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Biology sem 1 > 1.2: cell membranes > Flashcards

1.2: cell membranes Flashcards

1
Q

What is the structure/function of cell surface membranes?

A
  • separates cell contents from the outside environment
  • holds components of some metabolic pathways on place
  • regulates transport of materials in and out of the cell
  • cell recognition and signalling
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2
Q

What permeability are cell surface membranes?

A

partially permeable, as they allow water and some solutes through

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3
Q

What are the components of the plasma membrane?

A
  • phospholipids
  • proteins
  • cholestrol
  • glycolipids
  • glycoproteins
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4
Q

what components make up a phospholipid?

A

Hydrophilic head
hydrophobic tails

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5
Q

Phospholipids - hydrophilic head structure

A

attracted to water, called polar

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6
Q

Phospholipids - hydrophobic tail structure

A

not attracted to water, called non-polar

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7
Q

What do the phospholipids form?

A

Bilayers (2 layers of phospholipids with hydrophobic tails protected inside hydrophilic heads)

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8
Q

What is the phospholipid bilayer?

A

basic structure of membranes

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9
Q

How thick is the phospholipid bilayer?

A

7nm

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10
Q

What is the model for the structure of the membrane called?

A

fluid mosaic model

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11
Q

Why is the structure of the membrane called the ‘fluid’?

A

because individual phospholipids and proteins can move around freely within the layer, by diffusion, like it’s a liquid

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12
Q

Why is the structure of the membrane called the ‘mosaic’?

A

because of the pattern produced by the scattered protein molecules when the membrane is viewed from above

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13
Q

What is the correlation between membrane and temperature?

A
  • A higher temp gives molecules in the membranes more kinetic energy, so they move faster
  • this makes the membrane leaky
  • increases permeability
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14
Q

What is the structure of protein in cell membranes?

A
  • most protein molecules float like icebergs in layers, some are fixed ro structures inside the cell
  • some proteins are embedded in just the outer or inner layer
  • some span the two layers
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15
Q

What is the name of the proteins embedded in just the outer or inner layer?

A

extrinsic proteins

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16
Q

What is the name of the proteins that span the two layers?

A

intrinsic proteins

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17
Q

Where do the hydrophobic and hydrophilic parts of the protein sit?

A

They sit next to the hydrophobic and hydrophilic portions of the membrane. Ensuring proteins stay in the membrane

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18
Q

What are the phospholipids with carbohydrate chains attached to called?

A

glycolipids

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19
Q

What are the proteins with carbohydrate chains attached to called?

A

Glycoproteins

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20
Q

What do the membranes also contain molecules of?

A

Cholesterol

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21
Q

what is the role of phospholipids?

A
  • forms a bilayer
  • allow lipid soluble substances in and out of the cell
  • prevent water soluble substances moving in/out of the cell
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22
Q

What is the role of cholesterol?

A
  • reduces side to side movement of phospholipids in the bilayer
  • regulates fluidity
  • prevents leakage of ions and water
  • maintains the mechanical stability of the cell
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23
Q

What is the role of proteins?

A
  • may act as channel proteins for water soluble substances
  • can work as enzymes
  • form receptor sites for molecules
  • cell adhesion
  • transport proteins - actively move substances using ATP
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24
Q

What is the role of glycolipids?

A
  • forms binding sites for molecules
  • helps to maintain stability of membrane
  • role in cell attachment
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25
Q

What is the role of glycoproteins?

A
  • receptor site for hormones and neurotransmitters
  • role in cell adhesion
  • cell signalling
  • act as antigens so cells can recognise each other
  • intercellular lubrications
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26
Q

What are passive transport methods through cell membranes?

A
  • osmosis
  • simple diffusion
  • facilitative diffusion
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27
Q

What are active methods through cell membranes?

A
  • active transport
  • bulk transport
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28
Q

what is the difference between active and passive methods?

A

active requires ATP

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29
Q

what is simple diffusion?

A

diffusion is the passive net movements of molecules from a region of higher concentration to a region of lower concentration

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30
Q

Simple diffusion - movement

A
  • Moves down a concentration gradient
  • molecules have kinetic energy, which makes them move about randomly. It is passive and does not require ATP
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31
Q

What determines the rate of diffusion?

