1.4 Membrane Transport Flashcards
What are the two key qualities of cellular membranes?
They are semi permeable and selective
What is semi permeable?
Only certain materials may freely cross
What is selective?
Membrane proteins may regulate the passage of materials that cannot freely cross
What are the two different categories of transport across a membrane?
Passive and active
What is passive transport?
The movement of material along a concentration gradient
(high conc to low conc)
Why does passive transport not require the expenditure of energy?
Because materials are moving down a conc gradient
Does passive transport need the expenditure of energy?
No
What are the three types of passive transport?
Simple diffusion
Osmosis
Facilitated diffusion
What is active transport?
The movement of materials against a conc gradient using energy
(low conc to high conc)
Why does active transport need the expenditure of energy?
Because materials are moving against the gradient
Does active transport need the expenditure of energy?
Yes
What are the two main types of active transport?
Primary direct active transport
Secondary indirect active transport
What is diffusion?
The net movement of molecules from a region of high conc to a region of low conc
What type of transport is diffusion?
Passive
When will diffusion continue up until?
Until molecules become evenly dispersed
What will be able to freely diffuse across cell membranes?
Small and non polar molecules
What are the free factors that can affect the rate of diffusion?
Temperature
Molecular size
Steepness of gradient
How does temperature affect the rate of diffusion?
Affects kinetic energy of particles in solution
How does molecular size affect rate of diffusion?
Larger particles are subjected to greater resistance within a fluid medium
How does the steepness of gradient affect the rate of diffusion?
The rate of diffusion will be greater with a higher conc gradient
What is osmosis?
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
What is water considered to be?
The universal solute
Why is water considered to be the universal solute?
It will associate with and dissolve polar or charged molecules
Why must water move to equalise the two solutions?
Because solutes cannot cross a cell membrane unaided
When is there less free water molecules in solution?
At a higher solute concentration
Why is there less free water molecules in solution at a higher solute conc?
As water is associated with the solute
What is osmolarity?
A measure of solute concentration
What is the measurement of osmolarity?
osmol/L
What are the three categories of solution in accordance to their relative osmolarity?
Hypertonic
Hypotonic
Isotonic
What is a hypertonic solution?
Solutions with a relatively higher osmolarity
Gains water
What is a hypotonic solution?
Solutions with a relatively lower osmolarity
Loses water
What is an isotonic solution?
Solutions that have the same osmolarity
No net water flow
How can the osmolarity of a tissue be interpolated?
By bathing the sample in solutions with known osmolarities
How can you determine water loss or gain of a sample?
Weighing it before and after bathing in a solution
Why must tissues or organs used in medical procedures be kept in solution?
To prevent cellular dessication
For organs/tissues used in medical procedures why must the solution be the same osmolarity?
To prevent osmosis from happening
What happens to animal cells if left in hypertonic solutions?
Water will leave the cell causing it to shrivel
What happens to the animal cell left in a hypotonic solution?
Water will enter the cell causing it to swell and burst (lysis)
What moderates the effects of uncontrolled osmosis?
An inflexible cell wall
What happens to plant cells in hypertonic solutions?
Plasmolysis (shrink) in cytoplasm but cell wall will maintain a structured shape
What will happen to plant cells in a hypotonic solution?
The cytoplasm will expand but within the constraints of the cell wall
What are the three effects of solutions on animal cells?
Shriveled
Normal
Lysed
What are the three effects of solutions on plant cells?
Plasmolysed
Flaccid
Turgid
What is facilitated diffusion?
The passive movement of molecules across the cell membrane via the aid of a membrane protein
What molecules utilise facilitated diffusion?
Molecules that are unable to freely cross the phospholipid bilayer
What are the two types of proteins in facilitated diffusion?
Channel proteins and carrier proteins
What are carrier proteins?
Integral glycoproteins which bind to a solute and undergo a conformational change to translocate a solute across a membrane
What do carrier proteins bind to?
Only a specific molecule
How do carrier proteins attach to their molecules?
Via an attachment similar to an enzyme substrate interaction
What may carrier proteins do in the presence of ATP?
Move molecules against concentration gradients
Out of carrier and channel proteins which one has a faster rate of transport?
Channel proteins
What are channel proteins?
Integral lipoproteins that have a pore which ions may cross from one side of the membrane to the other
What are channel proteins selective about?
Ions
Why may channel proteins be gated?
