Transport Mechanisms Flashcards
What is the cell membrane highly permeable to ?
-Water
-Lipid-soluble substances
-Dssovled gasses(O2, CO2)
-Small uncharged molecules
What is the cell membrane less permeable to ?
-Larger molecules
-Charged particles
What is the cell membrane impermeable to ?
-Very large molecules
Characteristics of the cell membrane?
- Phospholipid bilayer
- Amphipathic (polar and nonpolar ends)
What does the cholesterol in the phospholipid bilayer do?
At higher temps. = keeps the membrane more rigid
At lower temps. = keeps the mebrane fluid
-Helps form lipid rafts
-Helps form vesicles
Is cholesterol slightly amphipathic?
Yes
What types of proteins are found in the cell membrane?
Integral proteins - Imbedded within the cell membrane
ex. Transmembrane proteins : type of integral protein that spans the cell membrane
Peripheral - found on the outside of the cell membrane, attached to it but not integrated within it
What does glycocalyx do in the cell membrane and what is it made of?
Sugar coating that surrounds the cell membrane made up of glycans, glycoproteins and glycolipids (sugary molecules)
-Function: contributes to cell-cell recognition, communication, adhesion and protection. Helps control vascular permeability (at the endothelial cells)
Why is the cell membrane called the fluid mosaic model?
- Not a static structure
-Proteins are constantly being turned over
Name the 6 functions of plasma proteins?
- Channels/Transporters
- Amino acid transport/ Na-K pump
- Cell surface receptor
- Cell surface identity marker
5.Cell adhesion
6.Attachment to the cytoskeleton
Name the two ways to cross the cell membrane?
Via the phospholipid bilayer
Or via interaction with a transmembrane protein (channel/carrier)
What is passive transport vs Active?
Passive : energy independent
Active : Energy dependent
What are examples of passive transport?
- Diffusion
- Facilitated Diffusion
- Osmosis (water)
What are examples of active transport?
- Primary active transport
- Secondary active transport
- Pino/Phagocytosis
What is simple diffusion?
The movement of molecules from one location to another as a result of random thermal motion goes with the concentration gradient
What is flux?
Amount of particles crossing a surface per unit time
What is Net flux?
Movement from high to low concentration
At equilibrium what is flux and net flux?
-Net flux is zero
-Fluxes are equal
Net movement is zero but movement never stops molecules are always moving just equally in all directions
Why is diffusion only effective over short distances?
Diffusion time increase in proportion to the square of the distance
What are the most important components of the cell membrane?
The proteins
What determines how well a molecule will diffuse across the membrane?
- Mass of the molecule
- Concentration Gradient
- Lipid Solubility
- Electrical Charge
- Ion channel
- Membrane Carriers
How do non-polar molecules and gasses diffuse?
Across the lipid bilayer
How do ions diffuse?
Through channels
What is an ion channel?
A transmembrane protein that shows ion selectivity
How many transmembrane proteins are required to assembele an ion channel and what does the channel look like?
-At least 4
-All channels have a hole down the middle where ions diffuse into the membrane or out
What is the electrochemical gradient?
The movement of ions is affected by both the concentration gradient but also by the electrical gradient both of these form the electrochemical gradient
What potential do cells have inside of them and what does this mean?
A negative potential, Positive charges will tend to want to flow into the cell
How is potassium affect by the electrochemical gradient?
The concentration gradient:
-There tends to be low potassium outside of the cell, which tends to pull potassium out
The electrical chemical gradient: Due to the negative potential inside the cell potassium ions tend to want to stay inside the cell
What is electrochemical equilibrium?
When the elctrical gradient balances the concentration gradient
What is gating?
The idea that ion channels can exist in an open or closed state depending on their conformation
What is ligand gating?
When a compound such as a neurotransmitter binds to the channels recptor and causes it to open and allow current to flow
What is voltage-gated?
Open/close during excitability to generate action potentials
What is mechnically-gated?
Gated by stress. Located in areas where they can sense volume stretch/touch/pressure can activate these channels
What are the four main voltage-gated ion channels?
- Na+
- K+
- Ca+
- Cl-
Current flow through single ion channels depends upon?
- Channel conductance (how much the channel conducts when it is open)
- Channel open time (how long it is open)
- Frequency of channel opening
What did the patch clamp experiment prove?
When an ion channel opens the current goes to a new level and when it closes it goes back to the original level
What is mediated transport?
The movement of ions and other molecules(glucose, amino acids) by integral membrane proteins called transporters/carriers (NOT channels)
Can ions be moved through channels and transporters/carriers?
Yes
Is ion movement faster through channels or transporters?
Channels
What are the 3 characteristics of mediated transport?
- Specificity
- Saturation
- Competition
What is specificity of mediated transport?
System usually only transports one particular type of molecule
What is saturation of transport?
Rate of transport reaches a maximum when all binding site on all transporters are occupied
What is Tm?
Transport maximum - the maximum amount of substance that can be transported across the membrane at a time
Does diffusian diffusion be saturated?
No, there is not maximum rate of transport
What is competition of mediated transport?
When structurally similar substances compete for the same binding site on a membrane carrier
Factors that affect mediated transport?
