Click this link for a Cell Structure/Function and Cell Membranes Student Learning Guide

1. The fluid mosaic model: membrane components in motion

One of the most important characteristics of membranes is their ability to control what passes through the membrane to enter or leave the cell (or a membrane-bound part within the cell). This is known as selective permeability (also semi-permeability).

But membranes can do even more. Here’s the verse from my Membranes! music video that describes some of these other functions:

But not just a guard, it sends signals in nerves
White blood cells use their membranes to eat germs like hors d’oeuvres,
Membranes have receptors, enzymes and junctions,
So what kinds of structure can have all these functions?

08_labeled, detailed membrane
modified from an image on Wikipedia.

As we saw in the previous tutorial, phospholipids make up the basic structure of the membrane. But additional membrane functions come from proteins, cholesterol, and carbohydrates that are embedded in the structure of the membrane, as shown below.

Using the numbered diagram below, let’s get a quick overview of some of the specific things that these membrane components do.

1a. Membrane Proteins

09_detailed phospholipid, numbered
Parts 1, 3, 5 and 6 are membrane proteins

Proteins are classified by their position in the membrane.

  • Any protein embedded in the phospholipid bilayer is called an integral protein. In the diagram at left, 1, 5, and 6 are integral proteins.
  • If the protein passes all the way through the membrane, like 1 and 6 above, it’s a transmembrane protein.
  • If the protein hangs on to the membrane, attached to the phospholipid heads (but not extending into the hydrophobic tails), then it’s a peripheral protein. Number 3 above is peripheral.

Here are some protein functions 

  • They act as channels or ports (6), allowing the cell to take in and let out molecules that can’t diffuse through the phospholipid bilayer portion of the membrane.
  • They act as carriers, allowing the cell to perform active transport, moving molecules from low concentration to high concentration.
  • They act as attachment points for the fibers of the cytoskeleton, allowing the cell to change its shape and move (3).
  • They act as membrane-embedded enzymes. We’ll see these at work in essential cell processes like photosynthesis and cellular respiration.
  • They act as receptors, receiving chemical messages (including hormones) and relaying these messages into the cytoplasm.
09_detailed phospholipid, numbered
Cholesterol (7) and carbohydrate (8)

1b. Cholesterol, and Membrane Carbohydrates

Other key membrane components include cholesterol and membrane carbohydrates.

  • Cholesterol (7) is a lipid that plays a key role in maintaining membrane integrity and fluidity. When cell membranes become too warm, cholesterol keeps the phospholipid bilayer intact. When cell membranes become too cold, cholesterol acts like an anti-freeze, keeping the membrane fluid.
  • Membrane carbohydrates (8) play a key role in allowing the immune system to recognize a cell as belonging to the multicellular organism that it’s a part of (as opposed to some invading bacterium). You can think of these carbohydrates as little flags. They’re the key markers, for example, in the A, AB, B and O blood type system.

1c. It’s all a fluid mosaic

Diagrams like these can leave you with the misunderstanding that membranes are fixed, kind of like a chocolate bar with almonds, with the almonds locked into place. In fact, the membrane is a dynamic fluid, with all of its parts in constant motion. This model of membrane structure is called the fluid-mosaic model. 

Use the flashcards below to master these membrane components.

2. Cell Membrane Structure Flashcards

[qdeck random = “true” style=”width: 528px; border: 2px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-Cell Membrane Structure Flashcards (M8)”]

[h] Flashcards: Cell Membrane Structure

[i] If you haven’t used a set of flashcards on sciencemusicvideos before, here’s what you need to know.

  • Click ‘Check Answer’ to see the answer to each card.
  • If you know it, click ‘Got it.”
  • If you don’t know it as well as you’d like, click ‘Need more practice,’ and that card will go to the bottom of the deck so you can practice it again.
  • ‘Shuffle’ lets you shuffle the deck.

 

[!] Card 3+++++++++++++++++++++++++++++++++++[/!]

[q]Membranes allow certain molecules to pass through but not others. In other words, membranes are ________-_______________.

[textentry]

[a] Membranes allow certain molecules to pass through but not others. In other words, membranes are selectively-permeable. (note that semi-permeable means just about the same thing).

[!] Card 3+++++++++++++++++++++++++++++++++++[/!]

