Lesson 2.2 - Membrane Structure and Functions

Question 1

Membrane _____ have four functions: transport, enzymatic activity, triggering signals, and attachment and recognition of molecules.

Answer 1

Membrane proteins have four functions: transport, enzymatic activity, triggering signals, and attachment and recognition of molecules.

Question 2

Cholesterol molecules are aligned with the lipid molecule on both sides of the bilayer. Is cholesterol polar or non-polar? Explain your answer.

Answer 2

Cholesterol’s hydrocarbon tail is made up of hydrogen and carbon that is non-polar but it also has a polar hydroxyl group so it is amphipathic (it has both a water-soluble and a fat-soluble region).

Question 3

What is meant by membrane fluidity?

Answer 3

“Membrane fluidity” is the dynamic nature of the membrane, which allows for it to be flexible. That is, membrane lipids undergo free movement on their side of the bilayer.

Question 4

Why is the word mosaic used as part of the fluid mosaic model to describe membrane structure?

Answer 4

The membrane is not only phospholipids, it is a mosaic of different compounds.

Question 5

Define Sterol

Answer 5

A type of steroid with an OH group at one end and a non-polar hydrocarbon chain at the other.

Question 6

If proteins are embedded in the lipid bilayer, they are called _____. If proteins are positioned on the surface of a membrane (and do not interact with the hydrophobic part of the membrane), we call them _____.

Answer 6

If proteins are embedded in the lipid bilayer, they are called integral membrane proteins. If proteins are positioned on the surface of a membrane (and do not interact with the hydrophobic part of the membrane), we call them peripheral membrane proteins.

Question 7

When comparing the outside and inside halves of a cell membrane’s phospholipid bilayer, the composition of lipids on the two surfaces is asymmetrical. Describe how membranes are asymmetric.

Answer 7

The membranes are asymmetrical because the proteins and other components of one half of the lipid bilayer differ from those that make up the other half.

Question 8

Our current view of membrane structure is based on the fluid mosaic model. What does the word “mosaic” refer to in the expression “fluid mosaic model”?

Answer 8

The “mosaic” in “fluid mosaic model” refers to the mixture of lipids and proteins in the plasma membrane.

Question 9

How are protein receptors and enzymes similar?

Answer 9

They both detect molecules and perform an action in response. They both recognize and bind only to specific molecules at a specific time, changing shape after binding.

Question 10

Define Glycolipid

Answer 10

Any membrane lipid that is bound to a carbohydrate.

Question 11

What is a protein on the surface of the membrane known as?

Answer 11

Peripheral Membrane Protein

Question 12

[The] dominant lipids that are found in membranes are _____.

Answer 12

[The] dominant lipids that are found in membranes are phospholipids.

Question 13

If fatty acid tails are made of saturated fats, will the lipids [in a lipid bilayer of a cell membrane] pakc tighter or looser & why?

Answer 13

Saturated fats are so linear that they can make stronger intermolecular bonds, making them tighter.

Question 14

[Membrane] proteins are scattered throughout the _____ and move around.

Answer 14

[Membrane] proteins are scattered throughout the membrane and move around.

Question 15

Define Peripheral Membrane Protein

Answer 15

A protein on the surface of the membrane.

Question 16

What is a membrane component that contains a sugar, or carbohydrate, bound to an amino acid known as?

Answer 16

Glycoprotein

Question 17

Explain the four functional categories of membrane proteins.

Answer 17

Transport proteins help substances move through the plasma membrane. Enzymatic proteins help with respiration and photosynthesis. Triggering signal proteins bind specific chemicals used in cellular communication. Attachment and recognition proteins act as attachment points for structural elements such as the cytoskeleton or as recognition sites for foreign substances such as microbes.

Question 18

[A cell] membrane is very _____ - proteins and other components of one half of the lipid bilayer differ from those that make up the other half of the bilayer (reflects the differences in the function performed by each half of the membrane).

Answer 18

[A cell] membrane is very asymmetrical - proteins and other components of one half of the lipid bilayer differ from those that make up the other half of the bilayer (reflects the differences in the function performed by each half of the membrane).

Question 19

Membranes contain sterols, which help to maintain their _____.

Answer 19

Membranes contain sterols, which help to maintain their fluidity.

Question 20

Which components affect the fluidity of a membrane?

