Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A level OCR Biology > Biological Membranes > Flashcards

Biological Membranes Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

What are the two components of a phospholipid?

A
  • Hydrophobic tail

- Hydrophilic head

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

What do membranes cover/surround?

A

The surface of every cell and most organelles

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

Functions of membranes

A
  • Keeping all cellular components inside the cell
  • Allowing selected molecules to move in and out of the cell
  • Isolating organelles from the rest of the cytoplasm, which allows cellular processes to occur separately
  • Site for biochemical reactions
  • Allows the cell to change shape
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What was further evidence against the Dawson-Danielli model?

A

Freeze-fracture images of cell membranes

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

What did freeze-fracture images of cell membranes lead to?

A

The development of the fluid mosaic model

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

Who development the fluid mosaic model?

A

Singer and Nicholson

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

When did Singer and Nicholson development the fluid mosaic model?

A

1972

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What did the fluid mosaic model suggest?

A

Proteins are within, not outside, the phospholipid bilayer

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

What is one of the main components of membranes?

A

Phospholipids

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

Why do phospholipids form the shape of the structure that they do?

A

Their polar nature and the way they interact with water

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

When exposed to water, what structures do phospholipids form?

A
  • Micelle

- Bilayer

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

What way do the hydrophilic heads face?

A

Towards water

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

What way do the hydrophobic tails face?

A

Away from water (inwards)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What behaviour of phospholipids is key to the role that they play in membranes?

A

How they react when they are in water

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

Explain why phospholipids form a bilayer in plasma membranes

A
  • Phospholipids have a polar phosphate group which is hydrophilic and will face the aqueous environment
  • The fatty acids are non-polar and will move away from an aqueous environment
  • As both tissue fluid and cytoplasm are aqueous, phospholipids form two layers with the hydrophobic tails facing inwards and the phosphate groups face outwards, interacting with the aqueous environment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How much of cells do proteins make up

A

Between 25-75% depending on the cell type

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Where are intrinsic/transmembrane proteins?

A

Proteins that span the whole width of the membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Where are extrinsic proteins?

A

Confined to the inner or outer surface of the membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Many of the proteins in a membrane are…?

A

Glycoproteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are glycoproteins?

A

Proteins with attached carbohydrate chains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are intrinsic/integral proteins?

A

Transmembrane proteins that are embedded through both layers of a membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What do intrinsic proteins have on their external surfaces?

A

Amino acids with hydrophobic R-groups

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What do the hydrophobic R-groups on intrinsic proteins interact with and why?

A

The hydrophobic core of the membrane as it keeps them in place

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What type of protein are channel and carrier proteins?

A

Intrinsic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What are channel and carrier proteins involved in?

A

Transport across the membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What do channel proteins do?

A

Provides a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What holds channel proteins in position?

A

By interactions between the hydrophobic core of the membrane and the hydrophobic R-groups on the outside of the proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What do carrier proteins have an important role in?

A

Passive transport (down a concentration gradient) and active transport (against a concentration gradient) into cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What does passive and active transport into cells via carrier proteins often involve?

A

Changing the shape of the protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What can the carrier proteins often be?

A
  • Receptor for hormones
  • Receptor for neurotransmitters
  • Enzymes for catalyst reactions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What type of proteins are glycoproteins?

A

Intrinsic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Where are glycoproteins?

A

Embedded in the cell-surface membrane with attached carbohydrate chains of varying lengths and shapes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What roles do glycoproteins have?

A
  • Cell adhesion

- Receptors for chemical signals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is cell adhesion?

A

When cells join together to form tight junctions in certain tissues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Describe the process of cell communication/cell signalling

A
  • When the chemical binds to the receptor it elicits a response from the cell
  • This may cause a direct response or set off a cascade of events inside the cell
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What are examples of cell signalling?

A
  • Receptors for neurotransmitters such as acetylcholine at nerve cell synapses. The binding of the neurotransmitters triggers or prevents an impulse in the next neurone
  • Receptors for peptide hormones, including insulin and glucagon, which affects the uptake and storage or glucose by cells
  • Some drugs act by binding to cell receptors. For instance, beta blockers are used to reduce the hearts response to stress
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What are glycolipids similar to?

A

Glycoproteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

What are glycolipids?

A

Lipids with attached carbohydrate chains

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What are glycolipids also called?

A

Cell markers or antigens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What can recognise glycolipids and what do they recognise glycolipids as?

