • important in apoptosis (release into the cytosol)
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Inner Membrane

  • Highly folded to form cristae
    • Increase surface area of inner membrane (5x larger than outer membrane)
    • Enhance ability to produce ATP
  • Mitochondria of cells with ATP demand contain more cristae compared to a typical microchondria
    • E.g. muscle cells vs. skin cells
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Matrix

  • Contains most of mitochondrial proteins/enzymes (>100)
    • Pyruvate and fatty acid oxidation
    • Citric acid cycle
  • Mitochondrial ribosomes, tRNA and mtDNA and several copies of the mitochondrial genome
    • 37 total genes that encode:
      • tRNA and rRNA
      • Inner membrane proteins
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Lysosomes

  • Principal sites of intracellular digestion
  • Produced from golgi
  • Contain many hydrolytic enzymes
    • Lipases
    • Carbohydrases
    • Nucleases
    • Proteases
  • pH dependent activity
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Lysosomes

  • Function - digestion of macromolecules from:
  • Phagocytosis
    • (external pathogens)
  • Endocytosis 
    • receptor recycling
  • Autophagy 
    • excess/old organelles
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