Information

6.5: Channels and carriers - Biology

6.5: Channels and carriers - Biology


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Beginning around the turn of the last century, a number of scientists began working to define the nature of cell’s boundary layer. In the 1930's it was noted that small, water soluble molecules entered cells faster than predicted based on the assumption that the membrane acts like a simple hydrophobic barrier - an assumption known as Overton's Law. There are two generic types of membrane permeability catalysts: carriers and channels.

Carrier proteins are membrane proteins that shuttle back and forth across the membrane. They bind to specific hydrophilic molecules when they are located in the hydrophilic region of the membrane, hold on to the bound molecule as they traverse the hydrophobic region of the membrane, and then release their “cargo” when they again reach the hydrophilic region of the membrane. Both the movements of carrier and cargo across the membrane, and the release of transported molecules, are driven by thermal motion (collisions with other molecules), so no other energy source is necessary. We can write this class of reactions as:


Bookshelf

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science 2002.

  • By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.


Protein Channels/ Carrier proteins

Can someone please explain the difference between a protein channel and carrier proteins.

In my book it says that intrinsic proteins act as carriers to transport water soluble molecules.

But for facilitated diffusion it says that proteins channels transport water soluble molecules across the phospholipid bilayer.

So how do water-soluble molecules get transported - is it via a protein channel or a carrier protein?

Any help will be greatly appreciated.

Not what you're looking for? Try&hellip

Yo Linked. I totally didn't get this either, but after a while I worked it out. Lemme get my notes.

Firstly, extrinsic and intrinsic proteins are just types of protein. Intrinsic means it runs across the whole membrane. Extrinsic means it's just on one side of the membrane. That's all that means. The textbook has pictures of this. Now:

  • They are intrinsic proteins, so span across the whole membrane
  • They basically make a channel/pathway/hole for stuff to go through
  • The channel that the channel proteins make, is full of water. This means only water soluble substances can pass through.
  • Facilitated diffusion happens here. This is basically diffusion, from high to low concentration. Facilitated just means that it needs this protein to work, and the protein here is the channel protein that makes the hole in the membrane. (Don't say hole, use nicer words like channel/pathway)
  • Some channels are also gated and/or selective. Gated means it opens only when appropriately stimulated. Selective means it only lets certain substances through.
  • These can do both facilitated diffusion AND active transport
  • If you want an image of what it looks like, it picks up the molecule on one side of the membrane and then changes shape and deposits it on the other side.
  • The thing to remember here is the molecule that moves across the membrane actually binds with the protein, unlike channels where the protein just makes a hole for molecules to pass through.
  • For facilitated diffusion the molecules use their inbuilt kinetic energy means to bind with the channel protein, which moves it to the other side of the membrane. As this is diffusion it is moving from high concentration to low concentration.
  • For active transport ATP is used to move molecules from low concentration to high concentration.
  • In both situations, with carrier proteins, the molecule BINDS WITH THE PROTEIN.

If I'm wrong, someone tell me. And ask if you got any questions

(Original post by Linked)
Can someone please explain the difference between a protein channel and carrier proteins.

In my book it says that intrinsic proteins act as carriers to transport water soluble molecules.

But for facilitated diffusion it says that proteins channels transport water soluble molecules across the phospholipid bilayer.

cazmasetro has given a very good summary of the characteristics of channel proteins and carrier proteins above, and it is very simple at it's crux: channel proteins are a 'tunnel' through the cell membrane, carrier proteins grab a molecule, move it to the other side of the membrane, and let it go. Super simple stuff.

Carrier proteins are a little bit more complex in the mechanisms that they use, and they have a lot of different ways of working, but I don't think you need to worry about that, and the basic description is as I've already said.

To clear up something I don't feel is very apparent in the above reply: 'facilitated diffusion' in carrier proteins just means that the process requires no energy: you don't need to expend any energy to move the molecule from one side of the membrane to another.

You also don't need to memorise the list above if you understand your basics of diffusion and active transport, and can use a bit of common sense, you can work out what channel proteins and carrier proteins do!

So how do water-soluble molecules get transported - is it via a protein channel or a carrier protein?

Any help will be greatly appreciated.

It's both! Sometimes you use channels, sometimes you use carriers, depending on the situation.

