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How does soap affect membrane permeability? Which component of the membrane does it affect?

How does soap affect membrane permeability? Which component of the membrane does it affect?


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In a lab we used distilled water + 3 drops of soap to examine how beetroot would be affected by it. I believe the beetroots membrane denatured and a red pigment leaked from it. However, I cannot explain why this has happened. Can anyone explain the topic question to me?


@mdperry answered well. If you need some diagrams to help with understanding, this article Should be helpful.

As you surmised, when you add detergent, it is lysing some cells of the beetroot that contain pigment. That pigment then gets released into solution. I've annotated the image below for the micelles that gets formed, except I spelled it wrong :/


15.1: Membranes

Plasma membranes enclose and define the borders between the inside and the outside of cells. They are typically composed of dynamic bilayers of phospholipids into which various other lipid soluble molecules and proteins have also been embedded. These bilayers are asymmetric&mdashthe outer leaf being different than the inner leaf in lipid composition and in the proteins and carbohydrates that are displayed to either the inside or outside of the cell. Various factors influence the fluidity, permeability, and various other physical properties of the membrane. These include the temperature, the configuration of the fatty acid tails (some kinked by double bonds), the presence of sterols (i.e., cholesterol) embedded in the membrane, and the mosaic nature of the proteins embedded within it. The cell membrane has selectivity it allows only some substances through while excluding others. In addition, the plasma membrane must, in some cases, be flexible enough to allow certain cells, such as amoebae, to change shape and direction as they move through the environment, hunting smaller, single-celled organisms.

Cellular membranes

A subgoal in our "build-a-cell" design challenge is to create a boundary that separates the "inside" of the cell from the environment "outside". This boundary needs to serve multiple functions that include:

  1. Act as a barrier by blocking some compounds from moving in and out of the cell.
  2. Be selectively permeable in order to transport specific compounds into and out of the cell.
  3. Receive, sense, and transmit signals from the environment to inside of the cell.
  4. Project "self" to others by communicating identity to other nearby cells.

Figure 1. The diameter of a typical balloon is 25cm and the thickness of the plastic of the balloon of around 0.25mm. This is a 1000X difference. A typical eukaryotic cell will have a cell diameter of about 50µm and a cell membrane thickness of 5nm. This is a 10,000X difference.

The ratio of membrane thickness compared to the size of an average eukaryotic cell is much greater compared to that of a balloon stretched with air. To think that the boundary between life and nonlife is so small, and seemingly fragile, more so than a balloon, suggests that structurally the membrane must be relatively stable. Discuss why cellular membranes are stable. You will need to pull from information we have already covered in this class.

Fluid mosaic model

The existence of the plasma membrane was identified in the 1890s, and its chemical components were identified in 1915. The principal components identified at that time were lipids and proteins. The first widely accepted model of the plasma membrane&rsquos structure was proposed in 1935 by Hugh Davson and James Danielli it was based on the &ldquorailroad track&rdquo appearance of the plasma membrane in early electron micrographs. They theorized that the structure of the plasma membrane resembles a sandwich, with protein being analogous to the bread, and lipids being analogous to the filling. In the 1950s, advances in microscopy, notably transmission electron microscopy (TEM), allowed researchers to see that the core of the plasma membrane consisted of a double, rather than a single, layer. A new model that better explains both the microscopic observations and the function of that plasma membrane was proposed by S.J. Singer and Garth L. Nicolson in 1972.

The explanation proposed by Singer and Nicolson is called the . The model has evolved somewhat over time, but it still best accounts for the structure and functions of the plasma membrane as we now understand them. The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components&mdashincluding phospholipids, cholesterol, proteins, and carbohydrates&mdashthat gives the membrane a fluid character. Plasma membranes range from 5 to 10 nm in thickness. For comparison, human red blood cells, visible via light microscopy, are approximately 8 µm wide, or approximately 1,000 times wider than a plasma membrane.

Figure 2. The fluid mosaic model of the plasma membrane describes the plasma membrane as a fluid combination of phospholipids, cholesterol, and proteins. Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membrane.

