Cell Physiology - Topic 2 Slides Flashcards
What are the 3 types of Endocytosis?
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
What is Vesicular Transport?
Using vesicle to move substance into or out of the cell
What do substance bypass when using Vesicular Transport?
Substances do not need to cross the plasma membrane but instead use vesicles formed by the plasma membrane
What are Vesicles composed of?
Phospholipids and may contain proteins
What is Endocytosis?
A form of vesicular transport which used vesicles to bring molecules into the cell
What is Phagocytosis?
When cells engulf bacteria or large particles such as cell debris from damaged tissue
What is another name for Phagocytosis?
Cell Eating
What occurs in Phagocytosis?
A large particle is surrounded by pseudopodia and folds around the surface of the particle engulfing it completely and pinches off from the cell membrane within the cell
What is a Vesicle in Phagocytosis called?
A Phagosomes
After Phagocytosis occurs what happens to the Phagosome?
It fuses with the lysosome in the cell
What occurs after the Phagosome fuses with the Lysosomes in the cell?
The lysosome digests the contents of the phagosome with digestive enzymes
Which cells use Phagocytosis the most?
Macrophages of the immune system
What is another name for Pinocytosis?
Cell drinking
What occurs in Pinocytosis?
The membrane of the cell invaginates forming a pock with material from the cell exterior bringing things in via a vesicle
What is the specificity of Pinocytosis?
It is non specific
What can pinocytosis take in?
Ions or Nutrients
What is the specificity of Receptor Mediated Endocytosis?
It has high affinity so it very specific
What is the first step in Receptor Mediated Endocytosis?
A receptor on the cell membrane binds with high affinity to a ligand
What occurs after a ligand binds to a receptor in Receptor Mediated Endocytosis?
Clathrin is recruited to the membrane and links to the receptor ligand complex
What does the Receptor, Ligand and Clathrin form?
A cage like structure
What does the cage-like structure of the receptor, ligand and clathrin lead to?
The accumulation of receptor ligand complexes in a localized region of the membrane
What occurs after the accumulation of receptor, ligand and clathrin at the membrane?
The membrane indents forming a coated pit
What is the Coated Pit known as after it pinches off?
A Coated vesicle
What occurs after the Coated vesicle enters the cell?
It loses its Clathrin coat which is recycled
What occurs in Receptor Mediated Endocytosis after the coated vesicle loses clathrin?
The vesicle is free to fuse with other intracellular membranes
What are Endosomes?
Organelles which perform assorting functions and sort contents of the vesicle
In what way does Cholesterol enter the cell?
Receptor Mediated Endocytosis
What is Cholesterol important in?
Building the plasma membrane and the intracellular membranes in the cell
What is most of the Cholesterol in the bloodstream associated with?
Proteins forming a complex term load density lipo proteins or LGLs
How can cells take up Cholesterol?
By the binding of LGLs of to receptors on the membrane
Once LGLs have been ingested by the membrane what separates them from the receptor protein?
When they fuse with a lysosomes the enzymes separate the proteins from cholesterol so it can be used by the cell
What are the 3 functions of Exocytosis?
- Secrete membrane impermeable molecules synthesized by the cell
- Release waste products that cannot be digested by the cell
- Add components to the plasma membrane
What examples of Membrane impermeable molecules synthesized by the cell?
Antibodies synthesized by WBCs or Protein hormones
Which process replaces portions of the membrane that were removed by Endocytosis?
Exocytosis
What occurs in Exocytosis?
A secretory vesicle in the cell migrates to the surface and dock to peripheral proteins of the plasma membrane. The proteins pull the plasma membrane inward forming a dimple that fuses with the membrane of the vesicle
What is Transcytosis?
The movement of receptor bound macromolecules through the cell using endocytosis and exocytosis
Where is Transcytosis more common?
In polarized cells like epithelials
What makes Epithelia polar?
They have distinctly two different membranes on the two sides that differ in structure and function
What does the Basolateral membrane refer to?
The membrane on the base and sides of the cell
What is the best studied example of Transcytosis?