Channels, Carriers, and Pumps

An introduction to the principles of membrane transport: How molecules and ions move across the cell membrane by simple diffusion and by making use of specialized membrane components (channels, carriers, and pumps). The text emphasizes the quantitative aspects of such movement and its interpretation in terms of transport kinetics. Molecular studies of channels, carriers, and pumps are described in detail as well as structural principles and the fundamental similarities between the various transporters and their evolutionary interrelationships. The regulation of transporters and their role in health and disease are also considered.

An introduction to the principles of membrane transport: How molecules and ions move across the cell membrane by simple diffusion and by making use of specialized membrane components (channels, carriers, and pumps). The text emphasizes the quantitative aspects of such movement and its interpretation in terms of transport kinetics. Molecular studies of channels, carriers, and pumps are described in detail as well as structural principles and the fundamental similarities between the various transporters and their evolutionary interrelationships. The regulation of transporters and their role in health and disease are also considered.


Channels

The integral proteins involved in facilitated transport are collectively referred to as transport proteins, and they function as either channels for the material or carriers. In both cases, they are transmembrane proteins (they span across the membrane). Channels are specific for the substance that is being transported. Channel proteins have hydrophilic domains exposed to the intracellular and extracellular fluids they additionally have a hydrophilic channel through their core that provides a hydrated opening through the membrane layers (Figure 1). Passage through the channel allows polar compounds to avoid the nonpolar central layer of the plasma membrane that would otherwise slow or prevent their entry into the cell. Aquaporins are channel proteins that allow water to pass through the membrane at a very high rate.

Figure 1 Facilitated transport moves substances down their concentration gradients. They may cross the plasma membrane with the aid of channel proteins. (credit: modification of work by Mariana Ruiz Villareal)


Step by Step Explanation of Electron Transport System

The electron transport system can be summarized into the following steps:

Step 1: Generation of proton motive force

In the first step of the electron transport chain, the NADH + and FADH2 molecule of glycolysis and Kreb’s cycle is oxidized into NAD + and FAD, respectively, along with the release of high energy electrons and protons. The electrons diffuse into the inner mitochondrial membrane that consists of a series of large protein complexes.

The passage of electrons from one carrier protein to another results in the loss of some energy or ATP. The ATP is then used up by the protein complexes to move the protons from the matrix to the intermembrane space. Thus, the diffusion of protons across the inner mitochondrial membrane is mediated via chemiosmosis, which creates a proton motive force across the electrochemical gradient.

Step 2: Synthesis of high energy molecule ATP

The H + ions generate a proton motive force that facilitates the downhill movement across the concentration gradient of the inner mitochondrial membrane. H + ions tend to diffuse back into the mitochondrial matrix through the channel proteins via a transmembrane enzyme (ATP synthase), and thereby producing ATP.

Step 3: Oxygen reduction

For the continuation of the electron transport system, the de-energized electrons must be release out via an electron acceptor O2molecule. Oxygen accepts the electrons from the fourth complex. Eventually, the oxygen carrier associates with the free protons and reduces to yield H2O.

Components of ETS

The electron transport system is the combination of the following elements:

Complex I

It is composed of flavin mononucleotide and iron-sulphur protein. Complex I or “NADH dehydrogenase” oxidizes NADH + into NAD + and releases two electrons and four protons. NADH dehydrogenase pumps out four protons from the matrix to the cytosol and transfers two electrons in the inner mitochondrial membrane. Thus, NADH dehydrogenase creates a high H + ion concentration across the electrochemical gradient.

Coenzyme-Q or “Ubiquinone” connects complex I and II. Ubiquinone is a lipid-soluble complex, which can move freely in the hydrophobic core of the mitochondrial membrane. Q reduces into QH2 and delivers its electron to the third complex. Coenzyme-Q receives the electron released from the NADH and FADH2 molecules.

Complex II

It consists of an enzyme, “Succinate dehydrogenase”, and contains iron and succinate. Complex II oxidizes FADH2 into FAD + . Succinate dehydrogenase plus FADH2 directly transfers the electrons to the ETC, bypassing complex I. It does not energize the complex I and produce a few ATPs.

Complex III

Cytochrome-b, Oxidoreductase or complex III consists of Fe-S protein with Rieske centre (2Fe-Fs). In cytochromes, the prosthetic group is heme, carrying electrons. As the electrons pass, the iron is reduced to Fe 2+ and oxidized to Fe 3+ . Therefore, cytochrome-b transfers electrons to the next complex, i.e. cytochrome c.

