[Biology Form 4] How to Synthesis Extracellular Protein?

  • Extracellular protein is the protein that is destined for export from a cell such as digestive enzyme that is made by pancreas cell.

  • The organelles that involved in the process are nucleus, ribosome, RER,Golgi apparatus and mitochondria.

  • Flow chart shows how the internal membrane system of a cell packages a protein for export.

  • 1. Instructions for making protein are transcribed from DNA by RNA in the nucleus.
    2. RNA leaves the nucleus through nuclear pore and proceeds to a ribosome located on the RER.

    3. Ribosome synthesis the correct sequence of amino acids for synthesizing that particular protein as instructed.

    4. When protein synthesis is complete, the protein travels through the RER and is then encapsulated in a transport vesicle.

    5. The transport vesicle fuses with a Golgi apparatus, releasing the protein.

    6. In the Golgi apparatusthe protein is further modified and is then shunted to the ends of Golgi apparatus or cisternae. There, the protein waits for a secretory vesicle.

    7. The secretory vesicle will carry the protein to the plasma membrane of the cell and fuses with it. Then, the protein is released outside the cell.


    [Biology Form 4] Enzyme

    1. Structure: What chemical compound is an enzyme made up of? 

    2. Function: What is the role played by enzymes in living organisms?
    Enzymes speed up the rate of chemical reactions in living organisms.

    3. State the characteristics of enzymes:
    a) Enzymes are made up of proteins.
    b) They are catalysts that speed up the rate of a reaction.

    c) They are not destroyed / altered by the reactions they catalyse.

    d) Enzymes have specific active sites where they bind with substrates.

    e) Enzymes show substrate specificity - they can only bind with specific substrates.

    f) Enzymes are needed only in small amounts.

    g) Enzyme-catalysed reactions are reversible - they catalyse reactions in either direction.

    h) The activity of enzymes can be slowed down by inhibitors.

    i) Enzymes work more effectively with the help of co-factors.

    j) Enzymes are affected by factors such as temperaturepHsubstrate concentration and enzyme concentration.

    4. Define enzyme
    An enzyme is a biological catalyst that speeds up the rate of chemical reactions occurring in living organisms.

    5. Where are enzymes synthesised in a cell?
    In ribosomes.

    6. Where are enzymes modified and packaged in a cell?
    In the Golgy body.

    7. Example: State an example of enzymes involved in the digestion or hydrolysis of each of the following substrates:
    a) StarchAmylase
    b) ProteinsPepsin
    c) FatsLipase
    d) MaltoseMaltase
    e) LactoseLactase
    f) SucroseSucrase
    g) CelluloseCellulase

    8. Effect: What would be the effect on digestion if enzymes were unavailable?
    Digestion would be slowed down drastically.

    9. State four factors that affect enzyme activity.
    Temperature, pH, enzyme concentration and substrate concentration.

    10. Sketch a graph for each of the factors on enzyme activity. Label the x-axis and y-axis correctly.


    [Biology Form 4] Animal Cell & Plant Cell

    • The cell is the basic unit of all organism. It is made up of a cell membrane that encloses the cytoplasm.
    • Contained within the cytoplasm are not only the nucleus but also organelles, whose specific functions help the cell perform a range of activities.
    • While plant and animal cells are similar, the plant cell has, in addition to the cell membrane, another boundary that separates it from its external environment. This is called the cell wall.
    • As most plant cells carry out photosynthesis - the synthesis of organic substances - they contain chloroplasts.
    • In plant cells, vacuoles also tend to be larger in size and smaller in number than those found in animal cells.
                                                                       Typical Plant Cell :

    Typical Animal Cell :

    In the laboratory, you have learned how to prepare a microscope slide of human cheek cells as well as the epidermal cells of onions.

    a) The differences you can observe between the two types of cells in term of the following:
    • Shape                                                                                                                     Onion cells have a regular shape while cheek cells have an irregular shape.
    • Presence or absence of cell wall                                                                           Onion cells have a cell wall while cheek cells do not.                                                                                               
    • Presence or absence of vacuoles                                                                          Onion cells have a large vacuole while vacuoles in cheek cells, if present, are small.                                                                                    
    b) Can you observe chloroplasts in the epidermal cells of onions? Explain your answer.                                
                                                                                                                                              => No chloroplasts can be observed in the epidermal cells of onions because epidermal cells do not carry out photosynthesis.