The absorption and transport of antibodies across the epithelial lining of the gut
What occurs in Transcytosis in the gut?
- An antibody binds to specific receptors on the apical surface of intestinal cell
- It is internalized by receptor mediated endocytosis
- It is transported to an endosome
- The endosome delivers it to the opposite end of the cell
- The receptor and antibody dissociate and the antibody can now enter the bloodstream
What are the two types of Passive Transport?
Channel mediated and carrier mediated transport
What is Simple Diffusion?
When a substance move through the membrane down its concentration gradient without the use of a transport protein
What occurs in Channel Mediated Transport?
The Channel opens and the ions simply move through the channel down in electrochemical gradient
What occurs in Carrier Mediated Transport
A protein carrier and ligand binds to the binding sites on the carrier on one side of the membrane. The carrier then reorientated so the binding site is facing the other side of the membrane and the ligand is released
Is Carrier Mediated Transport Passive or Active?
Passive
What does Active transport require?
Energy in the form of ATP or an Electrochemical gradient
What is Simple Diffusion?
The Passive movement of molecules through a biological membrane lipid bilayer
What is the order of permeability of things that can move by simple diffusion through the lipid bilayer?
- Nonpolar uncharged molecule
- Small uncharged polar molecules
- Water
- Large uncharged polar molecules
- Ions
- Charged polar molecules
What are examples of Nonpolar uncharged molecules?
CO2
O2
Fatty acids
What is an example of a small uncharged polar molecule?
Ethanol
What is an example of Large uncharged polar molecules?
Glucose
What are examples of Charged Polar Molecules?
ATP and Glucose 6-phosphate
What is the permeability of Nonpolar uncharged molecules?
Very Permeable
What is the Permeability of Small uncharged polar molecules?
Very Permeable
What is the Permeability of water?
Slightly permeable
What is the permability of LArge uncharged polar molecules?
Impermeable
What is the Permeability of Ions?
Impermeable
What is the Permeability of Charged polar molecules?
Impermeable
Which molecules are Impermeable?
- Large uncharged polar molecules
- Ions
- Charged polar molecules
Which molecules on Permeable?
- Nonpolar uncharged molecules
* Small uncharged polar molecules
Which molecules are slightly permeable?
Water
What materials can penetrate the bilayer by simple diffusion?
Lipid soluble substances
What energy causes diffusion?
The energy of the normal kinetic motion of matter
What two properties determine whether or not a molecules can cross the plasma membrane by simple diffusion?
- Solubility of the molecule in the lipid
* Size of the molecule
What causes the flux due to simple diffusion to increase?
The concentration of the gradient increases
What factors influence the rate of Simple Diffusion?
- Magnitude of driving force (conc. gradient)
- Membrane surface area
- Membrane permeability
How does Temperature increase diffusion rate?
Increasing temperature increases diffusion rate
How does the Thickness of the barrier affect diffusion rate?
The bigger the barrier the lower the diffusion rate
How does surface area affect the rate of Diffusion?
The greater the surface area, the greater the number of molecules which can diffuse across the membrane
What are examples of tissues that have high surface area?
Intestinal epithelia and pulmonary epithelia
What can act as a driving force?
Any difference of energy across a membrane
What is always the direction of forces?
From high to low energy
What are the 3 types of driving forces?
- Chemical
- Electrical
- Electrochemical
What causes a Chemical Driving Force?
Difference in concentration of a substance on either side of a membrane
In which direction do chemicals flow in chemical driving forces?
Molecules move in the direction of the the driving force
What is Membrane Potential?
The difference in electrical potential or voltage across a cell membrane
What is Separation of Charge?
Unequal distribution charges across the cell membrane
What would cause an ion to cross a membrane?
The opposite charge on the other side of the membrane and the repulsive forces of the same charge
What do electrical driving forces not act on?
Uncharged particles
What are Electrochemical driving forces?
The sum of the electrical and chemical driving forces acting on an ion
What does the direction of Electrochemical driving forces depend on?
The net direction of the electrical and chemical driving forces
Why is transport accelerated by specific proteins?
