Cell Membrane and its features

Cell Membrane
Cell Membrane is a "Differentially Permeable" as welI as  "Selective Permeable"  sheath arround a ceIl that separates the cytoplasm of its cell from neighbouring cells. The membranes of the membranous organelles (called Endomembranes or Plasmamembranes) provide partitions that separate these organelles from the cytoplasm.
Common Features Of Plasma Membranes: 
Plasma Membranes show a great diversity of structure and functions. They show, however, a number of features in common. Some of the most important features are:-
1. Membranes are sheath like structures, only a few molecules thick and form °boundries
between compjirtments of different composition. For example, the membranes of mitochondria separate these organelles from the cytoplasm. Lysosome is a membranous vesicle, its membrane allows itself to maintain a different chemical composition inside the organelle.
2. Membranes are mainly composed of Lipids and Proteins. They also contain Carbohydrates in the form of Glycolipids and Glycoproteins.
3. Membrane Lipids are amphipathetic molecules (a molecule that has most of its part Hydrophobic non-ionizable and one end Hydrophylic ionizable). Stearic Acid (CI7H35COOH), for example, is amphipathetic molecule because it has 17 Carbon atoms containing hydrocarbon chain which does not ionize hence is hydrophobic. The Carboxyl (COOH) group is Hydrophylic because it ionizes as COO- group.

CH3(CH2)16  ---->  COO-
Non-Ionized            Ionized
Hydrophobic part      Hydrophylic part

Stearic Acid
The membrane lipids are arranged within the membrane to form biomolecular layer.
This lipid layer makes the membrane differentially permeable barrier because water and water soluble (ionic materials) cannot 'pass across them but fat soluble non-polar materials (oil-droplets, Fatty acis and organic solvants like Ethr, or Benzene) can move across membranes freely. Hence membranes differentiate between polar and non-polar materials.
4. Membrane Proteins help the membranes to function as selective permeable barriers. They help to regulate the movement of water and other ionic materials across the membranes. Membrane Proteins also function as molecular pumps and gates through which ionic materials enter or leave the cells. Membrane Proteins also work as enzymes and reeptors that respond to different stimuli. Some Membrane Proteins of mitochondria an chloroplasts work as members of electron transport chains that help in energy transformation.
5. The Structural Components of membranes, i.e. Lipids and Proteins are beld together by very weak hydrophobic forces.
6. The membrane Carbohydrates are present either attached to a lipid molecule and thus are called Glycolipids or attached to Proteins as Glycoproteins. Carbohydrates are present only on outer face of the membrane thus makes the membrane as asymmetric structure. Membrane Carbohydrates function as receptors that select food and reject non-food molecules react with antigens and thus stimulate the cell to produce antibodies.
7. Membranes are fluicl structures. Both Lipids and Proteins can diffuse rapidly in the plane of the membrane. Thus the membranes are regarded as two dimensional colloidal solutions of o~nted Lipids and Proteins.

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Posted in Plant Anatomy

Types of cells

Cell Types
On the basis of structural organization, the cells are divided into two main classes, i.e. prokryotic and Eukaryotic. Prokaryotic (pro-before; Karyon-nucleus) cells are simple in organization, lack certain organelles like Nucleus Mitochondria, Endoplasmic Reticulum and Golgi Complex etc. Prokaryotes like Bacteria and Blue-Green-Algae  are also called Non- nucleated cellss, because they do not have True-Nucleus and chromosomes. Instead their genetic material is present as a single circular Duplex (double-stranded) molecule of DNA, freely nded in a defmite region of cytoplasm called Nucleoid. Prokaryotic cells as they are lout nucleus, divide by direct or Amitotic cell division. Provides a comparative view of generalized plant's, Animal's and Bacterial cells.
Eukaryotic cells (Eu-True, Karyon - Nucleus) are cells that possess true nucleus (chromosomes by nuclear membrane) and membranous organelles like
Mitochondria, Endoplasmic Reticulum and Golgi complex etc. Eukaryotic cells divide to produce daughter cells by Indirect or Mitotic ceIl division. In this chapter we will describe the following Organelles of Eukaryotic celIs.

1. CELL MEMBRANE 
2. ENDOPLASMIC RETICULUM 
3. GOLGI COMPLEX
4. LYSOSOMES
5. MICROBODIES 
6. NUCLEUS
7. CYTOSKELETON 
8. CILIA AND FLAGELLA 

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Posted in Plant Anatomy

Components of structural and functional unit of life - Cell

CELL COMPONENTS 
The cell is a membrane bounded unit of Protoplasm (living matter),.. The protoplasm of the cell (Cytoplasm) is a mixture of organic and inorganic materials, which are arrangp..d to make a frame work of the cell called Matrix. Suspended in the matrix are two types of cell's Components. These are cell Inclusions and Cell Organelles.
Cell Inclusions: 
Cell Inclusions are the cell comp~nents that do not perform life activities of the cell directly but only are present in the cytoplasm: Starch Particles in Plant cells, Glycogen granules of animal cells and Polyhydroxy - Butyric Acid (PRB) crystals in some bacterial cells etc. are some examples of inclusions. Thesy inclusions function as energy storing materials inside the cells.
Cell Organelles: 
Cell Organelles (Organs - functional structure; Biles - small) means the functional structures of the cells. Organelles, therefore, are the cell components which perform life. functions of the cell. Cell membrane, Nucleus, Mitochondria, Ribosomes, and Golgi complex etc, for example, are some of the important Organelles of the cell. Each organelle performs a specific function of the cell. Organelles are divided into two main groups. These are Membranous Organelles and Non-Membranous Organelles.
Membranous Organelles: 
Cen Organelles, like cell-membrane; Nuclear membrane, Mitochondria, Endoplasmic Reticulum, Goigi complex, Lysosomes, Microbodies and Food Vacuoles etc. are called Membranous because they are made up of Unit Membrane.
Non-Membranous Organelles. 
Organelles of a cell like Ribosomes, Chromosomes, Centriole, Cilia br Flagella and Cytoskeleton etc. are called Non-Membranous because they are not composed of unit membrane, instead each is composed of some specific materials.

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Posted in Plant Anatomy

An introduction to Anatomy of Cell

Cell Anatomy
Microscopic and Physiological studies have proved that "Cell" is a unit of structure and function of "Life". A unicellular Organism like Amoeba not only lives independently but also forms all the vital activities of life like movement, Ingestion of food, metabolism, reproduction, sense of response and evolutionary progress etc. All these biological activities are not haphaazard, instead each is performed by a, structural frame work of the cell called Function Anatomy of the cell Coprdinated and directional functioning of these Organelles integrate them a unity and their dependence upon environmental "energy" Constitute what we call life in the Biological sense.
In the cell bio-molecules like Nucleic acids, Proteins, Lipids and Carbohydrates are organized into complex structures called Organelles, each of which, is responsibile for the carrying out of a specific function. For examyle, Nucleus controls cell's heredity, Mitochondria oxidize food and thus generate metabolic' energy essential for Physiological needs of the cell etc. are some of the organelles of Eukaryotic (nucleated) cells.

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Posted in Plant Anatomy