Lecture 9: Cell Transport (part 1) Flashcards
What contributes to the permeability of the cell membrane?
both the lipid bilayer and the transporters present
What is selective permeability?
Some substances can penetrate the membrane while others cannot.
Do all cells have the same permeabilty?
no
What are the transport mechanisms for transport of substances in and out of the cell?
Membrane Transport
On which membrane transport mechanisms used depend on?
1) the physical properties of the substance
2) whether the process is spontaneous or non-spontaneous.
What are the three “levels” of the permeability of substances?
A. Can not cross the membrane at all.
B. Can cross the phospholipid bilayer directly.
C. Need help from transporters.
What are transporters?
transmembrane proteins
What do transporters do?
Help substances that can’t cross the phospholipid bilayer.
How specific are transporters?
- A transporter is specific for the substance(s) it allows to pass.
- Cells in the body will have different transporters leading to specific permeability characteristics.
What are the 5 types of membrane transport?
- Simple diffusion
- Facilitated diffusion
- Osmosis
- Active transport
- Bulk Transport
For Simple diffusion:
- Transport via?
- Energy required from cell?
- For which types of substances?
lipid bilayer
No
Small and/or hydrophobic (non-poplar)
For Facilitated diffusion:
- Transport via?
- Energy required from cell?
- For which types of substances?
transporters
No
Large and/or hydrophilic (polar), ions (charged atoms/molecules)
For Osmosis:
- Transport via?
- Energy required from cell?
- For which types of substances?
lipid bilayer (but mainly transporters)
No
Water
For Active transport:
- Transport via?
- Energy required from cell?
- For which types of substances?
transporters
Yes
Large and/or hydrophilic
For Bulk transport:
- Transport via?
- Energy required from cell?
- For which types of substances?
vesicles
Yes
Very large in large amounts
What are the two passive type of transport?
diffusion and osmosis
What is passive transport?
mechanisms used by the cell to transport substances across the membrane that don’t require energy.
Why can passive transport mechanisms not require energy?
they are driven by concentration gradients
What is a gradient?
What is a concentration gradient?
- A gradient is a gradual difference in a variable in one area compared to an adjacent area.
- A difference in solute concentrations in a solution creates a concentration gradient.
In biology, what areas have concentration gradients?
the inside and outside of the cell that are separated by the cell membrane.
Describe the motions of molecules:
_________ motion
_________ direction of motion
And collisions or the molecules:
*
*
constant motion
random direction of motion
And collisions of the molecules:
*Molecules can collide and bounce off each other and other matter which changes the direction of motion of these molecules
*Collisions influence the diffusion of substances.
If a concentration gradient exists, the net movement of a substance will proceed in which direction?
from the area of high concentration to low concentration.
Does diffusion stop?
*Diffusion will continue until there is no more concentration gradient producing equilibrium.
*In equilibrium, molecules are still moving randomly but there is no more net movement of the substance.
How do concentration gradients work in the presence of many substances?
Diffusion of a substance is based on its concentration gradient and not affected by another substance.
In cells does diffusion reach equilibrium?
In cells, diffusion may not reach equilibrium as cells are “open” and a concentration gradient can be maintained by cell activities.
What is diffusion rate?
By what factors can diffusion rate be affected?
(only know these 3)
- Temperature
- Size of the molecules
- The size of the concentration gradient
How do each of these factors affect the rate of diffusion?
1. Temperature
2. Size of the molecules
3. The size of the concentration gradient
think of how they increase the amount of collisions between molecules in a given time
1.Temperature: Increasing temperature generally increases the rate of diffusion.
Explanation: Higher temperatures lead to increased kinetic energy of molecules. As molecules move faster, they collide more frequently and with greater force
- Size of the Molecules: Smaller molecules tend to diffuse more rapidly than larger molecules.
Explanation: Smaller molecules have higher molecular speeds and can navigate the spaces between other molecules more easily.
- Size of the Concentration Gradient: A larger concentration gradient results in a faster rate of diffusion.
Explanation: The concentration gradient represents the difference in concentration between two regions. A steeper gradient means a more significant difference in concentration, providing a stronger driving force for molecules to move from an area of higher concentration to an area of lower concentration.
What are the two classes of transporters for facilitated diffusion?
A. Channels
B. Carriers
What are channels in term of structure and specific function? (what type of molecules do they carry)
- Channels have a structure that allows it to selectively admit a particular type of ion or small molecule passage through the plasma membrane.
- Some of these channels can be gated (regulated by doors that open when a particular stimulus is present).
What are gated channels?
Gated Channels open or close in response to a stimulus
What are the types of stimulus that open different gated channels?
chemical, electrical or mechanical stimuli
What type of molecules do carriers carry? What happens to they structure?
larger, hydrophilic molecules
These transporters change shape when binding glucose and releasing it during the transport process.
