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Biology > 2.5 - E - Biological Membranes > Flashcards

2.5 - E - Biological Membranes Flashcards

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1
Q

Explain what a phospholipid consists of

A

1 phosphate head

2 fatty acid tails

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2
Q

Define hydrophilic

A

Water-loving

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3
Q

Define hydrophobic

A

Water-hating

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4
Q

Why are phosphate heads hydrophilic?

A

The charges on the head are unevenly distributed (polar)

This lets it interact with the water molecules easily

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5
Q

Why are fatty acid tails hydrophobic?

A

The charges on them are evenly distributed (non-polar)

This means they won’t mix with water and will repel the molecules

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6
Q

When in water, why can phospholipids slide around one another?

A

Because the lack of bonds causes fluidity

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7
Q

What is the average thickness of a phospholipid bilayer?

A

7-10nm

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8
Q

What should you always refer to the cell membrane as and never refer to it as?

A

Refer to it as: the plasma membrane or the cell surface membrane
Never refer to it as: the cell membrane

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9
Q

What do some phospholipid bilayers contain and how does this affect them?

A

Aquaporins (protein channels which allow water through) which make them much more permeable to water.

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10
Q

What is a liposome?

A

An artificially prepared vesicle made of a lipid bilayer

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11
Q

List 7 roles of the plasma membrane

A

Separating cell contents from outside environments and cell components from cytoplasms
Regulating transport of materials in and out of cells
Holding components of some metabolic pathways in place
May contain enzymes involved in specific metabolic pathways
Has antigens, so the immune system doesn’t attack it
May release chemicals for other cells (cell signalling), contains receptors for chemicals, site for cell communication/signalling
May be the site of chemical reactions

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12
Q

What does delta mean and what is the sign?

A

Like an 8 without the top right but yaknow

Delta - a little bit

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13
Q

What is the difference between polar and non-polar

A

Polar - uneven charge

Non-polar - even charge

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14
Q

Explain the charge of a water molecule

A

2 delta + hydrogen ions
1 delta - oxygen ion
Overall, + polar

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15
Q

Who proposed the fluid mosaic model?

A

Singer and Nicolson

1972

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16
Q

What is a glycoprotein?

A

A carbohydrate chain attached to a protein molecule

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17
Q

What is a glycolipid?

A

A carbohydrate chain attached to a lipid

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18
Q

What is the function of cholesterol and where is it found?

A

Gives mechanical stability and flexibility
It fits between fatty acid tails and ‘plugs gaps’ ‐ makes the membrane less permeable to water molecules and to ions
It restricts too much movement within the phospholipid layer

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19
Q

What do carbohydrate molecules do around the membrane and what is another name for them?

A

Glycocalyx
They are hydrophilic and attract water with dissolved solutes, helping the cell interact with its watery environment and obtain dissolved substances

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20
Q

What is the difference between an intrinsic protein and an extrinsic protein? Give an example of each

A

Intrinsic protein - goes through the entire membrane (channel protein)
Extrinsic protein - partially embedded inside or outside the membrane (carrier protein)

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21
Q

What is the purpose of glycoproteins and glycolipids?

A

They are involved in cell signalling - they are “self “to allow recognition by the immune system.
They are receptors for hormones/drugs
On the surface of pathogens they are antigens ‐ immune system can
recognise them as ‘foreign’
Glycoproteins can bind cells together in tissues

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22
Q

Are intrinsic proteins hydrophobic or hydrophilic and why?

A

Hydrophobic - due to passing through the hydrophobic region as they span the whole membrane

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23
Q

What are channel proteins?

A

They have pores for small ions or small water soluble molecules to diffuse through the membrane - intrinsic

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24
Q

What are carrier proteins?

A

They help larger molecules to diffuse through the membrane, or can be used for active transport across the membrane - extrinsic

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25
Q

How is the cytoskeleton related to the fluid mosaic model?

A

Actin microfilaments and its proteins help anchor membranes and stop them moving around too much.

