1.4 Membrane Transport Flashcards
1
Q
What are the two key qualities of cellular membranes?
A
They are semi permeable and selective
2
Q
What is semi permeable?
A
Only certain materials may freely cross
3
Q
What is selective?
A
Membrane proteins may regulate the passage of materials that cannot freely cross
4
Q
What are the two different categories of transport across a membrane?
A
Passive and active
5
Q
What is passive transport?
A
The movement of material along a concentration gradient
(high conc to low conc)
6
Q
Why does passive transport not require the expenditure of energy?
A
Because materials are moving down a conc gradient
7
Q
Does passive transport need the expenditure of energy?
A
No
8
Q
What are the three types of passive transport?
A
Simple diffusion
Osmosis
Facilitated diffusion
9
Q
What is active transport?
A
The movement of materials against a conc gradient using energy
(low conc to high conc)
10
Q
Why does active transport need the expenditure of energy?
A
Because materials are moving against the gradient
11
Q
Does active transport need the expenditure of energy?
A
Yes
12
Q
What are the two main types of active transport?
A
Primary direct active transport
Secondary indirect active transport
13
Q
What is diffusion?
A
The net movement of molecules from a region of high conc to a region of low conc
14
Q
What type of transport is diffusion?
A
Passive
15
Q
When will diffusion continue up until?
A
Until molecules become evenly dispersed
16
Q
What will be able to freely diffuse across cell membranes?
A
Small and non polar molecules
17
Q
What are the free factors that can affect the rate of diffusion?
A
Temperature
Molecular size
Steepness of gradient
18
Q
How does temperature affect the rate of diffusion?
A
Affects kinetic energy of particles in solution
19
Q
How does molecular size affect rate of diffusion?
A
Larger particles are subjected to greater resistance within a fluid medium
20
Q
How does the steepness of gradient affect the rate of diffusion?
A
The rate of diffusion will be greater with a higher conc gradient
21
Q
What is osmosis?
A
The net movement of water molecules across a semi permeable membrane from an area of low solute conce to an area of high solute conc until equilibrium is reached
22
Q
What is water considered to be?
A
The universal solute
23
Q
Why is water considered to be the universal solute?
A
It will associate with and dissolve polar or charged molecules
24
Q
Why must water move to equalise the two solutions?
A
Because solutes cannot cross a cell membrane unaided
25
When is there less free water molecules in solution?
At a higher solute concentration
26
Why is there less free water molecules in solution at a higher solute conc?
As water is associated with the solute
27
What is osmolarity?
A measure of solute concentration
28
What is the measurement of osmolarity?
osmol/L
29
What are the three categories of solution in accordance to their relative osmolarity?
Hypertonic
Hypotonic
Isotonic
30
What is a hypertonic solution?
Solutions with a relatively higher osmolarity
Gains water
31
What is a hypotonic solution?
Solutions with a relatively lower osmolarity
Loses water
32
What is an isotonic solution?
Solutions that have the same osmolarity
No net water flow
33
How can the osmolarity of a tissue be interpolated?
By bathing the sample in solutions with known osmolarities
34
How can you determine water loss or gain of a sample?
Weighing it before and after bathing in a solution
35
Why must tissues or organs used in medical procedures be kept in solution?
To prevent cellular dessication
36
For organs/tissues used in medical procedures why must the solution be the same osmolarity?
To prevent osmosis from happening
37
What happens to animal cells if left in hypertonic solutions?
Water will leave the cell causing it to shrivel
38
What happens to the animal cell left in a hypotonic solution?
Water will enter the cell causing it to swell and burst (lysis)
39
What moderates the effects of uncontrolled osmosis?
An inflexible cell wall
40
What happens to plant cells in hypertonic solutions?
Plasmolysis (shrink) in cytoplasm but cell wall will maintain a structured shape
41
What will happen to plant cells in a hypotonic solution?
The cytoplasm will expand but within the constraints of the cell wall
42
What are the three effects of solutions on animal cells?
Shriveled
Normal
Lysed
43
What are the three effects of solutions on plant cells?
Plasmolysed
Flaccid
Turgid
44
What is facilitated diffusion?
The passive movement of molecules across the cell membrane via the aid of a membrane protein
45
What molecules utilise facilitated diffusion?
Molecules that are unable to freely cross the phospholipid bilayer
46
What are the two types of proteins in facilitated diffusion?
Channel proteins and carrier proteins
47
What are carrier proteins?
Integral glycoproteins which bind to a solute and undergo a conformational change to translocate a solute across a membrane
48
What do carrier proteins bind to?
Only a specific molecule
49
How do carrier proteins attach to their molecules?
Via an attachment similar to an enzyme substrate interaction
50
What may carrier proteins do in the presence of ATP?
Move molecules against concentration gradients
51
Out of carrier and channel proteins which one has a faster rate of transport?
Channel proteins
52
What are channel proteins?
Integral lipoproteins that have a pore which ions may cross from one side of the membrane to the other
53
What are channel proteins selective about?
Ions
54
Why may channel proteins be gated?
To regulate the passage of ions in response to certain stimuli
55
Can you use channel proteins in active transport?
No only passive transport
56
Can you use carrier proteins in active transport?
Yes
57
How do axons of nerve cells transmit electrical impulses?
