Name: how cell membranes form domains
Uploaded: 2023-04-30T10:41:51.000Z
Duration: 59 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

9-12.B.1.4.a

Mechanisms of Membrane Domain Formation

Os domínios da membrana se formam quando interações proteína-proteína, proteína-lipídio e lipídio-lipídio específicas criam áreas distintas dentro da membrana.
Algumas proteínas de membrana interagem para formar grandes complexos proteicos na membrana que inibem seu movimento lateral.
Os domínios de membrana também podem se formar quando as proteínas estão presas ao citoesqueleto ou restritas a um compartimento de membrana específico devido a cercas do citoesqueleto.
Proteínas e lipídios específicos podem interagir preferencialmente e se organizar em pequenos domínios.
Fosfolipídios, esfingolipídios e esteróis menos solúveis na membrana podem se agregar para formar domínios de membrana de vários tamanhos.
Algumas proteínas têm alta afinidade com lipídios específicos, criando domínios maiores induzidos por lipídios. Esses domínios concentram proteínas e permitem a formação de complexos proteicos funcionais.

mecanismos de formação de domínios de membrana

Diferentes propriedades físicas de lipídios e proteínas permitem que eles localizem e formem ilhas, ou domínios, distintos na membrana. Alguns domínios de membrana são formados devido a interações proteína-proteína, enquanto outros são formados devido à presença de lipídios específicos, como esfingolipídios e esteróis – por exemplo, proteínas grandes, como a bacteriorodopsina, agregam-se e criam domínios distintos. 

 Outro mecanismo para a formação de domínios de membrana envolve proteínas de membrana interagindo com proteínas do citoesqueleto, ou exoplásmicas. Por exemplo, a espectrina, a proteína do citoesqueleto encontrada nos glóbulos vermelhos, interage diretamente com proteínas integrais da membrana e as imobiliza. A camada interna de uma membrana plasmática intimamente associada à rede do citoesqueleto proteico forma compartimentos, ou currais, distintos. A movimentação das proteínas presentes dentro dos currais é muitas vezes restringida pela cerca dos currais. Tais restrições impedem a difusão lateral das proteínas e resultam na formação dos domínios proteicos. 

 As proteínas envolvidas nas interações célula-célula ligam-se às proteínas das células vizinhas. Essas interações entre as duas superfícies celulares fixam as proteínas da membrana no lugar e resultam na formação de domínios proteicos. Por exemplo, junções estreitas são microdomínios de membrana que formam uma vedação estanque entre duas células animais adjacentes. Predominantemente duas proteínas, claudinas e ocludinas, mantêm firmemente as células umas contra as outras. Além disso, nas células animais, os desmossomos são outros domínios de membrana altamente ordenados que agem como pontos de solda entre células epiteliais adjacentes. As caderinas, proteínas curtas na membrana plasmática, conectam-se aos filamentos intermediários por meio de proteínas ligantes como desmoplacina, placoglobina e placofilina para criar desmossomos. As caderinas conectam duas células adjacentes e mantêm as células em uma formação semelhante a uma folha em órgãos e tecidos que se esticam, como pele, coração e músculos. 

 Some part of this text is adapted from Openstax, Biology 2e, <a href="https://openstax.org/books/biology-2e/pages/4-6-connections-between-cells-and-cellular-activities">4.6 Connections between Cells and Cellular Activities</a>

Mecanismos de Formação de Domínios de Membrana

Diferentes propriedades físicas de lipídios e proteínas permitem que eles localizem e formem ilhas ou domínios distintos na membrana. Alguns domínios de membrana ...

Education

JoVE Core

Cell Biology

Biologia Celular

Unit 1

Unidade 1

Membrane Structure and Components

Estrutura e Componentes da Membrana

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

how cell membranes form domains

Cell membranes form domains when lipids and proteins gather into distinct regions. These regions, or membrane domains, are shaped by different physical properties that help some molecules stay together while others move apart.

Some domains form through protein-protein interactions. Others depend on specific lipids, such as sphingolipids and sterols. Large proteins, including bacteriorhodopsin, can also cluster and create visible membrane domains.

Membrane proteins can be held in place by cytoskeletal or exoplasmic proteins. In red blood cells, spectrin, a cytoskeletal protein, directly interacts with integral membrane proteins and immobilizes them. The membrane region linked to the protein cytoskeleton can form compartments, or corrals, where protein movement is restricted by a fence-like boundary. This limited lateral diffusion helps produce protein domains.

