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PinkMonkey Online Study Guide-Biology

3.2 Structure of cell

Both prokaryotic and eukaryotic cells possess the basic features of a plasma membrane and cytoplasm. The plasma membrane is the outermost surface of the cell which separates the cell from the environment. The cytoplasm is the aqueous content within the plasma membrane.

Plasma membrane : It is like any other membrane in the cell but it plays a very important function. It forms the border of a cell, so it is also called the cell membrane. It is primarily composed of proteins and phosphalipid. The phospholipids occur in two layers referred to as a bilayer. Protein is embedded within the lipid layer, or attached to the surface of it. The plasma membrane is elastic and very fluid because of protein and lipid. Normally the function of the plasma membrane is that of a gate-keeper. It allows certain important substances to enter and exit the cell.


Cytoplasm and organelles : The cytoplasm is a semi-solid substance which is present in the cell and which gives structure, size, shape and foundation to the cell. It is enclosed by the plasma membrane. Within the cytoplasm are a number of microscopic bodies called organelles that perform various functions essential for the survival of the cell.

Figure 3.2 Endoplasmic reticulum with the nucleus and the Golgi complex

Endoplasmic reticulum (ER) : is one of the important organelles present in the cytoplasm. Endoplasmic reticulum is a series of membranes which extend throughout the cytoplasm in eukaryotic cells. In certain cases in ER there are submicroscopic bodies called ribosomes which are involved in production of protiens.

Rough ER : In this kind of ER the ribosomes are presenton the surface.The endoplasmic reticulum is responsible for protein synthesis in a cell. Ribosomes are suborganelles in which the amino acids are actually bound together to form proteins. There are spaces within the folds of ER membrane are known as cisternae.

Smooth ER : This type of ER does not have ribosomes.

Another organelle is the Golgi body or Golgi apparatus (G.A.). The Golgi body is a series of flattened sacs usually curled at the edges. Proteins which have formed in ER are processed in G.A. After processing, the final product is discharged form the G.A. At this time the G.A. bulges and breaks away to form a dropline vesicle known as secretory vesicles. The vesicles move butward to the cell membrane and either insert their protien contents in the membrane, or release their contents outside the cell.

There is another organelle which is related to the Golgi apparatus called the lysosome. The lysosome is derived from the Golgi body. It is a sac of enzymes in the cytoplasm, used for digestion within the cell. These enzymes break down particles of food taken into the cell and make the food product available for use. There are also cytoplasmic organelles called peroxisomes in the cell which produces the enzymes to degrade fatmolecules.

Table of Contents

3.0 Introduction
3.1 Modern cell theory
3.2 Structure of cell
3.3 Movement through the plasma membrane

Chapter 4





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