Cell Membrane Structure

Illustrative beetroot membrane permeability practical — Original AI-generated editorial illustration for this lesson; not a micrograph, field record or experimental result.

Study sequence: Microscopy and Cell Size · Cell Membrane Structure · Membrane Transport · Cell Division · Inheritance and Genetic Variation · Evolution and Natural Selection · Ecology and Ecosystems · Ecosystem Services and Conservation · Climate Change and Biodiversity

Quick Definition

The cell membrane (also called the plasma membrane) is the thin, flexible boundary around a cell. It is built mainly from a double layer of phospholipids (fat-like molecules with a water-loving head and two water-fearing tails), with proteins embedded in or attached to that layer, cholesterol in animal cells, and sugar chains on the outside face. It separates the inside of the cell from its surroundings, yet it is not a sealed wall: it controls what crosses, receives signals, and holds the cell together.

Why It Matters

Almost every later cell topic depends on this structure. You cannot explain transport without knowing why ions need proteins, or signalling without receptors, or cell recognition without the sugar coat. A student who pictures the membrane as a solid plastic bag will misread every transport and signalling question that follows. The correct picture is a busy, moving boundary — a two-molecule-thick sheet that is both a barrier and a workplace.

Learning Objectives

Describe the phospholipid bilayer and explain why it forms in water.
Explain the fluid mosaic model and how it improved on earlier models.
Distinguish integral, transmembrane and peripheral proteins, and give a job for each protein type.
Explain the roles of cholesterol, glycoproteins, glycolipids and the glycocalyx.
Predict how temperature, tail saturation and cholesterol change fluidity.
Explain membrane asymmetry and why the two faces of a membrane are not identical.
Use a membrane diagram to identify the outside face and to reason about a new example.

Key Terms

Phospholipid — a lipid with a phosphate-containing head and two fatty-acid tails. Amphipathic — having both a water-loving (hydrophilic) part and a water-fearing (hydrophobic) part. Bilayer — two layers of phospholipids arranged tail-to-tail. Integral protein — a protein embedded in the bilayer; a transmembrane protein is an integral protein that spans the whole bilayer. Peripheral protein — a protein attached to a membrane surface, not embedded in the bilayer. Glycoprotein — a protein with a sugar chain attached. Glycolipid — a lipid with a sugar chain attached. Glycocalyx — the sugar-rich coat on the outside of a cell, made of the sugar chains of glycoproteins and glycolipids. Fluid mosaic model — the current model of membrane structure: a fluid lipid bilayer with a mosaic of proteins, cholesterol and carbohydrates. Selective permeability — allowing some substances to cross more easily than others (the transport mechanisms themselves are covered in the separate Membrane Transport lesson).

Core Concept

A membrane is a dynamic phospholipid bilayer. The polar heads face extracellular fluid and the cytosol, while the non-polar tails form an internal hydrophobic region. Many lipids and proteins move laterally, but some proteins are anchored or confined by other proteins and the cytoskeleton. Fluidity does not mean that every component moves freely.

The Phospholipid Bilayer

A phospholipid is amphipathic. Its head contains a phosphate group and is hydrophilic, so it is comfortable in water. Its two fatty-acid tails are hydrophobic, so water pushes them away — not because the tails are repelled by a force, but because water molecules prefer to interact with each other and with hydrophilic heads. Put phospholipids in water and they arrange themselves so the tails are shielded: in a cell, that arrangement is a bilayer, two layers with heads out and tails in (Figure 1). The result is a sheet only about 5–10 nm thick — the same thin line a light microscope cannot resolve, which is why Article 1 described the membrane as looking like a single line in light microscopy.

Exposed hydrophobic edges are energetically unfavourable, so small defects in a lipid bilayer can reseal. Repair of an injured living-cell membrane also involves cellular machinery and depends on the size and type of damage; resealing does not guarantee that a punctured cell survives.

Figure 1. A phospholipid has a water-loving head and two water-fearing tails. In water, phospholipids form a bilayer: heads face water on both sides and tails hide tail-to-tail in the middle, forming a hydrophobic interior.

The Fluid Mosaic Model — and Why Earlier Models Failed

The older picture, commonly credited to Danielli and Davson in 1935, was a "sandwich": a lipid layer with a continuous protein layer on each side. Later, Robertson's unit membrane model (1959) described the membrane as a repeating unit about 7.5 nm thick, seen in electron micrographs as two dark lines with a light layer between them. Both models captured something real — membranes do have a lipid core — but both put proteins mainly on the surfaces, as if the membrane were a coated sheet.