Cell-cell interactions can also lock membrane proteins into place. Tight junctions are membrane microdomains that form a watertight seal between adjacent animal cells. Claudins and occludins are the main proteins that hold these cells tightly together.

Desmosomes are another highly ordered type of membrane domain in animal cells. They act like spot welds between adjacent epithelial cells. Cadherins in the plasma membrane connect to intermediate filaments through linker proteins such as desmoplakin, plakoglobin, and plakophilin. These connections help keep cells in a sheet-like arrangement in tissues that stretch, including the skin, heart, and muscles.

How Cell Membranes Form Domains

what are membranes?

Membrane Receptors and Cell Signals

The plasma membrane sets the outer boundary of a cell and helps control how the cell interacts with its environment. It lets some substances enter, keeps others out, and releases some materials in controlled amounts. The membrane also needs to stay flexible so cells such as red and white blood cells can change shape as they move through narrow capillaries. The membrane surface also carries markers that help cells recognize one another. This recognition is important during early development,...

membrane fluidity

How Cell Membranes Stay Flexible

Cell membranes stay flexible because of the fluid mosaic model. The plasma membrane is a mosaic of phospholipids, cholesterol, proteins, and carbohydrates. These parts are separate but loosely attached, so the membrane keeps a fluid character. The membrane is still fairly rigid, but it can flow and self-seal after a very fine needle passes through it. Phospholipid tails also affect membrane fluidity. Saturated fatty acids in phospholipids have straight tails because they are packed with...

fluid mosaic model

Fluid Mosaic Model of the Membrane

The fluid mosaic model explains the structure and function of the plasma membrane. Scientists first identified the plasma membrane in the 1890s, and by 1915 they had identified its main chemical parts: lipids and proteins. Early electron micrographs showed a railroad track pattern, which helped lead to the first widely accepted membrane model in 1935.

membrane lipids

Membrane Lipids in Cells and Tissues

Membrane lipids give biological membranes their structure and help set their properties. In mammalian cells, lipids make up about 50% of the membrane on average. The amount can be much lower in the inner mitochondrial membrane or much higher in the myelin sheath around nerve cells. Several phospholipids are common in mammalian membranes. These include phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin. At physiological pH, phosphatidylserine carries a negative...

asymmetric lipid bilayer

Membrane Lipid Unevenness

Biological membranes have an uneven mix of lipids between the inner and outer layers. This membrane asymmetry gives each side a different chemical makeup and supports different cell functions. Evidence for this uneven layout came from treating an erythrocyte membrane with phospholipase. Phospholipase is an enzyme that breaks lipids into fatty acids and hydrophilic groups. It acted only on the outer layer, while the inner layer stayed intact. The treatment degraded about 80% of total membrane...

membrane asymmetry regulating transporters

membrane-asymmetry-regulating-transporters

Membrane Lipid Flipping and Transport

Membrane lipid flipping and transport help cells keep an uneven, or asymmetric, distribution of phospholipids across the membrane. This balance is controlled by flippase, floppase, and scramblase enzymes, which move lipids between the two membrane leaflets. Flippases move specific phospholipids from the outer leaflet to the inner leaflet. In eukaryotes, these enzymes are type-IV P-type ATPases, also called P4-ATPases. They are membrane pumps that use ATP and contain one transmembrane domain...

membrane carbohydrates

Membrane Sugars and Cell Identity

Membrane carbohydrates help give cells their surface identity and support plasma membrane function. The plasma membrane is a dynamic barrier made of lipids, proteins, and carbohydrates. These sugar chains have unique structural and chemical traits that help the membrane work properly for cell growth and survival. Membrane carbohydrates do not have a hydrophobic region, so they are found only on the outer surface of the cell. Sugar addition, or glycosylation, of proteins occurs in the lumens of...

membrane proteins

Facilitated Transport Across Cell Membranes

Facilitated transport uses membrane proteins to help materials cross the plasma membrane. These integral transmembrane proteins act as channels or carriers. They move selected substances through the membrane more easily than the lipid layer alone would allow. Channel proteins provide a hydrophilic, or water-friendly, path through the membrane. Their core forms a hydrated opening that lets solutes pass between the inside and outside fluids of the cell. This helps polar compounds avoid the...

