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Cell wall and cell membrane - Biology

Most prokaryotic organisms, particularly bacterial cells, have a chemically complex cell membrane. The cell envelope comprises three layers: an exterior glycocalyx, a cell wall, and a plasma membrane that are all tightly linked together.

Cell Wall

The plasma membrane is surrounded by a non-living, rigid structure termed the cell wall in bacteria, fungus, algae, and plants. It protects internal systems and offers cell structure because of its rigidity. Its primary purpose, however, is to keep the cell from growing and bursting. Most bacteria thrive in hypotonic conditions, where they are more likely to absorb a large amount of water and ultimately break. Various groups of cells have different cell wall compositions, such as:

Cell and cell membrane

  1. Fungal cell wall: The fungal cell wall is made up of chitin, a polymer made up of N-acetyl glucosamine (NAG) units.
  2. Algal cell wall: Cellulose, mannans, galactans, and minerals such as calcium carbonate comprises the algal cell wall.
  3. Plant cell wall: A plant cell wall is mainly made up of cellulose and other insoluble polysaccharides. Hemicelluloses, pectin, and proteins are among the other substances found. Plant cell walls are divided into two sections: the main wall as well as the secondary wall.

Primary wall: A single layer of wall material develops in a young plant cell. The primary cell wall is the first layer. In a developing cell, the main wall is thin, elastic, and capable of growth. It expands by incorporating additional wall material into the existing structure. Only primary cell walls exist in meristematic and parenchymatous cells.

Secondary wall: Internally, additional wall material layers adds to the primary wall in mature cells. The secondary cell wall is made up of these layers. Thus, the cell wall thickens as a core component of a secondary wall. Thickening of cell walls is more common in cells that make up the plant's harder woody elements, like lignified and suberized cell walls.

Middle lamella: A thin, dense, granular layer of cementing material holds adjacent cells in plant tissue collectively. The middle lamella is the name given to this layer. Magnesium and Calcium pectate constitute the majority of the middle lamella. The pectate molecules in ripening fruits dissolve to form a jelly-like consistency, making the fruits squishy. In addition, plasmodesmata, which connects the cytoplasm of adjacent plant cells, may pass through the cell wall with the middle lamella.

Functions of cell wall

The cell wall involves various processes:

  • It keeps the cells in their original shape.
  • It shields the cells from mechanical damage.
  • It protects against infections such as viruses, bacteria, and fungus.
  • It allows substances to enter and exit the cell.
  • It facilitates cell-to-cell contact and acts as a barrier to unwanted macromolecules.

Cell membrane or plasma membrane

The plasma membrane is essential for all living things as it's crucial for a cell's connection with the outside environment. The precise structure of the membrane was not examined until the 1950s when the electron microscope was invented. However, scientists were able to determine the probable structure of the plasma membrane through chemical analyses of the cell membrane. The scientists were able to figure out the possible shape of the plasma membrane thanks to chemical studies, particularly on human red blood cells.

As a result of their study, scientists have found that the cell membrane comprises lipids organized in a bilayer. These lipids' polar heads are placed on the membrane's outer borders, while their hydrophobic (non-polar) tails are placed on the interior. The polar ends (head) react with water, making it hydrophilic. It protects saturated hydrocarbons' nonpolar tail, often known as the hydrophobic tail, from water solution.

Biochemical research later showed that cell membranes also comprise protein and carbohydrates. The proportion of protein to lipids, on the other hand, varies significantly across cell types. In humans, the erythrocyte (RBC) membrane, for instance, contains about 52 per cent protein and 40% lipids.

Membrane proteins are categorized as integral and peripheral depending on how easy they are to extract—the peripheral. The membrane characterizes as "Protein icebergs floating in a sea of phospholipids" because of these proteins.

Functions of cell membrane

  • Cell growth, intercellular junction formation, secretion, endocytosis, and cell division are all dependent on its fluid nature.
  • It enables molecules to go over it. Some molecules on either side of it are selectively permeable through it.
  • Active and passive transport help move chemicals throughout the cell membrane.

 

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