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Biology Module 2 Foundations In Biology > Chapter 5 The Structure Of Plasma Membranes > Flashcards

Chapter 5 The Structure Of Plasma Membranes Flashcards

1
Q

What is the structure of a phospholipid?

A

Contains a charged hydrophilic head and non-polar hydrophobic tails
When exposed to water the hydrophilic phosphate head will always face towards the water forming the inner and outer surface, while the hydrophobic tails will point inwards away from the water forming the core.

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2
Q

What structures can phospholipids form when exposed to water?

A

A Micelle or a Bilayer

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3
Q

What is Cell Membrane theory?

A

1972 Singer and Nicolson proposed Fluid-Mosaic model
-Phospholipids are free to move (fluid)
-Embedded proteins vary in shape, size and position

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4
Q

What components make up a cell membrane?

A

Cholesterol
Glycolipids
Membrane Proteins - Consisting of intrinsic and extrinsic proteins
Intrinsic proteins include: Carrier proteins, Channel proteins, Glycoproteins

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5
Q

What are Intrinsic proteins?

A

Transmembrane proteins embedded through both phospholipid layers.
They contain amino acid groups with hydrophobic-R groups which interact with the hydrophobic membranes core to keep them in place. Eg, Channel and Carrier proteins.

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6
Q

What are the function of Channel proteins?

A

Provide a hydrophobic channel for passive movement of polar molecules down a concentration gradient by diffusion.

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7
Q

What are the function of Carrier proteins?

A

Involved in passive and active transport which often involves change in the protein configuration.

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8
Q

What is the structure of Glycoproteins?

A

Embedded intrinsic proteins which have attached carbohydrate chains

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9
Q

What is the function of Glycoproteins?

A

Play a role as receptors and in cell adhesion.
When chemicals bind to these receptors this causes a direct response or chemical cascade known as cell signalling.
For example,
Receptors for neurotransmitters
Receptors for peptide hormones like insulin

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10
Q

What are Extrinsic proteins?

A

Proteins free on the membrane surface or bound to an intrinsic protein.
They are only bound to one side of the bilayer, but can be present on either side.
They contain hydrophilic R-groups on the outer surfaces and they interact with the polar heads of phospholipids or intrinsic proteins.

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11
Q

What is the structure of Glycolipids?

A

Lipids with attached carbohydrate chains

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12
Q

What is the function of Glycolipids?

A

Act as cell markers or antigens for cell recognition

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13
Q

What is the structure of cholesterol?

A

Lipids with hydrophilic and hydrophobic ends. They are positioned between phospholipids in a membrane bilayer, with the hydrophilic end interacting with the polar heads and the hydrophobic end interacting with the tails of the phospholipid.

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14
Q

What is the function of Cholesterol?

A

Important in controlling membrane fluidity
Affects stability of membranes without rigidity- prevents lysis.
Regulates the fluidity of membranes as the more cholesterol there is, the less fluid that can pass through therefore making it less permeable.

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15
Q

What is the function of Actin Microfilaments in a membrane?

A

Give mechanical strength
Determines the cell shape
Allows movement of the cell surface

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16
Q

What are chemical reaction sites?

A

The membranes of organelles often carry proteins in fixed positions in order for chemical reactions to take place.

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17
Q

What is the function of the phospholipids?

A

They act as a barrier to control what enters and exits the cell
The smaller and less polar the molecule the faster it can diffuse across the membrane.

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18
Q

Why is membrane fluidity necessary?

A

Diffusion of substances
Membranes to fuse
Cells to move and change shape

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19
Q

What are the factors that can affect membrane structure?

A

Temperature
Solvents

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20
Q

How does temperature affect membrane structure?

A

As the temperature increases, the kinetic energy of the phospholipids increases, this therefore makes the membrane more fluid and structure is lost.
Consequently, this creates a gap between the bilayer, where molecules can pass through so the permeability of the membrane increases. At higher temperatures carrier and channel proteins can denature also affecting membrane permeability.

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21
Q

Why is water important for the membrane structure of a phospholipid bilayer?

A

Water, a polar solvent, is important in keeping the phospholipid bilayer intact by interacting with the charged hydrophilic heads.

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22
Q

What types of organic solvents are there?

A

Less polar than water- alcohols
Non-polar - Benzene

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23
Q

What is the effect organic solvents on cell membranes?

A

Organic solvents dissolve membranes and disrupt cells

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24
Q

What is the effect of pure or strong alcohol solutions?

A

They destroy body cells as they are toxic.

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25
Q

What is the effect of weaker solutions of alcohol?

A

Weaker solutions of alcohol can’t dissolve membranes, but can still damage cells.

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26
Q

What is the impact of non-polar alcohols entering the cell membrane?

A

The membrane will be disrupted which causes it to become more fluid and permeable

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27
Q

What is diffusion?

A

Passive net movement of particles down a concentration gradient from an area of high concentration to an area of low concentration.
Diffusion will occur until equilibrium has been reached.

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28
Q

What factors affect diffusion?

A

Temperature
This is because an increase in temperature will increase the rate of diffusion as the particles have a greater kinetic energy

Concentration gradient
The greater difference in concentration the greater rate of diffusion as the net movement of particles is larger

29
Q

What is the membranes permeability determined by?

A

The permeability of the membrane is determined by the nature of the particle and its interaction with the phospholipid bilayer.

30
Q

What do the hydrophobic tails of the phospholipid bilayer repel?

