Name: membrane lipid flipping and transport
Uploaded: 2023-04-30T10:41:36.000Z
Duration: 1 min 19 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

membrane-asymmetry-regulating-transporters

Membrane Asymmetry Regulating Transporters

يتم تنظيم عدم تناسق الغشاء بواسطة ثلاثة أنواع من الناقلات التي تنقل الدهون الفوسفورية عبر الطبقة الثنائية.
Flippases هي مستوردة للدهون تعتمد على ATP وتنقل الفوسفاتيديل سيرين والفوسفاتيديل إيلانولامين من الطبقة الخارجية إلى الطبقة الداخلية.
Floppases هي مصدرات دهون غير محددة تعتمد على ATP وتنقل الدهون من الطبقة الداخلية إلى الطبقة الخارجية. يلعب كل من الفليباز والفلوب دور مهم في توليد عدم تناسق الغشاء.
Scramblases عبارة عن ناقلات مستقلة عن ATP تسمح بالحركة العشوائية للدهون في كلتا الطبقتين ، وبالتالي تقليل عدم تناسق الغشاء. في كريات الدم الحمراء ، تكون التدافعات غير نشطة عند المستويات الفسيولوجية الطبيعية للكالسيوم داخل الخلايا وتصبح نشطة عندما يزداد تركيز أيون الكالسيوم. 
يمكن أن يؤدي تنشيط التدافع إلى نقل الفوسفاتيديل سيرين من طبقة الغشاء الداخلية إلى الطبقة الخارجية. يشير التعرض الخارجي للفوسفاتيديل سيرين إلى كريات الدم الحمراء لموت انتحاري يعرف باسم داء الكريات الحمر ويؤدي إلى إزالتها بواسطة الضامة.

عدم تناسق الغشاء الذي ينظم الناقلات

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تقوم الإنزيمات مثل فليباز، فلوباز، و سكرامبلاز بنقل الفسفوليبيدات من طبقة إلى أخرى في الغشاء، مما يؤثر على عدم تناسق الغشاء.

فليبباز

إن فليبباز في حقيقية النواة هي الـ ATPases من النوع الرابع و النوع P أو P4-ATPases التي تنتمي إلى بروتينات عائلة P-type ATPase وهي عبارة عن مضخات مرتبطة بالغشاء تشارك في نقل الأيونات والجزيئات بوساطة الـ ATP عبر الغشاء. تعمل فليباز على قلب فسفوليبيدات معينة من النشرة الخارجية إلى الداخلية للغشاء. تحتوي جميع P4-ATPases على مجال غشاء واحد يحتوي على عشرة حلزونات ألفا عبر الغشاء وثلاثة مجالات سيتوبلازمية. تشتمل المجالات السيتوبلازمية الثلاثة على مجال ربط النوكليوتيدات، ومجال الفسفرة، ومجال المحرك المشارك في خطوة نزع الفسفرة.

فلوباز

تنتمي فلوباز إلى الكاسيت المرتبط بـ ATP أو بروتينات عائلة الناقل ABC التي تنقل مجموعة متنوعة من الفوسفوليبيدات من النشرة الداخلية إلى الخارجية للغشاء. بعض البروتينات الأساسية لهذه العائلة هي ABCA1، ABCA4، ABCB1، وABCB4. يستطيع إنزيم ABCA1 floppase نقل الكولسترول من الوريقة الداخلية إلى الوريقة الخارجية للغشاء، ويمكن أن تؤدي طفرته إلى مرض تنجير.