Cytochrome c

Cytochrome-c also contains Fe-S protein and prosthetic heme group. It only accepts one electron at a time and further transports electrons to the fourth complex.

Complex IV

It is composed of Cytochrome a and a3, which contains two heme groups (one in each). Cytochrome-a3 consists of three copper ions (two CuA and one CuB). The function of complex IV is to hold the oxygen carrier firmly between the iron and copper ions until the reduction of oxygen into a water molecule. Oxygen combines with the two proton molecules and releases water by maintaining the membrane ion potential.

Complex V

It is the protein ion channel consisting of a transmembrane enzyme (ATP-synthase or ATP-synthase complex). Complex V allows the passage of protons from a high to low concentration against the potential gradient. The chemiosmotic passage of the protons results in molecular rotation of the enzyme ATP synthase and thereby causing a release of ATP.

Electron Transport Chain Summary

ETS refers to a system producing energy in the form of ATP via a series of chemical reactions. The ETS is located in the inner membrane of mitochondria, containing electron carrier protein complexes, electron carriers and channel proteins. Electrons pass from one complex to the other by redox reactions.

The free energy during electron transfer is captured as a proton gradient and used up by the ATP synthase to derive ATP. The electron carrier Co-Q receives the electrons formed by the reduction of FADH2 and NADH. Coenzyme-Q reduces into QH2 and passes the electrons to the third protein complex (cyt-b).

Complex III contains a heme group, where the Fe 3+ reduces into Fe 2+ after accepting the electrons coming from Co-Q. The third complex further transfers the electrons to cyt-c, where Fe 3+ reduces into Fe 2+ and transfers electrons to the fourth complex.

Complex IV accepts the electrons and transfers them to the oxygen carrier. The oxygen carries the de-energized electrons and combines with the free proton ions in the matrix, and releases waste in the form of water.

Mechanism of Electron Transport System

The electron transport chain sometimes refers to the “Respiratory chain”, which is the third or final stage of cellular respiration. It requires the presence of oxygen to carry out cellular respiration. The energy is produced during the transfer of electrons from one carrier to the other.

A cell harnesses the energy loss during electron transport to pump protons into the cytosol. It creates a chemiosmotic gradient. A chemiosmotic gradient becomes charged by the potential energy of the electrons. Finally, the potential energy converts into chemical energy (ATP) by the ATP synthase complex.

Thus, the electron transport system is an energy-producing mechanism, which obeys the principle of “Takes energy to make energy”. The ETS possesses a series of redox reactions where the electrons lose energy. The membrane uses the energy loss during the diffusion of protons back into the matrix and creates a high energy molecule, ATP.

Location of ETS

The electron transport system and its protein complexes, along with the ATP synthase channel protein, are located in the inner mitochondrial membrane. In a diagram, we could see the site of the electron transport chain, which is present in between the cytosol and matrix.

There are four large protein complexes in the electron transport chain, which mediate the transfer of electrons. In addition to protein complexes, there are individual electron carriers present like Co-Q and Cyt-C.

Both coenzyme-Q and cytochrome-C are diffusible electron carriers, which can travel within the membrane. Besides this, there is one ion channel protein (ATP-synthase) that mediates the transport of protons down the concentration gradient by generating ATP.

Equation of ETC

The overall reaction in the electron transport chain can be equated in a way given in a picture. In the electron transport chain, per molecule of glucose can produce 34 molecules of ATP, as given in the equation below:


Thus, the net production of energy in the electron transport chain is 34 ATP molecules.


Active Transport

Active transport mechanisms require the use of the cell’s energy, usually in the form of adenosine triphosphate (ATP). If a substance must move into the cell against its concentration gradient—that is, if the concentration of the substance inside the cell is greater than its concentration in the extracellular fluid (and vice versa)—the cell must use energy to move the substance. Some active transport mechanisms move small-molecular weight materials, such as ions, through the membrane. Other mechanisms transport much larger molecules.