[q]Just for review (from the last tutorial). The arrangement of phospholipids shown below is called a  phospholipid ________ [textentry]

[a]The arrangement of phospholipids shown below is called a  phospholipid bilayer.

[!] Card 13+++++++++++++++++++++++++++++++++++[/!]

[q]The dynamic model of cell membrane structure which involves phospholipids, proteins, cholesterol, and carbohydrates in constant motion in the membrane is the _______-_______ model.[textentry]

[a]The dynamic model of cell membrane structure which involves phospholipids, proteins, cholesterol, and carbohydrates in constant motion in the membrane is the fluid-mosaic model.

[!] Card 14+++++++++++++++++++++++++++++++++++[/!]

[q]In the diagram below, membrane proteins like the ones at 1, 5, and 6, all of which are embedded in the phospholipid bilayer, are known as_____________ proteins. [textentry]

[a]In the diagram below, membrane proteins like the ones at 1, 5, and 6, all of which are embedded in the phospholipid bilayer, are known as integral proteins.

[!] Card 15+++++++++++++++++++++++++++++++++++[/!]

[q]In the diagram below, membrane proteins like the ones at 1 and 6, both of which span the width of the phospholipid bilayer, are known as_____________ proteins. [textentry]

[a]In the diagram below, membrane proteins like the ones at 1 and 6, both of which span the width of the phospholipid bilayer, are known as transmembrane proteins. .

[!] Card 16+++++++++++++++++++++++++++++++++++[/!]

[q]In the diagram below, the molecule shown at 7 is a lipid, but not a phospholipid. Its function is to stabilize the membrane at high temperatures, and to keep it fluid at low termperatures. This molecule must be ________[textentry]

[a]In the diagram below, the molecule shown at 7 is a lipid, but not a phospholipid. Its function is to stabilize the membrane at high temperatures, and to keep it fluid at low termperatures. This molecule must be cholesterol. 

[!] Card 17+++++++++++++++++++++++++++++++++++[/!]

[q]Because of the way that it’s positioned in the membrane, you can tell that protein # 3 must be a  _______ protein. [textentry]

[a]Because of the way that it’s positioned in the membrane (hanging off the bottom) you can tell that protein # 3 must be a peripheral protein. 

[x]

If you want more practice, please press the restart button below. Otherwise, follow the links below.
[restart]
[/qdeck]

 

3. Quiz: Cell Membrane Structure

This quiz tests you on the diagram you just worked with above, plus this one:

11_Cell_membrane_diagram (cronodon).
From www.cronodon.com. Big circles or ellipses represent proteins. Study the key for details.
  • A – phospholipid molecule;
  • A1 – hydrophilic phosphate head group of phospholipid;
  • A2 – Fatty acid tail (x 2) of phospholipid;
  • B – a phospholipid with a carbohydrate chain attached to it)
  • C– a protein with a carbohydrate chain attached to it);
  • D – carbohydrate chain of glycoprotein;  
  • E – cholesterol;  
  • F – protein;  
  • G – a protein channel (pore)
  • H-I: Phospholipid bilayer

 

[qwiz random = “true;” style = ” border: 3px solid black; ” qrecord_id=”sciencemusicvideosMeister1961-Cell Membrane Structure Quiz (M8)”]

[h]Cell Membrane Structure Quiz

[i]

 

[q labels = “top”]

 

[l]phospholipid bilayer

[fx] No.  Please try again.

[f*] Correct!

[l]phospholipid
head

[fx] No.  Please try again.

[f*] Excellent!

[l]phospholipid
tail

[fx] No, that’s not correct.  Please try again.

[f*] Good!

[l]protein channel

[fx] No, that’s not correct.  Please try again.

[f*] Good!

[q labels = “top”]

 

 

[l]cholesterol

[fx] No.  Please try again.

[f*] Good!

[l]integral protein

[fx] No.  Please try again.

[f*] Excellent!

[l]membrane carbohydrate

[fx] No, that’s not correct.  Please try again.

[f*] Good!

[l]peripheral protein

[fx] No, that’s not correct.  Please try again.

[f*] Excellent!

[l]phospholipid bilayer

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[l]phospholipid head

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[l]phospholipid tail

[fx] No, that’s not correct.  Please try again.

[f*] Good!

[l]protein channel

[fx] No, that’s not correct.  Please try again.

[f*] Great!

