Transport across cell membranes Flashcards

1
Q

What is a cell surface membrane?

A

The plasma membrane that surrounds cells and forms a boundary between the cytoplasm and the environment.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does the cell surface membrane allow for?

A

It allows different conditions to be established inside and outside of the cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does the cell surface membrane control?

A

It controls the movement of substances in and out of cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What makes up a cell membrane?

A

A phospholipid bilayer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why is the phospholipid bilayer an important component of cell membranes?

A

Because: - the hydrophilic heads of both phospholipid layers point to the outside of the cell-surface membrane attracted by water on both sides and - the hydrophobic tails of both layers point into the centre of the cell membrane, repelled by water on both sides. Therefore, the membrane has a non-polar core which prevents the passage of polar molecules across it, e.g. water, and allows relatively free diffusion of non-polar molecules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How do lipid-soluble material move through the membrane?

A

Via the phospholipid portion.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Name 3 functions of phospholipids in the membrane

A
  • Allow lipid-soluble substances to enter and leave the cell. - Prevent water-soluble substance entering and leaving the cell. - Make the membrane flexible and self-sealing.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How are proteins embedded in the cell-surface membrane?

A

Some proteins occur only in the surface of the bilayer whereas others completely span the phospholipid bilayer from one side to the other.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the function of proteins which only occur in the surface of the phospholipid bilayer?

A

The act either to give mechanical support to the membrane or, in conjunction with glycolipids, as cell receptors for molecules e.g. hormones.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Give 2 examples of proteins that completely span the phospholipid bilayer.

A

Carrier proteins, channel proteins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What do carrier proteins do?

A

They bind to ions or molecules like glucose or amino acids, then change shape in order to move these molecules across the membrane.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What do protein channels / channel proteins do?

A

They form water-filled tubes to allow water-soluble ions to diffuse across the membrane.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Name 6 functions of the proteins in membranes.

A
  • Provide structural support. - Act as channels transporting water-soluble substances across the membrane. - Allow active transport across the membrane through carrier proteins. - Form cell-surface receptors across the membrane for identifying cells. - Act as receptors e.g. for hormones. - Help cells stick/adhere together.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Where do cholesterol molecules occur?

A

Within the phospholipid bilayer.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What do cholesterol molecules add to the membrane?

A

Strength.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Are cholesterol molecules very hydrophobic or hydrophilic? What does this mean for the cell?

A

Hydrophobic. Therefore plays an important role in preventing loss of water and dissolved ions from the cell

17
Q

What do cholesterol molecules pull together? What does this achieve?

A

They pull together the fatty acid / hydrophobic tails of the phospholipid molecules. This limits their movement and that of other molecules but doesn’t make the membrane too rigid.

18
Q

Name the 3 overarching functions of cholesterol.

A
  • Reduce lateral movement of other molecules including phospholipids. - Make the membranes less fluid at high temperatures. - Prevent leakage of water and dissolved ions from the cell.
19
Q

What are glycolipids made up of?

A

A carbohydrate covalently bonded with a lipid

20
Q

What does the carbohydrate portion of a glycolipid act as?

A

It acts as a cell-surface receptor for specific chemicals.

21
Q

Name 3 functions of glycolipids in the membrane.

A
  • Acts as recognition sites. - Helps maintain the stability of the membrane. - Helps cells to attach to one another and therefore form tissues.
22
Q

Where are glycoproteins found?

A

On the outer surface of the cell membrane.

23
Q

What are glycoproteins made up of?

A

Carbohydrate chains attached to many extrinsic proteins.

24
Q

What are the functions of glycoproteins in the membrane?

A
  • Act as recognition sites (allows cells to recognise one another - lymphocytes can recognise an organism’s own cells). - Help cells attach to one another and form tissues. - Act as cell-surface receptors, more specifically for hormones and neurotransmitters
25
Q

What controls the movement of substances in and out of cells?

A

The cell surface membrane.

26
Q

Why does a molecule not being soluble in lipids affect its movement across a membrane?

A

Because if it is not soluble in lipids, it can’t pass through the phospholipid bilayer.

27
Q

Why does a molecule being large affect its movement across a membrane?

A

Because it is too large to pass through protein channels in the membrane.

28
Q

Why does a molecule having the same charge as the protein channel affect its movement across the membrane?

A

Because like charges repel one another.

29
Q

Why do polar molecules, e.g. water, have difficulty passing through the membrane?

A

Because the membrane has a non-polar core (from the hydrophobic tails) which prevents the passage of polar molecules across it.

30
Q

Why is the model of a cell surface membrane described as fluid?

A

Because the individual phospholipid molecules can move relative to one another. This gives the molecule a flexible structure that is constantly changing in shape.

31
Q

Why is the model of a cell surface membrane described as a mosaic?

A

Because the proteins embedded in the bilayer vary in size, shape and pattern.