Electrochemical Gradient

We have discussed simple concentration gradients—differential concentrations of a substance across a space or a membrane—but in living systems, gradients are more complex. Because ions move into and out of cells and because cells contain proteins that do not move across the membrane and are mostly negatively charged, there is also an electrical gradient, a difference of charge, across the plasma membrane. The interior of living cells is electrically negative with respect to the extracellular fluid in which they are bathed, and at the same time, cells have higher concentrations of potassium (K + ) and lower concentrations of sodium (Na + ) than does the extracellular fluid. So in a living cell, the concentration gradient of Na + tends to drive it into the cell, and the electrical gradient of Na + (a positive ion) also tends to drive it inward to the negatively charged interior. The situation is more complex, however, for other elements such as potassium. The electrical gradient of K + , a positive ion, also tends to drive it into the cell, but the concentration gradient of K + tends to drive K + out of the cell (Figure 1). The combined gradient of concentration and electrical charge that affects an ion is called its electrochemical gradient.

Practice Question

Figure 1. Electrochemical gradients arise from the combined effects of concentration gradients and electrical gradients. (credit: “Synaptitude”/Wikimedia Commons)

Injection of a potassium solution into a person’s blood is lethal this is used in capital punishment and euthanasia. Why do you think a potassium solution injection is lethal?

Moving Against a Gradient

To move substances against a concentration or electrochemical gradient, the cell must use energy. This energy is harvested from ATP generated through the cell’s metabolism. Active transport mechanisms, collectively called pumps, work against electrochemical gradients. Small substances constantly pass through plasma membranes. Active transport maintains concentrations of ions and other substances needed by living cells in the face of these passive movements. Much of a cell’s supply of metabolic energy may be spent maintaining these processes. (Most of a red blood cell’s metabolic energy is used to maintain the imbalance between exterior and interior sodium and potassium levels required by the cell.) Because active transport mechanisms depend on a cell’s metabolism for energy, they are sensitive to many metabolic poisons that interfere with the supply of ATP.

Two mechanisms exist for the transport of small-molecular weight material and small molecules. Primary active transport moves ions across a membrane and creates a difference in charge across that membrane, which is directly dependent on ATP. Secondary active transport describes the movement of material that is due to the electrochemical gradient established by primary active transport that does not directly require ATP.

Carrier Proteins for Active Transport

An important membrane adaption for active transport is the presence of specific carrier proteins or pumps to facilitate movement: there are three types of these proteins or transporters (Figure 2). A uniporter carries one specific ion or molecule. A symporter carries two different ions or molecules, both in the same direction. An antiporter also carries two different ions or molecules, but in different directions. All of these transporters can also transport small, uncharged organic molecules like glucose. These three types of carrier proteins are also found in facilitated diffusion, but they do not require ATP to work in that process. Some examples of pumps for active transport are Na +– K + ATPase, which carries sodium and potassium ions, and H +– K + ATPase, which carries hydrogen and potassium ions. Both of these are antiporter carrier proteins. Two other carrier proteins are Ca2 + ATPase and H + ATPase, which carry only calcium and only hydrogen ions, respectively. Both are pumps.

Figure 2. A uniporter carries one molecule or ion. A symporter carries two different molecules or ions, both in the same direction. An antiporter also carries two different molecules or ions, but in different directions. (credit: modification of work by “Lupask”/Wikimedia Commons)

Primary Active Transport

The primary active transport that functions with the active transport of sodium and potassium allows secondary active transport to occur. The second transport method is still considered active because it depends on the use of energy as does primary transport (Figure 3).

Figure 3. Primary active transport moves ions across a membrane, creating an electrochemical gradient (electrogenic transport). (credit: modification of work by Mariana Ruiz Villareal)

One of the most important pumps in animals cells is the sodium-potassium pump (Na + -K + ATPase), which maintains the electrochemical gradient (and the correct concentrations of Na + and K + ) in living cells. The sodium-potassium pump moves K + into the cell while moving Na+ out at the same time, at a ratio of three Na + for every two K + ions moved in. The Na + -K + ATPase exists in two forms, depending on its orientation to the interior or exterior of the cell and its affinity for either sodium or potassium ions. The process consists of the following six steps.

  1. With the enzyme oriented towards the interior of the cell, the carrier has a high affinity for sodium ions. Three ions bind to the protein.
  2. ATP is hydrolyzed by the protein carrier and a low-energy phosphate group attaches to it.
  3. As a result, the carrier changes shape and re-orients itself towards the exterior of the membrane. The protein’s affinity for sodium decreases and the three sodium ions leave the carrier.
  4. The shape change increases the carrier’s affinity for potassium ions, and two such ions attach to the protein. Subsequently, the low-energy phosphate group detaches from the carrier.
  5. With the phosphate group removed and potassium ions attached, the carrier protein repositions itself towards the interior of the cell.
  6. The carrier protein, in its new configuration, has a decreased affinity for potassium, and the two ions are released into the cytoplasm. The protein now has a higher affinity for sodium ions, and the process starts again.

