The Molecular Biology Notebook Online
A Beginners' Guide to Molecular Biology

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The biology of the cell

Table of contents

Organisation of the cell

• The whole picture
• The cell elements, sorted by function
• The components of a cell... a short summary

Molecular content of the cell

Organization of the cell

The whole picture

There is not one cell , but many different types of cells . Cells are like people. Look around you and you will see that everyone has their own job. Cells are the same. They all have their own job, and are therefore specialised. The theoretical plant cell used in these pages does not exist, it is just an example I created in order to show all the elements at once. Often, in a specialised cell, not all the elements are present, but some are numerous. We will see that when examining some examples of cells .

The elements of a cell, sorted by function

Growth	At the cellular level, whichever element is involved in cell division, or the production of protein, takes part in the growth of the cell
	The nucleus The ribosomes The endoplasmic reticulum The Golgi apparatus The vacuoles The centrioles
Moving	Movements at the cellular level, are performed with the contribution of :
	The centriole The cytoskeleton Actin and tubulin proteins Flagella or undulipodia - external to the cell
Eating	Or incorporating nutrients, metabolising, producing energy, excreting involving:
	The membrane Some vacuoles The mitochondrion The chloroplast , only in plant cells The cytoplasm : many enzymatic reactions take place there.
Multiplying	A cell does not, properly speaking, breed! The reproduction of some organisms contains a step when gametes are produced. This involves a cell division called meiosis . In an organism, the multiplication of cells is called mitosis . The structures involved are:
	The nucleus and its contents The centriole The membrane The structures involved in growing or production of matter

The elements (description)

Main Component	Subcomponent	Main Function
The Cell Membrane	plasma membrane	protection cell interaction permeability, endocytosis , and exocytosis
The Nucleus	chromatin and chromosomes nucleolus nucleoplasm	genetic information storage system synthesis of ribosomes
The Cytoplasm	cytoskeleton matrix, cytosol ribosomes	cell mobility and shape Glycolysis
Endomembrane System	nuclear envelope endoplasmic reticulum Golgi complex	nuclear permeability synthesis and transport of material, protein synthesis, secretion.
Membrane organelles	mitochondria chloroplasts lysosomes peroxisomes	cell respiration photosynthesis digestion peroxidation (reaction involving H 2 O 2 oxidation )
Microtubule organelles	centriole and spindle basal body, cilia, and flagella	cell division cell motility

Chemistry of the cell : the basics

Water, salts, ions, and trace elements.	You need a bit of everything, and a lot of water...
Nucleic acids	Macromolecules of the utmost importance: DNA is the major store of genetic information, and is transcribed into RNA . RNA is then translated into protein. This sequence of events is often referred as the central DOGMA of Molecular Biology and can be summarised in the form: DNA -->(transcription)--> RNA--> (translation) --> Proteins
Sugars...	Carbohydrates, the main source of cellular energy, and also structural components of cells.
Lipids	Bipolar molecules whose configuration accounts for many of the biological membrane's properties. Some hormones (steroids ) are derived from lipids
Proteins ...	Built up from amino acids , they are the working parts of the whole. Enzymes , receptors, channels, pores, hormones, ....

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