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Module 2.5- Biological Membranes > Cell Membranes > Flashcards

Cell Membranes Flashcards

1
Q

How are cell membranes described

A

Partially permeable

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2
Q

Define permeability

A

The ability to let substances pass through

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3
Q

What are the three ways that substances can pass through to get into a membrane

A

1) some very small molecules simply diffuse through
2) some substances dissolve in the lipid layer and pass through
3) other substances pass through special protein channels or are carried by carrier proteins

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4
Q

Why are membranes described as partially permeable

A

Because they do not let all types of molecules pass through them

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5
Q

What is the 10 roles of the plasma membrane

A

1) compartmentalisation= different functions and structure
2) binding to other cells
3) recognition (hormone receptors e.g insulin)
4) cell signalling (white blood cells in order to destroy pathogens)
5) intergrin (cytoskeleton attachment support)= different parts holing cells together
6) signal transduction (converts messages from one to another)
7) movement -> cell membrane allows movement
8) bulk transport (endcytosis/ exocytosis)
9) surface area extension
10) active transport

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6
Q

What separates the organelles contents from the cell cytoplasm

A
  • the membranes around the organelles
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7
Q

What membrane do mitochondria have and what does this give them

A
  • inner membrane called cristae
  • this gives them a large surface area for some of the reactions of aerobic respiration
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8
Q

What membrane do chloroplasts have and what does this help them with

A
  • inner membranes called thylakoid membranes, houses chlorophyll
  • this is the membrane where some of the reactions of photosynthesis occur
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9
Q

What is the name of the model used to describe the cell membrane structure

A

Fluid mosaic model

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10
Q

Describe the term fluid mosaic model

A

‘Fluid’ because phospholipids and proteins can move around via diffusion
‘Mosaic’ because of the scattered pattern produced by the proteins within the phospholipid bilayer looked somewhat mosaic

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11
Q

What are the four main components of the fluid mosaic model

A

1) Phospholipids
2) Cholesterol
3) Gylcoproteins and glycolipids
4) Transport proteins

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12
Q

Name and describe the 3 types of proteins present in the cell membrane

A

1) proteins with pores (channel proteins) => act as channels to allow ions, which have an electrical charge and are surrounded by water molecules to pass through
2) protein carries => by changing their shape, carry specific molecules across the membrane
3) other proteins => attached to carrier proteins and function as enzymes, antigens or receptor sites for chemicals such as hormones

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13
Q

What are the cell membranes mainly made up of

A
  • phospholipids
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14
Q

What is the structure of phospholipids

A

HYDROPHILIC HEAD (POLAR):
1) phosphate group
2) phosphodiester bond

HYDROPHOBIC TAIL (NON-POLAR)
3) glycerol
4) ester bond
5) fatty acid

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15
Q

Where is the hydrophobic tail situated in the plasma cell membrane

A
  • innermost part of the membrane
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16
Q

Where is the hydrophilic head situated in the plasma cell membrane

A
  • on the outermost part of the membrane
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17
Q

What is the role of the phospholipid belayer

A
  • acts as a barrier to most-water soluble substances (the non-polar fatty acid tails prevent polar molecules or ions from passing across the membrane)
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18
Q

What is the role of cholesterol

A
  • regulates fluidity of the membrane
  • gives mechanical stability and flexibility
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19
Q

How does cholesterol regulate fluidity of the membrane

A
  • by stopping the phospholipid tails packing too closely together
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20
Q

Where do glycolipids and glycoproteins occur on the plasma membrane

A
  • exist on the surface (the periphery)
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21
Q

Glycoproteins and glycolipids exist on the surface of cell membranes , what does this allow them to do

A
  • act as receptor molecules
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22
Q

What are the three main receptor types

A

1) signalling receptors for hormones and neurotransmitters
2) Receptors involved in endocytosis
3) Receptors involved in cell adhesion and stabilisation

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23
Q

Fill in the blanks:
Some glyocolipids and glycoproteins acts as cell _____ or ________ for cell-to-cell recognition