A 
Cells of the immune system
As self (of the organism) or non-self (of cells belonging to another organism)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

Where can extrinsic proteins be found?

A

Free on the cell membrane or bound to an intrinsic protein. Can only be found on one side of the bilayer, but can move in between layers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

If an extrinsic protein is on the extracellular side then it?

A
  • Acts as receptors for hormones or neurotransmitters

- Involved in cell recognition (many are glycoproteins)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

If an extrinsic protein is on the cytosolic side then it?

A
  • Involved in cell signalling

- Involved in chemical reactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What can extrinsic proteins on the cytosolic side do?

A

Can dissociate from the membrane and move into the cytoplasm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

What do extrinsic proteins normally have and do?

A

Have hydrophilic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

What type of biological molecule is cholesterol

A

Lipids

47
Q

What are the roles of cholesterol in membranes?

A
  • Controlling membrane fluidity

- Keeps membranes stable at normal body temperature, without it, cells would burst

48
Q

The membrane is this when there is more cholesterol

A

Less fluid and less permeable

49
Q

Without cholesterol, what would happen to cells?

A

Cells would burst

50
Q

What does cholesterol have (in terms of water)?

A

Hydrophilic end

Hydrophobic end

51
Q

What is the molecular formula of cholesterol?

A

C27H46O

52
Q

Where is cholesterol located in cell membranes?

A

Positioned between phospholipids in a membrane bilayer, with the hydrophilic end interacting with the tails, pulling them together

53
Q

What gives membranes stability without making them too rigid?

A

Cholesterol

54
Q

How does cholesterol give membranes stability?

A

The hydrophilic end interacting with the tails, pulling them together

55
Q

How does cholesterol not make membranes too rigid?

A

By stopping the phospholipids from grouping too closely and crystallising

56
Q

The smaller and less polar a molecule the…

A

Easier and faster it will diffuse across a cell membrane

57
Q

How fast do small, non-polar molecules such as oxygen and carbon dioxide diffuse across a membrane?

A

Rapidly

58
Q

How fast do small, polar molecules, such as water and urea, diffuse across a membrane?

A

More slowly than small, non-polar molecules

59
Q

How fast do charged particles (ions) diffuse across a membrane?

A

They are unlikely to diffuse across, even if they are very small

60
Q

Why is it important for a cell membrane to maintain its fluidity?

A

The cell would not be able to function

61
Q

A fluid membrane is needed for?

A
  • Diffusion of substances across the membrane
  • Membranes to fuse e.g. a vesicle fusing with the cell membrane during exocytosis
  • Cells to move and change shape e.g. macrophages during phagocytosis
62
Q

What is the effect of temperature on membranes?

A

An increase in the kinetic energy of phospholipids disrupts the structure of the membrane, creating gaps between the phospholipids making it more permeable as the molecules can pass through the gaps

63
Q

What is the effect of solvents on membranes?

A
  • Water is a polar molecule and it is important in creating membrane stability with the phospholipids
  • Other solvents, like alcohols, are less polar, or benzene, which is not polar
    - This can move into the bilayer, disrupting the
    structures
64
Q

Explain a graph of the permeability of membranes

A
  • Phospholipids don’t have much energy, so can’t move much, so they are packed close together, which forms a rigid layer.
    Channel and carrier proteins denature
    Ice crystals may pierce membrane, which increases permeability significantly
  • Phospholipids can move as they aren’t packed closely together.
    The membrane is partially permeable
    The temperature gives the phospholipids more energy, which increases the permeability
  • Phospholipid bilayer starts to melt and become more permeable
    The water on the inside of the cell puts pressure on the membranes
    Channel and carrier proteins denature, increasing permeability
65
Q

All cells are surrounded by a?

A

Partially-permeable membrane

66
Q

How does the cell get what it needs and get rid of what it does not want?

A

“Imports” substances it needs

“Exports” waste and substances needed outside of the cell

67
Q

Define diffusion

A

The net movement of molecules down a concentration gradient

68
Q

What type of transport is diffusion and why?

A

Passive, as no metabolic energy is used

69
Q

Give an example of where diffusion is used in humans

A

Gas exchange across respiratory systems i.e. lungs and gills

70
Q

What is Fick’s law used to summarise?

A

The rate of diffusion in a given direction across an exchange surface

71
Q

What is Fick’s law?

A

Rate of diffusion is proportionate to: surface area x difference in concentration / length of diffusion path (thickness of membrane)

72
Q

What are the factors that affect diffusion?

