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2..5 Biological membranes > 2.5.1 The structure of cell membranes > Flashcards

2.5.1 The structure of cell membranes Flashcards

1
Q

what type of barriers are membranes?

A

partially permeable

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2
Q

what determines the membrane’s permeability?

A

the properties of the component molecules of the cell membrane

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3
Q

name 3 roles (out of 10) of the plasma membrane? (at the surface of the cell)

A

-compartmentalisation
-regulates transport
-contain enzymes
-has antigens
-communication
-chemical reactions
-chemical gradients
-protection
-surface area
-permeability

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4
Q

explain the compartmentalisation role of the plasma membrane

A

the formation of separate membrane bound areas allows for separate parts to have specific conditions required for cellular reactions

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4
Q

explain the regulation role of the plasma membrane

A

the plasma membrane regulates the transport in/out of the cell

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5
Q

explain the enzyme role of the plasma membrane

A

may contain enzymes involved in specific metabolic pathways

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6
Q

explain the antigen role of the plasma membrane

A

it has antigens so that the cell’s immune system recognises the cell was being ‘self’ and not attack it

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7
Q

explain the communication role the plasma membrane

A

the plasma membrane is responsible for communicating with each other (they do this through cell signalling)

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8
Q

what is cell signalling?

A

chemicals can be released and membranes have receptors on their surface that detect the chemicals and respond (hormones and drugs may also bind to the membrane bound receptors)

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9
Q

explain the chemical reactions role of the plasma membrane

A

the plasma membrane may be a site of chemical reactions

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10
Q

explain the chemical gradients role of the plasma membrane

A

the plasma membrane allows chemical gradients to be maintained (eg osmosis/ diffusion)

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11
Q

explain the protection role of the plasma membrane

A

the plasma membrane protects vital cell components

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12
Q

explain the surface area role of the plasma membrane

A

the plasma membrane creates a large surface area for increased diffusion

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13
Q

explain the permeability role of the plasma membrane

A

the plasma membrane allows certain molecules or ions to pass through easily but prevents others

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14
Q

what is a membrane formed from?

A

membranes are formed from a phospholipid bilayer

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15
Q

what is the structure of a phospholipid?

A

a hydrophilic phosphate head (polar) and 2 hydrophobic fatty acid tails (non-polar)

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16
Q

why is the structure of a plasma membrane maintained? hint aqueous

A

cells are normally in aqueous environments so structure is maintained, due to the hydrophilic head and hydrophobic tails

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17
Q

what does hydrophilic mean?

A

water loving

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18
Q

what does hydrophobic mean?

A

water hating

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19
Q

what are the qualities of polar molecules?

A

-partially charged
-fat insoluble
-hydrophilic
-cannot diffuse through
eg phosphate head

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20
Q

what the qualities of non-polar molecules?

A

-uncharged
-soluble in fats
-hydrophobic
-can diffuse through
eg fatty acid tail from phospholipid

21
Q

do gases pass through membranes?

A

yes

22
Q

do hydrophobic molecules pass through membranes?

A

yes

23
Q

do small polar molecules pass through membranes?

A

yes, they are an exception though

24
Q

do large polar molecules pass through membranes ?

A

no

25
Q

do charged molecules pass through membranes?

A

no

26
Q

what is the criteria for passing through membranes?

A

non-polar molecules

27
Q

when was the fluid mosaic model proposed?

A

1972

28
Q

who proposed the fluid mosaic model?

A

Singer and Nicholson

29
Q

explain the fluid part of the fluid mosaic model (1972)

A

-the phospholipids and protein molecules can move around via diffusion
-the phospholipids mainly move sideways, within their own layers
-the many different types of proteins interspersed throughout the bilayer move about within it (a bit like icebergs in the sea) although some may be fixed in position

30
Q

explain the mosaic part of the fluid mosaic model (1972)

A

because the proteins form a pattern of molecules in the lipid (different types of proteins scattered across membrane

31
Q

what did the fluid mosaic model (1972) say regarding protein location?

A

proteins embedded in bilayer, both intrinsic or extrinsic

32
Q

what are intrinsic proteins?

A

proteins embedded through both layers of a membrane

33
Q

what are extrinsic proteins?

A

peripheral proteins that appear on one side of the bilayer

34
Q

what are the intrinsic proteins in the plasma membrane?

A

channel proteins, carrier proteins and glycoproteins

35
Q

what is the extrinsic protein in the plasma membrane?

A

peripheral proteins

36
Q

what is the structure of a channel protein?

A

hydrophilic channels

37
Q

what is the function of a channel protein?

A

involved in transport across membranes

38
Q

how does a channel protein function?

A

they have hydrophilic channels that allow passive movement of polar molecules down the concentration gradient

39
Q

what is the fluid mosaic model (1972)?

A

explains how biological molecules are arranged to form cell membranes

40
Q

what does the fluid mosaic model (1972) also help explain, aside from the arrangement of biological molecules that form plasma membranes?

A

-passive and active movement between cells and their surroundings
-cell-to-cell interactions
-cell signalling

41
Q

what are the 4 main components of the fluid mosaic model (1972)?

A

-phospholipids
-cholesterol
-glycoproteins and glycolipids
-transport proteins (channel and carrier)

42
Q

what do phospholipids form?

A

the basic structure of the plasma membrane (the bilayer)

43
Q

what do the fatty acid tails in phospholipids form?

A

they form a hydrophobic core comprising the innermost part of both the outer and inner layer of the membrane

44
Q

how does the phospholipid bilayer protect the cell?

A

it act as a barrier to most water-soluble substances

45
Q

how does the phospholipid bilayer act as a barrier to most water-soluble substances?

A

the non-polar fatty acid tails prevent polar molecules or ions from passing across the membrane

46
Q

what does the non-polar fatty acids tails ensure?

A

ensures water-soluble molecules such as sugars, amino acids and proteins cannot leak out of the cell and unwanted water-soluble molecules cannot get in

47
Q

what are the two functions of the phospholipid bilayer?

A

-signalling
-keep water molecules in/out

48
Q

how can phospholipids can be chemically modified to act as signalling molecules?

A

-moving within the bilayer to activate other molecules (eg. enzymes)
-being hydrolysed, which releases smaller water-soluble molecules that bind to specific receptors in the cytoplasm

49
Q

what is meant by transport proteins?

A

channel and carrier proteins

2..5 Biological membranes (6 decks)

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