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26
Q

List the 3 factors that affect membrane permeability

A

Temperature
Cholesterol
Saturation

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27
Q

Explain how an increase in temperature affect membrane permeability (4)

A

The phospholipids acquire more kinetic energy and move around more. This increases fluidity and therefore permeability.
It also affects the way membrane-embedded proteins are positioned and may function. If they move, rate of reactions change.
Temp may affect the infolding of membranes during phagocytosis.
It may also change the ability of cell signalling by releasing chemicals (exocytosis)

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28
Q

Explain how a decrease in temperature affects membrane permeability

A

Phospholipids cluster - crystallised state

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29
Q

Explain how cholesterol affects membrane permeability

A

Less cholesterol - lower temp
They sometimes insert themselves between phospholipids
Membranes vary in their amount of cholesterol
Less cholesterol increases distance between phospholipids. This increases fluidity
More cholesterol - higher temp
Inserting cholesterol means the phospholipids are already distant, and the cholesterol pulls them together, decreasing fluidity

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30
Q

Explain the saturation of fats and how it affects membrane permeability

A

Saturated - longer and thinner fatty tails
This means less distance between phospholipids so less fluidity
Unsaturated - shorter, double bonds create kinks/gaps
More distance between phospholipids so more fluidity

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31
Q

List the features of Mrs Gren

What are they all together?

A 
Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition
The 7 life processes ‐ all living things do ALL of them [viruses don't ‐ technically not living!]
32
Q

Define cell signalling

A

When cells communicate with one another by signals to help them work together and coordinate their actions.

33
Q

Give 2 examples of cell signals secreted by cells

A

Cytokines and hormones

34
Q

What are target cells?

A

Cells with specific receptors for the hormones

35
Q

When and where is insulin made?

A

Beta‐cells in islets of Langerhans in pancreas

When blood glucose is too high

36
Q

What are the target cells and the effect insulin has on them?

A

Insulin receptors on many cells inc. muscle and liver cells

Cells take up more glucose from blood = reduces blood glucose level

37
Q

List the 7 functions of glycoproteins

A

Cell signalling ‐ communication between cells to help them work together/
They coordinate actions
They act as antigens for cell recognition ‐ recognition as self/non‐self, allows the immune system to not attack it
They are receptors found on target cells… for hormones/cytokines to trigger reactions/responses in cells
They cause cell adhesion ‐ hold cells together in tissues
They form bonds with water molecules to stabilise membrane
They are receptors on transport proteins

38
Q

Define diffusion

A

The net movement of molecules from a region of high concentration to a region of low concentration of that molecule, down a concentration gradient. This is a passive process.

39
Q

Define osmosis

A

The net movement of water molecules from a region of high concentration of water molecules to a region of low concentration of water molecules down the concentration gradient, across a partially permeable membrane. This is a passive process.

40
Q

Define active transport

A

The movement of molecules or ions across membranes from a region of low concentration to a region of higher concentration of that molecule against the concentration gradient. It requires energy in the form of ATP.

41
Q

A quicker rate of diffusion is caused by…

A

A steeper concentration gradient

42
Q

List and explain the 5 factors that affect the rate of diffusion

A

Temperature ‐ higher temp = more kinetic energy for molecules = higher rate of random movement = higher rate of diffusion
Stirring/moving ‐ stirring increases movement of molecules = higher rate of diffusion
Surface area ‐ diffusion across membranes is faster if there is a larger SA to diffuse across. e.g. alveoli
Distance/thickness ‐ thinner membrane = faster diffusion e.g. alveoli
Size of molecule = smaller molecules = faster diffusion

43
Q

List and explain the 2 substances that can diffuse directly across the bilayer

A

Lipid‐based molecules ‐ are fat soluble so dissolve and diffuse readily across the bilayer e.g. steroid hormones
Very small molecules ‐ oxygen and carbon dioxide are small enough to pass between phospholipid molecules. Water and urea molecules are very small but because they are polar (charged) they pass across the bilayer much slower

44
Q

What features of a molecule cause a quicker rate of diffusion?

A

The smaller and less polar a molecule, the quicker it will diffuse
across a membrane.

45
Q

Define facilitated diffusion

A

The net movement of molecules from a region of high concentration to a region of lower concentration of that molecule, down the concentration gradient, across a partially permeable membrane via carrier or channel proteins. It is a passive process

46
Q

Explain how channel proteins are a part of facilitated diffusion

A

They form pores in membranes.
There are hydrophilic conditions inside pore
They are specific to certain small‐water soluble molecules or ions e.g. sodium and calcium ions
They allow diffusion in or out of cell/organelle

47
Q

How does a channel protein being gated impact the membrane

A

They can be opened or closed by a signal or change in voltage across the membrane - they can choose what to let in and out of the cell

48
Q

Explain how carrier proteins are a part of facilitated diffusion

A

They carry larger molecules e.g. glucose & amino acids ‐ shaped for specific molecules to bind to
The molecule binding changes the shape of the carrier protein
This causes the molecule to be carried to and released on the other side of the membrane

49
Q

Defin water potential

A

The measure of the tendency of water molecules to diffuse from one region to another

50
Q

What is the highest water potential?