[l]trans-membrane protein

[fx] No.  Please try again.

[f*] Correct!

[!] Question 1++++++++++++++[/!]

[q] In the diagram below, which number is pointing to the phospholipid bilayer?

[c] 1   [c] 2   [c] 3   [c*] 4

[f] No. Number 1 is pointing to the tail of a phospholipid. Here’s a hint: the term “bilayer” means “two layers.” What looks like it’s made of two layers?

[f] No. Number 2 is pointing to a phospholipid head. Here’s a hint: the term “bilayer” means “two layers.” What looks like it’s made of two layers?

[f] No. Number 3 is pointing to a protein channel. Here’s a hint: the term “bilayer” means “two layers.” What looks like it’s made of two layers?

[f] Excellent. Number 4 is pointing to the phospholipid bilayer.

[!] Question 2++++++++++++++[/!]

[q] In the diagram below, which number is pointing to the hydrophobic tail of a phospholipid?

[c*] 1    [c] 2    [c] 3    [c] 4

[f] Yes. Number 1 is pointing to the tail of a phospholipid.

[f] No. Number 2 is pointing to a phospholipid head. What looks like a tail?

[f] No. Number 3 is pointing to a protein channel. What looks like a tail?

[f] No. Number 4 is pointing to the phospholipid bilayer. What looks like a tail?

[!] Question 3++++++++++++++[/!]

[q] In the diagram below, which number is pointing to a protein channel?

[c] 1     [c] 2     [c*] 3     [c] 4

[f] No. Number 1 is pointing to the tail of a phospholipid. In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[f] No. Number 2 is pointing to a phospholipid head. In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[f] Yes. Number 3 is pointing to a protein channel.

[f] No. Number 4 is pointing to the phospholipid bilayer. In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[!] Question 4+++++ [/!]

[q] In the diagram below, which number is pointing to the phospholipid bilayer?[c] 1     [c*] 2     [c] 3     [c] 4     [c]5    [c]6     [c]7     [c]8    [c]9

[f] No. Number 1 is pointing two transmembrane proteins. The phospholipid bilayer is the main structure of the membrane, and it’s made of two layers of phospholipids, the lower one with its heads down, the top one with its heads up. What number points to something that fits that description?

[f] Yes. Number 2 is pointing to the phospholipid bilayer.

[f] No. Number 3 is pointing to a peripheral protein. The phospholipid bilayer is the main structure of the membrane, and it’s made of two layers of phospholipids, the lower one with its heads down, the top one with its heads up. What number points to something that fits that description?

[f] No, but you’re close. Number 4 is pointing to the tail of a single phospholipid. The phospholipid bilayer is the main structure of the membrane, and it’s made of two layers of phospholipids, the lower one with its heads down, the top one with its heads up. What number points to something that fits that description?

[f] No. Number 5 is pointing to an integral protein. The phospholipid bilayer is the main structure of the membrane, and it’s made of two layers of phospholipids, the lower one with its heads down, the top one with its heads up. What number points to something that fits that description?

[f] No! Number 6 is pointing a protein channel.The phospholipid bilayer is the main structure of the membrane, and it’s made of two layers of phospholipids, the lower one with its heads down, the top one with its heads up. What number points to something that fits that description?

[f] No. Number 7 is pointing to cholesterol. The phospholipid bilayer is the main structure of the membrane, and it’s made of two layers of phospholipids, the lower one with its heads down, the top one with its heads up. What number points to something that fits that description?

[f] No. Number 8 is pointing to a membrane carbohydrate. The phospholipid bilayer is the main structure of the membrane, and it’s made of two layers of phospholipids, the lower one with its heads down, the top one with its heads up. What number points to something that fits that description?

[f] No, but you’re close. Number 9 is pointing to the head of a phospholipid. The phospholipid bilayer is the main structure of the membrane, and it’s made of two layers of phospholipids, the lower one with its heads down, the top one with its heads up. What number points to something that fits that description?

[!] Question 5+++++[/!]

[q] In the diagram below, which number is pointing to a molecule of cholesterol?
[c] 1     [c] 2     [c] 3     [c] 4     [c]5    [c]6     [c*]7     [c]8    [c]9

[f] No. Number 1 is pointing two transmembrane proteins. Cholesterol is a lipid that’s embedded in the membrane, but it’s not a phospholipid. Eliminate the proteins (all shaded in blue), and see if you can figure out the answer.