The principal components of a plasma membrane are lipids (phospholipids and cholesterol), proteins, and carbohydrates. The proportions of proteins, lipids, and carbohydrates in the plasma membrane vary with organism and cell type, but for a typical human cell, proteins account for about 50 percent of the composition by mass, lipids (of all types) account for about 40 percent of the composition by mass, and carbohydrates account for the remaining 10 percent of the composition by mass. However, the concentration of proteins and lipids varies with different cell membranes. For example, myelin, an outgrowth of the membrane of specialized cells, insulates the axons of the peripheral nerves, contains only 18 percent protein and 76 percent lipid. The mitochondrial inner membrane contains 76 percent protein and only 24 percent lipid. The plasma membrane of human red blood cells is 30 percent lipid. Carbohydrates are present only on the exterior surface of the plasma membrane and are attached to proteins, forming , or to lipids, forming .

Phospholipids

are major constituents of the cell membrane, the outermost layer of cells. Like fats, they are composed of fatty acid chains attached to a polar head group. Specifically, there are two fatty acid tails and a phosphate group as the polar head group. The phospholipid is an molecule, meaning it has a hydrophobic part and a hydrophilic part. The fatty acid chains are hydrophobic and cannot interact with water, whereas the phosphate-containing head group is hydrophilic and interacts with water.

Make sure to note in Figure 3 that the phosphate group has an R group linked to one of the oxygen atoms. R is a variable commonly used in these types of diagrams to indicate that some other atom or molecule is bound at that position. That part of the molecule can be different in different phospholipids&mdashand will impart some different chemistry to the whole molecule. At the moment, however, you are responsible for being able to recognize this type of molecule (no matter what the R group is) because of the common core elements&mdashthe glycerol backbone, the phosphate group, and the two hydrocarbon tails.

Figure 3. A phospholipid is a molecule with two fatty acids and a modified phosphate group attached to a glycerol backbone. The phosphate may be modified by the addition of charged or polar chemical groups. Several chemical R groups may modify the phosphate. Choline, serine, and ethanolamine are shown here. These attach to the phosphate group at the position labeled R via their hydroxyl groups.
Attribution: Marc T. Facciotti (own work)

A phospholipid bilayer forms as the basic structure of the cell membrane. The fatty acid tails of phospholipids face inside, away from water, whereas the phosphate group faces outside, hydrogen bonding with water. Phospholipids are responsible for the dynamic nature of the plasma membrane.

Figure 4. In the presence of water, some phospholipids will spontaneously arrange themselves into a micelle. The lipids will be arranged such that their polar groups will be on the outside of the micelle, and the nonpolar tails will be on the inside. A lipid bilayer can also form, a two layered sheet only a few nanometers thick. The lipid bilayer consists of two layers of phospholipids organized in a way that all the hydrophobic tails align side by side in the center of the bilayer and are surrounded by the hydrophilic head groups.
Source: Created by Erin Easlon (own work)

Note: possible discussion

Above it says that if you were to take some pure phospholipids and drop them into water that some if it would spontaneously (on its own) form into micelles. This sounds a lot like something that could be described by an energy story. Go back to the energy story rubric and try to start creating an energy story for this process&mdashI expect that the steps involving the description of energy might be difficult at this point (we'll come back to that later) but you should be able to do at least the first three steps. You can constructively critique (politely) each other's work to create an optimized story.

Note that the phospholipid depicted above has an R group linked to the phosphate group. Recall that this designation is generic&mdashthese can be different than the R groups on amino acids. What might be a benefit/purpose of "functionalizing" or "decorating" different lipids with different R groups? Think of the functional requirements for membranes stipulated above.