- Solute concentration
- Affinity of transporter for the solute
- Numbers of transporters
- Rate of transporter conformational change
What are the types of mediated transport?
- Facilitated diffusion
- Primary active transport
- Secondary active transport
What is facilitated diffusion?
Involves the use of a transporter or carrier molecules which enables a solute to penetrate more readily than expected through simple diffusion
-It is passive
-From high concentration to low concentration
Steps of facilitated diffusion?
- Solute binds to the transporter
- Transporter changes configuration
- Solute is delivered to the other side of the membrane
- Transporter resumes original configuration
How can hormones affect facilitated diffusion, describe insulin hormone?
Hormones can increase the number and/or affinity of transporters in some membranes
Ex. Glut-4 transport glucose in muscle in the prescence of insulin the amount of glucose transported can increase or decrease
Describe the 4 characteristics of active transport?
- Transporter-mediated
- Requires chemical energy typically from the hydrolysis of ATP
- Susceptible to metabolic inhibitors
- Can transport solute against the concentration gradient
How is ATP hydrolyzed in active transport?
By the transporter/carrier
The transporter/carrier is phosphorylated which results in a conformation change of the transporter and its solute binding affinity
Why does the sodium potassium pump exist?
Without it potassiumn would constantly flow out of cells and sodium would constantly flow into cells . Eventually cells would run out of sodum and potassium
What does the sodium potassium pump do?
Moves 3 Na+ outside the cell and moves 2 K+ inside the cell
How does the sodium/potassium pump work?
- When the pump is open to the inside of the cell it has a high binding affinity for Na+ when Na+ binds the hydrolysis of ATP and phosphorylation of the pump occurs
- The pump will now undergo a conformational change and opens to the outside of the cell
- In this conformation the affinity for sodium goes down so it diffuses out, but the affinity for potassium goes up so it diffuses in.
- The binding of K+ causes the P to be released and the pump to change back to its original conformation
Name 3 active transporter and what is their role?
- Ca 2+ -ATPase (Maintains low intracellular Ca 2+ levels)
- H+ - ATPase (Maintains low lysosomal pH)
- H+/K+ -ATPase (Acidification of the stomach)
What is secondary active transport?
The movement of Na+ down its concentration gradient (Into the cell) is coupled to the transport of another molecule against its concentration gradient.
How does secondary active transport take advantage of primary active transport?
Takes advantage of the concentration gradient generated by primary active transport. The sodium concentration outside the membrane acts as a potential eergy source to drive secondary active transport
How does secondary active transport work?
- Na+ binds to a transporter outside the cell (conc. high) allowing glucose or amino acid to bind to the same carrier
- Through a change in configuration, the transporter “delivers” both Na+ and glucose/amino acid into the cell
- The transporter then reverts to its original configuration, and the Na+ is brought back out of the cell by the sodium potassium pump
How are glucose and amino acids transported?
Secondary active transport
Glucose can also be moved by facilitated diffusion in muscle cells
What is symport or cotransport?
When the solute is transported in the same direction as Na+ (into the cell)
What is antiport, countertransport or exchange?
When the solute is transported in the opposite direction to Na+ (Splute moves out of the cell)
Examples of symport secondary active transport?
- Na+/HCO3- (NBC) cotransporter (movement of bicarbonate into cells)
- Na+/amino acid cotransporter (amino acid into cells)
- Na+/glucose cotransporter (glucose into cells this is in the kidneys and GI tract)
Examples of antiport secondary active transport?
- Na+/H+ exchanger (moving H+ ions out changes the pH)
- Na+/Ca2+ exchanger (moving Ca2+ out to maintain low calcium levels in cells)
How are fatty acids moved across the membrane?
Via diffusion since they are non-polar molecules
What type of transport are endocytosis and exocytosis?
Active transport mechanisms that involve the participation of the cell membrane
What is endocytosis?
cell membrane invaginates and pinches off to form a vesicle that goes into the cell and releases its contents
What is exocytosis?
an intracellular vesicle fuses with the cell membrane, and its content are released into the ECF
What is constituitive exocytosis?
Non-regulated(continuous). Continual interaction of vesicles with the cell membrane to replace membrane proteins, the cell membrane and get rid of substances from the cell.
What is regulated exocytosis?
Triggered by extracellular signals and the increase of cytosolic Ca2+. Responsible for the secretion of hormones, digestive enzymes and neurotransmitters
Name the two types of endocytosis?
- Pinocytosis
- Phagocytosis
What is pinocytosis(fluid endocytosis)?
Endocytic vesicle engulfs the ECF including whatever solutes are present. It is nonspecific and non-regulated. The vesicle travel into the cytoplasm and fuse with other vesicles such ad endosomes or lysosomes
What is phagocytosis?
The process by which cells bind and internalize particulate matter such as dust particle, cell debris or microorganism (cell eating). It is specific and triggered. Pseudopodia (extenstion of the cell membrane) fold around the particle and fully engulf it. Pseudopodia fuse to form larger phagosomes that migrate and fuse to lysosomes that degrade the contents of the phagosome.
-This helps defend infection and find dead cells
What is receptor-mediated endocytosis?