Because simple diffusion does not occur rapidly enough to meet cellular needs
What are the characteristics of Channels?
- Usually multimeric proteins
- Span the lipid bilayer
- Substrate specific (ions, water)
- Open and closed states
- Very rapid movement of solute
- Can function as receptors
- Characterized by gating and selectivity
What does it mean to be a Multimeric Protein?
It means that it is made out of different proteins
How are Channels substrate specific?
They only what is made to allow through
What are Aquaporins?
Water channels that only allow water through
What is the selectivity of a channel determined by?
The diameter of its central port and by the electrical charge of the amino acids that line the channel
How can channels function as receptors?
They can bind to ligands such as hormones or neurotransmitters which change its conformation
What is the Selectivity Filter?
The narrowest part of conduction pathway through the pore of the channels that discriminates between different ionic species
Describe the channel that allows ions through the cell membrane?
They are channels that are water filled
What does the water in ion channels do?
They stabilize ions as they pass through the membrane
What contributes to stabilizing ions in ion channels?
- Water
* Polar properties of amino acids that make up the protein
What does Charge selectivity depend on?
The electrostatic attraction or repulsion depending on the amino acid inside the ion channel
What might the selectivity filter require an ion to do?
- Lose its water molecules (hydration shell)
* Keep some of its water molecules
Describe the selectivity of the Potassium channel?
It is so constricted that it requires potassium to lose most of the waters forming its hydration cell
What are water molecules replaced by in the selectivity filter?
Polar oxygen atoms of the protein
What is Channel gating?
Opening by activation or closing by deactivation or inactivation of ion channels
What is the gate of ion channels composed of?
Amino acids and proteins
What are Gating Currents?
Very small currents in the membrane prior to the increase in ionic permeability or the opening of the ion channel due to charged particles within the membrane
What are the 3 ways we can describe gating?
- Voltage gated
- Ligand gated
- Stretch activated
What acts as a voltage sensor in an amino acid channel?
A sequence of amino acids
How does the voltage sensor in a gated channel work?
When the voltage or membrane potential changes, the amino acids move and the channel opens up
What do ligand gated channels open in response to?
The binding of a ligand
What do stretch activated channels open in response to?
Cell stretching such as swelling of the membrane from the influx of water
How are Voltage gated channels usually activated?
With depolarization with positively charged amino acids acting as voltage sensors
What are the characteristics of transporter proteins?
•Monomeric or multimeric -Passive or active •Span the lipid bilayer •Substrate specific •Activity can be regulated •May couple movement of solutes •May move substrate uphill against concentration gradient •Usually slower than channels
What are faster? Ion channels or Transporter proteins?
Ion channels
What are Transporter Proteins?
Proteins that have specific binding sites for the ligand or ligand
What is a monomeric protein?
A protein that has a single polypeptide chain
What is a multimeric protein?
A protein that has multiple polypeptide chains
How can the activity of Transport proteins be be regulated?
Effector molecules or controlling its amount and lifetime in the cell membrane
How do Effector molecules work?
The induce a conformational change that produce active or inactive forms of transport proteins
How many substances can Transport Proteins transport?
One substance or multiple substances
How can Glucose be coupled to the movement of sodium in Transport proteins?
Glucose will bind to the protein with sodium and both are transported into the cell
What is required for Transport proteins to move things across the concentration gradient?
Energy in the form of ATP or an electrochemical gradient is required
Why do Transformation Proteins take time?
Because the binding and unbinding and conformational changes take time
What is the GLUT protein?
Glucose transporters
How many GLUTs are in the human genome?
14
How do the GLUTs differ from each other?
- Affinity for glucose
- Where they’re expressed
- How they’re regulated
- Transported substrate
If there is a concentration gradient around a Transporter protein is it passive or active?
Passive
How does a cell continue to move glucose inside when the concentration gradient is even?
It converts glucose inside the cell to different forms
What are the two types of Active Transport?
Primary and Secondary
How do Primary and Secondary active transport differ?
- Primary uses energy from ATP hydrolysis or breakdown for energy
- Secondary uses energy from electrochemical gradients
What is another name for Primary Active Transporters?