Evidence against that picture accumulated. Freeze-fracture electron microscopy, which splits a frozen membrane along the middle of the bilayer, showed protein particles embedded inside the lipid, not only on its surfaces. Biochemical work showed that many membrane proteins have water-fearing regions that sit happily inside the hydrophobic core, and that proteins move sideways in the membrane rather than staying in fixed positions. The model that fitted all of this, commonly credited to Singer and Nicolson in 1972, is the fluid mosaic model: a fluid phospholipid bilayer in which proteins, cholesterol and carbohydrates form a varied mosaic that can move (Figure 2). The model has since been refined — for example, with lipid rafts and cytoskeleton fences, discussed under Advanced Understanding — but its core picture still stands.

Figure 2. The fluid mosaic membrane in cross-section. The phospholipid bilayer is the fabric; integral and channel proteins span it, a peripheral protein sits on the cytoplasmic surface, cholesterol sits among the lipids (in animal cells), and a glycoprotein carries a sugar chain on the outside face.

What the Membrane Is Made Of

Component	Where it sits	Main job
Phospholipids	Two layers, heads out, tails in	Form the basic barrier and fabric of the membrane
Cholesterol (animal cells)	Among the phospholipids, in both layers	Buffers fluidity against temperature change; helps organise membrane domains
Plant sterols	Among the phospholipids	A similar fluidity-buffering role in plant membranes (for example sitosterol)
Integral proteins	Embedded in the bilayer; some span it	Transport, signalling, catalysis, structure
Peripheral proteins	On one surface, attached to lipids or integral proteins	Support, signalling relays, anchoring to the cytoskeleton
Glycoproteins and glycolipids	Outside face only, sugar chains pointing out	Cell recognition, adhesion, protection (the glycocalyx)

The proportions vary. A membrane is not a fixed recipe: the plasma membrane of a red blood cell, the inner membrane of a mitochondrion and the myelin sheath around a nerve fibre all have different lipid-to-protein ratios, because they do different jobs. Myelin is lipid-rich, which suits insulation; the mitochondrial inner membrane is protein-rich, which suits the many protein machines of respiration. When a question gives you a membrane composition, ask what job that membrane does — the composition usually follows the job.

Membrane Proteins: Embedded, Spanning, or Attached

An integral protein is embedded in the hydrophobic core. It stays there because part of its structure is itself hydrophobic and comfortable among the tails. A transmembrane protein is a type of integral protein that crosses the entire bilayer, so it has parts exposed on both faces — useful for moving something across or passing a signal from one side to the other. A peripheral protein, by contrast, is not embedded at all: it sits on a surface, held by weaker interactions with lipid heads or with integral proteins. A useful laboratory test follows from that difference: peripheral proteins can often be washed off with a salt solution or a change in pH, while integral proteins need a detergent that breaks up the lipid bilayer itself.

Some proteins are lipid-anchored: they are attached to a lipid that is itself embedded in one layer, so the protein rides on one face of the membrane without crossing it. Do not confuse this with a peripheral protein that is merely stuck to the surface — the anchor is a covalent (chemically bonded) lipid attachment, and it matters for proteins that must stay on one face, such as many signalling proteins on the inside face.

Six membrane protein jobs: channel, carrier, receptor, enzyme, recognition and anchor, each shown as a protein in a membrane strip — Figure 3. The same bilayer carries proteins with different jobs. A channel forms a pore; a carrier changes shape to move a substance; a receptor binds a signal; an enzyme catalyses a reaction; a recognition protein (often a glycoprotein) identifies the cell; an anchor links the membrane to the cytoskeleton.

Protein jobs, with examples

Channels provide selective aqueous pores. Many channels open or close through conformational changes called gating. During passage through an open pore, a solute does not require the alternating-access cycle used by a carrier for each transport event. Carriers bind a solute and change access from one side to the other; carriers can support facilitated diffusion or active transport, depending on the coupling mechanism.