Membrane proteins

Proteins make up the second major component of plasma membranes. are, as their name suggests, integrated completely into the membrane structure, and their hydrophobic membrane-spanning regions interact with the hydrophobic region of the the phospholipid bilayer. Single-pass integral membrane proteins usually have a hydrophobic transmembrane segment that consists of 20&ndash25 amino acids. Some span only part of the membrane&mdashassociating with a single layer&mdashwhile others stretch from one side of the membrane to the other, and are exposed on either side. This type of protein has a hydrophilic region or regions, and one or several mildly hydrophobic regions. This arrangement of regions of the protein tends to orient the protein alongside the phospholipids, with the hydrophobic region of the protein adjacent to the tails of the phospholipids and the hydrophilic region or regions of the protein protruding from the membrane and in contact with the cytosol or extracellular fluid.

are found on either the exterior or interior surfaces of membranes and weakly or temporarily associated with the membranes. They can interact with either integral membrane proteins or simply interact weakly with the phospholipids within the membrane.

Figure 5. Integral membranes proteins may have one or more &alpha -helices (pink cylinders) that span the membrane (examples 1 and 2), or they may have &beta-sheets (blue rectangles) that span the membrane (example 3). (credit: &ldquoFoobar&rdquo/Wikimedia Commons)

Carbohydrates

Carbohydrates are the third major component of plasma membranes. They are always found on the exterior surface of cells and are bound either to proteins (forming glycoproteins) or to lipids (forming glycolipids). These carbohydrate chains may consist of 2&ndash60 monosaccharide units and can be either straight or branched. Along with peripheral proteins, carbohydrates form specialized sites on the cell surface that allow cells to recognize each other (one of the core functional requirements noted above in "cellular membranes").

Membrane fluidity

The mosaic characteristic of the membrane, described in the fluid mosaic model, helps to illustrate its nature. The integral proteins and lipids exist in the membrane as separate molecules and they "float" in the membrane, moving somewhat with respect to one another. The membrane is not like a balloon, however, in that can expand and contract dramatically rather, it is fairly rigid and can burst if penetrated or if a cell takes in too much water. However, because of its mosaic nature, a very fine needle can easily penetrate a plasma membrane without causing it to burst, and the membrane will flow and self-seal when the needle is extracted.

The mosaic characteristics of the membrane explain some but not all of its fluidity. There are two other factors that help maintain this fluid characteristic. One factor is the nature of the phospholipids themselves. In their saturated form, the fatty acids in phospholipid tails are saturated with hydrogen atoms. There are no double bonds between adjacent carbon atoms. This results in tails that are relatively straight. By contrast, unsaturated fatty acids do not have a full complement of hydrogen atoms on their fatty acid tails, and therefore contain some double bonds between adjacent carbon atoms a double bond results in a bend in the string of carbons of approximately 30 degrees.

Figure 6. Any given cell membrane will be composed of a combination of saturated and unsaturated phospholipids. The ratio of the two will influence the permeability and fluidity of the membrane. A membrane composed of completely saturated lipids will be dense and less fluid, and a membrane composed of completely unsaturated lipids will be very loose and very fluid.

Organisms can be found living in extreme temperature conditions. Both in extreme cold or extreme heat. What types of differences would you expect to see in the lipid composition of organisms that live at these extremes?

Saturated fatty acids, with straight tails, are compressed by decreasing temperatures, and they will press in on each other, making a dense and fairly rigid membrane. When unsaturated fatty acids are compressed, the &ldquokinked&rdquo tails elbow adjacent phospholipid molecules away, maintaining some space between the phospholipid molecules. This &ldquoelbow room&rdquo helps to maintain fluidity in the membrane at temperatures at which membranes with high concentrations of saturated fatty acid tails would &ldquofreeze&rdquo or solidify. The relative fluidity of the membrane is particularly important in a cold environment. Many organisms (fish are one example) are capable of adapting to cold environments by changing the proportion of unsaturated fatty acids in their membranes in response to the lowering of the temperature.