Scramblase

يمكن لـ Scramblase، على عكس فليبباز وفلوباز، القيام بالنقل ثنائي الاتجاه للدهون الفوسفاتية في الغشاء دون استخدام الطاقة من التحلل المائي للـ ATP. هناك نوعان من بروتينات الاختلاط في الخلية - بروتين غشائي 16F أي (TMEM16F) والبروتين المرتبط بـ XK8 أي (Xkr8). يقع TMEM16F scramblase داخل غشاء الصفائح الدموية ويحتاج إلى تركيز عالٍ من أيونات الكالسيوم للتنشيط. في المقابل، يقوم كاسباس بتنشيط Xkr8 في غشاء الخلية أثناء موت الخلايا المبرمج. يؤدي التعبير المعيب عن Scramblase إلى اضطراب نزيف يسمى متلازمة سكوت.
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تنقل الإنزيمات مثل الفليباز والفلوب والكلمباز الدهون الفوسفورية من طبقة إلى أخرى في الغشاء ، مما يؤثر على عدم تناسق الغشاء.
...

Education

JoVE Core

Cell Biology

بيولوجيا الخلية

Unit 1

الوحدة الأولى

Membrane Structure and Components

بنية الغشاء ومكوناته

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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 with ten transmembrane alpha-helices and three cytoplasmic domains: a nucleotide-binding domain, a phosphorylation domain, and an actuator domain that helps with dephosphorylation.

Floppases move phospholipids in the opposite direction, from the inner leaflet to the outer leaflet. They belong to the ATP-binding cassette, or ABC-transporter, family. Important members include ABCA1, ABCA4, ABCB1, and ABCB4. ABCA1 can move cholesterol to the outer leaflet, and mutation of ABCA1 can lead to Tangier disease.

Scramblases work differently from flippases and floppases. They move phospholipids in both directions and do not use ATP hydrolysis for energy. Two scramblases found in cells are TMEM16F and Xkr8. TMEM16F is found in platelet membranes and needs a high calcium ion level for activation, while caspase activates Xkr8 during apoptosis. When scramblase expression is defective, it can cause the bleeding disorder Scott syndrome.

Membrane Lipid Flipping and Transport

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 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

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...

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

Learn how flippases, floppases, and scramblases move phospholipids across membranes and help maintain membrane asymmetry in cells.

Membrane Lipid Flipping and Transport | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

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ATP Energy Storage and Release

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1. Engage in evidence-based argument to relate a cell's function to the structure, function, and diversity of its components. Examples: Muscle cells have a large number of mitochondria, which create energy for contraction in the form of ATP. Some plant cells have a large vacuole which is used for storage and transport of excess nutrients in changing environments.

9-12.B.1.1

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Types of RNA

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Bacterial RNA Polymerase

Eukaryotic RNA Polymerases

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Transcription Elongation Factors

pre-mrna-processing-modification-of-pre-mrna-ends

Pre-mRNA Processing: Modification of pre-mRNA Ends

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Pre-mRNA Processing: RNA Splicing

Chromatin Structure and RNA Splicing

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Transfer RNA Synthesis

Ribosomal RNA Synthesis

The Nucleolus

Additional Subnuclear Structures

Translation

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Initiation of Translation

Termination of Translation

Improving Translational Accuracy

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Prokaryotic Transcriptional Activators and Repressors

Nonsense-mediated mRNA Decay

The Eukaryotic Promoter Region

Molecular Chaperones and Protein Folding

Co-activators and Co-repressors

The Proteasome

Master Transcription Regulators

Regulated Protein Degradation

Regulated mRNA Transport

Proteins: From Genes to Degradation

mRNA Stability and Gene Expression

Cell Specific Gene Expression

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regulation-of-expression-occurs-at-multiple-steps

Regulation of Expression Occurs at Multiple Steps

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Cis-regulatory Sequences

lncRNA - Long Non-coding RNAs

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Cooperative Binding of Transcription Regulators

Epigenetic Regulation

Epigenetic changes alter the physical structure of the DNA without changing the genetic sequence and often regulate whether genes are turned on or off. ...

2. Obtain and evaluate information to explain the role of DNA and RNA in transcription and translation leading to protein synthesis and cellular function.

9-12.B.1.2

Nucleic Acids and Nucleotides

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The DNA Helix

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a. Use a model to describe the structure and sequence of DNA, including nucleotide structure, base pairing, and the structure of the helix.

9-12.B.1.2.a

Membrane Lipid Flipping and Transport

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