Several things have happened as a result of this process. At this point, there are more sodium ions outside of the cell than inside and more potassium ions inside than out. For every three ions of sodium that move out, two ions of potassium move in. This results in the interior being slightly more negative relative to the exterior. This difference in charge is important in creating the conditions necessary for the secondary process. The sodium-potassium pump is, therefore, an electrogenic pump (a pump that creates a charge imbalance), creating an electrical imbalance across the membrane and contributing to the membrane potential.

Secondary Active Transport (Co-transport)

Secondary active transport brings sodium ions, and possibly other compounds, into the cell. As sodium ion concentrations build outside of the plasma membrane because of the action of the primary active transport process, an electrochemical gradient is created. If a channel protein exists and is open, the sodium ions will be pulled through the membrane. This movement is used to transport other substances that can attach themselves to the transport protein through the membrane (Figure 4). Many amino acids, as well as glucose, enter a cell this way. This secondary process is also used to store high-energy hydrogen ions in the mitochondria of plant and animal cells for the production of ATP. The potential energy that accumulates in the stored hydrogen ions is translated into kinetic energy as the ions surge through the channel protein ATP synthase, and that energy is used to convert ADP into ATP.

Practice Question

An electrochemical gradient, created by primary active transport, can move other substances against their concentration gradients, a process called co-transport or secondary active transport.

Figure 4. (credit: modification of work by Mariana Ruiz Villareal)


Facilitated diffusion

Many water-soluble molecules that cannot penetrate the lipid bilayer are too large to fit through open channels. In this category are sugars and amino acids. Some ions too do not diffuse through channels. These vital substances enter and leave the cell through the action of membrane transporters, which, like channels, are intrinsic proteins that traverse the cell membrane. Unlike channels, transporter molecules do not simply open holes in the membrane. Rather, they present sites on one side of the membrane to which molecules bind through chemical attraction. The binding site is highly specific, often fitting the atomic structure of only one type of molecule. When the molecule has attached to the binding site, then, in a process not fully understood, the transporter brings it through the membrane and releases it on the other side.

This action is considered a type of diffusion because the transported molecules move down their concentration gradients, from high concentration to low. To activate the action of the transporter, no other energy is needed than that of the chemical binding of the transported molecules. This action upon the transporter is similar to catalysis, except that the molecules (in this context called substrates) catalyze not a chemical reaction but their own translocation across the cell membrane. Two such substrates are glucose and the bicarbonate ion.


Differences Between Carrier and Channel Proteins

Mechanism

▶ Carrier proteins transfer solutes across the biological membrane by binding to the solute and alternate between two conformations. Their mechanism is similar to enzyme-substrate reactions following Michaelis-Menten equation (however, they do not change the substrate, i.e., the solute).

▶ Channel proteins interact the least with the solute they transfer.

Nature of Solute

▶ Carrier proteins transfer both polar and nonpolar solutes across the biological membrane.

▶ Channel proteins transfer only small and polar solutes across the biological membrane.

Specificity

Would you like to write for us? Well, we're looking for good writers who want to spread the word. Get in touch with us and we'll talk.

▶ Specificity of carrier proteins is due to the specific binding sites to which the solute molecules bind.

▶ Specificity of channel proteins is due to an ion selectivity filter.

Ion selectivity filter: In simplest words, it can be defined as the narrowest part of the pore which will only allow the passage of specific molecules with a particular size and charge to pass through.

Rate of Transfer of Solute

▶ The rate of transfer of solute by carrier proteins is about 10 4 ions per second.

▶ As the proteins do not flip from one conformation to the other, the rate of transfer of solute by channel proteins is much higher, i.e., 10 8 ions per second.

Nature of Transport

▶ Carrier proteins usually transport molecules against the concentration gradient to do so, they require energy. This energy can be supplied to it either by hydrolysis of ATP (known as active transport) or can be coupled with the transfer of another solute molecule (known as facilitated diffusion).

