Page 19 - PRE-U STPM BIOLOGY TERM 1

Biology Term 1 STPM Chapter 2 Structure of Cells and Organelles

(ii) Mesomolecules such as monosaccharides which include
glucose and fructose, disaccharides which include maltose,
sucrose (plant cells), amino acids, organic acids, nucleotides
and vitamins.
(b) Colloids. These include macromolecules such as proteins
(enzymes, hormones and structural proteins), glycogen in liver
2 cells and muscle tissues.
(c) Particles, droplets and vesicles. These include glycogen granules
in liver cells and muscle tissues, starch granules in plant cells,
fine fat droplets and minute vesicles, which contain liquid.

3. The functions of cytosol are as follows:
(a) It stores vital chemicals including fats.
(b) It is the site for certain metabolic pathways such as glycolysis,
synthesis of fatty acids, amino acids and proteins.
(c) It enables organelles to move about in it. These organelles include
mitochondria, chloroplasts, ribosomes, lysosomes and vacuoles.

Cytoskeleton
1. The cytoskeleton determines the three dimensional shape of the
animal cells and give certain firmness in the plant cells.
2. The fine fibrils can be divided into three types i.e. microtubules,
microfilaments and intermediate filaments.
(a) Microtubules
2010 (i) The microtubules are fine, unbranched tubules with a
diameter of 25 nm, a wall of 5 nm thick and vary in length.
(ii) The wall is composed of 13 rows of globular protein
subunits called tubulin, which are arranged helically.
(iii) Tubulin can grow from a certain organisation centre, which
is made of dense protein. Tubulin can be added at the
base or at one end of microtubule causing it to increase in
length or be removed, causing it to decrease in length.
(iv) The microtubules in cells are usually stable. However, some
may be unstable as they can change their length suddenly.
(v) Other tubulin subunits are able to attach to the base of cilia
and flagella, participating in their growth and movement.
(vi) The spindle fibres during cell divisions are microtubules.
In animal cells, they are organised by the centrioles. Their
formation can be inhibited by colchicine, causing non-
disjunctions (chromatids not separating) and mutation in
the number of chromosomes.

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