Name: transport across cell membranes
Uploaded: 2023-06-23T15:38:45.000Z
Duration: 1 min 19 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Biology

BIO.5

BIO.5.C

Facilitated Transport

Solutes like charged ions are repelled by the hydrophobic layer of the membrane, thereby halting diffusion. During the process of facilitated transport or facilitated diffusion, molecules can travel across the membrane via channels and carrier proteins that enable diffusion without requiring additional energy.
The first type, channel proteins, form a hydrophilic pore through which charged molecules can pass, thus avoiding the hydrophobic layer of the membrane. These channels are either always open or gated by some mechanism to control flow.
The second type, carriers, bind to a specific solute that changes the protein conformation, enabling the movement of solute down the gradient. For this reason, the rate of transport is not dependent on the concentration gradient, but rather on the number of carrier proteins available.
Even though it is more complex than simple diffusion, facilitated transport enables diffusion to occur at incredible rates, with channel proteins moving tens of millions of molecules a second and carrier proteins moving 1,000 to a million molecules a second.

facilitated transport

The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and hydrophilic regions, substances need to be able to transverse both regions. The hydrophobic area of membranes repels substances such as charged ions. Therefore, such substances need special membrane proteins to cross a membrane successfully. In&#160; facilitated transport, also known as facilitated diffusion, molecules and ions travel across a membrane via two types of membrane transport proteins: channel proteins&#160; and carrier proteins. These membrane transport proteins enable diffusion without requiring additional energy.
<h4>Channel Proteins</h4>
Channel proteins form a hydrophilic pore through which charged molecules can pass through, thus avoiding the hydrophobic layer of the membrane. Channel proteins are specific for a given substance. For example, aquaporins are channel proteins that specifically facilitate the transport of water through the plasma membrane.
Channel proteins are either always open or gated by some mechanism to control flow. Gated channels remain closed until a particular ion or substance binds to the channel, or some other mechanism occurs. Gated channels are found in the membranes of cells such as muscle cells and nerve cells. Muscle contractions occur when the relative concentrations of ions on the interior and exterior sides of a membrane change due to the controlled closing or opening of channel gates. Without a regulated barrier, muscle contraction would not occur efficiently.
<h4>Carrier Proteins</h4>
Carrier proteins bind to a specific substance causing a conformational change in the protein. The conformational change enables movement down the substance&#39;s concentration gradient. For this reason, the rate of transport is not dependent on the concentration gradient, but rather on the number of carrier proteins available. Although it is known that proteins change shape when their hydrogen bonds are destabilized, the complete mechanism by which carrier proteins change their conformation is not well understood.
<h4>Diffusion Rates</h4>
Even though more involved than simple diffusion, facilitated transport enables diffusion to occur at incredible rates. Channel proteins move tens of millions of molecules a second, and carrier proteins move a thousand to a million molecules a second.

The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and ...

Education

JoVE Core

Anatomy and Physiology

Unit 1

Cell Membrane Structure and Functions

KEY TERMS AND CONCEPTS

transport across cell membranes

Transport across cell membranes helps cells move needed substances in and out. Facilitated transport is one way this happens. It uses membrane proteins to move materials that cannot pass easily through the lipid bilayer on their own.

This process still follows the concentration gradient, so it moves from higher concentration to lower concentration. Because of that, it does not require cellular energy. The membrane proteins provide a path that helps the substance cross the membrane more efficiently.

Facilitated transport is important for many small molecules and ions. These solutes are often too polar or charged to slip through the membrane interior. By using specific transport proteins, cells can control what enters and leaves while keeping the membrane selective.

Transport Across Cell Membranes

what are membranes?

Membrane Layers in Cells and Tissues

Membranes are thin layers that help define cells and tissues. They act as boundaries and support important biological roles in the body. In cells, membranes help separate the inside of a cell from its surroundings. They also help control what moves in and out of the cell. In tissues, membranes can form covering layers that protect and support body structures. The video focuses on membranes as key parts of cell biology. It shows how these layers are organized and why they matter in living...

membrane proteins

Membrane Proteins and Cell Transport

Membrane proteins help cells move materials across the cell membrane. They are part of the membrane structure and are closely linked to how cells function. Some membrane proteins act as channels or carriers. These proteins help selected substances pass through the membrane when direct movement through the lipid layer is not possible or is limited. Other membrane proteins help cells respond to signals. They can bind to molecules outside the cell and pass information inward. Membrane proteins...

membrane lipids

Membrane Lipids and Cell Membranes

Membrane lipids are the main building blocks of cell membranes. They help form the thin barrier that surrounds cells and many cell parts. This barrier controls what can enter and leave the cell. The most common membrane lipids are phospholipids. These molecules have a water-loving head and water-fearing tails. In a membrane, they arrange themselves into a bilayer, with the heads facing water and the tails tucked away inside. Other membrane lipids also play important roles. Some lipids help...