A

0 KPa

51
Q

What is a solute?

A

A solid that dissolves

52
Q

What is a solvent?

A

A liquid that dissolves solids

53
Q

What is a solution?

A

The liquid containing dissolved solids

54
Q

What does it mean if a cell is haemolysed/cytolysed?

A

When animal cell surface membranes burst

55
Q

What happens to cells in higher water potential?

A

Water moves into the cell by osmosis and the cell swells.
Animal cells burst (become haemolysed/cytolysed)
Plant cells become turgid

56
Q

What does it mean if a plant cell is turgid?

A

In a higher water potential the cells swell as water moves in.
It is then ready to burst but the cell wall restricts it from doing so.
The cell is now turgid and osmosis into the cell stops

57
Q

What does it mean if an animal cell is crenated?

A

Osmosis out of the cell takes place and the cell begins to shrink and wrinkle

58
Q

What does it mean if a plant cell is plasmolysed?

A

In a lower water potential the cells shrink as water moves out.
The cytoplasm then pulls away from the cell wall.
The cell is now plasmolysed

59
Q

What is incipient plasmolysis?

A

The point when the cell membrane is about to pull away from the cell wall

60
Q

What happens to cells in low water potential?

A

Water moves out of the cell by osmosis and the cell shrinks.
Animal cells wrinkle (become crenated)
Plant cells become plasmolysed

61
Q

Explain the process of active transport using carrier proteins

A

Carrier proteins work as pumps.
Specific and complementary shaped molecule binds
Molecules can’t diffuse (due to gradient)
ATP provides the energy needed for the protein to change shape and transport the molecule across the membrane.
Shape change only allows the molecule to fit in the protein on one side
of the membrane ‐ it will not fit on the other side ‐ stops transport in
the wrong direction.
Much faster than diffusion
Can go inside cells/organelles or outside cells ‐ dependant on gradient.

62
Q

What are the 2 types of bulk transport?

A

Endocytosis and exocytosis

63
Q

Define endocytosis

A

Moving in

64
Q

Define exocytosis

A

Moving out

65
Q

Phago means…

A

Solids

66
Q

Pino means…

A

Liquids

67
Q

Define exophagocytosis, endopinocytosis, endophagocytosis and exopinocytosis

A

Solids moving out
Liquids moving in
Solids moving in
Liquids moving out

68
Q

Explain the process of exocytosis

A

Vesicle moves towards the cell surface membrane on microtubles using ATP.
The vesicle fuses with the cell surface membrane ‐ requires ATP
The molecules are ejected from the cell

69
Q

Explain the process of endocytosis

A

A molecule binds to a receptor and this causes the cell surface membrane to fold in ‐ invaginates
This requires ATP
The cell surface membrane fuses with itself to form a vesicle

70
Q

What is invaginating?

A

When a cell surface membrane folds in on itself

71
Q

What’s the difference between the process of carrier proteins in facilitated diffusion and active transport?

A

In both processes the carrier protein needs to change shape for the molecule. However, due to the negative concentration gradient in active transport, ATP changes to ADP and releases energy which the protein uses to change its conformation (shape) and in doing so carries the ion from one side to the other.

72
Q

What does phagocytosis mean?

A

“Eating by cells”

73
Q

When is ATP hydrolysed?

A

A molecule of ATP is hydrolysed for every step that a motor protein takes along the cytoskeleton thread as it drags the vesicles
(Exocytosis)

74
Q

What does integral mean?

A

A membrane protein that is permanently attached to the plasma membrane

75
Q

Describe and explain the role of cholesterol in the plasma membrane

A

It partially immobilises nearby phospholipids in plasma membranes. This decreases the permeability and maintains the mechanical stability of the plasma membrane.

76
Q

Define hypertonic, isotonic and hypotonic

A

Hypertonic - water potential outside the cell is lower than inside
Isotonic - water potential is equal inside and outside the cell
Hypotonic - water potential is higher outside the cell than inside

77
Q

What is the difference between cytolysis and heamolysis?

A

Cytolysis happens to any animal cell

Heamolysis happens to red blood cells only

Biology (25 decks)

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