Membrane Transport Flashcards
Polar
Any molecule carrying charge or having an unequal distribution of electrons
Hydrophilic and lipophobic
Ex. Water, ions, carbs
Can’t diffuse across the membrane
Fluid mosaic model
Reflects the allowable movement of proteins within the phospholipid bilayer
Amphipathic
Half polar, half non polar,
Non polar
They are hydrophobic and lipophillic
Can diffuse across the membrane
Brownian motion
Says molecules are moving in random patterns, as they move they bump into each other and then move apart (they bounce off of each other )
Over time they will spread as far apart as possible
Dynamic equilibrium
Diffusion will continue until this is reached
At this point there is no NET shift in movement, but the molecules are still constantly moving ( in both directions)
Diffusion
Is passive (requires no energy) Molecules move down the concentration gradient Continues until dynamic equilibrium is reached Occurs faster when: -larger conc. gradient -smaller distance -higher temp. -smaller molecules
Molecules the membrane is permeable to
O2, CO2, lipids, small non polar molecules
Molecules the membrane is selectively permeable to
Ions, polar molecules, water, glucose, large molecules (most proteins)
These need help (sometimes energy) to get across the membrane
Passive transport
Movement must be with the concentration gradient
Can be simple (diffuse freely across membrane) or mediated (uses channels or carrier proteins)
Simple diffusion
Type of passive transport
Non polar molecules (lipids and steroids) can cross the membrane
Rate depends on solubility of the molecule in lipids
Rate is proportional to the surface area and conc. gradient
Rate is inversely proportional to the thickness of the membrane
Cell can not control this movement
Permeability follows ficks law
Ficks law
Determines rate of effusion
- more surface area = faster rate if diffusion
- bigger conc. gradient = faster rate of diffusion
- increased permeability = faster rate of diffusion
- increased membrane thickness= slower rate of diffusion
Protein channels
Assist in mediated diffusion- still has to go in direction of conc. gradient
Are made of several subunits, are polar on the inside to allow polar molecules to diffuse
Channels are close able- so they are selectively permeable
Are usually gated, so have a trigger causing it to open
Carriers or pumps
Assist with mediated transport and active transport
Can open to outside of the cell, then change conformation to allow the molecule to enter the inside of the cell
Can be controlled by closing, or fully pinching the membrane and removing the protein front the membrane
Specific to a molecule
Can move with conc. gradient or against them ( if energy is provided)
Chemically gated channels
Specific molecules bind and cause the channel to open/close
Neurons, muscle cells, smell and taste receptors
Voltage gated channels
Electrical state of the membrane opens or closes the channel
Neurons, muscle cells
Mechanically gated channels
Physical force opens or closes the channel
Touch receptors
Time gated channel
A specific unit if time passes before they change configuration
Heart muscle cells
Light gated channel
Change configuration based on exposure to photons of light
In retina, photoreceptors cells
3 properties of mediated transport
Specificity, saturation, competition
Active transport
Moves against conc. gradient
Requires cellular energy
Creates disequilibrium
Exhibit competition, saturation, specificity and are limited by amount of energy
Primary active transport
Uses ATP as energy source
Transporter protein = ATPase, this breaks down ATP to ADP and P, the protein is phosphorylation and undergoes a conformational change which allows the molecule to be transported
Secondary active transport
Uses an electrochemical gradient as energy source
The movement of an ion down its concentration gradient is used to move another molecule with it
Na/k pump
3 na out, 2 k in
Uses ATP
Creates both chemical and electrical disequilibrium – creates potential energy that can be used later via secondary transport
Osmosis
Diffusion of water, it moves across a semi permeable membrane in response to a conc. gradient
Moves from a higher [water] to a lower [water], aka water moves from a lower [solute] to a higher [solute]
Osmolarity
The number of particles in a solution– how much osmotic pressure it creates
Different from molarity because it takes dissociation into account. Ex 1M nacl is 2in osmolarirty
Tonicity
Is the relative osmolarity of a solution surrounding a cell.
It describes the changes in cell volume if a cell is placed in a solution.
Is determined by the permeability of the solutes
- if solute can penetrate the membrane, it will move so no net water movement and no volume change
- if solute can’t penetrate, the water will move by osmosis
Can urea penetrate the membrane? Can glucose?
