Eukaryotic Cell Organelles

Structure and function of eukaryotic cell organelles

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Nucleus

Structure:

  • largest organelle enclosed within an envelope (double membrane)
  • contains chromosomal DNA which may be extended (euchromatin) or condensed (heterochromatin)
  • perforated envelope (possesses pores)
  • contains one or several nucleoli

Function:

  • DNA codes for the synthesis of proteins in the cytoplasm 
  • pores in the envelope allow large molecules in (enzymes) and out (RNA)
  • nucleolus synthesises ribosomal RNA and manufactures ribosomes
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Ribosomes

Structure

  • small bodies of protein and rRNA
  • found free in cytoplasm or attached to rough endoplasmic reticulum

Function

  • site of protein synthesis
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Endoplasmic Reticulum (ER)

Structure

  • membrane system of sacs and tubes permeates the cytoplasm
  • flattened rough ER - studded with ribosomes
  • tubular smooth ER - lacks ribosomes

Function

  • proteins made in ribosomes accumulate in the rough ER and passed on to Golgi apparatus
  • smooth ER is involved with lipid metabolism
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Golgi Apparatus

Structure

  • stack of membrane-cound sacs (cisternae)
  • forming face - has vesicles from the rough ER joining
  • mature face - has vesicles pinching off

Function

  • dynamic structure in which proteins are modified 
  • e.g have carbohydrate attached to form glycoprotein
  • packaged into vesicles either for secretion by exocytosis or for delivery elsewhere in the cell
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Lysosomes

Sturcture

  • vesicles which are produced by the Golgi apparatus which contain hydrolytic enzymes

Function

  • comine with membrane bound degenerate organelles or ingested particles (e.g. bacteria) to form secondary lysosomes
  • hydrolytic enzymes digest the contents
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Mitochondria

Structure

  • sausage shaped
  • surrounded by an envelope
  • inner membane of which is folded to form cristae
  • fluid filled matrix
  • several to thousands per cell

Function

  • synthesis of ATP by aerobic respiration
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Chloroplasts

Structure

  • oviod
  • surrounded by an envelope
  • elaborate internal membrane system of lamellae with thylakoids stacked into grana
  • contain lipid droplets and starch grains
  • occur in some plant cells

Function

  • site of photosynthesis
  • chlorophyll molecules are attached to the lamellae
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Vesicles and vacuoles

Structure

  • bound by a single membrane
  • vesicles are much smaller than vacuoles
  • vacuoles are permanent in plant and fungal cells
  • membrane of the sap vacuole in plant cells is called the tonoplast

Function

  • vesicles may be used for storage and transport of substances
  • e.g. transport to and from the cell-surface membrane or within the cytoplasm
  • vacuoles are for storage of water and ions
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Microtubules

Structure

  • tubular
  • formed from the protein tubulin
  • occur within centrioles (as 9 triplets of microtubues in a circular arrangement) and throughout the cytoplasm
  • animal and fungal cells contain a pair of centrioles

Function

  • centrioles form the spindle fibres during cell division of animal and fungal cells
  • microtubules also form part of the cytoskeleton and allow movement of cell organelles
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Plasmodesmata

Structure

  • strands of cytoplasm between nighbouring plant cells that pass through pores in the walls

Function

  • facilitate transport of materials between adjacent cells in plants
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