A
  • Surface area
  • Thickness
  • Concentration gradient
  • Temperature
  • Length of diffusion path (diffusion distance)
73
Q

What acts as a barrier to most substances in membranes?

A

The non-polar, hydrophobic tails of the phospholipid molecules

74
Q

What is simple diffusion?

A

Molecules go straight through the bilayer

75
Q

What type of molecules can use simple diffusion?

A

Lipid soluble

76
Q

What is facilitated diffusion?

A

Large and/or hydrophilic particles can use facilitated diffusion

77
Q

What type of molecules cannot pass straight through the bilayer?

A

Polar/large molecules

78
Q

What lets polar/large molecules through the bilayer?

A

Carrier/Channel proteins

79
Q

What type of transport is facilitated diffusion?

A

Passive

80
Q

Define osmosis

A

The net movement of water molecules from a region of high water concentration to a region of low water concentration, through a partially permeable membrane

81
Q

What is osmosis used for?

A

The process by which cells exchange water with their environment, such as in the mammalian kidney

82
Q

What is osmosis determined by?

A

The difference in water potential between two solutions connected by a partially-permeable membrane

83
Q

What is water potential?

A

The tendency of water molecules in a system to move

84
Q

What symbol denotes water potential?

A

Ψ (psi)

85
Q

What is water potential measured in?

A

kiloPascals (kPa)

86
Q

What is the water potential of pure water?

A

0 kPa

87
Q

What water has the highest water potential?

A

Pure water

88
Q

Solutions have a … water potential than pure water

A

Lower, negative

89
Q

What is true of water molecules in terms of what areas they move to and from based on their water potential?

A

Water molecules always move from a region of high water potential to a region of low water potential

90
Q

What is the water potential of a solution affected by?

A

The amount of solute it contains

91
Q

What happens to the water potential of a solution when there is a high amount of solute?

A

It is lower

92
Q

Why does an increase in the amount of solute decrease the water potential?

A

The water molecules bind to the solute molecules, reducing the number of water molecules that are free to diffuse

93
Q

Is the solute potential positive or negative?

A

Negative

94
Q

What is the symbol for solute potential?

A

Ψs (psi)

95
Q

Other than the amount of solute in a solution, what also affects the water potential of a solution?

A

The pressure applied to it

96
Q

The greater the pressure…?

A

The higher the water potential

97
Q

What is the symbol for pressure potential?

A

Ψp

98
Q

Is the pressure potential positive or negative?

A

Positive

99
Q

In plant cells, what is the pressure potential a result of?

A

The cell wall exerting pressure on the cytoplasm

100
Q

What is the calculation for water potential?

A

Ψ = Ψs + Ψp

Water potential = solute potential + pressure potential

101
Q

What does osmotic concentration relate to?

A

The amount of dissolved solutes in a solution

102
Q

What does not affect osmotic concentration?

A

Insoluble molecules

103
Q

What do partially permeable membranes only let through?

A

Water and very small molecules

104
Q

What does a partially permeable membrane result in?

A

An uneven distribution across the membrane

105
Q

What osmotic concentration do isotonic solutions have?

A

The same as the cytoplasm of the cell

106
Q

What happens to the cell when it is placed in an isotonic solution (both plant and animal)?

A

The cell does not change (both animal and plant)
In a plant cell, incipient plasmolysis (the protoplast is just pulled away from the cell wall) (plant only)
The net movement of water into and out of the cell

107
Q

What osmotic concentration do hypertonic solutions have?

A

A higher osmotic concentration than the cytoplasm of the cell

108
Q

What happens to the cell when it is placed in a hypertonic solution (both plant and animal)?

A

The animal cell shrinks
Cell wall exerts an inward pressure. Cell is turgor
The net movement of water out of the cell

109
Q

What do hypertonic solutions contain more of, water or solute, compared to the cell?

A

Solute

110
Q

What do isotonic solutions contain more of, water or solute, compared to the cell?

A

The same amount of each

111
Q

What do hypotonic solutions contain more of, water or solute, compared to the cell?

A

Water

112
Q

What osmotic concentration do hypotonic solutions have?

A

A lower osmotic concentration than the cytoplasm of the cell

113
Q

What happens to the cell when it is placed in a hypotonic solution (both plant and animal)

A

Can cause animal cells to burst
Plant - full plasmolysis; causes a plant to wilt
The net movement of water into the cell

A level OCR Biology (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions