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Chapter 2
Structure and functions
Of the Cell
Nucleus:
For storage of genetic information.
Rough Endoplasmic reticulum (rough ER)
For protein synthesis
Smooth Endoplasmic reticulum (smooth ER)
For intra-cellular transport
Golgi apparatus
Related to secretory function
Mitochondrion
For aerobic respiration
mitochondria (pl)
Chloroplast
For photosynthesis
Lysosome
For intra-cellular digestion
The fluid mosaic model of cell membrane
ATPase is an example of enzyme.
Recognition protein to distinguish foreign molecules from self molecules.
Receptor protein to recognize a signal (e.g. hormone) and then starts a
specific biochemical reaction.
Microvilli and pseudopodia
These are the extensions of the cell membrane.
Microvilli are common along the surface of absorptive
cell. They increase the surface area for absorption.
Pseudopodia are outgrowth from phagocytic cell to
enclose and swallow the foreign materials.
Nucleus:
Contains chromatins which carry DNA.
DNA consists of a number of genes.
Genes produce mRNA which controls the ribosome to
synthesize specific polypeptide/ protein. mRNA leaves the
nucleus through the nuclear pores.
Nucleolus (Nucleoli pl.)
To produce ribosomal RNA which is the structural material of
ribosome.
In other words, nucleoli produce rRNA which is to build up
ribosome. Ribosome is the site to carry out protein synthesis.
Protein synthesis is based on the information of mRNA. The
information of mRNA is copied from the DNA of the nucleus.
Endoplasmic reticulum:
Two types: Rough ER and Smooth ER
Rough ER connects the external nuclear membrane.
Both are for intra-cellular transport and act as cytoplasmic
skeleton.
Rough ER is for protein synthesis.
Smooth ER is the site where lipids and steroids are made.
Golgi apparatus:
Protein synthesized by rough ER is transported to Golgi
apparatus for storage, processing and modification into
different forms such as enzymes, hormones.
Golgi apparatus is related to secretion.
Lysosome:
Lysozome is originated from Golgi apparatus.
It encloses hydrolytic enzymes called lysozymes.
Functions:
For break down of aged or worn out organelles.
Acts as “suicide bag” to destroy the whole cell.
For phagocytic cell, lysosome is for intra-cellular digestion
of foreign materials e.g. pathogens, aged red blood cells.
Mitochondrion
It is bounded by double membranes.
The inner membrane has many infolds
called cristae to increase the surface
area for attachment of enzymes and
coenzymes.
crista
Aerobic respiration consists of three main stages,
namely glycolysis, Krebs cycle and oxidative
matrix
phosphorylation. Glycolysis takes place in the
cytoplasmic matrix. The other two stages take
place at the cristae and the matrix of the
mitochondrion.
Anaerobic respiration consists of glycolysis which takes place in
the cytoplasmic matrix. Therefore no mitochondrion is needed.
Vacuole and tonoplast
Tonoplast is the internal boundary
of vacuole.
Vacuole contains cell sap which gives
the turgidity to the cell and for
storage of materials.
Cilium and flagellum (Pl. forms: cilia and flagella)
Cilium is short and numerous. Flagellum is long and few.
They have the same internal structure.
Each has two central microtubules and 9 peripheral microtubules.
It gives a (9+2) pattern. These microtubules are contratile, giving
the beating movement of cilium or flagellum.
Cell wall, middle lamella (5), pit and plasmodesmata (2)
Thin Cell wall is composed of cellulose with pectin.
In addition, lignin or suberin is present in thick cell wall.
E.g. xylem
Middle lamella is a cementing layer between the cell wall of
two adjacent cells.
Some plant cells have pit for communication with the
adjacent cells.
Plasmodesma (plasmodesmata pl.) is the cytoplasm
present along the pit. It can stream from one cell to
another.
Eukaryotic cells and prokaryotic cells
Eucaryotic cell has membrane bounded nucleus and other
organelles such as mitochondria. The membrane bounded
organelles provide compartmentation to give specific
conditions for the various biochemical reactions.
Prokaryotic cell:
Bacterial cells and blue green algae are of this type. The DNA is
not bounded by nuclear envelop. It does not have other
membrane bounded organelles.