To regulate the passage of ions in response to certain stimuli
Can you use channel proteins in active transport?
No only passive transport
Can you use carrier proteins in active transport?
Yes
How do axons of nerve cells transmit electrical impulses?
By translocating ions to create a voltage difference across the membrane
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
What happens to the ions when the neuron fires?
They swap locations via facilitated diffusion via sodium and potassium channels
What are potassium channels?
Integral proteins with a hydrophilic inner pore via which potassium ions can be transported
What is the potassium channel comprised of?
Four transmembrane subunits
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
What are potassium channels typically?
Voltage gated
What do potassium channels do depending on the the transmembrane voltage?
Cycle between an opened and closed conformation
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
Apart from energy what does active transport involve?
The use of carrier proteins aka protein pumps
In active transport what does a specific solute bind to?
The protein pump on one side of the membrane
What causes a conformational change in the carrier protein?
The hydrolysis of ATP
What is the final step of active transport?
The solute molecule is translocated across the membrane and is released
What is the sodium potassium pump?
An integral protein that exchanges 3 sodium ions with two potassium ions
In the sodium potassium pump, Where do the three sodium ions move to?
Out of the cell
In the sodium potassium pump, Where do the two potassium ions move to?
Inside the cell
In the sodium potassium pump, What is the process of potassium and sodium ion exchange dependent on?
Energy
In the sodium potassium pump, Where do the sodium ions bind to?
The intracellular sites on the sodium potassium pump
In the sodium potassium pump, What is transferred to the pump?
A phosphate group
In the sodium potassium pump, How is a phosphate group transferred to the pump?
Via the hydrolysis of ATP
In the sodium potassium pump, How is the sodium translocated across the membrane?
The pump undergoes a conformational change
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
In the sodium potassium pump, What happens when the phosphate group is released?
The pump returns to its original conformation
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
What are vesicles?
Membranous containers which materials destined for secretion are transported around the cell in
What is the endoplasmic reticulum?
A membranous network responsible for synthesising secretory materials
What does the Rough ER do?
Synthesises proteins destined for extracellular use
What is the rough ER embedded with?
Ribosomes
What is the smooth ER involved with?
Lipid synthesis and carbohydrate metabolism
When are materials transported from the ER?
When the membrane bulges
What happens after the membrane bulges?
It buds to create a vesicle surrounding the material
Where does the vesicle go after the ER?
The golgi apparatus
Where does the vesicle fuse onto the golgi apparatus?
The internal cis face of the complex
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
What moves materials in the golgi apparatus?
Vesicles
What can happen to materials whilst within the golgi apparatus?
They may be structurally modified
What happens to the material that has been sorted within the golgi apparatus?
Either secreted externally or transported to the lysosome
Where will vesicles containing materials destined for extracellular use be transported to?
The plasma membrane
Where will the vesicle fuse after being expelled by the golgi apparatus?
To the cell membrane
What will happen to the materials within the vesicles after the golgi apparatus?
Expelled into the extracellular fluid
What is constitutive secretion?
Released immediately into the extracellular fluid
What is regulatory secretion?
Stored within an intracellular vesicle for a delayed release in response to a cellular signal
What principally holds the membrane together?
Weak hydrophobic associations between the fatty acid tails of phospholipids
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
What type of process is the spontaneous breaking and reforming of the bilayer?
An active process which needs ATP hydrolysis
What is endocytosis?
The process by which large substances enter the cell without crossing the membrane
What envelopes the extracellular material in endocytosis?
An invagination of the membrane which forms a flask like depression
What happens once the extracellular material is enveloped in endocytosis?
The invagination is sealed off to form an intracellular vesicle
What are the two types of endocytosis?
Phagocytosis and Pinocytosis
What is phagocytosis?
The process by which solid substances are ingested
Where are the products of phagocytosis usually transported to ?
The lysosome
What is pinocytosis?
The process by which liquids/dissolved substances are ingested
Why is pinocytosis better than protein channels?
It allows faster entry
What is exocytosis?
The process by which large substances exit the cell without crossing the membrane
What does the process of exocytosis add to the cell membrane?
Vesicular phospholipids
Why are vesicular phospholipids added to the membrane in exocytosis?
To replace those lost when vesicles were formed during endocytosis
What is the main way of exocytosis?
Vesicles that fuse with the cell membrane to expel contents into the extracellular environment
