Cell Structure

   Now I will explain the basis of cell structure, The cell is the functional basic unit of life, discovered by Robert Hooke and it is the functional and structural unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life.

   First developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that all cells come from preexisting cells.
The word cell comes from the Latin cellula, meaning, a small room. The descriptive term for the smallest living biological structure was coined by Robert Hooke in a book he published in 1665 when he compared the cork cells he saw through his microscope to the small rooms monks lived in.

Cell Structure

  

TYPES OF CELL
There are two types of cells, eukaryotic and prokaryotic.

 Procariot

   Prokaryotic cells are cells that are simpler than eukaryotic cells, prokaryotes do not have a nuclear membrane so that its genetic material in the cytoplasm, called cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. Cells generally consisting of a cell wall covering a plasma membrane though some bacteria also have a further covering layer called a capsule.

Eucariot

   Eukaryotic cells is the cell that have nuclear membrane, causing the separation of genetic material with the cytoplasm. The major difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specific metabolic activities take place. Plants, animals, fungi, slime moulds, protozoa, & algae are all Eukaryotic.

No	Organele	Procariot	Eucariot
1	Typical organisms	bacteria, archaea	protists, fungi, plants, animals
2	Type of nucleus	nucleoid region; no real nucleus	real nucleus; double membrane
3	Ribosomes	50S+30S	60S+40S
4	Mitochondria	none	one to several thousand (though some lack mitochondria)
5	Chloroplasts	None; though some have other pigments	in algae and plants
6	DNA	circular (usually)	linear molecules (chromosomes) with histone proteins
7	RNA-/protein-synthesis	coupled in cytoplasm	RNA-synthesis inside the nucleus protein synthesis in cytoplasm
8	Cytoplasmatic structure	very few structures	highly structured by endomembranes and a cytoskeleton
9	Cell movement	flagella made of flagellin	flagella and cilia containing microtubules; lamellipodia and filopodia containing actin
10	Organization	usually single cells	single cells, colonies, higher multicellular organisms with specialized cells

Subcellular components

   There are also other kinds of biomolecules in cells. This article lists these primary components of the cell, then simply describe their function.

<div style="margin: 5px 20px 20px;"><div class="smallfont" style="margin-bottom: 2px;">plasma membrane : <input value="Show" style="margin: 0px; padding: 0px; width: 60px; font-size: 10px;" onclick="if (this.parentNode.parentNode.getElementsByTagName('div')[1].getElementsByTagName('div')[0].style.display != '') { this.parentNode.parentNode.getElementsByTagName('div')[1].getElementsByTagName('div')[0].style.display = ''; this.innerText = ''; this.value = 'Hide'; } else { this.parentNode.parentNode.getElementsByTagName('div')[1].getElementsByTagName('div')[0].style.display = 'none'; this.innerText = ''; this.value = 'Show'; }" type="button"> </div><br /><div class="alt2" style="margin: 0px; padding: 6px; border: 1px inset;background: #f5f5f5 none repeat scroll 0% 50%; -moz-background-clip: -moz-initial; -moz-background-origin: -moz-initial; -moz-background-inline-policy: -moz-initial; color: rgb(127, 69, 0); line-height: 1.5em;"><div style="display:none;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="http://img841.imageshack.us/img841/9089/cellmembranedrawing.jpg"><img style="float:center; margin:0 10px 10px 0;cursor:pointer; cursor:hand;width: 128px; height: 128px;" src="http://img246.imageshack.us/img246/1215/photodofollowcopy.gif" border="0" alt="dofollow" title="dofollow" /></a>Membrane

   The cytoplasm of a cell is surrounded by a cell membrane or plasma membrane. The plasma membrane in plants is usually covered by a cell wall. This membrane serves to separate and protect a cell from its surrounding environment. <br /></div></div></div>

Cytoskeleton

    The cytoskeleton acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, the uptake of external materials by a cell, and cytokinesis, the separation of daughter cells after cell division; and moves parts of the cell in processes of growth and mobility.

Genetic material

    Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most organisms use DNA for their long-term information storage.

Organelles

    There are several types of organelles in a cell. Some (such as the nucleus and golgi apparatus) are typically solitary, while others (such as mitochondria, peroxisomes and lysosomes) can be numerous (hundreds to thousands). The cytosol is the gelatinous fluid that fills the cell and surrounds the organelles.

now i'll explain about organelles in cell, 

+ Cell nucleus

   Eukaryotes only, the nucleus is spherical and separated from the cytoplasm by a double membrane called the nuclear envelope. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing.

+ Mitochondria

   Eukaryotes only, Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. Mitochondria play a critical role in generating energy in the eukaryotic cell. Mitochondria generate the cell's energy by oxidative phosphorylation, using oxygen to release energy stored in cellular nutrients (typically pertaining to glucose) to generate ATP. Mitochondria multiply by splitting in two. Respiration occurs in the cell mitochondria.

+ Chloroplasts   

   Organelles that are modified chloroplasts are broadly called plastids, and are involved in energy storage through photosynthesis, which uses solar energy to generate carbohydrates and oxygen from carbon dioxide and water.

+ Endoplasmic reticulum

   Eukaryotes only, he endoplasmic reticulum (ER) is the transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that float freely in the cytoplasm.

+ Golgi apparatus

   Eukaryotes only, The primary function of the Golgi apparatus is to process and package the macromolecules such as proteins and lipids that are synthesized by the cell. It is particularly important in the processing of proteins for secretion.

+ Ribosomes

   The ribosome is a large complex of RNA and protein molecules. They each consist of two subunits, and act as an assembly line where RNA from the nucleus is used to synthesise proteins from amino acids.

+ Lysosomes and Peroxisomes

    Eukaryotes only, Lysosomes contain digestive enzymes (acid hydrolases). They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. Peroxisomes have enzymes that rid the cell of toxic peroxides.

+ Centrosome

    The centrosome produces the microtubules of a cell – a key component of the cytoskeleton. It directs the transport through the ER and the Golgi apparatus. Centrosomes are composed of two centrioles, which separate during cell division and help in the formation of the mitotic spindle. A single centrosome is present in the animal cells.

+ Vacuoles

    Vacuoles store food and waste. Some vacuoles store extra water. They are often described as liquid filled space and are surrounded by a membrane.