Name: how proteins shape cell membranes
Uploaded: 2023-04-30T09:16:36.000Z
Duration: 1 min 15 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-bending

Bir zar, iç veya sitoplazmik tarafa doğru büküldüğünde pozitif bir eğriliğe sahiptir. Buna karşılık, bir zar dış veya hücre dışı tarafa doğru bükülürse negatif bir eğriliğe sahiptir.
Membran bükülmesine neden olabilecek birden fazla mekanizma vardır.
Lipid kaynaklı zar bükülmesi, zardaki spesifik lipitlerin asimetrik toplanmasından kaynaklanır.
Büyük kafa gruplarına sahip lipitler pozitif zar eğriliğine neden olurken, küçük kafa gruplarına sahip lipitler negatif zar eğriliği üretir.
Protein iskelesi, proteinlerin ya zarı deforme ettiği ya da zaten deforme olmuş bir zarı stabilize ettiği başka bir mekanizmadır.
Farklı bir mekanizmada, hidrofobik protein alanları, diğer katmana kıyasla alanını artırmak için zarın bir katmanına geri dönüşümlü olarak yerleştirilir. Bu asimetri zarı bükülmeye zorlar.
Son olarak, hücre iskeletinin ve onunla ilişkili motor proteinlerin montajı ve sökülmesi tarafından üretilen itme ve çekme kuvvetleri, epitel hücrelerinde filopodia gibi çıkıntılar oluşturmak için zarı da bükebilir.

membran bükme mekanizmaları

Canlı membranlar akışkan mozaik yapıları nedeniyle esnektir; ancak bunların farklı şekillere bükülmesi, spesifik lipitler ve proteinler tarafından düzenlenen aktif bir süreçtir. Membran bükülmesi veziküllerde görüldüğü gibi geçici olabileceği gibi mikrovilluslarda olduğu gibi uzun süre stabil de olabilir. Hücreler, membran eğriliğinin boyutunu, konumunu ve süresini düzenler. Membran bükülmesi, lipit bileşimindeki içsel değişiklikler veya farklı proteinlerle dışsal ilişki nedeniyle meydana gelebilir. Membran asimetrisinin yaratılmasında veya spesifik lipitlerin kümelenmesinde rol oynayan proteinler, lipit kaynaklı membran bükülmesinde önemli bir rol oynar. İntegral proteinlerin şekli de membranın bükülmesini etkileyebilir. Örneğin konik veya ters konik şekilli transmembran proteinleri, membranda bükülme meydana getirir. Epsin gibi amfipatik proteinlerin katmanlardan birine yerleştirilmesi de membranın bükülmesine neden olur. Bin/amfifizin/Rvs veya BAR dimer proteinleri gibi kavisli proteinler, pozitif membran eğriliği yaratırken, ters BAR veya I-BAR proteini, membranda negatif bir eğriliğe neden olur. BAR proteinleri ayrıca hidrofobik alanlarını membrana yerleştirir ve bu da membranın eğriliğini daha da arttırır. Yerleşik mekanizmaların yanı sıra, protein kalabalıklaşması, protein-protein etkileşimleri tarafından üretilen yanal basıncın membran bükülmesini yönlendirdiği, membran bükülmesi için yakın zamanda keşfedilen bir mekanizmadır. Hücre iskeletleri aynı zamanda membran bükülmesinde de önemli bir oyuncudur ve bunların oluşturduğu kuvvetler, endoplazmik retikulum ve golgi aygıtı gibi bazı organellerin morfolojisinden sorumludur. Endoplazmik retikulum, golgi aygıtı ve mitokondri gibi hücre organelleri karmaşık biçimde katlanmış membranlara sahiptir; bu kıvrımlar işlevleri için gereklidir. Membran bükülmesi aynı zamanda membranın kesilmesi, membran füzyonu ve membran eğriliğini algılayan enzimin aktivasyonu için de gereklidir. Miyotubülerin, amfifizin-2 ve dinamin-2 gibi membran bükücü proteinleri üreten genlerdeki mutasyonlar, sentronükleer miyopatiler olarak bilinen bir grup nöromüsküler bozukluğa yol açabilir.

Membran Bükme Mekanizmaları

Canlı zarlar, akışkan mozaik yapıları nedeniyle esnektir; Bununla birlikte, farklı şekillerde bükülmeleri, tarafından düzenlenen aktif bir süreçtir ...

Education

JoVE Core

Cell Biology

Hücre Biyolojisi

Unit 1

Ünite 1

Membrane Structure and Components

Membran Yapısı ve Bileşenleri

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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 matters. Conical or inverse-conical transmembrane proteins can push the membrane to bend.

Some proteins bend membranes by inserting part of themselves into one layer of the membrane. Amphipathic proteins, such as epsin, do this and promote curvature. BAR proteins, short for Bin/amphiphysin/Rvs proteins, create positive curvature, while I-BAR proteins create negative curvature. BAR proteins can also add to bending by placing a hydrophobic domain into the membrane.

Protein crowding is another way membranes bend. In this case, proteins packed close together create lateral pressure, and that pressure drives curvature. The cytoskeleton also helps shape membranes. Its forces are important for the form of organelles such as the endoplasmic reticulum and Golgi apparatus.

The folded membranes of the endoplasmic reticulum, Golgi apparatus, and mitochondria are important for their function. Membrane bending also supports membrane scission, membrane fusion, and the activation of enzymes that sense curvature. Changes in genes for membrane-bending proteins, including myotubularin, amphiphysin-2, and dynamin-2, can cause centronuclear myopathies, a group of neuromuscular disorders.

How Proteins Shape Cell Membranes

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

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

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 lipids, BAR proteins, protein crowding, and the cytoskeleton bend cell membranes. See how curvature helps organelle shape, fusion, and scission.

How Proteins Shape Cell Membranes | JoVE K12

cell biology

JoVE Core Hücre Biyolojisi, anlaşılması kolay ancak kapsamlı animasyonlu video derslerde karmaşık hücresel süreçleri gösterir. Bu koleksiyon, organeller ve zarlar, hücresel taşıma ve hücre enerjileri dahil olmak üzere hücrelerin temel bileşenlerine ve işlevlerine odaklanır. Gerçek dünya araştırma deneylerinde hücre biyolojisinin uygulanmasını gösteren bilim insanı eylem videoları ile tamamlanmaktadır.

What are Cells?

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Cell Size

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Eukaryotic Compartmentalization

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Cytoplasm

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The Nucleus

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Ribosomes

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Lysosomes

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Introduction to Actin

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Overview of Myosin Structure and Function

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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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Transcription

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Eukaryotic RNA Polymerases

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Transcription Elongation Factors

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Pre-mRNA Processing: RNA Splicing

Chromatin Structure and RNA Splicing

Alternative RNA Splicing

Nuclear Export of mRNA

Transfer RNA Synthesis

Ribosomal RNA Synthesis

The Nucleolus

Additional Subnuclear Structures

Translation

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tRNA Activation

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Termination of Translation

Improving Translational Accuracy

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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

MicroRNAs

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Cis-regulatory Sequences

lncRNA - Long Non-coding RNAs

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Cooperative Binding of Transcription Regulators

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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

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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

How Proteins Shape Cell Membranes

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