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Cell Membrane Flashcards

1
Q

Why is cell membrane described as ‘fluid mosaic’ model ?

A

Fluid - ability of the phospholipids and proteins in the cell membrane to move laterally within each layer

Mosaic - patchwork distribution of proteins within the phospholipid bilayer

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2
Q

What kind of molecules make up the phospholipid membrane ?

A

Phospholipids
Proteins
Cholesterol
Carbs - only extend from exterior surface of cell surface membrane

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3
Q

Are the two sides of the phospholipid bilayer symmetrical ?

A

No, may differ in lipid and protein composition

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4
Q

What are the two main interactions present to help stabilise the cell surface membrane ?

A

Hydrophobic interactions
Hydrophilic interactions

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5
Q

Hydrophobic interactions are formed between … in cell membrane

A

Hydrophobic portion of proteins and hydrocarbon tails of phospholipids

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6
Q

Hydrophilic interaction are formed between … in cell membrane

A

Hydrophilic portions of proteins and phosphate group of phospholipids, the aqueous medium of the cytoplasm and outside the cell

Carbohydrate antennae and aqueous medium outside the cell

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7
Q

What are the five roles of cell membrane ?

A
  1. Act as barrier
  2. Regulate passage of substances
  3. Allows cell to communicate with external env
  4. Maintain structural relations with neighbouring cells
  5. Allows for compartmentalisation (within cell)
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8
Q

Why does cell membrane acting as a barrier between cell contents and external environment important ?

A

Allows cell to exist as an entity separated from env
Enables cell to maintain constant env within cell

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9
Q

How does cell membrane allow cell to communicate with external environment ?

A

Cell membranes contain receptors and enzymes that allow the cells to respond to chemical messengers
Glycoproteins and glycolipids can also act as recognition sites for cell to cell recognition for immune response

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10
Q

What are structural relationships between cells

A

Cell to cell adhesion for tissue formation

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11
Q

Why is compartmentalisation in cells important ?

A

Allows formation of organelles, setting up of different conditions to provide optimum conditions for enzymes to work
Membrane bound organelles allow for structural adaptations

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12
Q

How are phospholipids arranged in cell membrane ?

A

Arranged in bilayer due to amphipathic nature with polar phosphate heads interacting with aqueous medium and hydrophobic hydrocarbon tails facing the inside

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13
Q

Where are cholesterol found in cell membrane ?

A

Fits between the phospholipid molecules with hydrophobic hydroxyl groups interacting with hydrophilic heads of phospholipids while hydrophobic portion fits between the FA hydrocarbon tails

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14
Q

Which part of cholesterol is hydrophilic ?

A

The hydroxyl group

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15
Q

What are the two kinds of membrane proteins?

A

Peripheral/extrinsic proteins
Integral/intrinsic proteins

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16
Q

Where are peripheral proteins found ?

A

Loosely attached at the polar surfaces of the phospholipids or proteins
Found on both interior and exterior of cell

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17
Q

What are the two types of integral proteins ?

A

Proteins that either partially penetrate membrane or span the entire membrane

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18
Q

What are proteins that span the entire membrane called ?

A

Transmembrane proteins

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19
Q

Where are carbohydrates found in cell membrane ?

A

Attached to proteins to form glycoproteins or attached to lipids to form glycolipids

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20
Q

What are the functions of phospholipid in cell membrane ?

A
  1. Constitutes basic bilayer structure - orientation of phosphate head and hydrocarbon tails ensure stability of membrane
  2. Separates cell contents from surrounding, allows for compartmentalisation
  3. Allows only some specific molecules to pass through
  4. Provides fluidity to membrane
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21
Q

What molecules are allowed to pass through phospholipid bilayer and what are not ?

A

Fat-soluble substances and small molecules
Barrier against most water-soluble molecules and ions due to hydrophobic core

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22
Q

Why is fluidity of phospholipid bilayer important ?

A

Important for self repair / sealing and fusion of transport vesicles to organelles or cell surface membrane`

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23
Q

What are the three functions of cholesterol ?

A

Mechanical stability
Maintain membrane fluidity
Reduce uncontrolled leakage

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24
Q

Why does cholesterol give mechanical stability to membrane ?