By translocating ions to create a voltage difference across the membrane
58
What does the sodium potassium pump do when the neuron is at rest?
Expels sodium ions from the nerve cell whilst potassium ions are accumulated within
59
What happens to the ions when the neuron fires?
They swap locations via facilitated diffusion via sodium and potassium channels
60
What are potassium channels?
Integral proteins with a hydrophilic inner pore via which potassium ions can be transported
61
What is the potassium channel comprised of?
Four transmembrane subunits
62
What does the inner pore of the potassium channels contain and what does it do?
A selectivity filter at its narrowest region which restricts passage of alternative ions
63
What are potassium channels typically?
Voltage gated
64
What do potassium channels do depending on the the transmembrane voltage?
Cycle between an opened and closed conformation
65
How may the energy used in active transport be generated?
The direct hydrolysis of ATP
Indirectly coupling transport with another molecule that is moving along its gradient
66
Apart from energy what does active transport involve?
The use of carrier proteins aka protein pumps
67
In active transport what does a specific solute bind to?
The protein pump on one side of the membrane
68
What causes a conformational change in the carrier protein?
The hydrolysis of ATP
69
What is the final step of active transport?
The solute molecule is translocated across the membrane and is released
70
What is the sodium potassium pump?
An integral protein that exchanges 3 sodium ions with two potassium ions
71
In the sodium potassium pump, Where do the three sodium ions move to?
Out of the cell
72
In the sodium potassium pump, Where do the two potassium ions move to?
Inside the cell
73
In the sodium potassium pump, What is the process of potassium and sodium ion exchange dependent on?
Energy
74
In the sodium potassium pump, Where do the sodium ions bind to?
The intracellular sites on the sodium potassium pump
75
In the sodium potassium pump, What is transferred to the pump?
A phosphate group
76
In the sodium potassium pump, How is a phosphate group transferred to the pump?
Via the hydrolysis of ATP
77
In the sodium potassium pump, How is the sodium translocated across the membrane?
The pump undergoes a conformational change
78
In the sodium potassium pump, What does the conformational change of the pump expose?
Two potassium binding sites on the extracellular surface of the pump
79
In the sodium potassium pump, What happens when the phosphate group is released?
The pump returns to its original conformation
80
In the sodium potassium pump, what happens when the pump returns to its original conformation?
The potassium is translocated across the membrane completing ion exchange
81
What are vesicles?
Membranous containers which materials destined for secretion are transported around the cell in
82
What is the endoplasmic reticulum?
A membranous network responsible for synthesising secretory materials
83
What does the Rough ER do?
Synthesises proteins destined for extracellular use
84
What is the rough ER embedded with?
Ribosomes
85
What is the smooth ER involved with?
Lipid synthesis and carbohydrate metabolism
86
When are materials transported from the ER?
When the membrane bulges
87
What happens after the membrane bulges?
It buds to create a vesicle surrounding the material
88
Where does the vesicle go after the ER?
The golgi apparatus
89
Where does the vesicle fuse onto the golgi apparatus?
The internal cis face of the complex
90
Where do materials move from and to in the golgi apparatus?
From the internal cis face of the golgi to the externally oriented trans face
91
What moves materials in the golgi apparatus?
Vesicles
92
What can happen to materials whilst within the golgi apparatus?
They may be structurally modified
93
What happens to the material that has been sorted within the golgi apparatus?
Either secreted externally or transported to the lysosome
94
Where will vesicles containing materials destined for extracellular use be transported to?
The plasma membrane
95
Where will the vesicle fuse after being expelled by the golgi apparatus?
To the cell membrane
96
What will happen to the materials within the vesicles after the golgi apparatus?
Expelled into the extracellular fluid
97
What is constitutive secretion?
Released immediately into the extracellular fluid
98
What is regulatory secretion?
Stored within an intracellular vesicle for a delayed release in response to a cellular signal
99
What principally holds the membrane together?
Weak hydrophobic associations between the fatty acid tails of phospholipids
100
What allows for larger materials to enter or leave the cell without having to cross the membrane?
The spontaneous breaking and reforming of the bilayer
101
What type of process is the spontaneous breaking and reforming of the bilayer?
An active process which needs ATP hydrolysis
102
What is endocytosis?
The process by which large substances enter the cell without crossing the membrane
103
What envelopes the extracellular material in endocytosis?
An invagination of the membrane which forms a flask like depression
104
What happens once the extracellular material is enveloped in endocytosis?
The invagination is sealed off to form an intracellular vesicle
105
What are the two types of endocytosis?
Phagocytosis and Pinocytosis
106
What is phagocytosis?
The process by which solid substances are ingested
107
Where are the products of phagocytosis usually transported to ?
The lysosome
108
What is pinocytosis?
The process by which liquids/dissolved substances are ingested
109
Why is pinocytosis better than protein channels?
It allows faster entry
110
What is exocytosis?
The process by which large substances exit the cell without crossing the membrane
111
What does the process of exocytosis add to the cell membrane?
Vesicular phospholipids
112
Why are vesicular phospholipids added to the membrane in exocytosis?
To replace those lost when vesicles were formed during endocytosis
113
What is the main way of exocytosis?
Vesicles that fuse with the cell membrane to expel contents into the extracellular environment