What is the relation between solute concentration (size of gradient) and the rate of transport?
an increase in solute concentration (larger gradient) increases the rate of transport.
Is facilitated diffusion or simple diffusion faster for the same solute concentration?
facilitated
Why does the curve hit a maximum rate for facilitated diffusion?
transporters can be saturated at high solute concentrations and the rate of transport can hit a maximum rate (plateau in graph).
What is osmosis?
movement of water across a semi-permeable membrane
By what is osmosis driven?
osmotic gradient
Water will also diffuse from an area of high concentration to an area of low concentration.
What is the relation between the concentration of the solute dissolved and water concentration?
they are inversely related
So, you can also say that water will diffuse towards the area with the higher solute concentration.
an what about the effective osmolarity?
it is 100% effective
There will be a net movement of water molecules to the compartment with the higher solute concentration.
When is the equilibrium of osmolarity reached?
when the concentrations of solutes in each compartment are equal.
What is the idea of “free water”?
The water that is not used to create hydration shell during osmosis
How is free water and solute concentration related?
they are inversely proportional
Which factors that affected the rate of diffusion would also affect the rate of osmosis?
- concentration gradient (osmosis gradient)
- size of the molecules (surface area)
- temperature (increase/decrease of kinetic energy)
What is the osmotic pressure of a solution?
the pressure that needs to be applied to stop the influx of water across the membrane.
How is the osmotic pressure of a solution related to its osmolarity?
They are directly proportional
What is osmolarity?
measure of the total solute particles (in osmoles) per unit volume.
How do ionic compounds affect osmolarity?
They dissociate into 2 or more particles, with each particle contributing to the osmolarity of the solution.
When is equilibrium established in osmosis?
once the two compartments have an equal concentration of solutes.
Does water move at equilibrium?
yes, they are still moving into each compartment but at equal rates and so there is no more net movement of water.
When does osmosis stop?
it will proceed until equilibrium is reached
Is osmosis reached in cells?
Unlike diffusion, in most cells, osmosis usually reaches equilibrium, so cells do not gain or lose water.
What is tonicity? What is it typically used for?
measure of the osmotic pressure of a solution in reference to a particular membrane.
What is tonicity typically used for?
to describe the ability of a surrounding solution to cause a cell to gain or lose water.
What are the three tonicities that a solution can be described as?
A. Isotonic
B. Hypertonic
C. Hypotonic
What does the tonicity of a solution depend on?
the effective osmolarity of a solution in respect to the inside of the cell
Which type of solutes contribute to a solution’s effective osmolarity and determines tonicity? How come?
only the solutes that cannot cross the membrane
- Only these solutes are locked in the compartment and can contribute to an osmotic gradient.
How does tonicity come into play in the study of RBC ghosts?
The use of a hypotonic solution with cells will cause them to burst and for their ghosts to be collected, purified and studied in detail
What are red blood cell ghosts?
simple membranes that can be purified and studied in detail.
How do we isolated membrane proteins?
Detergents can be used to get membrane proteins into solution and then separated by gel electrophoresis and purified for further study.
What is osmoregulation?
homeostatic mechanisms in organisms
(complex or simple) that maintain water balance.
How does osmoregulation work?
Requires regulation of osmotic pressure in cells and other body fluids by controlling solute concentration and/or water content.
Give an example of osmoregulation in humans
Some cells in the kidney can be regulated to allow osmosis so that water can be conserved and not excreted in urine.
Give an example of osmoregulation in protists
How does osmosis occur in cells? (by which “diffusion” method through membrane)
facilitated diffusion via water channels called aquaporins.
In which tonicity of solution are cells in the body in?
they are bathed in an isotonic solution.
In which tonicity of solution are cells in plants in?
hypotonic solution
Why do plant cells need to be in a hypotonic solution?
the osmotic pressure created by the osmotic gradient make the cells and tissues turgid (stiff) and provides support to help plant tissue to grow and stand upright.
How do you call the osmotic pressure in plants that allow them to stay upright?
turgor pressure
How do stomata open and close?
by changes in osmotic pressure:
when the guard cells are turgid, they are opened (C shaped)
When they are ‘deflated’ they close up
What is the function of stomata?
plant’s gas exchange
How are animal cells in a hypotonic solution? How is it called when they are in this condition?
they burst
How are animal cells in an isotonic solution? How is it called when they are in this condition?
they are properly shaped
How are animal cells in a hypertonic solution? How is it called when they are in this condition?
they shrink
How are plant cells in a hypotonic solution? How is it called when they are in this condition?
they are normal
How are plant cells in an isotonic solution? How is it called when they are in this condition?
they are a little bit shrinked
How are plant cells in a hypertonic solution? How is it called when they are in this condition?
they are very shrinked
What prevents a plant cell from bursting?
its cell wall