Examples of Carrier Protein-mediated Active Transport

1. Na + /K + ATPase: It plays an important role in the uptake of glucose by the cell. Three Na + ions are pumped out of the cell, and two K + ions are pumped inside the cell. This takes place against the concentration gradient, and 1 ATP is consumed for this process. These Na + ions help to bring glucose inside the cell (discussed below).

2. SR Ca 2+ ATPase: It is present in the Sarcoplasmic Reticulum (abbreviated as SR specialized Endoplasmic Reticulum present in muscle cells). Two Ca 2+ ions are transported from the cytosol into the SR. This step consumes 1 ATP and is required for the contraction of muscles.

Examples of Carrier Protein-mediated Facilitated Diffusion

1. Symport: Co-transport of molecules or ions in the same direction of the biological membrane.

E.g. Na + -driven glucose pump: It is present in the intestinal epithelial cells. Glucose is taken up by the intestinal cells with this pump. Here, the glucose moves against its concentration gradient. The energy to perform this is supplied by the movement of Na + ions into the cells this movement is down its concentration gradient and is favored.

2. Antiport: Co-transport of molecules or ions in the opposite direction of the biological membrane.

E.g. Na + /Ca 2+ exchanger: Here, Na + ions move down their concentration gradients, and this provides energy for the movement of Ca 2+ against its concentration gradient. Three Na + ions are transported inside the cell, and one Ca 2+ ion is pumped out of the cell.

Channel proteins always transport molecules down the concentration gradient by a process of diffusion and, hence, mediate passive transport.

Examples of Channel Protein-mediated Passive Transport

Ion channels are not continuously open and are said to be gated, which open only in response to specific stimulus.

1. Voltage-gated Channels: These ion channels are activated when there is a potential difference generated across the biological membrane. An example is voltage-dependent calcium channels, which are found on the cell membrane of neurons, glial cells, and muscle cells. These channels are activated when there is a potential difference across the membrane and cause an influx of Ca 2+ ions inside the cells. They may play a role in neurotransmission, muscle relaxation, gene expression, etc., depending on the type of cell on which they are present.

2. Ligand-gated Channels: Nicotinic Acetylcholine Receptor (nAchR) channel is usually found in neuromuscular junctions. When the nAchR channel binds to the neurotransmitter, acetylcholine (ligand), the closed channels open and allow the influx of Na + ions, thus helping in the contraction of muscles.

Related Posts

A membrane protein refers to a protein molecule that is associated with or attached to the membrane of a cell. BiologyWise explains the difference between peripheral and integral membrane proteins.

The following article presents before us monocot vs. dicot differences by considering their various features. Read on to known more about dicotyledon and monocotyledon classifications.

Cytosol is basically the liquid or an aqueous part of cytoplasm, where the other parts of the cytoplasm such as various organelles and particles remain suspended. Read on to find&hellip


Difference Between Channel and Carrier Proteins

Definition

Channel Proteins: Channel proteins are proteins that have the ability to form hydrophilic pores in cells’ membranes, transporting molecules down the concentration gradient.

Carrier Proteins: Carrier proteins are integral proteins that can transport substances across the membrane, both down and against the concentration gradient.

Direction of transport

Channel Proteins: Channel proteins transport substances down the concentration gradient.

Carrier Proteins: Carrier proteins transport substances both down and against the concentration gradient.

Mechanism of the transport

Channel Proteins: Channel proteins form pores crossing the membrane, thus allowing the target molecules or ions to pass through them by diffusion, without interaction.

Carrier Proteins: Carrier proteins bind to molecules or ions on one side of the membrane and release them on the other.

Types

Channel Proteins: Depending on the factor that activates or inactivates them, the channel proteins arepotential-dependent, ligand-dependent, mechanically dependent channel proteins, etc.

Carrier Proteins: Depending on the characteristic of the transport carrier proteins are uniporters, symporters, antiporters, etc .

Energy consumption

Channel Proteins: Channel proteins do not consume energy to transport molecules and ions down the concentration gradient.

Carrier Proteins: Carrier proteins need energy to transport substances against the concentration gradient. The transport of molecules and ions down the concentration gradient does not require energy.

Examples

Channel Proteins: Examples of channel proteins include chloride, potassium, calcium, sodium ion channels, aquaporins, etc.

Carrier Proteins: Examples of carrier proteins are sodium-potassium pump, glucose-sodium cotransport, valinomycin, etc.


Watch the video: Facilitated diffusion. Membranes and transport. Biology. Khan Academy (November 2022).