Urea can- is lipophillic
Glucose can slowly with the help of carriers
Crenate
To shrink/shrivel ( if outside has a higher [solute]
Hemolysis
When red blood cells swell and burst due to tonicity
What happens if you put a cell in a concentrated saline solution?
Is it permeating? No
The cell shrinks
What happens if you put a cell in distiller water?
Water rushes in, the cell swells
What happens if you put a cell in a high urea solution?
Is it permeating? Yes
The urea will move, no change in cell size
Phagocytosis
Rids the extra cellular space of unwanted material. Involves digestion
Ligand
Something that binds to a receptor
Cytokines
A chemical used for communication. More for local communication, rarely travels in bloodstream
Hormone
A chemical secreted into the blood stream, used for communication. Is systemic. In the blood stream
Systemic
All over the body
Endogenous
Coming from within
Exogenous
Coming from outside
Electrical signals
Changes in ion concentrations
Chemical signals
Chemicals are secreted into the extra cellular fluid
Gap junctions
Method of cell to cell communication.
Two neighboring cells join plasma membranes and share interstitial fluid
Contact dependent signals
Molecules on the surface of one cell interact with molecules on the surface of another. The cells must be physically close
Involves a receptor and ligand
Binding of ligand triggers intercellular changes
Local communication
One cell secretes a chemical into the ECF and it is detected by receptors on neighboring cells
Example. Scrape on arm, histamine is released, but only locally
Autocrine
One cell secretes a substance and activates itself
Paracrine
One cell secretes a substance to activate the cells around it
Long distance communication
Electrical, chemical or both.
Can only be carried out by certain cell types
- endocrine cells: secrete chemicals into blood stream. Can have effects all over the body, on cells that have receptors
-nervous system: achieves communication by changing ion conc. in and out of a cell, para cringe signaling between one cell and another
Long distance communication endocrine example
Breast tissue has receptors for estrogen.
Estrogen triggers breast cell reproduction, tissue growth and Oreo for lactation
If patients are given estrogen after menopause it still triggers these responses and can cause breast cancer
Long distance communication nervous system example
Electronic signal travels down an axon, reaches the end and triggers the release if a chemical into a synapse with another cell. The chemical binds to receptor on the next cell and triggers a response
Cytokines
Usually work in short distances, are less specific
Work on many cell types
Made on demand
Differences between cytokines and hormones
They work on many cell types and are made on demand, are not stored,
Cytokine storm
In rare cases systemic cytokines secretion can lead to severe disease or death
Some cytokines work on a positive feedback loop, once you get above threshold the positive feedback loop rages out of control and leads to severe inflammations
Happens in sepsis, SARS,
Lipophillic ligands
Bind to intracellular receptors
Are slow acting ( over an hour)
Usually turn on gene transcription or proteins synthesis (actions that happen within ht nucleus)
Lipophobic ligands
Bind to membrane receptors
Very fast– within seconds
Usually change ion flow or intracellular responses
Lipophillic ligand
Receptor location/cellular action?
Cytosol, protein synthesis
Or nucleus, gene transcription
Lipophobic ligand
Receptor location/cellular action?
Membrane, ion permeability or other cellular changes
Receptors can be…
Transcription factors, kinases that trigger signaling cascades, ion channels, water channels, enzymes
Kinase
Catalyzes transfer of phosphate from ATP to a protein. Changes protein shape, can alter signaling and function. Molecular change means molecular function change.
Down regulation
A decrease in the number or sensitivity of receptors in response to a high concentration of ligand over time
Ex type II diabetes
Up regulation
An increase in the number or sensitivity orpf receptors in response to a low concentration of ligand. This increases the sensitivity of the cell.
Ex low levels of a hormone, also a treatment for diabetes.
How to stop a signaling pathway
Remove the signal, remove the receptor
Ways to remove the signal
Extra cellular: have enzymes that degrade the signal in the ECF
Intracellular: have pumps that sequester the intracellular signal
Agonists
Excites, mimic signal molecules and cause action.
Ex. Artificial estrogen in birth control
Antagonists
Inhibitors, block receptor and signal blockers.
Ex beta blockers to control high blood pressure.
Functional Unit
The smallest portion of a whole that is capable of carrying out the entire function.
4 types of tissues
epithelial, nervous, muscle, connective
What % of body is water?
55-60
How much is intracellular? extracellular?
2/3 intra, 1/3 extra
What % of ECF is plasma?
20-25%