Cholesterol

Animals have an additional membrane constituent that assists in maintaining fluidity. Cholesterol, which lies alongside the phospholipids in the membrane, tends to dampen the effects of temperature on the membrane. Thus, this lipid functions as a "fluidity buffer", preventing lower temperatures from inhibiting fluidity and preventing increased temperatures from increasing fluidity too much. Thus, cholesterol extends, in both directions, the range of temperature in which the membrane is appropriately fluid and consequently functional. Cholesterol also serves other functions, such as organizing clusters of transmembrane proteins into lipid rafts.

Figure 7. Cholesterol fits between the phospholipid groups within the membrane.

Review of the components of the membrane

Archaeal membranes

One major difference between archaea and either eukaryotes or bacteria is the lipid composition of the archaeal membranes. Unlike eukaryotes and bacteria, archaeal membranes are not made up of fatty acids attached to a glycerol backbone. Instead, the polar lipids consist of isoprenoid (molecules derived from the five carbon lipid isoprene) chains of 20&ndash40 carbons in length. These chains, which are usually saturated, are attached by bonds to the glycerol carbons at the 2 and 3 positions on the glycerol backbone, instead of the more familiar linkage found in bacteria and eukaryotes. The polar head groups differ based on the genus or species of the Archaea and consist of mixtures of glyco groups (mainly disaccharides), and/or phospho groups primarily of phosphoglycerol, phosphoserine, phosphoethanolamine or phosphoinositol. The inherent stability and unique features of archaeal lipids have made them a useful biomarker for archaea within environmental samples, though approaches based on genetic markers are now more commonly used.

A second difference between bacterial and archaeal membranes that is associated with some archaea is the presence of , as depicted below. Notice that the isoprenoid chain is attached to the glycerol backbones at both ends, forming a single molecule consisting of two polar head groups attached via two isoprenoid chains.

Figure 8. The exterior surface of the archaeal plasma membrane is not identical to the interior surface of the same membrane.

Figure 9. Comparisons of different types of archaeal lipids and bacterial/eukaryotic lipids


1. Introduction

Cryosurgery is becoming an established therapy for prostate cancer [1,2]. The general mechanisms of injury during cryosurgery typically include direct injury to the cancer cells due to the freezing event, as well as host-mediated events such as vascular injury and immunological effects, which occur after thawing.

One of the factors that determine the type of damage during freezing is the cooling rate [3]. At fast cooling rates, intracellular ice formation is primarily responsible for the destruction of cells. By contrast, at slow cooling rates, where dehydration predominates, osmotic injury due to solute effects causes damage. During slow cooling, ice forms outside the cell before propagating inside the cell [4]. As soon as ice forms outside of a cell in solution, the cell dehydrates, and endogenous biomolecules are exposed to high concentrations of solutes [5]. Rapid freezing, on the other hand, results in lethal intracellular ice formation. The mechanism by which intracellular ice damages cells is not entirely clear, but it has been suggested that cells do not die during the freezing event itself, but during thawing [4]. One other important determinant of intracellular ice formation is the nucleation temperature of ice formation in the extracellular space [6]. Kinetic model studies have shown that the lower the nucleation temperature, the greater is the incidence of intracellular ice formation [7,8].

At the molecular level, freezing affects membrane lipids, proteins and nucleic acids by changing the hydrophobic and hydrophilic interactions determining structure and function. It is well established that cooling alters the physical state of lipids, thus altering lipid organization and fluidity [9]. Biological membranes often exhibit a liquid crystalline to gel phase transition during cooling and vice versa during re-warming [10]. The consequences of such phase transitions are thought to include increased membrane permeability and lateral phase separation of membrane components. Intracellular proteins may undergo irreversible structural alterations with freezing, due to exposure to high solute concentration [5]. In addition, proteins and lipids are exposed to reactive oxygen species, because enzymatic scavenging systems are compromised by freezing. Reactive oxygen species result in lipid peroxidation and phospholipid de-esterification [11]. In a previous study, we have shown that freezing of AT-1 Dunning tumor cells results in accumulation of free fatty acids [12]. The changed physical properties and chemical composition of the plasma membrane may lead to leakage of cytoplasmic solutes. Proteins are also subject to free radical attack by reactive oxygen species [13]. Moreover, proteins may also be degraded by proteases originating from lysosomes that lost membrane integrity during freezing or thawing [12].