A

Membranes without cholesterol tend to break easily

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25
When does cholesterol maintain fluidity of membrane ?
At Low temperatures, cholesterol increase fluidity At high temperatures, it decreases fluidity
26
How does cholesterol reduce uncontrolled leakage of the cell membrane ?
Divert certain polar molecules and ions to proper channels where their movement can be properly regulated instead of diffusing through the membrane
27
What is the function of transport proteins ?
Allow water-soluble ions, glucose, AA and proteins to be transported into or out of the cells as these molecules cannot diffuse through the hydrophobic core of the cell membrane
28
What are some types of transport proteins ?
Channel proteins Carrier proteins Protein pump
29
What is the function of an energy transducer (protein), with reference to specific examples ?
Electron carriers and ATP synthase allow the transport of electrons and protons respectively during respiration and photosynthesis for ATP synthesis
30
What is the function of cell surface receptor ?
Act as receptor, binding with chemicals allowing cells to respond to external stimuli
31
What are the 5 functions of membrane proteins ?
1. Transport 2. Energy transducer 3. Cell surface receptor 4. Enzymes 5. Structural support
32
What are the 3 functions of carbohydrates in cell membrane ?
1. Orientation of the membrane structures 2. Cell communication 3. Structural relationships
33
How do carbohydrates help with orientation of membrane structures ?
Carbs are highly hydrophilic and helo orientate glycoproteins and glycolipids to face the exterior It also forms H bond with water and thereby stabilising the membrane structures
34
How do carbs allow cell communication ?
Carbs are involved in a variety of physiological phenomenon like recognition of the same cell type for immune response - cell to cell recognition
35
How do carbs allow for structural relationships between cells ?
Carbs act as glue for adhesion of cells to neighbouring cells for tissue formation - cell to cell adhesion
36
Why is fluidity of membrane important ?
Allows membrane to fuse which is important for self repair / sealing and fusion of transport vesicles to organelles or cell surface membrane Allows for ease of binding of metabolites and hormones to surface receptors Allows for activity of membrane-bound enzymes and transport enzymes
37
What will decrease in membrane fluidity result in ?
Decreased ability of membrane to fuse Inactivation of membrane-bound enzymes and transport proteins resulting in reduction in membrane permeability
38
What factors affect fluidity of membrane ?
Temperature Length of hydrocarbon tails of phospholipids Degree of saturation of hydrocarbon chains of phospholipid Presence of cholesterol
39
How does temperature affect fluidity of membrane ?
As temperature increases membrane becomes more fluid as kinetic energy of phospholipids increase. This results in breaking of the intermolecular interaction and bonds between its components
40
How does length of hydrocarbon tail of phospholipids affect fluidity of membrane ?
As length increases, fluidity decreases as there is more intermolecular interaction between te hydrocarbon tails and vice versa
41
How does degree of saturation of hydrocarbon chains of phospholipids affect fluidity of membrane ?
The more unsaturated (C=C leading to kinks in the straight chains) the hydrocarbon chains are, the more fluid the membrane is. This is because the unsaturated hydrocarbon chains have kinks which prevent the packing of the phospholipids resulting in weaker intermolecular interaction between the chains
42
How does the presence of cholesterol affect fluidity ?
Cholesterol acts as buffer against resisting changes caused by changes in temperature At Low temperatures, cholesterol increases fluidity by disrupting the close packaging of phospholipids thus lowering the temperature at which the membrane solidifies At high temperatures, cholesterol decreases fluidity as it hinders movement of phospholipids by interacting with the hydrocarbon tails
43
What are the five methods used to transport substances across the cell surface membrane ?
Simple diffusion Facilitated diffusion Active transport Bulk transport Osmosis
44
What is simple diffusion?
Net movement of molecules of any substance from a region of higher concentration to a region of lower concentration, down a concentration gradient until equilibrium is achieved
45
Does simple diffusion require energy ?
No it does not require expenditure of energy by cell thus will occur readily in living and non-living systems
46
What type of substances enter cell through simple diffusion ?
Small, non-polar or hydrophobic substances
47
What is facilitated diffusion ?
Net movement of particles down a concentration gradient through protein molecules
48
Is energy required for facilitated diffusion ?
No
49
Compare simple and facilitated diffusion
Both : Net movement of particles down concentration gradient Does not require energy from cell Differs : Simple does not require membrane proteins, facilitated requires