[f] No. Number 2 is pointing to the phospholipid bilayer. Cholesterol is a lipid that’s embedded in the membrane, but it’s not a phospholipid. Eliminate the proteins (all shaded in blue), and see if you can figure out the answer.

[f] No. Number 3 is pointing to a peripheral protein.Cholesterol is a lipid that’s embedded in the membrane, but it’s not a phospholipid. Eliminate the proteins (all shaded in blue), and see if you can figure out the answer.

[f] No. Number 4 is pointing to the tail of a phospholipid. Cholesterol is a lipid that’s embedded in the membrane, but it’s not a phospholipid. Eliminate the proteins (all shaded in blue), and see if you can figure out the answer.

[f] No. Number 5 is pointing to an integral protein. Cholesterol is a lipid that’s embedded in the membrane, but it’s not a phospholipid. Eliminate the proteins (all shaded in blue), and see if you can figure out the answer.

[f] No. Number 6 is pointing a protein channel. Cholesterol is a lipid that’s embedded in the membrane, but it’s not a phospholipid. Eliminate the proteins (all shaded in blue), and see if you can figure out the answer.

[f] Yes. Number 7 is pointing to cholesterol.

[f] No. Number 8 is pointing to a membrane carbohydrate. Cholesterol is a lipid that’s embedded in the membrane, but it’s not a phospholipid. Eliminate the proteins (all shaded in blue), and see if you can figure out the answer.

[f] No. Number 9 is pointing to the head of a phospholipid. Cholesterol is a lipid that’s embedded in the membrane, but it’s not a phospholipid. Eliminate the proteins (all shaded in blue), and see if you can figure out the answer.

[!] Question 6+++++[/!]

[q] In the diagram below, which number is pointing to a phospholipid head?
[c] 1     [c] 2     [c] 3     [c] 4     [c]5    [c]6     [c]7     [c]8    [c*]9

[f] No. Number 1 is pointing two transmembrane proteins. The phospholipids are the main structural molecules making up the membrane. The polar “heads” of the phospholipids face towards the outside of the membrane (which means up, toward the extracellular fluid, and down, towards the cytoplasm). With that in mind, see if you can find a phospholipid head.

[f] No, but you’re close. Number 2 is pointing to the entire phospholipid bilayer. The polar “heads” of the phospholipids face towards the outside of the membrane (which means up, toward the extracellular fluid, and down, towards the cytoplasm). With that in mind, see if you can find a phospholipid head.

[f] No. Number 3 is pointing to a peripheral protein. The phospholipids are the main structural molecules making up the membrane. The polar “heads” of the phospholipids face towards the outside of the membrane (which means up, toward the extracellular fluid, and down, towards the cytoplasm). With that in mind, see if you can find a phospholipid head.

[f] No, but you’re close. Number 4 is pointing to the tail of a phospholipid. The polar “heads” of the phospholipids face towards the outside of the membrane (which means up, toward the extracellular fluid, and down, towards the cytoplasm). With that in mind, see if you can find a phospholipid head.

[f] No. Number 5 is pointing to an integral protein. The phospholipids are the main structural molecules making up the membrane. The polar “heads” of the phospholipids face towards the outside of the membrane (which means up, toward the extracellular fluid, and down, towards the cytoplasm). With that in mind, see if you can find a phospholipid head.

[f] No. Number 6 is pointing a protein channel. The phospholipids are the main structural molecules making up the membrane. The polar “heads” of the phospholipids face towards the outside of the membrane (which means up, toward the extracellular fluid, and down, towards the cytoplasm). With that in mind, see if you can find a phospholipid head.

[f] No. Number 7 is pointing to cholesterol. The phospholipids are the main structural molecules making up the membrane. The polar “heads” of the phospholipids face towards the outside of the membrane (which means up, toward the extracellular fluid, and down, towards the cytoplasm). With that in mind, see if you can find a phospholipid head.

[f] No. Number 8 is pointing to a membrane carbohydrate. The phospholipids are the main structural molecules making up the membrane. The polar “heads” of the phospholipids face towards the outside of the membrane (which means up, toward the extracellular fluid, and down, towards the cytoplasm). With that in mind, see if you can find a phospholipid head.

[f] Yes. Number 9 is pointing to the head of a phospholipid.