One of the few suitable techniques to study freezing-induced changes in structure and conformation of cellular biomolecules is Fourier transform infrared spectroscopy (FTIR). The CH2 stretching vibration of lipids, for example, has been used to detect lipid phase transitions in lipids, isolated biological membranes and in whole cells [10,14]. The amide-I, -II, and -III bands, arising from vibrations of the protein backbone, have been widely used to determine the protein secondary structure of isolated proteins [15,16,17], and are diagnostic for the overall protein secondary structure of cells and tissues [18]. Most FTIR studies rely on the amide-I band for protein secondary structure analysis. Recent studies, however, have implicated the amide-III band for FTIR protein analysis, because the different types of secondary structure are better resolved, and because this region of the spectrum does not find interference from water and water vapor bands [19,20].

In this work, FTIR was used to study changes in membrane lipid phase behavior and overall protein secondary structure during freezing of LNCaP prostate tumor cells. Samples were nucleated at temperatures ranging from 𢄣ଌ to �ଌ. We show that the temperature at which ice is formed in the system affects the membrane phase behavior of the cells. This is explained in terms of cellular dehydration and intracellular ice formation, which both critically depend on the nucleation temperature. Proteins were found to be relatively stable during freezing.


What is selective permeability How does the cell achieve this?

Selective permeability is a property of cellular membranes that only allows certain molecules to enter or exit the cell. This is important for the cell to maintain its internal order irrespective of the changes to the environment.

Furthermore, what role do proteins play in transport? Functions of Transport Proteins Transport proteins function in both active and passive transport to move molecules across the plasma membrane. These channel proteins are responsible for bringing in ions and other small molecules into the cell.

Regarding this, why does soap dissolve the membrane easily?

Because the membrane is made up of lipids. The cell does this using the cell membrane. Phospholipids allow small and uncharged molecules through and proteins allow large and charged molecules to get through.

What is the meaning of selectively permeable?

Definition of Selectively Permeable Membranes All cells are enclosed with a cell membrane. A selectively permeable cell membrane is one that allows certain molecules or ions to pass through it by means of active or passive transport.


How does the autophagy pathway interact with nanomaterials?

Autophagy is an evolutionarily conserved process that proceeds through the sequestration of cargo material inside double-membrane vesicles in preparation for degradation. Natural as well as engineered nanomaterials are often tagged with “eat-me” signals such as poly-ubiquitin chains which are recognized by autophagy adaptor proteins and targeted to isolation membranes (Fig. 1) [4]. Elongation of the isolation membranes results in the formation of autophagosomes that entrap the cargo material. Fusion of autophagosomes with lysosomes leads to the formation of autolysosomes, which, in turn, results in cargo degradation by hydrolytic enzymes or secretion via exocytosis [5].

Autophagic response to engineered nanomaterials. Upon internalization, nanomaterials may escape the endocytic vesicle through disruptions of the endosomal membrane. Once in the cytoplasm, nanomaterials can be recognized by autophagy adaptors proteins or danger receptors that recruit isolation membranes. Elongation of the isolation membranes sequesters nanomaterials inside vesicles called autophagosomes, which fuse with lysosomes to form autolysosomes. Autolysosome formation may be followed by enzymatic degradation or secretion. The mechanism of autophagy activation in response to nanomaterials that remain within the endocytic pathway remains unclear

While some nanomaterials can enter the cytoplasm, internalized nanomaterials are mainly localized in endocytic vesicles. It is unclear, however, how nanomaterials inside vesicles are recognized by the autophagy pathway. Some nanoparticles are capable of endosomal escape through mechanisms such as the “proton sponge” effect, which ruptures the endosomal membrane [6]. Rupture of the endosomal membrane is likely to be recognized by the autophagy system through the same mechanism that recognizes bacteria-induced membrane disruption. Invasion of Salmonella typhimurium, for instance, proceeds through the disruption of enclosing double-membrane vesicles and exposure of complex β-galactoside-containing glycans to the cytoplasm [4]. Because the cytoplasm is free of complex sugars under physiological conditions, the glycans from the inner membrane of the damaged vesicles are rapidly recognized by the danger receptor galectin-8 that mediates the recruitment of the autophagy machinery. Nanomaterials that reach the cytosol through membrane disruptions will likely also be recognized by galectin-8 and promote an autophagic response (Fig. 1) [7].