A
  • concentration gradient
  • temperature
  • area over which diffusion takes place
  • size and nature of the molecule
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32
Q

Factors rate of diffusion - concentration gradient

A

The steeper the conc gradient the quicker the rate of diffusion

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33
Q

Factors rate of diffusion - Temperature

A

Higher temp gives molecules or ions more kinetic energy. Molecules move around faster, so diffusion is faster

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34
Q

Factors rate of diffusion - Area over which diffusion takes place

A

The greater the surface area the faster the rate of diffusion

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35
Q

Factors rate of diffusion - Size and nature of the molecule

A
  • large molecules need more energy to move so they diffuse more slowly
  • Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non-polar phospholipid tails

Distance traveled will also effect rate

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36
Q

What is facilitated diffusion?

A

Large polar molecules (E.g. glucose and amino acids, and ions E.g. Na + or Cl- can’t diffuse across the phospholipid bilayer)
- diffuse through channel or carrier proteins often shaped to allow only one type of molecule through
- passive

37
Q

What is the definition of osmosis?

A

The diffusion go water molecules down a water potential gradient, from an area of higher water potential to an area of lower water potential across a partially permeable membrane

38
Q

What is water potential?

A

The tendency of water molecules to move from one place to another
- Measured in Kpa

39
Q

What is a solute?

A

Dissolves in water

40
Q

When is equilibrium reached in osmosis?

A

When the water potential is equal on either side of the cell

40
Q

What is the definition of Active Transport?

A
  • Against a concentration gradient
  • from a lower to a higher concentration
  • uses energy supplied by ATP
  • Carrier proteins are involved - complementary in shape to the molecule it transports
41
Q

Is diffusion or active transport faster rate?

A

Diffusion

42
Q

What is an hypotonic solution (ANIMALS)

A

high water potential outside the cell, low water potential inside cell.
Causes the cell to burst (LEFT PICTURE)

43
Q

`what is an isotonic solution?

A

Equal water potential inside and outside the cell.
EQUILIBRIUM REACHED
(MIDDLE PICTURE)

44
Q

What is an hypertonic solution?

A

Higher water potential inside the cell, lower water potential outside the cell.
Cell shrinks (RIGHT PICTURE)

45
Q

What molecules can diffuse through cell membranes?

A
  • Oxygen
  • Carbon Dioxide
  • Water
46
Q

How quickly do each of these molecules diffuse through cell membrane and why:
- oxygen
- carbon dioxide
- water

A
  • oxygen: Non-polar so diffuses very quickly
  • Carbon dioxide: Polar but very small so diffuses quickly
  • Water: Polar but also very small so diffuses quickly
47
Q

What are turgid plant cells in relation to osmosis?

A

When water moves into a cell because the water potential outside the cell is higher than inside the cell.

48
Q

Why do the turgid cells not burst when water enters the cell via osmosis?

A

Because the cellulose cell wall is strong enough to stop the cell bursting. It pushes back against the protoplast

49
Q

What are flaccid plant cells in relation to osmosis?

A

When water leaves the cell because the water potential is higher in the cell compared to lower water potential outside the cell.

50
Q

What happens to flaccid cells in terms of the shape?

A

The protoplast shrivels and plasmolysis occurs

51
Q

What is plasmolysis?

A

When cell membrane pulls away from the cell wall

52
Q

What is incipient plasmolysis?

A

When a cell is placed in an equal water potential so there is no net movement of water.

53
Q

What is the equation for water potential?

A

water potential of cell = solute potential of the cell + pressure potential of the cell

54
Q

What does the solute potential do to the water potential?

A

decreases it, makes it more negative in Kpa

55
Q

What does the pressure potential do to the water potential?

A

increases it, makes it less negative in Kpa

56
Q

In incipient plasmolysis what is the water potential in Kpa?

A

0 Kpa

57
Q

What is the process of exocytosis?

A
  • vesicle moves towards plasma membrane
  • Vesicle joins with plasma membrane
  • Vesicle contents released, the vesicle membrane is now part of the plasma membrane
58
Q

What is the process of endocytosis?

