Name: how cell membranes stay flexible
Uploaded: 2023-04-30T09:15:21.000Z
Duration: 1 min 26 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 Fluidity

막 유동성(membrane fluidity)은 인지질과 단백질이 막 내부에서 자유롭게 이동할 수 있는 능력입니다. 그것은 막의 인지질 유형, 주변 온도, 콜레스테롤 농도의 영향을 받습니다.
포화 인지질은 이중 결합이 없는 직선형 지방산 사슬을 갖는 반면, 불포화 인지질은 적어도 하나의 이중 결합으로 지방산 사슬이 구부러져 있습니다. 
포화된 인지질은 조밀하게 채워진 막을 형성하여 막의 유동성을 낮춥니다. 불포화 인지질은 인지질 패킹을 파괴하여 멤브레인 유동성을 높입니다.
저온에서는 멤브레인 지질이 거의 움직임 없이 단단히 채워져 단단한 멤브레인을 형성합니다. 지질은 고온에서 움직임이 증가하여 멤브레인을 더 유동적으로 만듭니다.
또 다른 막 구성 요소인 콜레스테롤은 인지질 사이에 삽입되어 더 낮은 온도에서 유동성을 증가시키는 공간을 만듭니다.
따뜻한 온도에서는 콜레스테롤의 스테로이드 고리가 인지질을 고정시켜 막이 너무 유동적이 되는 것을 방지합니다.
유기체는 포화 인지질과 불포화 인지질의 비율과 콜레스테롤 농도를 조절하여 다양한 조건에서 최적의 막 유동성을 유지합니다.

막 유동성

막 유동성은 원형질막 구조를 인지질, 콜레스테롤, 단백질, 탄수화물 등 막에 유동적인 특성을 부여하는 구성 요소의 모자이크로 설명하는 세포막의 유동 모자이크 모델로 설명됩니다.

막의 모자이크 특성

막의 모자이크 특성은 원형질막이 유동적으로 유지되도록 돕습니다. 필수 단백질과 지질은 분리되어 있지만 막에 느슨하게 부착된 분자로 존재합니다. 막은 비교적 단단한 구조로 되어 있어 침투하거나 세포가 물을 너무 많이 흡수하면 터질 수 있습니다. 그러나 모자이크 특성으로 인해 매우 가는 바늘은 막을 터뜨리지 않고 쉽게 막을 관통할 수 있습니다. 바늘이 추출되면 막이 흐르고 자체 밀봉됩니다.

인지질의 성질

다음은 지질 이중층을 구성하는 인지질의 성질입니다. 포화 형태에서는 인지질 꼬리의 지방산이 결합된 수소 원자로 포화되어 직선 꼬리가 됩니다. 대조적으로, 불포화 지방산은 인접한 탄소 원자 사이에 이중 결합을 포함하고 있어 탄소 끈이 약 30도 구부러집니다. 불포화지방산이 압축되면 꼬리의 "꼬임"이 인접한 인지질 분자를 밀어내어 인지질 분자 사이에 약간의 공간을 유지합니다. 이 "팔꿈치 공간"은 인지질에 포화 지방산 꼬리가 있는 막이 "동결"되거나 응고되는 온도에서 막의 유동성을 유지하는 데 도움이 됩니다. 추운 환경에서는 막의 상대적 유동성이 매우 중요합니다. 추운 환경은 주로 포화지방산으로 구성된 막을 압축하는 경향이 있어 유동성이 떨어지고 파열되기 쉽습니다.

콜레스테롤

동물에서 콜레스테롤은 막 유동성을 유지하는 데 도움이 되는 또 다른 요소입니다. 이는 막의 인지질 옆에 위치하며 온도가 막에 미치는 영향을 감소시키는 경향이 있습니다. 따라서 콜레스테롤은 완충 역할을 하여 낮은 온도가 유동성을 방해하는 것을 방지하고, 높은 온도가 유동성을 너무 많이 증가시키는 것을 방지합니다. 콜레스테롤은 막이 적절하게 유동적이고 기능적으로 활성화되는 온도 범위를 양방향으로 확장합니다. 콜레스테롤은 또한 막횡단 단백질 클러스터를 지질 뗏목으로 구성하는 것과 같은 다른 기능도 수행합니다. 막 유동성은 단백질과 지질이 현장에서 이동하고 축적되어 지질 뗏목과 세포간 접합을 형성하여 막 투과성을 유지하도록 합니다.