A

Repel particles which are positively or negatively charged (ions)

31
Q

What type of molecule will diffuse fast across a membrane?

A

The smaller and less polar the molecule, the faster and easier it will diffuse across a membrane

32
Q

What molecules can diffuse across the cell surface membrane?

A

Hydrophobic molecules
Small uncharged polar molecules

33
Q

What molecules are deflected across the cell surface membrane?

A

Large uncharged polar molecules
Ions

34
Q

Why can’t charged particles diffuse across a membrane?

A

Repelled by the hydrophobic tails

35
Q

What is the equation for the rate of diffusion?

A

Rat of diffusion is proportional to:= Surface area x difference in concentration
———————————————————-
Length of diffusion path (membrane thickness)

36
Q

What is Facilitated Diffusion?

A

Protein channels or carrier proteins in the membrane allows ions, polar molecules and larger molecules to pass through, down a concentration gradient.
No energy input is involved so facilitated diffusion is passive.

37
Q

What type of transport is Facilitated Diffusion?

A

Passive

38
Q

What is Active Transport?

A

The movement of molecules or ions across a membrane up a concentration gradient

39
Q

What does Active Transport require?

A

Energy (ATP)
Carrier Proteins
Carrier proteins act as ‘pumps’

40
Q

What is another form of Active Transport?

A

Bulk Transport

41
Q

What is Bulk Transport used for?

A

It is used to get materials into or out of cells that are too large to move through channel or carrier proteins.

42
Q

What is Endocytosis?

A

Bulk transport into cells

43
Q

What is Exocytosis?

A

Bulk transport out of cells

44
Q

What is energy from ATP used for during exocytosis and endocytosis?

A

Move vesicles along the cytoskeleton
Change the cell shape to engulf materials
The fusion of membranes to form vesicles or join vesicles to the surface membrane.

45
Q

What is Osmosis?

A

The net movement of water molecules down a water potential gradient, from a region of higher water potential to a region of lower water potential (more negative) through a partially permeable membrane.

46
Q

What is water potential measured in?

A

Pa/ KPa

47
Q

What is water potential?

A

This is the pressure exerted by water molecules onto membranes.

48
Q

What is the water potential of pure water?

A

Pure water has the highest water potential of 0KPA, this is because the presence of solutes lowers the water potential below zero.

49
Q

What does a higher water potential mean?

A

A higher water potential means the solution is less concentrated and has low osmotic concentration.

50
Q

What does a lower water potential mean?

A

The solution is more concentrated and has a high osmotic concentration

51
Q

How can the water potential be affected?

A

By the amount of solute it contains, a low water potential means the water molecules have bound to solute molecules, reducing the number of water molecules able to diffuse.

Also, the water potential is also affected by the pressure applied, the greater the pressure the higher the water potential.

52
Q

How can water potential be calculated?

A

Water potential= Solute potential + Pressure potential

53
Q

What are Hypertonic Solutions?

A

This means that the solution has a lower water potential and higher osmotic concentration than that of the cytoplasm. Therefore, water will move out of the cell into the solution by osmosis.

54
Q

What are isotonic solutions?

A

This means that the solution has the same osmotic concentration as the cytoplasm of the cell. Therefore, there is no net movement of water.

55
Q

What are Hypotonic Solutions?

A

This means that the solution has a higher water potential and lower osmotic concentration than that of the cytoplasm of the cell. Therefore, water will move into the cell by osmosis.

56
Q

How do Hypertonic solutions affect animal cells?

A

The net movement of water molecules will move out of the cell by osmosis, therefore this can cause the animal cell to shrivel/shrink.

57
Q

How do Hypotonic solutions affect animals cells?

A

There is a higher water potential than the cytoplasm of the cell, therefore more water will move into the cell by osmosis causing the animal cell to swell and burst.

58
Q

How do Hypertonic solutions affect plant cells?

A

Because more water moves out of the cell by osmosis, this causes the Plasma membrane to detach from the cell. This is known as Plasmolysed

59
Q

How do Isotonic solutions affect plant cells?

A

There is no net movement of water so the plasma membrane will just touch the cell wall. This is known as Flaccid.

60
Q

How do Hypotonic solutions affect plant cells?

A

As water will move out of the cell by osmosis, this causes the plasma membrane to push against the cell wall, this is known as being Turgid.

61
Q

What is the process of endocytosis?

A

The cell surface membrane will bend inwards
The membrane then enfolds the material until eventually the membrane fuses forming a vesicle
The vesicle then pinches off and moves into the cytoplasm to transfer the material for further processing within the cell

62
Q

What is the process of Exocytosis?

A

The vesicles within the cytoplasm will move towards and fuse with the cell surface membrane. The contents of the vesicle is then released outside the cell.

63
Q

What is compartmentalisation?

A

The formation of membrane-bound areas in a cell

64
Q

What is the rate at which molecules or ions diffuse across the membrane affected by?

A

Surface area- the larger the area of an exchange surface the higher the rate of diffusion.
Thickness of the membrane- the thinner the exchange surface, the higher the rate of diffusion.

65
Q

What is the rate of facilitated diffusion affected by?

A

The rate of facilitated diffusion is dependent on the temperature, concentration gradient, membrane surface area and thickness and the number of channel protein present.

66
Q

What is the process of active transport?

A
67
Q

What are the two types of endocytosis?

A

Phagocytosis for solids
Pinocytosis for liquids

68
Q

What is not a role of membranes in cells?

A

Providing support for cells

Biology Module 2 Foundations In Biology (6 decks)

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