Cell Structure and Cell Membrane

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Nucleus

Structure

  • Surrounded by a nuclear envelope, made of two membraneswith fluid between them. Nuclear pores go right through the envelope
  • Nuclear pores - large enough for relatively large molecules to pass through
  • Dense spherical structure called neucleolus inside the nucleus 

Function

  • Nucleus houses nearly all genetic material
  • Chromatins consists of DNA  and proteins - when cells divide chromatin condenses into visible chromosomes
  • Nucleolus makes RNA and ribosomes - these pass into cytoplasm and proteins are assembled at them
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Endoplasmic Reticulum (ER)

Structure

  • Consists of series of  flattened membrane sacs called cisternae - continuous with outer nuclear membrane
  • Rough ER (RER) studded with ribosomes
  • Smooth ER (SER) does not have ribosomes

Function

  •  RER transports proteins that are made on the attaches ribosomes - some of proteins secreted from cell, some replaced on cell surface membrane
  • SER makes lipids that cell needs
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Golgi Apparatus

Structure

  • Stack of membrane-bound, flattened sacs

Function

  • Receives proteins from ER and modifies them - may add carbohydrate chains
  • Packages modified proteins into vesicles that can be transported
  • Some modified proteins may go to surface of cell so that it may be secreted
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Mitochondria (Singular: Mitochondrion)

Structure

  • May be spherical or sausage-shaped
  • Have two membranes seperated by fluid filled space
  • Inner membrane highly folded to form cristae
  • Central part of mitochondria called matrix

Function

  • Site where ATP produced during anerobic respiration
  • ATP sometimes called universal energy carrier - almost all activities that need energy in cell driven by energy released by ATP
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Chloroplasts

Structure

  • Found only in plants and some protoctists.
  • Have two membranes separated by fluid-filled space
  • Inner membrane continuous with an elaborate network of flattened membrane sacs called thylakoids (stack of thylakoids called granum or grana (plural))
  • Chlorophyll molecules on thylakoid membranes and in internal membranes

Function

  • Site of photosynthesis in plant cells
  • Light energy used to drive reactions in photosynthesis in which carbohydrate molecules are made from carbon dioxide and water
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Lysosomes

Structure

  • Spherical sacs surrounded by single membrane

Function

  • Contain digestive enzymes
  • Break down materials e.g. Neutrophils' lysosomes break down invading microorganisims;specialised lysosomes (acrosome) in the head of sperm penetrate egg by breaking down material surrounding egg
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Ribosomes (not membrane bound)

Structure

  • Tiny organelles
  • Some in cytoplasm and some bound to ER
  • Each ribosome consists o two subunits

Function

  • Site of protein synthesis in the cell (where proteins are made)
  • Act as assembly line where mRNA from nucleus is used to assemble proteins from anmio acids
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Centrioles (not membrane bound)

Structure

  • Small tubes of protein fibres (microtubules)
  • There is a pair of them next to nucleus in animal cells and in cells of some protocists

Function

  • Take part in cell division
  • Form spindle fibres, which move chromosomes during nuclear division
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