[!] Question 7+++++[/!]

[q] In the diagram below, which number is pointing to a peripheral protein?
[c] 1     [c] 2     [c*] 3     [c] 4     [c]5    [c]6     [c]7     [c]8    [c]9

[f] No. Number 1 is pointing two transmembrane proteins. Peripheral proteins hang onto the phospholipid heads of the bilayer, without penetrating into the middle, hydrophobic portion. Given that in this diagram the proteins are shaded blue, which number is pointing to something that fits that description?

[f] No. Number 2 is pointing to the entire phospholipid bilayer. Peripheral proteins hang onto the phospholipid heads of the bilayer, without penetrating into the middle, hydrophobic portion. Given that in this diagram the proteins are shaded blue, which number is pointing to something that fits that description?

[f] Yes. Number 3 is pointing to a peripheral protein.

[f] No. Number 4 is pointing to the tail of a phospholipid. Peripheral proteins hang onto the phospholipid heads of the bilayer, without penetrating into the middle, hydrophobic portion. Given that in this diagram the proteins are shaded blue, which number is pointing to something that fits the description of a peripheral protein?

[f] No. Number 5 is pointing to an integral protein. Peripheral proteins hang onto the phospholipid heads of the bilayer, without penetrating into the middle, hydrophobic portion. Given that in this diagram the proteins are shaded blue, which number is pointing to something that fits the description of a peripheral protein?

[f] No. Number 6 is pointing a protein channel. Peripheral proteins hang onto the phospholipid heads of the bilayer, without penetrating into the middle, hydrophobic portion. Given that in this diagram the proteins are shaded blue, which number is pointing to something that fits the description of a peripheral protein?

[f] No. Number 7 is pointing to cholesterol. Peripheral proteins hang onto the phospholipid heads of the bilayer, without penetrating into the middle, hydrophobic portion. Given that in this diagram the proteins are shaded blue, which number is pointing to something that fits the description of a peripheral protein?

[f] No. Number 8 is pointing to a membrane carbohydrate. Peripheral proteins hang onto the phospholipid heads of the bilayer, without penetrating into the middle, hydrophobic portion. Given that in this diagram the proteins are shaded blue, which number is pointing to something that fits the description of a peripheral protein?

[f] No. Number 9 is pointing to the head of a phospholipid. Peripheral proteins hang onto the phospholipid heads of the bilayer, without penetrating into the middle, hydrophobic portion. Given that in this diagram the proteins are shaded blue, which number is pointing to something that fits the description of a peripheral protein?

[!] Question 8+++++ +++++++++[/!]

[q] In the diagram below, which number is pointing to a protein channel?
[c] 1     [c] 2     [c] 3     [c] 4     [c]5    [c*]6     [c]7     [c]8    [c]9

[f] No. Number 1 is pointing two transmembrane proteins. A channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[f] No. Number 2 is pointing to the phospholipid bilayer. In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[f] No. Number 3 is pointing to a peripheral protein.In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[f] No. Number 4 is pointing to the tail of a phospholipid. In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[f] No. Number 5 is pointing to an integral protein (but one that’s not a trans-membrane protein). In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[f] Excellent! Number 6 is pointing a protein channel.

[f] No. Number 7 is pointing to cholesterol. In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[f] No. Number 8 is pointing to a membrane carbohydrate. In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[f] No. Number 9 is pointing to the head of a phospholipid. In the context of membranes, a channel is a structure that lets molecules pass through (like a bridge or a tunnel). What looks like a channel?

[!] Question 9+++++  [c] 1     [c] 2     [c] 3     [c*] 4     [c]5    [c*]6     [c]7     [c]8    [c]9 +++++++++[/!]

[q] In the diagram below, which number is pointing to a phospholipid tail?
[c] 1     [c] 2     [c] 3     [c*] 4     [c]5    [c]6     [c]7     [c]8    [c]9

[f] No. Number 1 is pointing two transmembrane proteins. The phospholipids are the main structural molecules making up the membrane. The non-polar “tails” of the phospholipids face towards the inside of the membrane, away from the cytoplasm or the extracellular fluid. With that in mind, see if you can find a phospholipid head.

[f] No, but you’re close. Number 2 is pointing to the entire phospholipid bilayer. The non-polar “tails” of the phospholipids face towards the inside of the membrane, away from the cytoplasm or the extracellular fluid. With that in mind, see if you can find a phospholipid head.