A

1) markers
2) antigens

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24
Q

What do transport proteins create

A
  • hydrophilic channels to allow ions and polar molecules to travel through the membrane
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25
What are the 2 types of transport proteins in the cell membrane
1) channel (pore) proteins 2) carrier proteins
26
How does carrier proteins work
- they change shape to transport a substances across the membrane
27
How do channel proteins work
- by allowing polar, large or charged ions to pass through and across the cell membrane
28
What do transport proteins allow
- they allow the cell to control which substances enter or leave the cell
29
What are the factors affecting membrane structure and permeability
- temperature - solvent
30
Describe how high temperature affects the membrane structure and permeability
- phospholipids gains more kinetic energy and move around more, increasing the membranes fluidity - permeability increases - changes the ability of cells to signal to other cells - diffusion takes place at a higher speed - proteins tertiary structure is disrupted and they start to denature, which disrupts the membrane structure, meaning it is no longer an effective barrier - cholesterol molecules buffers the effect of increasing heat as it reduces the increase in membrane fluidity
31
How is changes to the membrane fluidity described and why
- reversible because if temperatures go back to optimum then the lipids will return to their normal levels of fluidity
32
How is changes to the membrane’s proteins describe as and why
- irreversible because the tertiary structure is disrupted and hydrogen bonds are broken which cannot be reformed even if temperature returns to optimum
33
Describe how low temperature affects the membrane structure and permeability
- saturated fatty acids become compressed - as the unsaturated fatty acids tails become compressed their kinks in their tails push adjacent phospholipids molecules away - cholesterol buffers the effect to prevent a reduction in the membrane’s fluidity by preventing the phospholipids molecules form packing too close together - proteins will work a lot slower or may not work at all
34
What type of solvent have an effect of membrane permeability
- organic solvents like acetone and ethanol
35
What effect do these organic solvents have on the cell and why
- increase the cell membrane permeability, as they dissolve the lipids in the membrane, causing the membrane to lose its structure
36
Define diffusion
- the net movement of molecules down the concentration gradient from an area of high concentration to an area of low concentration across a partially permeable membrane
37
How do water molecules move across the membrane
- through specific water channel proteins called aquaporins
38
How is the concentration gradient maintained
- because many molecules entering cells then pass into organelles and are used for metabolic reactions
39
What are the 5 factors that affects the rate of simple diffusion
1) Temperature 2) Diffusion distance 3) Surface area 4) Size of diffusing molecule 5) Concentration gradient
40
Describe how temperature affects the rate of simple diffusion
INCREASE IN TMEP - as temperature increases, molecules have more kinetic energy - so their rate of diffusion will increase DECREASE IN TMEP: - diffusion will slow down as the molecules don’t have a lot of kinetic energy
41
Describe how diffusion distance affects the rate of simple diffusion
- the thicker the membrane across which the molecules have to dissect the slower the rate of diffusion
42
Describe how surface area affects the rate of simple diffusion
- more diffusion can take place across a larger SA - cells specialised for absorption have extensions to their cell surface membrane called microvilli, these increase SA
43
Describe how size of diffusing molecule affects the rate of simple diffusion
- smaller ions or molecules diffuse more rapidly than larger molecules
44
Describe how concentration gradient affects the rate of simple diffusion
- the steeper the gradient (the more molecules are on one side of the membrane compared with he other side) the faster the diffusion to the side where there are fewer molecule, down concetration gradient
45
Define facilitated diffusion
- the net movement of molecules from an area of high concentrations to an area of low concentration across a partially permeable membrane via protein channels or carriers
46
What type of molecules does facilitated diffusion help to move
-large molecules - polar - non-lipid soluble
47
What do large, polar molecules require to aid their movements across membranes
- transmembrane proteins
48
What type of molecules does simple diffusion help to move
- small molecules - lipid-soluble
49
Define osmosis
- the net movement of water molecules down a water potential gradient from an area of high water potential to an area of low water potential across a partially permeable membrane
50
Define a solvent
- the liquid in which solute molecules are dissolved in
51
Define water potential
- the tendency of water molecules to diffuse from one place to another
52
What is water potential measured in
- kPa
53
What is the water potential of pure water
0 kPa
54
What is the highest water potential a solvent can have and what molecule has it
- 0 (pure water)
55
As water potential decreases what happens to the numerical value
- it becomes negative
56
What is the formulae for water potential
solute potential + pressure potential
57
Is the water potential inside the cell lower or higher than pure water
- lower
58
Descibre cytolysis
- when a lot of water enters an animal cell, it will swell and burst as the plasma membrane breaks
59
Descibre turgidity
- when lots of water enter a plant cell it will swell up to a certain size and its content pushes against the cell wall which resists any further swelling - the cells don’t burst because of the strong cellulose cell wall
60
Describe crenation
- in animal cells when cells are placed in a solution of lower water potential, water leaves the cells by osmosis and the cells shrivel which is described as crenation
61
Describe plasmolysis
- in plant cell when a cell is places in a solution of lower water potential, water leaves the cell by osmosis and this causes the cytoplasm of the cell to shrink and the membrane pulls away from the cell wall, the cells are described as plasmolysed and flaccid
62
A cell being plasmolysed is also described as
- Hypertonic (having lots of sugar and a low water potential)
63
A cell being flaccid is also described as
- Isotonic (same sugars and water potential as another cell)
64
A cell being described as turgid is also known as
- Hypotonic (low amounts of sugar high water potential basically pure water 0 kPa)
65
Define active transport
- the active movement of substances against their concentration gradient across a partially permeable membrane, using ATP and protein carriers
66
How are carrier proteins able to change their shape
- as they have a region that binds to and allows for the hydrolysis of a molecule of ATP to release energy
67
How does the carrier proteins carry an ion from one side of the cell membrane to another
- by changing its shape
68
Define endocytosis
- the bulk transport of molecules into a cell using ATP
69
How do larger particles enter the cell via endocytosis
- a segment of the plasma membrane surrounds and encloses the particle and brings it into a cell enclosed in a vesicle
70
Define phagocytosis
- eating by cells
71
Define pino(endo)cytosis
- cells ingesting liquids
72
Define exocytosis
- the bulk transport of molecules out of a cell using ATP
73
Describe exocytosis
1) a membrane- bound vesicle, containing the substances to be secreted is moved towards the cell surface membrane 2) the cell surface membrane and the membrane of the vesicle fuse together 3) the fused sit opens releasing the contents of the secretory vesicle

Module 2.5- Biological Membranes (1 decks)

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