Active Absorption: Primary Active Transport, Pumps, Secondary Active Transport, Symport, Antiport, and Cytochrome Pump
Transport of the solutes against the gradient of concentration constitutes Active Absorption. Ions and other substances are actively transported by membrane-based channels, pumps, and carriers. Cytochrome and electrogenic pumps are involved. Primary active transportation and secondary active transportation are the other two categories of active transportation.
Primary Active Transport
It is referred to as primary active transport when the movement of ions is directly linked to the use of metabolic energy, such as ATP hydrolysis, an oxidation-reduction reaction (the electron transport chain of mitochondria and chloroplast), or light absorption by the carrier protein (in halobacteria, bacteriorhodopsin).
Pumps are membrane proteins that take part in primary active transport. The majority of pumps move energetic ions like Ca2+ or H+. Additionally, the pumps can be classified as Electrogenic or electroneutral.
Electroneutral transport involves no net movement of charge, in contrast to Electrogenic transport, which is ion transport including the net flow of charge across the membrane. The ATPase enzyme, which is found at the plasma membrane and tonoplast, hydrolyzes ATP, releasing energy in the process. Because of its crucial function in controlling the cytoplasmic pH and acting as the catalyst for cation and anion absorption, this enzyme is known as a “master enzyme.” An animal cell’s Na+/K+-ATPase, for instance, pumps three Na+ ions for every two K+ ions it absorbs, resulting in a net outward movement of one positive charge. Therefore, the Na+/K+-ATPase is an electrogenic ion pump. The animal stomach mucosa’s H+/K+-ATPase, in contrast, pumps one H+ out of the cell for every one K+ that is taken in, preventing any net flow of charge across the membrane. The H+/K+-ATPase is an electroneutral pump as a result. The main ion that is electrochemically pushed through the cell membranes of bacteria, fungi, and plants is often H+. While the vacuolar H+-ATPase (V-ATPase) and the H+ pyrophosphatase (H+- ppase) pump proton into the lumen of vacuoles and Golgi cisternae, respectively, the plant H+-ATPases play a regulatory role in establishing the electrochemical potential gradient across the plasma membrane.
Secondary Active Transport
The coupling of an ion’s or solute’s “uphill” transport to a “downhill” transport is another significant method by which solutes can pass a membrane against the gradient of electrochemical potential. Such cotransport of ions/solutes is carried out by carrier proteins in membranes and is also known as “secondary active transport.” Pumps provide a secondary source of power for these carriers. When an ion is transported through a carrier protein, it is initially bound to that protein at a particular location. As a result of this interaction, the protein undergoes a conformational shift that makes the material on the opposite side of the membrane accessible to the solution. Substance dissociation from the binding site of the carrier indicates successful transport. In comparison to transport through a channel, the rate of transport by a carrier is approximately 106 times slower. The proton-motive force (PMF), or p, produced when protons are expelled from the cytosol by the electrogenic H+-ATPases, is used as energy for secondary active transport. Membrane potential and pH gradient form in place of ATP hydrolysis at the plasma membrane as well as the vacuolar membrane as a result. When utilized to propel the transport of other substances against their chemical potential gradient, the PMF reflects either stored free energy or the H+ gradient.
The secondary active transport can either be symport (two ions or solutes traveling in the same direction) or antiport (downhill proton movement drives active (uphill) transport of solute in the opposite direction). 100–1,000 ions or molecules per second could be transported via carriers. Ion channels are known to exist in plant cell membranes. These ion channels have a special capacity to control or “gate” ion flux in response to the physical and chemical surroundings of the channel protein. Transient solute binding to the channel protein may or may not occur during transport via the channel. In any instance, a solute that can enter the pore diffuses through it very quickly as long as the channel pore is open. Ion transfer through channels is passive at all times. The specificity of the transport depends on the size of the pores and the density of the charges on the interior lining; ion or water transport may be the major focus. The selectivity filter refers to the portion of the channel that controls specificity. The majority of the time, ion channels are closed, and there are just a few of them per cell. The term “aquaporins” refers to a class of proteins that create water channels and are rather common in membranes. Aquaporins are found in both plant and animal membranes; several processes, including protein phosphorylation, control how they express and function in response to water availability.
This theory was put forth by H. Lundegardh in 1954 after he saw that respiration and anion absorption had a quantitative link, but that cation absorption lacked such a relationship. Also observed was that cyanide or even carbon monoxide impeded salt respiration and anion absorption. He consequently proposed that the cytochrome system may transport anions across the membrane and that anion absorption is independent of the cation. Using respiratory intermediates directly as fuel, energy is produced. “Anion respiration” or “salt respiration” is the term used to describe the rate of respiration that is completely governed by anion absorption. Ground respiration is the rate of respiration (apart from anion respiration) that is seen in distilled water.
Total respiration t= Ground respiration + Salt or anion respiration
Frequently Asked Questions
Question: What is active absorption?
Ans: Transport of the solutes against the gradient of concentration constitutes active absorption. Ions and other substances are actively transported by membrane-based channels, pumps, and carriers.
Question: What is needed for active absorption?
Ans: It is referred to as primary active transport when the movement of ions is directly linked to the use of metabolic energy, such as ATP hydrolysis, an oxidation-reduction reaction (the electron transport chain of mitochondria and chloroplast), or light absorption by the carrier protein (in halobacteria, bacteriorhodopsin).
Question: Which organ is involved in active absorption?
Ans: Large intestine
Question: Can your stomach absorb water?
Question: Where is most water absorbed in the body?
Ans: Proximal small intestine
Question: How long does it take a glass of water to reach your bladder?
Ans: Water absorption can start as soon as five minutes after eating and reaches its peak 20 minutes later.
Question: What are Pumps in Active Absorption?
Ans: Pumps are membrane proteins that take part in primary active transport. The majority of pumps move energetic ions like Ca2+ or H+.