이 텍스트는 다음에서 수정되었습니다 <a href="https://openstax.org/books/biology-2e/pages/5-1-components-and-structure">Openstax Biology 2e, Section 5.1.</a>

막 유동성은 세포막의 유체 모자이크 모델에 의해 설명되며, 이는 원형질막 구조를 모자이크로 설명합니다.

Education

교육

JoVE Core

Cell Biology

세포생물학

Unit 1

제1단원

Membrane Structure and Components

막 구조 및 구성 성분

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 hydrogen atoms. Unsaturated fatty acids have double bonds that create a bend, or kink, of about 30 degrees in the carbon chain. When these bent tails are compressed, they push nearby molecules apart and leave enough space to help the membrane stay fluid.

This extra space matters in cold conditions. Membranes with mostly saturated fatty acid tails can become less fluid, and they may freeze, solidify, or rupture more easily in the cold. Unsaturated tails help prevent that by keeping the membrane from packing too tightly. In this way, membrane fluidity supports cell survival in cooler environments.

In animal cells, cholesterol also helps control membrane fluidity. It sits beside the phospholipids and reduces the effect of temperature changes. Cholesterol acts like a buffer, so low temperatures do not slow fluidity too much and high temperatures do not make the membrane too fluid. It widens the temperature range in which the membrane stays active and also helps organize clusters of transmembrane proteins into lipid rafts. Membrane fluidity also allows proteins and lipids to move and gather at places where lipid rafts and intercellular junctions form, which helps maintain membrane permeability.

How Cell Membranes Stay Flexible

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

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

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 phospholipids, unsaturated tails, and cholesterol help cell membranes stay flexible, self-seal, and function across temperature changes.

How Cell Membranes Stay Flexible | 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.

Florida Department of Education

High School

Life Science

SC.912.L.18

SC.912.L.18.3

What are Cells?

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Cell Size

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Lysosomes

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Peroxisomes

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overview-of-myosin-structure-and-function

Overview of Myosin Structure and Function

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Microtubules

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The Structure of Intermediate Filaments

The intermediate filaments are one of three widely studied cytoskeletal filaments. They are so named as their diameter (10 nm) is in between that of ...

Types of Intermediate Filaments

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Gap Junctions

Multicellular organisms employ a variety of ways for cells to communicate with each other. Gap junctions are specialized proteins that form pores between ...

The Extracellular Matrix

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Tissues

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Plasmodesmata

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pH Regulation in Cells

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Chemistry of the Cell

Introduction to Cellular Respiration

Organisms harvest energy from food, but this energy cannot be directly used by cells. Cells convert the energy stored in nutrients into a more usable ...

ATP Energy Storage and Release

ATP and Macromolecule Synthesis

Biological macromolecules are organic compounds, predominantly composed of carbon atoms. The carbon atoms are covalently bonded with hydrogen, oxygen, ...

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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RNA Structure

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Types of RNA

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Transcription

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Bacterial RNA Polymerase

Eukaryotic RNA Polymerases

General Transcription Factors

Tissue-specific transcription factors contribute to diverse cellular functions in mammals. For example, the gene for beta globin, a major component of ...

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Transcription Elongation Factors

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

Pre-mRNA Processing: Modification of pre-mRNA Ends

In eukaryotic cells, transcripts made by RNA polymerase are modified and processed before exiting the nucleus. Unprocessed RNA is called precursor mRNA or ...

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

Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following transcription, it constitutes ...

tRNA Activation

Initiation of Translation

Termination of Translation

Improving Translational Accuracy

prokaryotic-transcriptional-activators-and-repressors

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

MicroRNAs

MicroRNA (miRNA) are short, regulatory RNA transcribed from introns (non-coding regions of a gene) or intergenic regions (stretches of DNA present between ...

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

Regulation of Expression Occurs at Multiple Steps

Small interfering RNAs (siRNA)

Cis-regulatory Sequences

lncRNA - Long Non-coding RNAs

cooperative-binding-of-transcription-regulators

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

Nucleic acids are the most important macromolecules for the continuity of life. They carry the cell&#39;s genetic blueprint and have instructions for its ...

Nucleic Acid Structure

The pentose sugar in DNA is deoxyribose, while in RNA the pentose sugar is ribose. The difference between the sugars is the presence of the hydroxyl group ...

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 Cell Membranes Stay Flexible

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