Carbohydrates and the Glycocalyx

Carbohydrate chains are attached to some proteins (making glycoproteins) and some lipids (making glycolipids), and they are found on the outside face of the plasma membrane, pointing into the extracellular fluid. Together they form the glycocalyx, a fuzzy sugar coat around the cell. The glycocalyx protects the cell surface, helps cells stick to each other and to their surroundings, and — most importantly for exams — identifies the cell. A well-known example is the ABO blood group system: the A and B antigens are sugar patterns carried on glycolipids and glycoproteins on red blood cells, which is why a mismatched transfusion is recognised as foreign.

Because sugars are only on the outside, they are a reliable clue in a diagram: whichever face carries the sugar chains is the outside (extracellular) face. If a diagram question asks you to label the cytoplasmic side, find the side without sugar chains and with peripheral proteins and cytoskeleton links — that is the inside.

Figure 4. The glycocalyx: glycoproteins and glycolipids carry branched sugar chains on the extracellular face only; the cytoplasmic face has no sugar chains. These sugar patterns identify the cell — for example, ABO blood-group antigens.

Figure 5. Cholesterol buffers membrane fluidity. Each cholesterol molecule sits in a single leaflet, its OH group near the phospholipid heads and its rigid rings among the tails; cholesterol is found in both leaflets. At high temperature it restrains movement; at low temperature it prevents tight packing.

Fluidity: What Makes a Membrane More or Less Fluid

Fluidity includes lateral movement within a membrane leaflet. Spontaneous movement of most phospholipids between leaflets is slow because their polar heads must cross the hydrophobic region. Enzymes can accelerate this movement. Cholesterol behaves differently and can move between leaflets much faster.

Four factors dominate exam questions on fluidity (Figure 6). Temperature: warmer membranes are more fluid, colder membranes less so, because molecules move more at higher temperatures. Tail saturation: saturated fatty-acid tails are straight and pack tightly, reducing fluidity; unsaturated tails have a kink where a double bond bends the chain, so they pack loosely and increase fluidity. Tail length: shorter tails interact less with their neighbours and give a more fluid membrane. Cholesterol: as above, it buffers both extremes. A practical consequence: organisms that live in the cold tend to have more unsaturated fatty acids in their membranes, keeping them fluid at low temperatures. Fluidity: saturated tails pack tightly, unsaturated kinked tails leave gaps, cholesterol buffers both ways; and asymmetry: the outside face carries the glycocalyx while the inside face carries peripheral proteins and cytoskeleton links carries peripheral proteins and cytoskeleton links." loading="lazy" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjSWwnfoMoHKVIs_1VJ3uAqOwVsUveeuMl7qHR_wfTBfP7W3pscQM167w2HpODnnqkvav1RnTbnuA92SkEDRMHBMzYVqkisOxbxuCRnUeIE2LrzVQaOToSVovJ0F5DGKgslYkn8iR19XqJJyEOEtnNrEPESyV4ROjFXsLB3WCCtkCKc81NT_VJ-CXdlTJTU/s1600/clipboard.png" style="display: block; height: auto; margin: auto; max-width: 100%; width: 100%;" />

Figure 6. Left: saturated tails pack tightly and reduce fluidity; kinked unsaturated tails leave gaps and increase it; cholesterol buffers both extremes. Right: the two faces differ — the outside face carries glycolipids and glycoproteins (the glycocalyx), while the inside face carries peripheral proteins and cytoskeleton links.

Asymmetry: The Two Faces Are Not the Same

The two membrane leaflets differ in lipid composition, and membrane proteins have defined orientations. Carbohydrate chains on plasma-membrane glycoproteins and glycolipids face the extracellular space. The whole glycoprotein is not confined to the outer leaflet: many such proteins span the bilayer. Many flippases and floppases use ATP to help maintain lipid asymmetry; regulated scramblases can redistribute lipids without directly using ATP.

Related to asymmetry are lipid rafts: small, dynamic regions of the membrane enriched in cholesterol and sphingolipids (a class of lipids with long, saturated tails) that are more ordered than the surrounding membrane. Rafts are thought to gather certain proteins together, for example in signalling, but they are transient and small — not fixed plates floating in the membrane. Treat any textbook picture of a large, permanent raft with caution; the current view is of short-lived, nanoscale organisation.

Membrane, Cell Wall, and Organelle Membranes — Do Not Confuse Them

In plant cells, fungi and bacteria, there is a cell wall outside the plasma membrane. The wall is a rigid or semi-rigid layer (cellulose in plants, peptidoglycan in most bacteria, chitin in fungi) that supports and protects the cell; the plasma membrane is the living, selective boundary just inside it. A question that shows both layers is testing whether you can tell them apart: the wall is thick and outside, the membrane is the thin bilayer inside it. Animal cells have no cell wall, so their plasma membrane is the outermost boundary, with only the glycocalyx outside it.