[f] No. Number 3 is pointing to a peripheral protein. The phospholipids are the main structural molecules making up the membrane. The non-polar “tails” of the phospholipids face towards the inside of the membrane, away from the cytoplasm or the extracellular fluid. With that in mind, see if you can find a phospholipid head.

[f] Yes. Number 4 is pointing to the tail of a phospholipid.

[f] No. Number 5 is pointing to an integral protein. The phospholipids are the main structural molecules making up the membrane. The non-polar “tails” of the phospholipids face towards the inside of the membrane, away from the cytoplasm or the extracellular fluid. With that in mind, see if you can find a phospholipid head.

[f] No! Number 6 is pointing a protein channel. The phospholipids are the main structural molecules making up the membrane. The non-polar “tails” of the phospholipids face towards the inside of the membrane, away from the cytoplasm or the extracellular fluid. With that in mind, see if you can find a phospholipid head.

[f] No. Number 7 is pointing to cholesterol. The phospholipids are the main structural molecules making up the membrane. The non-polar “tails” of the phospholipids face towards the inside of the membrane, away from the cytoplasm or the extracellular fluid. With that in mind, see if you can find a phospholipid head.

[f] No. Number 8 is pointing to a membrane carbohydrate. The phospholipids are the main structural molecules making up the membrane. The non-polar “tails” of the phospholipids face towards the inside of the membrane, away from the cytoplasm or the extracellular fluid. With that in mind, see if you can find a phospholipid head.

[f] No. Number 9 is pointing to the head of a phospholipid. The phospholipids are the main structural molecules making up the membrane. The non-polar “tails” of the phospholipids face towards the inside of the membrane, away from the cytoplasm or the extracellular fluid. With that in mind, see if you can find a phospholipid head.

[!] Question 10++++++++++++++[/!]

[q]In the diagram below, which letter represents a membrane carbohydrate?

[c] A     [c*] D   [c]E       [c]H-I     [c]G

[f]No. A is pointing to a phospholipid. Membrane carbohydrates are usually short, branched polysaccharides. Look closely and see if you can find something that fits that description.

[f]Yes. D is pointing to a membrane carbohydrate.

[f]No. E is pointing to a molecule of cholesterol.Membrane carbohydrates are usually short, branched polysaccharides. Look closely and see if you can find something that fits that description.

[f]No. H-I is pointing to the  phospholipid bilayer. Membrane carbohydrates are usually short, branched polysaccharides. Look closely and see if you can find something that fits that description.

[f]No. G is pointing to a protein channel. Membrane carbohydrates are usually short, branched polysaccharides. Look closely and see if you can find something that fits that description.

[!] Question 11++++++++++++++[/!]

[q]In the diagram below, which letter represents protein channel?

[c] A     [c] D   [c]E       [c]H-I     [c*]G

[f]No. A is pointing to a phospholipid. A protein channel is like a pore, or a tunnel. It allows molecules to pass through. What, in this diagram, looks like a tunnel?

[f]No. D is pointing to a membrane carbohydrate.  A protein channel is like a pore, or a tunnel. It allows molecules to pass through. What, in this diagram, looks like a tunnel?

[f]No. E is pointing to a molecule of cholesterol. A protein channel is like a pore, or a tunnel. It allows molecules to pass through. What, in this diagram, looks like a tunnel?

[f]No. H-I is pointing to the  phospholipid bilayer.  A protein channel is like a pore, or a tunnel. It allows molecules to pass through. What, in this diagram, looks like a tunnel?

[f]Yes. G is pointing to a protein channel.

[!] Question 12++++++++++++++[/!]

[q]In the diagram below, which letter represents cholesterol?

[c] A     [c] D   [c*]E       [c]H-I     [c]G

[f]No. A is pointing to a phospholipid. Cholesterol is a lipid. It’s usually represented as a group of fused rings embedded in the membrane. What, in this diagram, fits that description?

[f]No. D is pointing to a membrane carbohydrate.  Cholesterol is a lipid. It’s usually represented as a group of fused rings embedded in the membrane. What, in this diagram, fits that description?

[f]Yes. E is pointing to a molecule of cholesterol.