The mechanisms underlying the interaction of the autophagy pathway with endocytosed nanomaterials that cannot escape into the cytosol remains poorly characterized. Evidence of crosstalk between the endocytic and autophagy pathways supports the notion of cargo movement between these systems [8]. While advanced imaging methods, such as confocal microscopy, have been critical in documenting cellular trafficking from endocytic vesicles to autophagosomes [8], we still lack a detailed understanding of the signaling cues that govern cargo movement between these pathways.


What is Selective Permeability? (with pictures)

In cell biology, selective permeability is the property of a living cell membrane that allows the cell to control which molecules can pass through the membrane, moving into or out of the cell. In order to understand this property, it helps to be aware that there are three different methods by which molecules can move into or out of cells: passive transport, active transport, and transport by the use of vesicles.

In passive transport across a selectively permeable membrane, molecules move across the membrane without the cell having to expend any extra energy. When water molecules move passively into or out of a cell, for example, this is called osmosis. Other small molecules may move across the membrane by the process of diffusion. This means that they move across the cell membrane from an area of high concentration to an area of low concentration. Oxygen molecules may diffuse from the lung cavity by passive transport into blood cells in the lung.

Active transport is a vital mechanism used by living cells for selective permeability. This method is necessary for small molecules to move across the cell membrane in situations where the molecules need to move against a concentration gradient. Unlike passive transport, active transport gives the cell the ability to move molecules from an area of low concentration to an area of high concentration. This works by means of special channels called pumps, which are present in the cell plasma membrane, and that use up energy when they move molecules across the membrane. Active transport is often used by cells lining the stomach to absorb glucose, amino acids, and other nutrients.

Vesicles are tiny pockets that may form in the cell membrane to aid in the transport of larger molecules. The vesicles allow the cell to take in or eject these molecules across the cell membrane. This process is called endocytosis when molecules are moved into the cell and exocytosis when molecules are moved out of the cell.

Selective permeability of membranes generally depends on the size of the molecules, the positive or negative charge of the molecules, and their solubility in water or oil. In plasma cell membranes, it also depends on many biological functions and biochemical reactions both within and outside each cell. It is one of a living cell's most vital biochemical attributes, and it is a fundamental part of most of the vital processes needed to support life.


The effect of ethanol on plasma membranes

Already established that the greater the concentration of ethanol, the greater the permeability of the plasma membrane. But why is this?

Is it:
To do with water potential. Ethanol lowers the water potential of the surrounding solution so water leaves cells by osmosis.

Or:
Ethanol dissolving the lipids in the plasma membrane? (If this is it, which bonds is it acting on?)

THANK YOU.
+rep for anyone who can help

Not what you're looking for? Try&hellip

What does it become more permeable to? Because if it becomes more permeable to hydrophilic molecules, it could be because the hydrophilic molecule (usually repelled by the hydrophobic carbon chain of the phospholipids) is surrounded by ethanol molecules, each with their OH bonds in the centre hydrogen bonding with the hydrophilic molecule, but exposing their hydrocarbon chains which are hydrophobic and can therefore pass through the phospholipid bilayer.
That's a complete guess though, and it probably doesn't make sense (and is also probably wrong).

That's kinda what I mean

(Original post by Lit2010)
Already established that the greater the concentration of ethanol, the greater the permeability of the plasma membrane. But why is this?

Is it:
To do with water potential. Ethanol lowers the water potential of the surrounding solution so water leaves cells by osmosis.

