Biology Reference
In-Depth Information
Table 17.2 The major structural components of the living cell and their functions
Cell component
Function
1 Cell membrane
To prevent cellular components from being lost by diffusion
and to protect the cell interior from the harmful influence
of its environment. Proteins embedded in (or spanning)
the membrane act as selective pathways for material
movement and information transfer in and out of the cell.
These proteins undergo
thermal fluctuations
leading to
their conformational, rotational, and translational
diffusions within the membrane. Cholesterol molecules
alter the fluidity of the membrane, lowering their levels
in the membrane having the same effects as raising local
temperature. Therefore, in principle, individual cells can
control their “local membrane temperature” by controlling
the expression of the genes coding for the enzymes
catalyzing the cholesterol biosynthesis.
2 Cytoskeleton
To provide the mechanical framework to organize intracellular
components in space and time, utilizing the free energy of
hydrolysis of GTP and ATP. The cytoskeleton determines
the cell shape, cell motility, cell cycle, and the organization
of organelles and vesicles in the cytosol. The eukaryotic
cytoskeleton consists of actin filaments, microtubules and
intermediate filaments. The network of the filamentous
elements are dynamic and deformable, providing the
flexible mechanical framework for organizing subcellular
components and their movements in space driven by
nucleotide triphosphate hydrolysis catalyzed by the
cytoskeletal components themselves.
3 Nucleus
To separate chromosomes from the cytoplasm in eukaryotes in
order to control their structure and function better without
being interfered by cytoplasmic elements.
4 Nuclear envelope
To control the trafficking of materials between the nucleus and
the cytoplasm and to help organize chromosomes and their
dynamics.
5 Chromosomes
To store genetic information of the cell for transmission from
one cell generation to the next in an orderly manner. They
are formed from the DNA double helix wrapped around the
histone complex to form
nucleosomes
, which in turn form
higher-order helical chains known as
chromatins
,
6 Nucleolus
To transcribe and assemble ribosomal RNA for export to the
cytosol
7 Centrosome
The controsome consists of two centrioles, each having ninefold
symmetry due to the nine triplets of microtubules. Centrioles
are self-replicating organelles found only in animal cells.
They help organize cell division but are not essential for it
(Doxsey 2001).
8 Mitochondria
(a) To serve as the power house of the cell, providing the free
energy needed to drive all endergonic physical and chemical
processes in the cell. (b) According to the
chemiosmotic
theory
(Mitchell 1961), the mitochondrial inner membrane
(continued)
