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 mitochondria (pl)

For aerobic respiration

Chloroplast

For photosynthesis

Lysosome

For intra-cellular digestion

The fluid mosaic model of cell membrane

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.

ATPase is an example of enzyme.

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

matrix

crista

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.

Aerobic respiration consists of three main stages, namely glycolysis, Krebs cycle and oxidative 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.