Transmembrane Transport

The cell membrane is semipermeable. Substances that pass through it can pass freely or with the help of membrane carriers. Substance transport can then be active or passive.

Passive transport
Passive transport is the transfer of substances across the cell membrane that occurs spontaneously through channels and ]]carrier proteins]]. Unlike active transport, this process does not consume any chemical energy ( ATP ). Passive transport depends on the permeability of the cell membrane, which is composed of a double layer of phospholipids and interspersed proteins. The basic types of passive transport are simple diffusion, facilitated diffusion and osmosis.



Diffusion
Diffusion is a spontaneous process of penetration of particles of one substance into another with an effort to spread evenly throughout the entire volume. It occurs due to disordered thermal movement of particles. Substances tend to move from an environment with a higher concentration to an environment with a lower concentration. Diffusion is not an energy-intensive process. Diffusion enables the movement of substances inside cells and thereby, metabolism.

Simple Diffusion
Simple diffusion enables  the transport of substances along a concentration gradient (from places with a higher concentration to places with a lower concentration). It takes place with polar molecules of small dimensions or various types of gases.

Facilitated diffusion
Facilitated diffusion is a type of passive transport in which substances cross the membrane  along their electrochemical gradient using carriers embedded in the membrane.

Osmosis
Osmosis is a type of passive transport in which a solvent (most often water) moves through a semi-permeable membrane from a space with a less concentrated solution to a space with a more concentrated solution.

Permeation through ion channels
on channels, along with transporter proteins, are structures that participate in transport across the biological membrane. We can divide them according to the principle of their opening.
 * Ion channels still open.
 * Voltage-gated ion channels.
 * Chemically gated ion channels
 * Both voltage- and chemically-gated ion channels.
 * Mechanically controlled ion channels.

Active transport
Active transport is the transfer of substances across the cell membrane, which, unlike passive transport, is associated with energy consumption. Thanks to the supplied energy, which is most often produced by splitting ATP, it is possible to carry out this transport even against the direction of the concentration gradient (concentration gradient). Active transport is enabled by specialized integral membrane proteins embedded in the cell membrane:
 * Ion pumps – ion channels equipped with the enzyme ATPase..
 * Carrier proteins equipped with an ATPase enzyme ..

Ion Pumps
Ion pumps penetrate integral proteins in the cell membrane that transport substances against a concentration gradient. During the transfer of substances, ATP is consumed.



Endocytosis
Endocytosis is an ' energy- and material demanding process characteristic of animal cells. During endocytosis,  particles from the external environment are absorbed. Cells are separated from the external environment by a cytoplasmic membrane. Some hormones, lipoprotein particles, viruses, and antibodies, but also damaged cells or bacteria, get into them through endocytosis.

Phagocytosis
Phagocytosis is the ability of cells to absorb foreign particles, microbes or damaged cells. [1] Cells capable of phagocytosis participate in the non-specific immunity of the organism – antigen presenting cells, monocytes, from which individual types of macrophages (Kupffer Cells, histiocytes, microglia and others), develop, and white blood cells (neutrophil leukocytes, eosinophil leukocytes).

Pinocytosis
Pinocytosis is one subtype of endocytosis. During pinocytosis, the cell receives extracellular fluid (extracellular fluids = ECF) and very small particles.

Exocytosis
Exocytosis is a continuous process in which the cell secretes larger particles (e.g. macromolecules) directly into the extracellular matrix through the cell membrane (plasmalemma). The membrane vesicle (vesicle) containing the secretion travels to the membrane, fuses with it and subsequently releases the internal contents into its surroundings.

Related Articles

 * Active transport
 * Antiport
 * Diffusion
 * Endocytosis
 * Phagocytosis
 * Ion Channels
 * Pinocytosis