Or:
Ethanol dissolving the lipids in the plasma membrane? (If this is it, which bonds is it acting on?)

THANK YOU.
+rep for anyone who can help

(Original post by Toneh)
What does it become more permeable to? Because if it becomes more permeable to hydrophilic molecules, it could be because the hydrophilic molecule (usually repelled by the hydrophobic carbon chain of the phospholipids) is surrounded by ethanol molecules, each with their OH bonds in the centre hydrogen bonding with the hydrophilic molecule, but exposing their hydrocarbon chains which are hydrophobic and can therefore pass through the phospholipid bilayer.
That's a complete guess though, and it probably doesn't make sense (and is also probably wrong).

That's kinda what I mean That sounds uber complicated :|
Thanks, though Rep when I'm able to Woo! That's put my mind at ease, i love simplicity

(Original post by Lit2010)
Already established that the greater the concentration of ethanol, the greater the permeability of the plasma membrane. But why is this?

Is it:
To do with water potential. Ethanol lowers the water potential of the surrounding solution so water leaves cells by osmosis.

Or:
Ethanol dissolving the lipids in the plasma membrane? (If this is it, which bonds is it acting on?)

THANK YOU.
+rep for anyone who can help

The plasma membrane is composed of phospolipids. ethanol prefers to bond just below the hydrophilic region of the phospholipids near the phosphate groups. The location of the ethanol creates a strong hydrogen bond between the water molecules.If the solute concentration outside the cell is greater than inside the cell,Ethanol which is a (non&ndashpolar / organic) solvent,enters the membrane and since lipids dissolve (in alcohol) increase in ethanol causes solution to be less polar leading to more osmosis and hence disruption of membrane.
PLEASE DON'T REP ME (Original post by Lit2010)
Woo! That's put my mind at ease, i love simplicity (Original post by jonathan3909)
The plasma membrane is composed of phospolipids. ethanol prefers to bond just below the hydrophilic region of the phospholipids near the phosphate groups. The location of the ethanol creates a strong hydrogen bond between the water molecules.If the solute concentration outside the cell is greater than inside the cell,Ethanol which is a (non&ndashpolar / organic) solvent,enters the membrane and since lipids dissolve (in alcohol) increase in ethanol causes solution to be less polar leading to more osmosis and hence disruption of membrane.
PLEASE DON'T REP ME

Would this then lead to an osmotic loss of water from the cell as the ethanol solution lowered the water potential of the surrounding fluid?

Want me to neg rep you as soon as I can?

Its still a simple answer />But we were told by our teacher that it was the second one!
- You were told at the beginning if the ISA ( if you did the same one as I did) that the pigment comes out of the beetroot when the cell surface membrane had been damaged. And ethanol dissolves the phospholipids that make up the cell membrane, so if you increase the conc of ethanol more pigment is released into the test tube and its more permeable BECAUSE its damaged. Oh dear I rambled a bit..But I hope this helped />x x

(Original post by Lit2010)
Already established that the greater the concentration of ethanol, the greater the permeability of the plasma membrane. But why is this?

Is it:
To do with water potential. Ethanol lowers the water potential of the surrounding solution so water leaves cells by osmosis.

Or:
Ethanol dissolving the lipids in the plasma membrane? (If this is it, which bonds is it acting on?)

THANK YOU.
+rep for anyone who can help

In attachment is a nice figure which shows how the ethanol gets into the plasma membrane and modifies its structure and permeability. It is represented by the black dotes on the right figure.


Here are some questions you might not have heard answered about the coronavirus and the disease it causes, COVID-19, in the media:

  • Why won’t an antibiotic be effective in treating COVID-19?
  • How can soap chemically destroy a coronavirus virion?
  • How does coronavirus defy traditional models of biology's central dogma?

They are part of a lesson plan put together by a team of Brandeis scientists for the National Center for Case Study Teaching in Science at the University at Buffalo, The State University of New York.

The center put out an urgent request for teaching tools on the coronavirus on March 19. Three days later, the Brandeis team submitted a draft. A final version was published on the organization's site on March 30.