Inside the cell, the same bilayer principle builds the membranes of organelles — nucleus, endoplasmic reticulum, Golgi, mitochondria, chloroplasts, vacuoles and vesicles — but each has its own protein and lipid mix, suited to its job. The endomembrane system (endoplasmic reticulum, Golgi, vesicles and the plasma membrane) is connected by vesicle traffic, which is why a protein made in the rough endoplasmic reticulum can end up in the plasma membrane. That journey is covered in the Cell Organelles lesson; here, the point is structural: one bilayer design, many local variations.

Structure Sets Up Selective Permeability (Preview)

The hydrophobic core is the reason the membrane is selectively permeable. Small, non-polar molecules such as oxygen and carbon dioxide can dissolve in the lipid core and cross it directly. Small, uncharged polar molecules such as water cross slowly on their own and much faster through aquaporins. Ions and large polar molecules, such as glucose, cannot cross the hydrophobic core unaided — they need a channel or carrier protein. That single rule predicts most transport questions, but the mechanisms — diffusion, facilitated diffusion, active transport, endocytosis and exocytosis — belong to the next lesson, Membrane Transport, and are deliberately not repeated here.

Selective permeability diagram: oxygen and carbon dioxide through the lipid core, water through an aquaporin, ion and glucose blocked from the core needing a channel or carrier protein

Figure 7. How membrane structure sets selective permeability. Small non-polar molecules (oxygen, carbon dioxide) diffuse directly through the hydrophophobic core; water passes mainly through aquaporins; ions and glucose cannot cross the core unaided and need a channel or carrier protein.

Worked Example: Reading a Membrane Diagram

Question. A diagram shows a bilayer. One face has branched sugar chains and a protein with a sugar chain; the other face has a peripheral protein and a filament labelled "cytoskeleton". Which face is outside the cell, and why?

Answer. The carbohydrate-bearing face is extracellular: the sugar chains of plasma-membrane glycoproteins and glycolipids project outward. A labelled cytoskeletal attachment identifies the cytosolic face. Peripheral proteins can occur on either face, so their presence alone does not determine orientation.

Common Misconceptions

The membrane is a solid wall. It is a fluid bilayer: lipids and proteins move sideways, and it can bend and reseal.
All proteins span the membrane. Many are peripheral (surface only) or lipid-anchored on one face.
Cholesterol always stiffens membranes. It buffers both ways: less runny when warm, less rigid when cold.
Sugars are on both sides. In the plasma membrane, glycoproteins and glycolipids are on the outside face only.
The cell wall and the cell membrane are the same thing. In plants, fungi and bacteria the wall lies outside the membrane and is a different structure.
Every membrane has the same composition. Lipid and protein mixes differ between the plasma membrane and organelle membranes, and between cell types.
Flip-flop is as easy as sideways movement. Sideways movement is fast and common; flip-flop is rare without enzymes.

Exam Focus

GCSE / IGCSE: bilayer structure, hydrophilic heads and hydrophobic tails, and the idea of a partially permeable membrane. A-Level: fluid mosaic model, integral versus peripheral proteins, cholesterol and fluidity, glycoproteins and cell recognition, and diagram labelling including the outside face. AP Biology: membrane structure as the basis for selective permeability, cell communication through receptors, and cell identity through surface carbohydrates. FSc Class 11 and MDCAT: the three historical models in outline (Danielli–Davson, unit membrane, fluid mosaic), protein types, cholesterol, and the difference between the cell membrane and the cell wall. BS Botany and introductory university: asymmetry, lipid rafts, membrane domains, sterol differences between plants and animals, and the evidence from freeze-fracture microscopy.

Advanced Understanding

Two refinements are worth knowing beyond the basic model. First, the cytoskeleton acts like a fence: the membrane skeleton (a network of proteins, such as spectrin in red blood cells, just under the membrane) corrals proteins into small areas, so proteins hop between compartments rather than wandering freely over the whole cell surface. This "fence and picket" picture explains why measured protein movement is often slower and more confined than free diffusion would predict. Second, asymmetry is maintained by enzymes: flippases move specific lipids from the outer to the inner leaflet, floppases move them the other way, and scramblases, activated during processes such as apoptosis or blood clotting, mix the leaflets and collapse asymmetry. These are ATP-using or regulated proteins, not passive diffusion — asymmetry costs energy to maintain, which is itself evidence that it matters to the cell.