When molecules in the ECF bind with high affinity to specific protein receptors on the plasma membrane
What is an example of receptor-mediated endocytosis?
clathrin-dependent receptor-mediated endocytosis
How does clathrin-dependent receptor-mediated endocytosis work?
- If cholesterol levels fall too low, low density lipoproteins (ligands) will bind to receptors.
- When the ligand binds the receptor undergoes a conformational change and clathrin is recruited to the plasma membrane
- Adaptor proteins link the ligand-receptor to the clathrin which form a cagelike structur and clathrin coated pit.
4.The pit is then invaginated and forms a “clathrin coated vesicle”. The vesicle will pinch off the cell membrane and sheds its clathrin coat
How is cholesterol transported in the blood?
As lipid-protein particles known as low-density lipoproteins (used in receptor-mediated endocytosis)
What is potocytosis?
Process by which molecules are sequestered and transported by tiny vesicles called calveolae. Calveolae deliver their contents directly into the cell cytoplasm and the ER or other organelles
Is potocytosis clathrin dependent?
No
What molecules doe spotocytosis typically move?
Low molecular weight molecules such as vitamins
Why is water able to diffuse so easily acroos most cell membranes?
Proteins called aquaporins that form water permeable channels facilitate the diffudion of water
Why do kidneys have more aquaporins than the brain?
Kidneys require more oxygen
What is osmosis?
The net diffusion of water across a semipermeable membrane
What is a semipermeable membrane?
A membrane that is permeable to solvent, but not to all solute
Where does water move?
To the location where there is less water concentration
What is osmotic pressure?
Prssure required to prevent movement of water across a semi-permeable membrane
How is osmotic pressure related to particle in solution?
it is proportional to the number of particles in solution not to their size, configuration or charge
What is osmolarity?
Total solute concentration of a solution
What does 1 molecule of glucose equal in osmol?
1 osmol
What does 1 mol of NaCl equal in osmol?
2 osmol (1 Na+ and 1 Cl-)
True or false: Osmotic pressure is proportional to osmolarity ?
True. The more osmols/particles the higher the pressure
What is the osmolarity inside of our cells?
300 mOsm
How would a different osmolarity affect cells?
Cells would shrink or swell
What is isosmotic?
Solutions that have the same osmolarity (concentration of osmotically active particles) as normal extracellular solution (both 300mOsm)
What is Hypoosmotic?
Solutions that have an osmolarity lower than 300mOsm
What is Hyperosmotic ?
Solution that have an osmolarity higher than 300mOsm
How is an osmotic pressure exerted?
Particles must be nonpenetrating (not able to cross the membrane) to exert osmotic pressure
How is sodium a nonpenetrating solute?
Extracellular Na+ must be moved into the cell with the sodium potassium pump
What is isotonic and what is the net movement of water?
Solution has a concentration of 300mOsm of nonpenetrating solute particles
-No net shift of water
What is Hypotonic and what is the net movement of wate?
Solution has a concentration of less than 300mOsm of nonpenetrating solute particles.
-Water will enter the cell and it will swell
What is Hypertonic and what is the net movement of water?
Solution has a concentration of more than 300mOsm of nonpenetrating solute particles.
-Water will leave the cell and it will shrink
Is urea a penetrating or nonpentrating solute?
Penetrating
If the concentration outside of the cell is 280mOsm of nonpenetrating solute what will happen?
Water will move into the cell to try and reduce the concentration in the cell to 280mOsm
Is NaCl nonpenetrating or penetrating?
Nonpenetrating
What makes up the capillaries?
A single layer of flattened endothelial cells and a basement membrane
How does excessive water intake affect osmolarity and the volume of the ICF and ECF?
-The volume of the ECF will increase
-The osmolarity of the ECR will decrease
-The ICF volume will increase to try and lower the osmolarity indside the cell (cell swells)
-The osmolarity inside the cells will decrease
How does an iv infusion of 0.9% saline affect osmolarity and the volume of the ICF and ECF?
- Volume of ECF: will increase
- Osmolarity of ECF: remains the same
- Volume of ICF : remains the same
- Osmolarity of ICF: remains the same
How does a hemorrhage affect osmolarity and the volume of the ICF and ECF?
- Volume of ECF: decreases
-Osmolarity of ECF: remains the same
-Volume of ICF: remains the same
-Osmolarity of ICF : remains the same
How does drinking sea water affect osmolarity and the volume of the ICF and ECF?
-Volume of the ECF: increases
-Osmolarity of the ECF: increases due to high NaCl outside of cell
-Volume of ICF: Decreases (cell shrinks)
- Osmolarity of the ICF: Increases
How does severe sweating affect osmolarity and the volume of the ICF and ECF?
-Volume of the ECF: decreases
-Osmolarity of ECF: increases
-Volume of ICF: decrease
-Osmolarity of ICF: increase
Name all of the types of transport across the capillary wall?
- Bulk flow
- Transcytosis - endocytosis on one side of the cell then exocytosis on the other side
- Water filled channels(diffusion) -water
- Diffusion- gasses, non-polar
What is the most important type of transport in capillaries?
Diffusion