Answer 20

Temperature and lipid composition affect membrane fluidity. For example, fatty acids composed of saturated hydrocarbons—in which each carbon is bound to a maximum number of hydrogen atoms—tend to have a straight shape, which allows the lipids to pack more tightly together. Alternatively, the double bonds in unsaturated fatty acids cause bent structure, so the lipid molecules are less straight and pack more loosely. Lipid molecules become more closely packed and rigid at low temperatures and more fluid at high temperatures. Cholesterol helps maintain the fluidity of the membrane by restraining lipid movement at high temperatures and preventing close packing at low temperatures.

Question 21

What is any membrane lipid that is bound to a carbohydrate known as?

Answer 21

Glycolipid

Question 22

At high temperatures, [sterols] _____ fluidity [in animal cell membrane]. They help to restrain the movement of the _____ molecules in a membrane (therefore reducing the fluidity of the membrane).

Answer 22

At high temperatures, [sterols] reduce fluidity [in animal cell membrane]. They help to restrain the movement of the lipid molecules in a membrane (therefore reducing the fluidity of the membrane).

Question 23

The fluidity of a plasma membrane depends on the composition of the _____ molecules that make up the membrane, as well as the temperature.

Answer 23

The fluidity of a plasma membrane depends on the composition of the lipid molecules that make up the membrane, as well as the temperature.

Question 24

Define Fluid Mosaic Model

Answer 24

The idea that a biological membrane consists of a fluid phospholipid bilayer, in which proteins are embedded and float freely.

Question 25

If fatty acid tails are made of unsaturated fats, will the lipids [in a lipid bilayer of a cell membrane] pakc tighter or looser & why?

Answer 25

Unsaturated fats are kinked and can't make as many intermolecular bonds as saturated fats, making them looser.

Question 26

[The] current view of membrane structure [is the] fluid _____ model.

Answer 26

[The] current view of membrane structure [is the] fluid **mosaic** model.

Question 27

Why is the word fluid used as part of the fluid mosaic model to describe membrane structure?

Answer 27

The membrane has movement (not rigid).

Question 28

When comparing the outside and inside halves of a cell membrane's phospholipid bilayer, the composition of lipids on the two surfaces is asymmetrical. Why is membrane asymmetry an important characteristic in cell membranes?

Answer 28

Membrane asymmetry reflects the differences in functions performed by each half of the membrane.

Question 29

Membranes remain in a fluid state over a relatively wide range of temperatures. If the temperature drops low enough, the lipid molecules in a membrane become closely packed and the membrane forms a highly fiscous semisolid \_\_\_\_\_. Fluidity of membranes is related to how many lipids are _____ (the more unsaturated a membrane is, the lower its gelling temperature).

Answer 29

Membranes remain in a fluid state over a relatively wide range of temperatures. If the temperature drops low enough, the lipid molecules in a membrane become closely packed and the membrane forms a highly fiscous semisolid **gel**. Fluidity of membranes is related to how many lipids are **unsaturated** (the more unsaturated a membrane is, the lower its gelling temperature).

Question 30

What is a protein that is embedded in the lipid bilayer known as?

Answer 30

Integral Membrane Protein

Question 31

A biological membrane consists of a bilayer of phospholipids and proteins that move around freely within the layer. This is described as the fluid _____ model.

Answer 31

A biological membrane consists of a bilayer of phospholipids and proteins that move around freely within the layer. This is described as the fluid **mosaic** model.

Question 32

When added to an aqueous solution, large numbers of phospholipids form a \_\_\_\_\_, or a structure that is two lipids molecules thick. A _____ from spontaneously in an aqueous environment because of the tendency of the non-polar, hydrophobic fatty acids to aggregate together while the polar, hydrophilic heads associate with \_\_\_\_\_. These arrangements are favoured because they represent the _____ energy state, and therefore are more likely than any other arrangement to occur.

Answer 32

When added to an aqueous solution, large numbers of phospholipids form a **bilayer**, or a structure that is two lipids molecules thick. A **bilayer** from spontaneously in an aqueous environment because of the tendency of the non-polar, hydrophobic fatty acids to aggregate together while the polar, hydrophilic heads associate with **water**. These arrangements are favoured because they represent the **lowest** energy state, and therefore are more likely than any other arrangement to occur.

Question 33

Explain how the chemical makeup of a membrane gives it fluidity.

Answer 33

Membranes are composed of a bilayer of phospholipids, which interact with each other by non-polar fatty acid chains and possess the ability to laterally flow around each other. This interchangeable nature gives the membrane its fluidity. Increased phospholipid movement increases membrane fluidity, while restrained phospholipid movement reduces fluidity.

Question 34

The basic components of a cell membrane are phospholipids, proteins, and carbohydrates. What are the function(s) of each component?

