Name: membrane proteins and cell transport
Uploaded: 2023-06-23T15:38:44.000Z
Duration: 1 min 30 s
Channel: JoVE

Membrane proteins fall into two major categories: peripheral and integral.
Peripheral membrane proteins associate with phospholipid heads or hydrophilic domains of integral proteins by non-covalent interactions.
In contrast, integral proteins are amphipathic molecules with their hydrophilic region facing the cytoplasm or extracellular fluid and the hydrophobic domain interacting with the phospholipid tails.
Integral membrane proteins can be further classified as monotopic, bitopic, and polytopic proteins.
Monotopic proteins are embedded into a single face of the membrane, whereas bitopic proteins with an alpha-helix structure span the entire lipid bilayer only once.
Polytopic proteins extend across the membrane multiple times and consist of multiple alpha-helices or a cylindrical beta-sheet, known as a beta-barrel. Bitopic and polytopic proteins are also known as transmembrane proteins.
Integral proteins perform diverse functions such as transferring molecules and signals across the cell membrane.
Many peripheral proteins also participate in cell signaling cascades as they can easily detach from the membrane. Other peripheral proteins link the membrane with the cytoskeleton, providing structural support.

membrane proteins

Membrane Proteins

Plasma membranes have integral transmembrane proteins involved in facilitated transport. These proteins are collectively referred to as transport proteins, and they function as either channels for the material or as carriers themselves. Channel proteins have hydrophilic domains exposed to the intracellular and extracellular fluids and a hydrophilic channel through their core that provides a hydrated opening for solutes to pass through the membrane layers. 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 high rate. Channel proteins are either open at all times or &#34;gated,&#34; with the opening of the channel being regulated. The attachment of a particular ion to the channel protein may control the opening, or other mechanisms or substances may be involved. In some tissues, sodium and chloride ions pass freely through open channels, whereas in other tissues, a gate must be opened to allow the passage. An example of this occurs in the kidney, where both forms of channels are found in different parts of the renal tubules. Cells involved in the transmission of electrical impulses, such as nerve and muscle cells, have gated channels for sodium, potassium, and calcium in their membranes.
Another type of protein embedded in the plasma membrane is a carrier protein. This protein binds a substance and, in doing so, triggers a change of its own shape, moving the bound molecule from the outside of the cell to its interior; depending on the gradient, the material may move in the opposite direction. Each carrier protein is specific to one substance, and there are a finite number of these proteins in any membrane. For example, glucose, water, salts, ions, and amino acids needed by the body are filtered in one part of the kidney. This filtrate, which includes glucose, is then reabsorbed in another part of the kidney. Because there are only a finite number of carrier proteins for glucose, if more glucose is present than the proteins carriers can handle, the excess is excreted from the body in the urine. In a diabetic individual, this is described as &#34;spilling glucose into the urine.&#34; A different group of carrier proteins called glucose transport proteins, or GLUTs, are involved in transporting glucose and other hexose sugars through plasma membranes within the body. Channel proteins transport much more quickly than carrier proteins.
This text is adapted from <a href="https://openstax.org/books/biology-2e/pages/5-2-passive-transport">Openstax Biology 2e, Section 5.2</a>

Plasma membranes have integral transmembrane proteins involved in facilitated transport. These proteins are collectively referred to as transport ...

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JoVE Core

Anatomy and Physiology

Unit 1

Cell Membrane Structure and Functions

KEY TERMS AND CONCEPTS

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 also support cell recognition and communication, which helps cells interact with their environment.

Membrane Proteins and Cell Transport

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 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...

facilitated transport

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...

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 membrane proteins support cell transport, signaling, recognition, and communication in the cell membrane for high school biology.

Membrane Proteins and Cell Transport | JoVE K12

anatomy and physiology

JoVE Core Anatomy and Physiology showcases the anatomical and physiological details of the human body in comprehensive, clear, and engaging video animations. This collection of lessons focuses on the structures, components, functions, and requirements of the human body. It is complemented by scientist-in-action videos that demonstrate the application of this knowledge in real-world medical and research settings.

Membrane Proteins and Cell Transport

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