Page 20 - PRE-U STPM BIOLOGY TERM 1

Biology Term 1 STPM Chapter 2 Structure of Cells and Organelles

Intermediate
filament
2
Microfilament
Microtubule
Arrangement of tubulin
Cytoskeleton
Figure 2.10 Cytoskeleton and arrangement of tubulin in microtubule

(vii) The functions of microtubules are as follows:
• They form the cytoskeleton that determines the shape of
the cell.
• They can divide the cytoplasm of the cell into
compartments so that specialised enzymes can be
isolated from others to function better.
• They can contract, causing movement in the cilia and
flagella.
• They can pull chromosomes or chromatids during
mitosis or meiosis.
• They can cause the movement of organelles, including
mitochondria, lysosomes and vesicles to move along like
railway tracks.
(b) Microfilaments
(i) The microfilaments are fine filaments made of protein with
a diameters of 7 nm and lengths of several µm.
(ii) They are composed of one or two types of protein including
actin and myosin.
(iii) They are dynamic which means they can change their
length very quickly depending on their locations and
functions.
(iv) Each type of protein forms subunits that are arranged
helically.
(v) The subunits can slide over one another causing the
microfilaments to contract.
(vi) Microfilaments exist in bundles and they are normally
found in layers in the cytoplasm.

Two strands of
actin subunits
Microfilament composed of two Intermediate filament with eight
strands of protein subunits strands of protein subunits
Figure 2.11 Microfilament and intermediate filament

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