The structure of the plasma membrane in detail

The cells of plants, fungi and animals consist of such three components as the nucleus, cytoplasm with organoids and inclusions located in it, and a plasma membrane. The nucleus is responsible for storing genetic material recorded on DNA, and also controls all cell processes. The cytoplasm contains organoids, each of which has its own functions, such as, for example, the synthesis of organic substances, cellular respiration, cellular digestion, etc. And the last component will be discussed in more detail in this article.

What is a membrane in biology?

In simple terms, this is the shell. However, it is not always completely impenetrable. Almost always transport of certain substances through the membrane is allowed.

In cytology, membranes can be divided into two main types. The first is a plasma membrane that covers the cell. The second is the membranes of organoids. There are organelles that have one or two membranes. The Golgi complex, endoplasmic reticulum, vacuoles, and lysosomes are one-membrane. The plastids and mitochondria belong to the two-membrane ones.

Also, membranes can be inside organoids. These are usually the derivatives of the inner membrane of the two-membrane organelles.

How are membranes of two-membrane organoids arranged?

Plastids and mitochondria have two membranes. The outer membrane of both organelles is smooth, but the inner membrane forms the structures necessary for the functioning of the organoide.

Thus, the mitochondrial membrane has projections inward - cristae or crests. They are the cycle of chemical reactions necessary for cellular respiration.

The derivatives of the internal membrane of chloroplasts are disk-shaped sacs - thylakoids. They are gathered in piles of granules. The individual granules are joined together by lamellae-long structures, also formed from membranes.

The structure of membranes of single-membrane organelles

Such organelles have one membrane. It is usually a smooth shell consisting of lipids and proteins.

Features of the structure of the plasma membrane of the cell

The membrane consists of substances such as lipids and proteins. The structure of the plasma membrane provides for its thickness of 7-11 nanometers. The bulk of the membrane is made up of lipids.

The structure of the plasma membrane provides for the presence of two layers in it. The first is a double layer of phospholipids, and the second is a layer of proteins.

Lipids of the plasma membrane

The lipids that make up the plasma membrane are divided into three groups: steroids, sphingophospholipids and glycerophospholipids. The molecule of the latter contains in its composition the trihydric alcohol residue of glycerol, in which the hydrogen atoms of the two hydroxyl groups are replaced by fatty acid chains, and the third hydroxyl group hydrogen atom is a phosphoric acid residue to which the residue of one of the nitrogen bases is attached.

The molecule of glycerophospholipids can be divided into two parts: the head and tails. The head is hydrophilic (that is, it dissolves in water), and the tails are hydrophobic (they repel water, but dissolve in organic solvents). Thanks to this structure, the molecule of glycerophospholipids can be called amphiphilic, i.e., hydrophobic, and hydrophilic simultaneously.

Sphingophospholipids are similar in chemical structure to glycerophospholipids. But they differ from those mentioned above in that they have the remainder of sphingosine alcohol instead of the remainder of glycerol. Their molecules also have heads and tails.

In the picture below, the structure of the plasma membrane is clearly visible.

Proteins of the plasma membrane

As for the proteins that make up the structure of the plasma membrane, these are mainly glycoproteins.

Depending on the location in the shell, they can be divided into two groups: peripheral and integral. The first are those that are on the surface of the membrane, and the latter are those that permeate the entire thickness of the membrane and are inside the lipid layer.

Depending on the functions that proteins perform, they can be divided into four groups: enzymes, structural, transport and receptor.

All proteins that are in the structure of the plasma membrane are not chemically bonded to phospholipids. Therefore, they can freely move in the main layer of the membrane, assemble in groups, etc. That is why the structure of the plasma membrane of the cell can not be called static. It is dynamic, as it changes all the time.

What role does the cell membrane play?

The structure of the plasma membrane allows it to cope with five functions.

The first and the main - the restriction of cytoplasm. Thanks to this, the cell has a constant shape and size. This function is achieved due to the fact that the plasma membrane is strong and elastic.

The second role is to provide intercellular contacts. Due to their elasticity, the plasma membranes of animal cells can form outgrowths and folds at their junctions.

The next function of the cell membrane is transport. It is provided by special proteins. Thanks to them, the necessary substances can be transported to the cage, and unnecessary - to be disposed of.

In addition, the plasma membrane performs an enzymatic function. It is also carried out through proteins.

And the last function is signaling. Due to the fact that proteins under the influence of certain conditions can change their spatial structure, the plasma membrane can send the cells signals.

Now you know everything about membranes: what is a membrane in biology, what they are like, how the plasma membrane and membranes of organoids are arranged, what functions they perform.