membrane carbohydrates

Cell Surface Carbohydrates

Cell surface carbohydrates are sugar molecules found on the outside of cell membranes. They are attached to lipids and proteins, and they help give cells their outer identity. These carbohydrates are often part of glycolipids and glycoproteins. They sit at the membrane surface, where they can affect how cells interact with their surroundings. In many cells, they also play a role in cell recognition. Membrane carbohydrates are an important part of membrane structure and function. They help...

glycocalyx and its functions

Glycocalyx in Cell Recognition

The glycocalyx is a carbohydrate-rich layer on the outside of the cell membrane. It has a fuzzy appearance and is highly hydrophilic, which means it attracts water. That helps the cell interact with its watery environment and helps it obtain substances dissolved in that water. The glycocalyx is also important for how cells identify one another. It supports self and non-self recognition, and it helps in embryonic development. Cells also use it for cell-to-cell attachment, which helps tissues...

the significance of membrane transport

How Membrane Transport Supports Cells

Membrane transport helps cells move materials across the cell membrane. This process is essential for cell function and survival. Cell membranes are selective barriers. They control what enters and leaves the cell. Some materials move passively, while others require active transport. Passive transport does not use cellular energy. It includes movement down a concentration gradient, from an area of higher concentration to an area of lower concentration. Active transport uses energy to move...

diffusion

Diffusion Rates and Concentration Gradients

Diffusion is a passive transport process that moves substances from an area of high concentration to an area of low concentration. The movement continues until the concentration becomes equal across the space. In cells and in the air, this spread happens without added energy. A familiar example is perfume in a room. The perfume is most concentrated in the bottle and least concentrated at the edges of the room. As the vapor diffuses outward, more people can smell it over time. The same kind of...

Transport across cell membranes helps cells move needed substances in and out. Facilitated transport is one way this happens. It uses membrane proteins to move materials that cannot pass easily through the lipid bilayer on their own. This process still follows the concentration gradient, so it moves from higher concentration to lower concentration. Because of that, it does not require cellular energy. The membrane proteins provide a path that helps the substance cross the membrane more...

non-gated ion channels

Ion Flow Through Open Channels

Non-gated ion channels let ions move across the cell membrane without a trigger. They are open channels, so ions can pass through them directly. These channels are part of the membrane’s electrical properties. Their steady ion movement helps shape how the membrane behaves. Non-gated ion channels are different from gated channels. Gated channels open or close in response to a signal, while non-gated channels remain available for ion flow.

osmosis

Osmosis and Water Balance

Osmosis is the movement of free water molecules through a semipermeable membrane. In this process, water moves from a region with a high concentration of free water molecules to a region with a lower concentration of free water molecules. The membrane allows water to pass, but it limits the diffusion of solutes dissolved in the water. Osmosis is a special case of diffusion. Diffusion moves material across membranes and within cells when molecules can spread out evenly. In a beaker with a...

tonicity in animals

How Cells Respond to Tonicity

Tonicity describes how solute levels in a solution affect cells. The amount of solute dissolved in a given amount of solution is called osmolarity. Cells and the fluid around them can then be compared as hypotonic, isotonic, or hypertonic. In a hypotonic solution, the extracellular fluid has a lower solute concentration than the fluid inside the cell. Tap water is one example. The water concentration outside the cell is higher, so water moves into the cell along its concentration gradient. In...

primary active transport

ATP-Powered Membrane Transport

Primary active transport uses ATP to move substances across a membrane against their concentration gradient. This process helps cells move molecules and ions from a lower concentration to a higher concentration when energy is needed. ATP hydrolysis supplies the energy for this movement. In primary active transport, the transport protein uses the energy released from ATP to change shape and move the substance across the membrane. This mechanism is important in many cell processes that depend...

secondary active transport

Coupled Solute Movement Across Membranes

Secondary active transport moves solutes across a membrane by using the energy stored in an ion gradient. The transporter itself does not use ATP directly. Instead, it links the movement of one solute to the movement of another. This process depends on a gradient that was built earlier by primary active transport. As ions move down their gradient, they provide the energy that drives another substance in the opposite direction or along with them, depending on the carrier. This coupling lets...

introduction to membrane traffic

Membrane Traffic in Cells

Membrane traffic in cells moves materials between organelles and the cell surface. It helps cells sort, package, and deliver cargo to the right place. This process is essential for normal cell function. Cells use membrane-bound compartments to handle this movement. Vesicles are small membrane sacs that carry cargo from one location to another. They bud from one membrane and fuse with another membrane to release their contents. Membrane traffic also helps maintain the balance of membranes...

receptor-mediated endocytosis

Ligand Binding in Endocytosis

Receptor-mediated endocytosis is a selective way cells take in material from outside the cell. It begins when a ligand, or binding molecule, attaches to a receptor on the cell membrane. This interaction helps the cell capture specific substances instead of taking in everything around it. After the ligand binds, the membrane folds inward and forms a small pocket. That pocket pinches off and brings the bound material into the cell. This process shows how receptor binding directs endocytosis and...

key terms and concepts

Learn how facilitated transport uses membrane proteins to move substances across cell membranes without energy. Designed for high school biology students.

Transport Across Cell Membranes | JoVE K12

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BIO.5.D

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Transport Across Cell Membranes

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