[f]No. H-I is pointing to the  phospholipid bilayer.  Cholesterol is a lipid. It’s usually represented as a group of fused rings embedded in the membrane. What, in this diagram, fits that description?

[f]No. G is pointing to a protein channel. Cholesterol is a lipid. It’s usually represented as a group of fused rings embedded in the membrane. What, in this diagram, fits that description?

[!] Question 13++++++++++++++[/!]

[q]In the diagram below, which letter represents a phospholipid?

[c*] A     [c] D   [c]E       [c]H-I     [c]G

[f]Yes. A is pointing to a phospholipid.

[f]No. D is pointing to a membrane carbohydrate.  You can identify phospholipids in several ways: 1) they make up the main structure or framework of the membrane. 2) They’re organized into a bilayer, with the tails facing inward and the heads facing outward. 3) They have a “head” and a “tail.”

[f]No. E is pointing to a molecule of cholesterol. You can identify phospholipids in several ways: 1) they make up the main structure or framework of the membrane. 2) They’re organized into a bilayer, with the tails facing inward and the heads facing outward. 3) They have a “head” and a “tail.”

[f]No, but you’re close. H-I is pointing to the  phospholipid bilayer.  Find what’s pointing to a single phospholipid molecule.

[f]No. G is pointing to a protein channel. You can identify phospholipids in several ways: 1) they make up the main structure or framework of the membrane. 2) They’re organized into a bilayer, with the tails facing inward and the heads facing outward. 3) They have a “head” and a “tail.”

[!] Card 3+++++++++++++++++++++++++++++++++++[/!]

[q]Membranes allow certain molecules to pass through but not others. In other words, membranes are ________-_______________.

[hangman]

[c]selectively-permeable

[f]Correct! Membranes allow certain molecules to pass through but not others. In other words, membranes are selectively-permeable. (note that semi-permeable means just about the same thing).

[!] Card 3+++++++++++++++++++++++++++++++++++[/!]

[q]Just for review (from the last tutorial). The arrangement of phospholipids shown below is called a  phospholipid ________

[hangman]

[c]bilayer

[f]Great! The arrangement of phospholipids shown below is called a  phospholipid bilayer.

[!] Card 13+++++++++++++++++++++++++++++++++++[/!]

[q]The dynamic model of cell membrane structure which involves phospholipids, proteins, cholesterol, and carbohydrates in constant motion in the membrane is the _______-_______ model.

[hangman]

[c]fluid-mosaic

[f]Correct! The dynamic model of cell membrane structure which involves phospholipids, proteins, cholesterol, and carbohydrates in constant motion in the membrane is the fluid-mosaic model.

[!] Card 14+++++++++++++++++++++++++++++++++++[/!]

[q]In the diagram below, membrane proteins like the ones at 1, 5, and 6, all of which are embedded in the phospholipid bilayer, are known as_____________ proteins.

[hangman]

[c]integral

[f]Yes! In the diagram below, membrane proteins like the ones at 1, 5, and 6, all of which are embedded in the phospholipid bilayer, are known as integral proteins.

[!] Card 15+++++++++++++++++++++++++++++++++++[/!]

[q]In the diagram below, membrane proteins like the ones at 1 and 6, both of which span the width of the phospholipid bilayer, are known as_____________ proteins.

[hangman]

[c]transmembrane

[f]Perfect! In the diagram below, membrane proteins like the ones at 1 and 6, both of which span the width of the phospholipid bilayer, are known as transmembrane proteins. .

[!] Card 16+++++++++++++++++++++++++++++++++++[/!]

[q]In the diagram below, the molecule shown at 7 is a lipid, but not a phospholipid. Its function is to stabilize the membrane at high temperatures, and to keep it fluid at low termperatures. This molecule must be ________

[hangman]

[c]cholesterol

[f]Nice! In the diagram below, the molecule shown at 7 is a lipid, but not a phospholipid. Its function is to stabilize the membrane at high temperatures, and to keep it fluid at low termperatures. This molecule must be cholesterol.

[!] Card 17+++++++++++++++++++++++++++++++++++[/!]

[q]Because of the way that it’s positioned in the membrane, you can tell that protein #3 must be a  _______ protein.

[hangman]

[c]peripheral

[f]Great! Because of the way that it’s positioned in the membrane (hanging off the bottom) you can tell that protein #3 must be a peripheral protein.

[x]

[restart]

[/qwiz]

Next