Quick Summary

The membrane is a phospholipid bilayer: hydrophilic heads face water on both sides, hydrophobic tails meet in the middle.
The fluid mosaic model (Singer and Nicolson, 1972) describes a fluid bilayer with a mosaic of proteins, cholesterol and carbohydrates.
Integral proteins are embedded (some span the bilayer); peripheral proteins sit on a surface; lipid-anchored proteins ride on one face.
Protein jobs include channel, carrier, receptor, enzyme, recognition and anchor.
Glycoproteins and glycolipids are on the outside face only and form the glycocalyx, used for recognition and adhesion.
Cholesterol (animals) and plant sterols buffer fluidity against temperature change.
Fluidity rises with temperature, unsaturated (kinked) tails and shorter tails; it falls with saturated, tightly packed tails.
The two leaflets differ (asymmetry): sugars outside, peripheral proteins and cytoskeleton links inside.
The hydrophobic core makes the membrane selectively permeable — the transport mechanisms follow in the next lesson.

FAQ

Why is the membrane called "fluid" if it holds the cell together? Fluid here means its components move sideways within the plane of the membrane, not that the membrane flows away. The bilayer stays intact because the hydrophobic effect constantly keeps tails shielded from water.

Do plant cells have cholesterol? Yes. In many plants, phytosterols such as sitosterol, campesterol and stigmasterol predominate, but cholesterol abundance varies among species and tissues. Avoid treating all plant membranes as having an identical sterol composition.

Why can't ions simply diffuse through the lipid bilayer? Ions are charged and surrounded by water. Crossing would mean passing through the water-fearing hydrophobic core, which is energetically unfavourable, so they need a channel or carrier protein.

What is the difference between a glycoprotein and a glycolipid? Both carry a sugar chain on the outside face; a glycoprotein carries it on a protein, a glycolipid on a lipid.

Is the fluid mosaic model still accepted? Yes, in refined form. Later work added lipid rafts, cytoskeleton fences and asymmetry maintenance, but the core picture — a fluid bilayer with a mosaic of mobile components — remains the standard model.

How is the plasma membrane different from the nuclear envelope? The nuclear envelope is two bilayers with nuclear pores, enclosing the nucleus; the plasma membrane is a single bilayer enclosing the whole cell. Both use the same bilayer principle with different proteins.

20 Explained MCQs — answers hidden until opened

Open each question to reveal its answer and explanation.

1. In a phospholipid bilayer, the hydrophilic heads face:

A. Only the outside of the cell B. Only the cytoplasm C. Water on both sides of the membrane D. Each other in the middle of the membrane
Answer: C. Heads face the aqueous fluid on both faces; tails meet in the middle.

2. A phospholipid is described as amphipathic because it has:

A. Two identical tails B. A water-loving head and water-fearing tails C. Two heads and one tail D. A sugar chain on both faces
Answer: B. Amphipathic means having both hydrophilic and hydrophobic parts in one molecule.

3. The plasma membrane is approximately how thick?

A. 0.5–1 nm B. 5–10 nm C. 50–100 nm D. 200 nm
Answer: B. Plasma membranes are about 5–10 nm thick, below the resolution of a light microscope.

4. The fluid mosaic model is commonly credited to:

A. Danielli and Davson, 1935 B. Robertson, 1959 C. Singer and Nicolson, 1972 D. Hooke and Leeuwenhoek, 1665
Answer: C. Singer and Nicolson proposed the fluid mosaic model in 1972.

5. A key flaw in the Danielli–Davson sandwich model was that it:

A. Denied the existence of lipids B. Placed proteins mainly as surface layers, not embedded in the bilayer C. Claimed membranes were made of cellulose D. Denied that cells have a boundary
Answer: B. Freeze-fracture and biochemical evidence later showed proteins embedded inside the lipid bilayer.

6. Which protein spans the entire bilayer?

A. A peripheral protein B. A transmembrane protein C. A lipid-anchored protein on one face D. A free cytoplasmic enzyme
Answer: B. Transmembrane proteins are integral proteins that cross the whole bilayer.