It's available for free as a download on the center's website, though the teaching notes and answer key are restricted to paid members.

Professor of biology Melissa Kosinski-Collins, who worked on the project, said the guide is specially designed for remote learning.

"I wanted to help biology students learn about what's happening," she said. "I wanted to make them understand that they have the tools to wrap their heads around this problem even from their home laptop."

Megan and Kat are sisters who find themselves quarantined in their home for two weeks after their mother's coworker tests positive for the virus. The high-school-age girls have plenty of questions about why they're stuck inside and search online for answers.

From here, the lesson plan covers the virus's structure and how it infects cells. When Kat winds up in the hospital with the virus, it deals with treatments.

In the final section, students draft a made-up email to the members of Kat's soccer team explaining what happened to Kat and offering them advice on how to avoid infection.

Assistant professor of biology Kene Piasta, PhD󈧏, who also worked on the lesson, said he and his coauthors wanted to "push students to think critically about the information. It's about how you can get them to go deeper and deeper until they have that aha! moment and get the conceptual knowledge cemented."

The other authors of the study guide are biology teaching lab supervisors Lindsay Mehrmanesh and Jessie Cuomo.

The group next plans to create teaching resources about coronavirus for upper-level biology students.

Why won’t an antibiotic be effective in treating COVID-19?

COVID-19 is caused by a virus, SARS-CoV-2. (Technically, COVID-19 is the name of the disease.) Antibiotics treat bacterial infections, not viral infections.

How can soap chemically destroy a coronavirus virion?

A virion is the technical term for a more specific form of the virus when it's outside the host cell and infectious. Soap molecules, which take the form of little spheres known as micelles, wedge themselves into the virion’s membrane, essentially breaking it into pieces. The virus can’t exist without the membrane.  

How does coronavirus defy traditional models of biology's central dogma?

The central dogma describes the process of transferring genetic information inside a cell. DNA passes the information to messenger RNA (mRNA) which then moves to the ribosome where it is used as instructions to build a protein. But the coronavirus does not use DNA the process starts with RNA passing the information to mRNA. 


Simple Diffusion

In simple diffusion, small molecules without charges such as oxygen and carbon dioxide flow through a plasma membrane without assistance and without expending energy. Other substances such as proteins, glucose and charged particles called ions cannot pass through the selectively permeable membrane. Oxygen and carbon dioxide move, or diffuse, from an area where they exist in high concentrations to an area where they have low concentrations. This means that in general, oxygen can move from blood vessels into cells, and carbon dioxide moves from inside cells back into the red blood cells inside blood vessels.


References

  1. Tom Herrmann1 Sandeep Sharma2. (March 2, 2019).“Physiology, Membrane”. StatPearls. 1 SIU School of Medicine 2 Baptist Regional Medical Center.PMID30855799.
  2. Alberts B, Johnson A, Lewis J, et al. (2002).Molecular Biology of the Cell(4th ed.). New York: Garland Science.ISBN978-0-8153-3218-3.Archivedfrom the original on 2017-12-20.
  3. Gorter E, Grendel F (March 1925).“On Bimolecular Layers of Lipoids on the Chromocytes of the Blood”. The Journal of Experimental Medicine.41(4): 439–43.doi:10.1084/jem.41.4.439.PMC2130960.PMID19868999.
  4. S J Singer and G L Nicolson.”The fluid mosaic model of the structure of cell membranes.” Science. (1972) 175. 720-731.
  5. Sharp, L. W. (1921).Introduction To Cytology. New York: McGraw Hill, p. 42.
  6. Kleinzeller, A. 1999. Charles Ernest Overton’s concept of a cell membrane. In: Membrane permeability: 100 years since Ernest Overton (ed. Deamer D.W., Kleinzeller A., Fambrough D.M.), pp. 1–18, Academic Press, San Diego,.


Watch the video: Practical Effects of temperature and organic solvents on the permeability of cell membrane (May 2022).