Cytoplasm

BIOCHEMISTRY 3(2+1)
Lesson 5 : Cell Structure and Functions

Cytoplasm

  1. Collective term for cytosol and organelles contained within
  2. Colloidal suspension
  3. Cytosol mainly composed of water with free-floating molecules
  4. Viscosity constantly changes
  1. Centrioles
    • Structure
      • Paired cylindrical organelles near nucleus
      • Composed of nine tubes, each with three tubules, two centrioles form one centrosome
    • Function
      • Involved in cellular division
      • Lie at right angles to each other
      • forms spindle fibres to separate chromosomes during cell division
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  1. Chloroplasts
    • Structure
      • A plastid usually found in plant cells
      • Contain green chlorophyll where photosynthesis takes place
      • composed of a double layer of modified membrane (protein, chlorophyll, lipid)
      • inner membrane invaginates to form layers called "grana" (sing., granum) where chlorophyll is concentrated
    • Function
      • site of photosynthesis chlorophyll
      • Carbon Dioxide + Water ---------------> Glucose + Oxygen radiant energy (food)
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  1. Cytoskeleton
    • Composed of microtubules
    • Supports cell and provides shape
    • Aids movement of materials in and out of cells
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  1. Endoplasmic reticulum
    • Structure
      • Smooth type: lacks ribosomes; sheets of unit membrane with ribosomes on the outside. Rough type: Ribosomes embedded in the surface
      • forms a tubular network throughout the cell
    • Function
      • Goes through cytoplasm onto cell membrane
      • Stores, separates, and serves as cell's transport system
      • transports chemicals between cells and within cells
      • provides a large surface area for the organization of chemical reactions and synthesis
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  1. Golgi apparatus
    • Structure
      • stacks of flattened sacs of unit membrane ( cisternae )
      • Protein 'packaging plant'
      • A membrane structure found near nucleus
      • Composed of numerous layers forming a sac
    • Function
      • modifies chemicals to make them functional
      • secretes chemicals in tiny vesicles
      • stores chemicals
      • may produce endoplasmic reticulum
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  1. Lysosome
    • Structure
      • Membrane bound bag containing hydrolytic enzymes
      • Hydrolytic enzyme= ( water split biological catalyst ) i.e uses water to split chemical bonds
      • Vary in shape depending on process being carried out
      • Cell breaks down if lysosome explodes
    • Function
      • break large molecules into small molecules by inserting a molecule of water into the chemical bond
      • Digestive 'plant' for proteins, lipids, and carbohydrates
      • Transports undigested material to cell membrane for removal
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  1. Mitochondria
    • Structure
      • Second largest organelle with unique genetic structure composed of modified double unit membrane (protein, lipid)
      • inner membrane infolded to form cristae . - Energy-producing chemical reactions take place on cristae
    • Function
      • site of cellular respiration ie. the release of chemical energy from food
      • Glucose + Oxygen ------> Carbon Dioxide + Water + Energy (ATP)

      • Controls level of water and other materials in cell
      • Recycles and decomposes proteins, fats, and carbohydrates, and forms urea
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  1. Ribosomes
    • Structure
      • non-membraneous, spherical bodies composed of RNA and protein enzymes
      • Each cell contains thousands of miniature 'protein factories'
      • Composes 25% of cell's mass
      • Stationary type: embedded in rough endoplasmic reticulum
      • Mobile type: injects proteins directly into cytoplasm
    • Function site of protein synthesis
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  1. Vacuoles
    • Structure a single layer of unit membrane enclosing fluid in a sack
    • Function
      • Membrane-bound sacs for storage, digestion, and waste removal
      • produces turgor pressure against cell wall for support
      • stores water and various chemicals
      • may store insoluble wastes
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Last modified: Tuesday, 17 January 2012, 10:42 AM