Organelles

Nucleus

Structure

  • double membrane (envelope) binds it
  • nuclear pores allow mRNA and ribosomes out
  • DNA loose inside nucleus as chromatin
  • nucleoplasm is granular material

Function

  • to contain codes for protein synthesis
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Nucleolus

Structure

  • darker staining region of nucleus
  • heterochromatin is densely packed
  • euchromatin is less densely packed (lighter coloured)

Function

  • synthesis of rRNA and ribosomes
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Rough Endoplasmic Reticulum

 

Structure

  • parallel double membranes form fluid-filled sacs: cisternae
  • cisternae are studded with ribosomes
  • cisternae sacs are interconnected
  • membranes continue from nuclear envelope

Functions

  • to transport materials through the cells
  • transport proteins made by the ribosomes
  • synthesise proteins (ribosomes' role)
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Smooth Endoplasmic Reticulum

Structure

  • cisternae interconnected
  • continuous of rough endoplasmic reticulum
  • no ribosomes

Function

  • synthesis and transport of lipids and steroids
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Ribosomes

Structure

  • made of a large subunit atop a smaller subunit
  • no membrane
  • two tRNA attachment sites

Functions

  • protein synthesis
  • site where mRNA is translated and polypeptide formed
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Golgi Body/Apparatus

Structure

  • series of separate, flatterened fluid-filled sacs: cisternae
  • made of transport vesicles which fuse together and then pinch off later

Functions

  • production and packaging of secretory enzymes
  • making lysosomes, glycoproteins - modification of proteins from the rER
  • transport and storage of lipids
  • secreting carbohydrates
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Mitochondria

Structure

  • cylindrical to enable large surface area to volume ratio, generslly 1-10 micrometers
  • organic matrix solution contains lipid/protein compounds
  • the double membrane is separated by inter-menbrane space, and the inner membrane folds into cristae
  • ribosomes present (70S or small) and a circle or DNA

Function

  • to produce ATP in aerobic respiration, which is the molecule used to release energy
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Lysosomes

Structure

  • small, temporary vacuoles with one membrane surrounding enzymes

Function

  • to isolate harmful enzymes which are released to repurpose old organelles
  • ingesting bacteria isolated by white blood cells in phagocytosis
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Centrioles

Structure

  • ring of nine microtubule triplets. microtubules are hollow cylinders
  • come in pairs ( a centrosome), at right angles to each other

Functions

  • organise the spindle (microtubules) during cell division
  • NOTE - only found in animal cells (some protoctistans too), and one centrosome per cell
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Chloroplasts

Structure

  • contains stroma (fluid) bound by a double membrane (envelope)
  • like the mitochondria, has 70S ribosomes in the stroma and circular DNA
  • thylakoids are the flattened sacks holding pigments (eg chlorophyll)
  • stack of thylakoids = a granum (plural: grana) 
  • also has starch grains

Function

  • to trap light energy (hence large thylakoid surface area) for photosynthesis
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Vacuole

Structure

  • membrane that binds it is the tonoplast
  • filled with sap/solution

Function

  • to store cell sap solution which may contain glucose, amino acids, minerals)
  • in plants it has a supportive role in the cell structure
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Plasmodesmata

Structure

  • cells have pores called cell pits
  • plasmodesmata are strands of cytoplasm through the cell pits

Functions

  • transport of nutrients between plant cells
  • the symplast (plasmodesmata network) is important in water transport
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