7. At low temperatures, cholesterol in an animal cell membrane mainly:

A. Makes the membrane completely rigid B. Prevents phospholipids packing too tightly, keeping some fluidity C. Removes all unsaturated tails D. Moves to the glycocalyx
Answer: B. Cholesterol disrupts tight packing at low temperatures, buffering against rigidity.

8. At high temperatures, cholesterol mainly:

A. Increases fluidity further B. Restrains phospholipid movement, preventing excess fluidity C. Melts the bilayer D. Converts saturated tails to unsaturated tails
Answer: B. Cholesterol buffers both ways: it restrains movement when warm and prevents tight packing when cold.

9. Why do unsaturated fatty-acid tails increase membrane fluidity?

A. They are longer than saturated tails B. Their double-bond kink prevents tight packing, leaving gaps C. They attract water into the core D. They remove cholesterol
Answer: B. The kink stops neighbouring tails packing closely, so the membrane stays looser.

10. Which way do carbohydrate chains on plasma-membrane glycoproteins and glycolipids face?

A. Toward the cytosol

B. Equally toward both sides

C. Toward extracellular fluid

D. Only into the bilayer core

Answer: C. These carbohydrate chains form the extracellular glycocalyx. The protein or lipid carrying them can be embedded in the membrane.

11. The glycocalyx is best described as:

A. The cell wall of animal cells B. A sugar-rich coat on the outside of the cell, used for recognition and protection C. A layer of cholesterol inside the bilayer D. The cytoskeleton under the membrane
Answer: B. The glycocalyx is the sugar chains of glycoproteins and glycolipids on the outer surface.

12. What is the main difference between a channel and a carrier protein?

A. Channels use ATP and carriers do not B. A channel forms an open pore; a carrier changes shape to move a substance C. Carriers only move water D. Channels are peripheral and carriers are integral
Answer: B. Channels provide a pore; carriers bind, change shape, and release on the other side.

13. Aquaporins are an example of which protein job?

A. Receptor B. Channel, allowing rapid water movement C. Enzyme D. Anchor
Answer: B. Aquaporins are water channels: a pore selective for water, excluding ions.

14. Why do ions not cross the lipid bilayer unaided?

A. Ions are too small to be noticed B. Ions are charged and water-associated, and the core is hydrophobic C. Ions dissolve the phospholipids D. Ions are blocked by the glycocalyx alone
Answer: B. A charged, hydrated ion cannot favourably cross the water-fearing core, so it needs a protein.

15. Spontaneous phospholipid flip-flop (movement between leaflets) is:

A. As fast and common as sideways movement B. Rare and slow without enzymes, because a hydrophilic head must cross the hydrophobic core C. Impossible in any cell D. The main cause of membrane fluidity
Answer: B. Sideways movement is common; flip-flop is rare without flippases or floppases.

16. Phosphatidylserine is normally found mainly on which leaflet of the plasma membrane?

A. The outer leaflet B. The inner (cytoplasmic) leaflet C. Equally on both leaflets D. In the glycocalyx
Answer: B. Phosphatidylserine is normally kept on the cytoplasmic leaflet; its appearance outside is a signal in apoptosis.

17. The main membrane sterols of plant cells are:

A. Cholesterol, exactly as in animal cells B. Phytosterols such as sitosterol C. No sterols at all D. Sphingolipids only
Answer: B. Plants use phytosterols as their principal membrane sterols; cholesterol abundance varies, while phytosterols predominate in many plants.

18. Myelin, the insulating sheath around nerve fibres, is best described as:

A. Protein-rich and lipid-poor B. Lipid-rich, suiting insulation C. Made of cellulose D. A double bilayer with nuclear pores
Answer: B. Myelin is unusually lipid-rich, which fits its insulating job — composition follows function.

19. A protein washed off a membrane by a salt solution, without detergent, is most likely:

A. An integral protein B. A transmembrane protein C. A peripheral protein D. A phospholipid
Answer: C. Peripheral proteins are held by weaker surface interactions and can be washed off; integral proteins need detergent.

20. In a membrane diagram, the face carrying branched sugar chains is:

A. The cytoplasmic face B. The extracellular face C. The hydrophobic core D. The nuclear envelope
Answer: B. Sugar chains of glycoproteins and glycolipids are on the outside face only.

Separate Interactive Quiz — 20 different questions

These quiz questions are different from the MCQs above. Select an answer for each question. You will not see whether an answer is correct until you submit all 20 questions. Use Reset to try again.