Answer 34

Phospholipids have a structural function. They form the lipid bilayer that makes up the plasma membrane itself. Proteins have several functions: they act as channels for substances to pass through the cell membrane, they act as cell identifiers, and they participate in adhesion complexes between cells or between the plasma membrane and cytoskeleton. Carbohydrates function in cell-cell interaction and as labels for the recognition of other cells.

Question 35

\_\_\_\_\_, like cholesterol (only found in animal cell membranes) help to stabilize the membrane.

Answer 35

**Sterols**, like cholesterol (only found in animal cell membranes) help to stabilize the membrane.

Question 36

Define Glycoprotein

Answer 36

A membrane component that contains a sugar, or carbohydrate, bound to an amino acid.

Question 37

What is the idea that a biological membrane consists of a fluid phospholipid bilayer, in which proteins are embedded and float freely known as?

Answer 37

Fluid Mosaic Model

Question 38

How does the structure of the plasma membrane facilitate its functio?

Answer 38

The phospholipids on the bilayer are oriented so that their hydrophilic heads point outwards towards the aqueous external environment and inward towards the aqueous cytosol of the cell. The hydrophobic tails point towards the interior of the membrane. This prevents most polar or ionic substances from diffusing through.

Question 39

What is the function of sterols?

Answer 39

Sterols act as membrane stabilizers. At high temperatures they help to restrain the movement of lipid molecules in a membrane, reducing the fluidity of the membrane. At low temperatures, sterols occupy the spaces between the lipid molecules preventing fatty acids from associating and forming a non-fluid gel, thus increasing fluidity of the membrane.

Question 40

[A] glycolipid [is a] _____ and a lipid. [A] glycoprotein [is a] _____ and [a] protein. [They] face the exterior of the cell and often play a role in cell-to-cell recognition and interactions.

Answer 40

[A] glycolipid [is a] **carbohydrate** and a lipid. [A] glycoprotein [is a] **carbohydrate** and [a] protein. [They] face the exterior of the cell and often play a role in cell-to-cell recognition and interactions.

Question 41

What is a type of steroid with an OH group at one end and a non-polar hydrocarbon chain at the other known as?

Answer 41

Sterol

Question 42

Define Integral Membrane Protein

Answer 42

A protein that is embedded in the lipid bilayer.

Question 43

When referring to membrane glycolipids and glycoproteins, what does the prefix "glyco" indicate?

Answer 43

The term “glyco” refers to polar carbohydrate groups that are attached to the molecules.

Question 44

Describe what is meant by integral and peripheral membrane proteins. How do they differ in their chemical makeup and their arrangement of amino acids.

Answer 44

Integral proteins are embedded in the lipid bilayer of the membrane and peripheral proteins are positioned on the surface of the membrane. Integral proteins interact with the hydrophobic core of the membrane and contain non-polar amino acids as well as polar amino acids. Peripheral proteins interact with hydrophilic regions of the membrane or exposed portions of integral proteins and are composed of polar amino acids.

Question 45

The dynamic nature of the lipid bilayer is dependent on how densely lipid molecules can pack together. This is influenced by two major factors: _____ (of the lipid molecules that make up the membrane) and \_\_\_\_\_.

Answer 45

The dynamic nature of the lipid bilayer is dependent on how densely lipid molecules can pack together. This is influenced by two major factors: **composition** (of the lipid molecules that make up the membrane) and **temperature**.

Question 46

At lower temperatures, [sterols] _____ fluidity [in animal cell membrane]. They occupy the spaces between the _____ molecules (therefore preventing tight packing of phospholipids).

Answer 46

At lower temperatures, [sterols] **increase** fluidity [in animal cell membrane]. They occupy the spaces between the **lipid** molecules (therefore preventing tight packing of phospholipids).

Question 47

If proteins were rigid, how would this affect their ability to act as receptors?

Answer 47

When a receptor binds to a chemical signal, it changes shape. This shape change is critical because it affects how receptors interact with other molecules. If proteins were rigid, receptors would not be able to change shape and would lose functionality.

Question 48

[Cell membranes are composed of a] _____ bilayer (double layer) with _____ embedded through out (and carbohydrates).

Answer 48

[Cell membranes are composed of a] **lipid** bilayer (double layer) with **proteins** embedded through out (and carbohydrates).

Question 49

Membrane proteins may be embedded into the lipid bilayer (\_\_\_\_\_ membrane proteins) or positioned on top of the phospholipid bilayer (\_\_\_\_\_ membrane proteins).

Answer 49

Membrane proteins may be embedded into the lipid bilayer (**integral** membrane proteins) or positioned on top of the phospholipid bilayer (**peripheral** membrane proteins).