A
  • the cell spreads around an object or area of the solution outside the cell
  • the area enclosed becomes a vesicle
  • The contents of the vesicle are absorbed into the cytoplasm and the vesicle membrane is recycled
59
Q

What is cell signalling?

A

When cells communicate with signals which can be molecules such as hormones, neurotransmitters or cytokines.

60
Q

What signals must cells be able to detect which coordinates processes?

A
  • growth
  • development
  • movement
  • excretion
61
Q

How does a cell detect a signal?

A

The cell has receptors (usually glycoproteins) on the cell surface membrane
- communication is often by hormones (chemical messengers)
- a cell with a receptor for the hormone molecule is a target cell
- when the signal molecule binds to the receptor, a response then occurs

62
Q

What is an example of a medicinal drug using cell signalling?

A

insulin

63
Q

What is the mechanism of cell signalling ‘receptor acts as an ion channel’

A

When a chemical signal attaches to the receptor, it makes the ion channel open, letting ions into the cell causing a response.

64
Q

What is the mechanism of cell signalling ‘receptor activates a G-protein’

A

When this happens, the G-protein then activates an enzyme which brings about a response

65
Q

What is the mechanism of cell signalling ‘receptor acts as an enzyme’

A

The receptor is made up of 2 parts. The signal molecule attaches to both parts, connecting them together and forming an active enzyme, which brings about reactions in the cell.

66
Q

How does the structure of the water channel protein relate to its function?

A

The phospholipid heads are hydrophilic so position themselves on the outside.
The fatty acid tails are hydrophobic so position themselves in the inside of the cell.
This means that the water can pass through the whole cell membrane.

67
Q

Draw and label a simple diagram of facilitated diffusion

A
68
Q

What reasons are exchange between the cell and the environment essential

A
  • allows them to obtain nutrients and energy
  • allows them to eliminate waste products
  • in order for communication
69
Q

What two types of molecules can diffuse through the bilayer?

A
  • ions
  • polar molecules (charged)
70
Q

What characteristic of a protein channel allows it to maintain its position within the phospholipid bilayer?

A

They are made up of amino acids which are non polar side chains. This allows them to contact the hydrophobic environment of the lipid bilayer

71
Q

What characteristics of a protein channel allows molecules such as glucose to pass through them

A

They have open pores in their membranes

72
Q

What is bulk transport?

A

Moving large quantities of materials in or out of the cell. This requires ATP

73
Q

What are the two types of bulk transport?

A
  • Endocytosis
  • Exocytosis
74
Q

What is endocytosis?

A

Bulk transport of a material into a cell

75
Q

What is exocytosis?

A

Bulk transport of a material out of a cell

76
Q

What is bulk uptake of solids called? Give an example

A

Endophagocytosis, White blood cells

77
Q

What is bulk uptake of liquids called?

A

Endopinocytosis

78
Q

Draw and label a diagram of bulk transport

A
79
Q

What do the receptors have in cell signalling?

A

A specific and complementary shape to the shape of the signalling molecule

80
Q

What are the 3 types of cell signalling?

A
  • Autocrine
  • endocrine
  • paracrine
81
Q

How does Autocrine signalling work?

A
  • cell stimulates a response within itself releasing chemical signals for its own cells.
    E.g. Immune cells
82
Q

How does Endocrine signalling work?

A
  • Occurs over large distances
  • signalling molecule is usually a hormone transported in the blood to the target cell
83
Q

How does Paracrine signalling work?

A

Between cells close together.
E.g. Neurotransmitters released between neurones

84
Q

Examples of hydrophobic molecules passing across cell membrane?

A

O₂ , CO₂ , N₂ , Steroids

85
Q

Examples of small uncharged polar molecules passing across cell membrane?

A

H₂o, Urea, ethanol

86
Q

Examples of large uncharged polar molecules passing across cell membrane?

A

Glucose, Sucrose, Amino acids

87
Q

Examples of ions passing across cell membrane?

A

Na +, K +, cl -

Biology sem 1 (9 decks)

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