lipids as anchors

Lipid Anchors in Membrane Proteins

Lipid anchors help attach proteins to the plasma membrane. In eukaryotic cells, the main lipid anchors are prenyl groups, fatty acyl groups, and glycosylphosphatidylinositol, or GPI, groups. Prenyl and fatty acyl groups anchor proteins on the cytosolic side of the membrane. GPI anchors proteins on the extracellular side. Prenylated proteins often have a CaaX motif at the carboxy terminus. In this sequence, C means cysteine, a means any aliphatic amino acid, and X means any other amino acid...

single-pass transmembrane proteins

How Membrane Proteins Span Cell Membranes

Membrane proteins help cells communicate, send signals, stick to other cells, and move molecules across the membrane. Integral membrane proteins are tightly linked to the cell membrane and carry out these jobs. Some integral membrane proteins sit only in one membrane layer. Fatty acid amide hydrolase is one example, and it is found on the cytoplasmic side of the membrane monolayer. Other integral membrane proteins are transmembrane proteins, which span across the membrane. These proteins have...

multi-pass transmembrane proteins and &#946;-barrels

multi-pass-transmembrane-proteins-and-barrels

Membrane-Spanning Helices and β-Barrels

Membrane-spanning proteins can cross the cell membrane more than once. Their transmembrane chain usually folds into either an alpha-helix or a beta-strand. Alpha-helix multi-pass proteins are common, while beta-strand proteins are found mainly in gram-negative bacteria, mitochondria, and chloroplasts. Some multi-pass alpha-helix proteins are G-protein-linked receptors, or GPCRs, and bacteriorhodopsin. GPCRs have seven transmembrane alpha-helices. Each receptor also has its own extracellular...

detergent purification of membrane proteins

detergent-purification-of-membrane-proteins

How Detergents Solubilize Membrane Proteins

Detergents help solubilize membrane proteins so they can be purified from the lipid bilayer. Their hydrophobic region can replace membrane phospholipids and keep integral membrane proteins in solution. A detergent works well only when its monomers reach the critical micelle concentration, or CMC. At that point, the molecules assemble into micelles, which are small clusters of detergent. Above the CMC, free detergent monomers stay in equilibrium with the micelles. The CMC varies with the...

protein diffusion in the membrane

How Membrane Proteins Move Side to Side

Membrane proteins can move across the cell surface by lateral diffusion, and they can also rotate in place. Scientists confirmed lateral movement with a cell fusion experiment. Mouse and human cells were fused to make hybrid cells. The membrane proteins on the two cells were tagged with red and green fluorescent markers. At first, each color stayed on its own side of the fused cell. After 40 minutes, the colors mixed across the whole cell surface, showing that the proteins had moved laterally. <br...

membrane domains

Lipid Rafts and Sperm Membrane Regions

Membrane domains organize specific lipids and proteins in defined parts of a cell membrane. This arrangement supports cell signaling, adhesion, and other important cellular processes. These domains can vary in size, composition, function, and how long they last. Some membrane domains are built from proteins. The membrane can contain distinct protein groups that carry out a cell’s specific functions. A clear example is the plasma membrane of a human sperm cell, which has different proteins in...

mechanisms of membrane domain formation

Cell membranes form domains when lipids and proteins gather into distinct regions. These regions, or membrane domains, are shaped by different physical properties that help some molecules stay together while others move apart. Some domains form through protein-protein interactions. Others depend on specific lipids, such as sphingolipids and sterols. Large proteins, including bacteriorhodopsin, can also cluster and create visible membrane domains. Membrane proteins can be held in place by...

mechanisms of membrane-bending

How Proteins Shape Cell Membranes

Cell membranes can bend into many shapes because they are flexible and made of a fluid mosaic. That bending can be temporary, as in vesicles, or long-lasting, as in microvilli. Cells control the size, place, and time of membrane curvature. Membrane bending can start inside the membrane itself or from proteins attaching to it. Changes in lipid makeup can create curvature, and proteins can help by making the membrane asymmetric or by clustering certain lipids. The shape of integral proteins also...

key terms and concepts

Explore how lipids, proteins, spectrin, tight junctions, and desmosomes help cell membranes form domains and hold animal cells together.

How Cell Membranes Form Domains | JoVE K12

cell biology

JoVE Core - Biologia Celular ilustra processos celulares complexos em vídeos de animação fáceis de entender e, ao mesmo tempo, abrangentes. Esta coleção foca nos componentes e funções essenciais das células, incluindo organelas e membranas, transporte celular e energia celular. É complementado por vídeos de Cientistas em ação que demonstram a aplicação da biologia celular em experimentos de pesquisa do mundo real.

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9-12.B.1.2.a

How Cell Membranes Form Domains

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