50
Why does facilitated diffusion require transport proteins ?
Charged particles and polar molecules do not readily pass through the plasma membrane as they are insoluble in lipids, cannot pass through the hydrophobic core of phospholipid bilayer Transport proteins allow passage into cell, shielding them from the hydrophobic core of the membrane
51
What are the two types of transport proteins ?
Channel protein Carrier protein
52
How does facilitated diffusion occur through channel proteins ?
Channel proteins forms a water-filled pore in the membrane. Unlike the hydrophobic core of the plasma membrane, the lining of the channel protein is hydrophilic so water-soluble substances can pass through
53
When do gated channel proteins open ?
When they receive appropriate signal
54
How does carrier protein work ?
Each type of carrier protein has one or more binding sites for specific solute Solute is transported across the membrane through conformational change of the protein
55
What are the two forms that a carrier protein exists in ?
One where the binding site for the solute is exposed to one side of the cell and another where the same binding site is exposed to the other side of the cell
56
What are the characteristics of transport proteins ?
Are specific - can only transport one type of substance Can be saturated - only a certain number of each type present Can be inhibited - competitive inhibition of structurally similar molecules
57
When is the max rate of facilitated diffusion reached ?
When all transport proteins are being utilised for the transport of substances
58
What is osmosis ?
Net movement of water molecules from a region of higher water potential to a region of lower water potential through a selectively permeable membrane
59
What are the two routes which water takes to enter the cell ?
Moving though lipid bilayer Through water channels called aquaporins
60
Can water enter cell through simple diffusion?
Yes due to its small size but is limited due to polar nature of water
61
What are aquaporins ?
Integral membrane proteins that form pores in the membrane of biological cells
62
Why are aquaporins important ?
Important for the bulk flow of water across the cell membrane
63
What is active transport ?
Movement of ions or molecules across a membrane from a region of lower concentration to a regions of higher concentration, against concentration gradient, by means of specific transport proteins with the expenditure of energy by the cell
64
Why is active transport important ?
Allow cells to take up nutrients even when their concentration outside cells are lower than those inside cell Enables cell to get rid of waste products when their concentration outside cells are higher than those inside cell
65
How does active transport differ from facilitated diffusion ?
Carrier proteins for active transport can bind with their molecules on one side of the membrane only which carrier proteins in facilitated diffusion can bind to specific molecules or ions on both sides Conformation changes in carrier protein for active transport requires input of energy
66
What substances does bulk transport transport across membrane ?
Substances that are too large to cross the membrane via transport proteins
67
What is bulk transport ?
The transport of material into or out of the cell by enclosing the material within a fluid-filled membrane-bound sac called a vesicle
68
What are the two types of bulk transport ?
Exocytosis Endocytosis
69
What is Exocytosis ?
Release of materials to the outside of the cell
70
What is endocytosis ?
Materials are taken into cells
71
What occurs during Exocytosis ?
Vesicles pinched off from the GA moves towards the cell surface membrane and fuses with it. The vesicle then opens to the exterior and its contents leave the cell
72
What ate the three types of endocytosis ?
Pinocytosis Phagocytosis Receptor-mediated endocytosis
73
What occurs during pinocytosis ?
Cell takes up droplets of extracellular fluid in tiny vesicles
74
Is pinocytosis selective ?
No Any solutes dissolved in the droplets are taken into cell
75
How does phagocytosis occur ?
Cell engulfs large particles by sending out pseudopodia to surround the particle The ends of the pseudopodia then join, resulting in formation of food vacuole, phagosome, within cell Lysosome then fuses with phagosome and hydrolytic enzymes will digest the large particles
76
What occurs in receptor-mediated endocytosis ?
Extracellular macromolecules bind to cell surface receptor proteins embedded in the cell surface membrane Proteins (clathrin) form a coated pit at teh cytoplasmic side which helps in the formation of a coated vesicle within the cytoplasm Once vesicle is formed within the cytoplasm, clathrin will disassemble and be recycled
77
What substances is taken into cell through receptor-mediated endocytosis ?
Allows cell to take up large quantities of specific substances even though the substances may not be very concentrated in the extracellular environment
78
What is pseudopodia ?
Extensions of the cytoplasm

bio (23 decks)

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