2.3: Eukaryotic Cells.

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2.3: Eukaryotic Cells.
2013-12-21 19:17:19
Eukaryotic Cells.
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  1. Define eukaryote.
    A eukaryote has membrane-bound organelles, e.g. nucleus, mitochondria.
  2. LIst some examples of eukaryotes.
    Eukaryotes include animals, plants, protists and fungi.
  3. Outline the function of: 

    - Lysosome
    - Plasma membrane
    - Free Ribosomes
    - Rough endoplasmic reticulum 
    - Golgi apparatus
    - Nucleus
    - Mitochondrion
    • Lysosome - sac with single membrane. Picks up and breaks down unwanted materials of foreign invaders, e.g. old organelles, bacteria, food. Contains enzymes which are produced in Golgi apparatus. 
    • Plasma membrane - holds the cell contents in place and controls the movement of substances into and out of the cell. 
    • Free ribosomes - are dark granules in the cytoplasm. They synthesise proteins and release them into the cytoplasm, e.g. enzymes. 
    • Rough endoplasmit reticulum - involved in the transport of materials in the cell and connects the cell membrane with the nuclear membrane. rER is flattened membrane sacs with ribosomes attached to outside. Protein is synthesised by ribosomes of rER and passes into the cisternae to be carried by vesicles to needed location. rER also synthesises new membranes by adding proteins and phospholipids
    • Golgi apparatus - is a single membrane structure with sacs, called cisternae, stacked like pancakes. The number of Golgi apparatus in a cell depends on cell type. Its function is the modification of lipids and proteins received from the endoplasmic reticulum, and their storage and transport within the cell or export from the cell. Transport of these macromolecules, e.g. enzymes,  hormones, and proteins, is achieved by their enclosure in vesicles which pinch off from the stack.
  4. Compare prokaryotic cells with eukaryotic cells.
    • Feature -- Prokaryoytic cells -- Eukaryotic cells 
    • DNA -- Naked DNA -- DNA associated with proteins (histones) 
    • Shape of DNA -- CIrcular DNA -- Linear DNA
    • Nuclear membrane -- Not present -- DNA enclosed in nuclear membrane 
    • Mitochondria -- not present -- present 
    • Ribosomes -- 70S (mass and size) -- 80S (mass and size) 
    • Internal membranes -- not present -- present (compartmentalise the cell into areas with different functions)
  5. Compare plant and animal cells.
    • Feature -- Plant cells -- Animal cells 
    • Outer boundary -- Has cell wall of cellulose outside the plasma membrane -- Plasma membrane is outer boundary 
    • Organelles present -- have nucleus, mitochondria and chloroplasts -- have nucleus, mitochondria, no chloroplasts. 
    • Vacuole - Large permanent vacuole often occupying most of cell -- have few and small vacuoles 
    • Centrioles -- not present -- present and involved in cell division 
    • Storage forms of energy -- carbohydrates such as starch, some storage as plant oils -- carbohydrates stored as glycogen and some storage as animal fat.
  6. Define extracellular component.
    Extracellular components are structures and materials that are external to the plasma membrane.
  7. List some extracellular components.
    Extracellular components include the cell wall of plants, plasmodesmata, which are channels that connect adjacent plant cells and the extracellular matrix of animal cells, e.g. glycoproteins such as collagen.
  8. Summarise an extracellular component of plants and an extracellular component of animals.
    • Plant - cellulose cell wall -- protects plant cells, helps maintain the shape of the cell and reduces water loss/uptake due to osmosis
    • Animal -- extracellular matrix -- collagen forms strong fibers outside the cell in a woven network that is involved in coordinating the behaviour of all cells within the particular tissue. Collagen is a structural protein that holds cells together.
  9. Outline the benefit of the plasmodesmata.
    Plasmodesmata connect the internal environments of adjacent plant cells. This helps unify conditions throughout a tissue/organ within the plant. Water and small molecules can travel via plasmodesmata from one cell to another to assist in the maintenance of homeostasis.
  10. Outline the benefit of desmosomes.
    Desmosomes are usually made of strong proteins, e.g. keratin that forms an anchoring junction between adjacent animal cells. THey hold the cells together and assist in forming the tissue.