Lesson test: The membrane

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The membrane

1.[2p]
What actually drives phospholipids to assemble into a bilayer in water?

The entropy gained when water ordered around the hydrocarbon chains is released

Correct

An electrostatic attraction between the fatty acid tails

The answer is: The entropy gained when water ordered around the hydrocarbon chains is released

Covalent bonding between neighbouring lipid molecules

The answer is: The entropy gained when water ordered around the hydrocarbon chains is released

Hydrogen bonds between the hydrocarbon chains

The answer is: The entropy gained when water ordered around the hydrocarbon chains is released

2.[1p]
Gorter and Grendel's 1925 experiment contained two errors whose effects largely cancelled.

True

Correct

False

The answer is: True

3.[2p]
Why does a two-tailed phospholipid form sheets while a single-tailed detergent forms small micelles?

A two-tailed lipid is roughly cylindrical and packs flat, while a wedge-shaped detergent packs into a sphere

Correct

Detergents carry no charge and lipids do

The answer is: A two-tailed lipid is roughly cylindrical and packs flat, while a wedge-shaped detergent packs into a sphere

Detergents are much larger molecules

The answer is: A two-tailed lipid is roughly cylindrical and packs flat, while a wedge-shaped detergent packs into a sphere

Only phospholipids can hydrogen bond to water

The answer is: A two-tailed lipid is roughly cylindrical and packs flat, while a wedge-shaped detergent packs into a sphere

4.[3p]
A red blood cell has about 140 µm² of membrane, and each lipid occupies 0.65 nm² of one leaflet. How many lipid molecules does the bilayer contain, in units of $10^{8}$ ?

CorrectNot quite: 4.3

5.[2p]
Which observations argued against the Danielli and Davson sandwich model of the membrane?

Select all that apply

Purified membrane proteins turned out to be largely hydrophobic on their outer surfaces

Correct

Freeze-fracture microscopy showed particles inside the membrane interior

Correct

Membranes were found to contain no protein at all

The answer is: Purified membrane proteins turned out to be largely hydrophobic on their outer surfaces, Freeze-fracture microscopy showed particles inside the membrane interior

Lipids were shown not to form bilayers

The answer is: Purified membrane proteins turned out to be largely hydrophobic on their outer surfaces, Freeze-fracture microscopy showed particles inside the membrane interior

6.[2p]
Frye and Edidin fused a mouse cell to a human cell and labelled the surface proteins of each with a different dye. What happened within forty minutes at 37 degrees Celsius?

The two labels intermixed completely over the whole hybrid surface

Correct

The two labels stayed in separate halves indefinitely

The answer is: The two labels intermixed completely over the whole hybrid surface

Both labels moved to the nucleus

The answer is: The two labels intermixed completely over the whole hybrid surface

Both labels were lost from the cell surface

The answer is: The two labels intermixed completely over the whole hybrid surface

7.[2p]
Match each membrane to its approximate protein content by mass.

Myelin
A typical plasma membrane
The inner mitochondrial membrane

18 per cent
76 per cent
50 per cent

Show the answer

Myelin: 18 per cent A typical plasma membrane: 50 per cent The inner mitochondrial membrane: 76 per cent

8.[3p]
Why does a lipid bilayer exclude sodium so much more effectively than water?

A sodium ion must shed its hydration shell to enter a low-permittivity medium, which costs a very large energy

Correct

Sodium is larger than a water molecule

The answer is: A sodium ion must shed its hydration shell to enter a low-permittivity medium, which costs a very large energy

Water is uncharged and sodium is polar

The answer is: A sodium ion must shed its hydration shell to enter a low-permittivity medium, which costs a very large energy

Sodium reacts chemically with fatty acid chains

The answer is: A sodium ion must shed its hydration shell to enter a low-permittivity medium, which costs a very large energy

9.[1p]
A phospholipid flips from one leaflet of a bilayer to the other about as easily as it diffuses sideways within a leaflet.

True

The answer is: False

False

Correct

1.[2p] What actually drives phospholipids to assemble into a bilayer in water?

2.[1p] Gorter and Grendel's 1925 experiment contained two errors whose effects largely cancelled.

3.[2p] Why does a two-tailed phospholipid form sheets while a single-tailed detergent forms small micelles?

4.[3p] A red blood cell has about 140 µm² of membrane, and each lipid occupies 0.65 nm² of one leaflet. How many lipid molecules does the bilayer contain, in units of 108?

5.[2p] Which observations argued against the Danielli and Davson sandwich model of the membrane?

6.[2p] Frye and Edidin fused a mouse cell to a human cell and labelled the surface proteins of each with a different dye. What happened within forty minutes at 37 degrees Celsius?

7.[2p] Match each membrane to its approximate protein content by mass.

8.[3p] Why does a lipid bilayer exclude sodium so much more effectively than water?

9.[1p] A phospholipid flips from one leaflet of a bilayer to the other about as easily as it diffuses sideways within a leaflet.

1.[2p]
What actually drives phospholipids to assemble into a bilayer in water?

2.[1p]
Gorter and Grendel's 1925 experiment contained two errors whose effects largely cancelled.

3.[2p]
Why does a two-tailed phospholipid form sheets while a single-tailed detergent forms small micelles?

4.[3p]
A red blood cell has about 140 µm² of membrane, and each lipid occupies 0.65 nm² of one leaflet. How many lipid molecules does the bilayer contain, in units of $10^{8}$ ?

5.[2p]
Which observations argued against the Danielli and Davson sandwich model of the membrane?

6.[2p]
Frye and Edidin fused a mouse cell to a human cell and labelled the surface proteins of each with a different dye. What happened within forty minutes at 37 degrees Celsius?

7.[2p]
Match each membrane to its approximate protein content by mass.

8.[3p]
Why does a lipid bilayer exclude sodium so much more effectively than water?

9.[1p]
A phospholipid flips from one leaflet of a bilayer to the other about as easily as it diffuses sideways within a leaflet.