Eukaryotic Cells

These cells have a true nucleus
Nucleus
1. Nuclear envelope
  1. A double membrane surround the nucleus
    1. The outer membrane is continuous with the endoplasmic reticulum
  2. Functions:
    1. Controls entry and exit of substances
    2. Contains reactions inside the nucleus
2. Nuclear pores
  1. Function:
    1. Allow passage of large molecules like mRNA our of the nucleus
3. Nucleoplasm
  1. Granular jelly-like material making up the bulk of the nucleus
4. Nucleolus
  1. Small spherical region of the nucleus (can be more than one)
  2. Function:
    1. rRNA manufactured and ribosomes assembled here
5. Chromosones
  1. it is protein bound
    1. (Wrapped around proteins called histones)
  2. Linear DNA
    1. In a straight line
Ribosomes
1. Small granules found in all cells
  1. Tend to be in cytoplasm or associated with ER
2. Made of two subunits made of rRNA and many proteins
3. Not enclosed by a membrane
4. Function:
  1. Sit of protein synthesis
Endoplasmic reticulum
1. Continuous with the outer nuclear membrane
  1. Cells that store lots of proteins, carbs and lipids have a very extensive ER
2. Rough ER (RER)
  1. This has ribosomes present on the outer surface of the membranes
  2. Functions:
    1. Large surface area for synthesis of proteins
    2. Pathway for transport of materials
3. Smooth ER (SER)
  1. This has no ribosomes and is more tubular in appearance
  2. Functions:
    1. Synthesises, stores and transfers lipids
    2. Synthesises, stores and transports carbs
4. There is only one cisternae per cell
  1. Depending on how the sample is cut, there may appear to be more
Golgi Apparatus
1. Spreads throughout the cytoplasm
2. More compact than the SER
3. Stack of membranes that make up flatten sacs or cisternae
  1. Also has small vesicles
4. Very well developed in secretory cells
  1. e.g. epithelial cells lining the intestines
5. Functions:
  1. Add carbs to glucose to form glycoproteins
  2. Produces secretory enzymes
  3. Secrete carbs such as those in plant cell walls
  4. Transports, modifies and stores lipids
6. The vesicles
  1. They are small rounded hollow structures
  2. Functions:
    1. Transport substances to and from the Golgi apparatus
      1. Some of these being lysosomes
Lysosomes
1. Vesicles produced by the Golgi apparatus
  1. Contains enzymes like proteases and lipases
    1. Also contain lysozymes
      1. An enzyme that can hydrolyse some bacterial cell walls
2. Functions:
  1. Hydrolyse material engulfed by phagocytic cells
  2. Release enzymes to the outside of the cell to destroy material around the cell
    1. This is called exocytosis
  3. Digest worn out organelles so that chemicals may be reused
  4. Completely break down cells after they have died
    1. This is called autolysis
Mitochondria
1. This is enclosed by a double membrane
  1. This controls the entry and exit of substances
2. The inner membrane is folded to form extensions called cristae
  1. This provides a larger surface area for enzymes and other proteins involved in aerobic respiration
3. The matrix contains protein, lipid, ribosomes and DNA.
  1. Many enzymes found it respiration are found here
4. Functions:
  1. Site of aerobic respiration
    1. This is releasing energy from food
  2. Produces ATP
    1. This is very important in active transport
      1. Going against the conc. gradient requires lots of ATP
5. Lots of these are needed in muscle cells for contraction
  1. Because muscle contraction needs ATP
Chloroplasts
1. Function
  1. Site of photosynthesis
2. Chloroplast envelope
  1. A double plasma membrane
    1. It is highly selective
3. Thylakoids
  1. Disc like membrane structures
  2. Contain chlorophyll
  3. Arranged in stacks called grana
    1. (Or one granum)
4. Stroma
  1. Fluid filled matrix
  2. Containing things like:
    1. Starch granules
    2. DNA
    3. Ribosomes
    4. Enzymes
5. Adaptions:
  1. Large surface area for chlorophyll in grana
  2. Stroma contains enzymes for second stage of photosynthesis
  3. DNA and ribosomes for quick synthesis of proteins for photosynthesis
Vacuoles
1. Fluid filled sacs bound by a single membrane
2. Plants usually have one large central
3. The membrane of the vacuole is called the tonoplast
4. It contains mineral salts, sugars, amino acids, wastes and sometimes pigments
5. Functions:
  1. Support herbaceous plants by making cells turgid
  2. Temporary stock of sugar and amino acids
  3. Holds pigment
Cell walls (plants)
1. Made up of cellulose microfibrils embedded in a matrix
  1. Matrix consists of other polysaccharides such as hemicellulose and pectin
2. The middle lamella is the boundary between cells and cements cells together
3. Functions:
  1. Stop the cell bursting under turgor pressure when water moves in by osmosis
    1. It adds mechanical strength
  2. Allows water to move along it
    1. Contributing to water movement
Cell fractionation
1. Homogenisation
  1. 1. Tissue to be used is chopped up and placed in an isotonic buffer solution (between 2 and 4 degrees)
    1. Isotonic = of the same water potential as tissue
      1. It is isotonic so that the cell does not burst or shrink
    2. 2. The buffered tissue is placed in a homogeniser and the tissue is homogenised
      1. Homogenised = blended
      2. 3. This breaks up the cells in the tissue and releases the organelles
        4. The homogenate is then filtered to remove complete cells and large debris
    3. The solution is cold to reduce enzyme activity
    4. It is buffered to keep the pH the same, so it prevents change in organelles or functioning of enzymes
2. Ultracentrifugation
  1. The principle is that the heavy organelles fall to the bottom in the first sediment, leaving the supernatant which can be spun again
  2. 1. Homogenised tissue placed in centrifuge and spun at low speed
    1. 2. After spinning sediment will be at the bottom, supernatant will be clear liquid
      1. 3. Take supernatant and spin it again faster to get even smaller organelles in sediment
        4. Take the supernatant out and spin again even faster keep repeating until you get the organelles you want
        Sediment 3 will contain organelles like lysosomes
        Sediment 4 would contain ribosomes
        Sediment 2 will contain organelles like mitochondria
      2. Sediment 1 will contain heaviest organelles e.g. nucleus
Cell specialisation
1. Tissues
  1. A collection of similar cells that perform a specific function
    1. e.g. xylem tissue in plants
2. Organs
  1. A combination of tissues that perform one major function
  2. e.g. Stomachs in animals
    1. 1. Muscle churns and mixes stomach contents
      1. 2. Epithelium produces secretions and protects stomach wall
        3. Connective tissue holds together the other tissues
3. Organ systems
  1. A number of organs working together
    1. e.g.
      1. Digestive system
        Stomach, pancreas, liver, mouth and anus
      2. Respiratory system
        Lungs, mouth, trachea, bronchus and diaphram
      3. Circulatory system
        Heart, blood vessels

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Eukaryotic Cells

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	Created by Jacob Shepherd about 9 years ago