ATPases
Why are Primary active transporters called ATPases?
Because they function like enzymes catalyzing the breakdown of ATP and phosphorylates itself
What does the addition of a Phosphate group do to Primary Transport Proteins?
It changes the conformation of the transporter and the affinity of the transportes binding sites for substrates
What is an example of a Primary Transporter?
The sodium potassium exchange pump
What are the binding sites on the sodium potassium exchange pump?
Three binding sites for sodium and two for potassium
What causes the release of the Phosphate group from the sodium potassium exchange pump?
The binding of potassium
Why is the Sodium Potassium exchange pump considered electrogenic?
Because there is a net movement of charge during the transport cycle
What is the net movement of charge of the sodium potassium exchange pump?
There is a net movement of one positive charge outside the cell
What are some of the functions of the sodium potassium exchange pump?
- contributes to establishing membrane potential of the cell
* Maintains sodium and potassium concentration gradients
How do large intracellular proteins affect water content of the cell?
They pull large amounts of water into the cell
How do sodium and potassium exert an osmotic pull on water?
Water enters the cell drawn by the impermeable proteins and potassium and water leaves the cell drawn by sodium
How does Ouabain prove the balance between the osmotic pull due to sodium and potassium?
Ouabain blocks the function of the sodium potassium exchange pump the cell swells and bursts as water enter is not balanced by exit
What does Secondary Active transport couple?
The movement of one ion down its electrochemical gradient to drive the uptake of another molecule against its concentration gradient
What binding sites do Secondary Active Transport molecules have?
A binding site for an ion (typically sodium) and another for a cotransported molecule
How is the gradient of the ion in secondary active transport restored?
By primary active transport
How does the Sodium Glucose Importer work?
It couples the movement of sodium down its concentration gradient with glucose
What is Cotransport?
When two substrates are transported together in the same direction
What occurs in the Sodium Proton Antiporter?
Sodium moves down its concentration gradient and a proton leave the cell
What is the Sodium Proton Anti porter an example of?
Countertransport
Why is the Sodium Glucose importer electrogenic?
Because a charge is transported with it
What does the Rate of Transport depend on?
The rate of transport by individual transporters and the number of active transporters in the plasma membrane
What happens as substrate concentration increases?
The rate of transport increases until it plateaus as there is a limited amount of transporters
What is Vmax in cellular physiology?
The maximum rate of transport
Where can we find Vmax in cell physiology?
We can look to where the curve plateaus and draw a line to the Y axis
What is Km?
The affinity of the transporter for the transported substrate
How do you find Km?
You look for 50% of the Vmax value then draw a horizontal line to the curve and drop straight down to the x-axis
What does a low Km value mean?
A higher affinity for the transporter to the substrate
What are the two families of Nucleoside transporters?
Concentrative Nucleoside Transporters (CNT) and Equilibrative Nucleoside Transporters (ENT)
What do Nucleoside Transporters do?
They move nucleosides, mainly drugs for treatment across the cell membrane
Why are Nucleosides important?
They are precursors to nucleotides and have principal roles in cellular energy metabolism and nucleic acid biosynthesis and can be used to inhibit nucleic acid synthesis
What do ENT Transporters do?
They mediate the bidirectional transport of nucleosides across membranes
What does the direction of transport if nucleosides by ENT depend on?
The concentration gradient
What are HENT’s?
The human equilibrate of Nucleoside transporters
What are the two types of HENT’s?
HENT1 and HENT2
What do HENT’s do?
Mediate Gemcitabine uptake in the direction of the concentration gradient
What type of proteins are the HENT proteins?
Transmembranes Glycoproteins
What does NBMPR inhibit?
HENT1 but not HENT2
What are HCN1 and HCN3 able to do?
Bring Gemcitabine into the cell coupled to the movement of sodium down its electrochemical gradient
How are HCN Transporters able to move Gemcitabine against its concentration gradient?
By coupling it to the movement of sodium
What is Gemcitabine primary uptake done by?
HENT1
What happens once Gemcitabine enters the cell?
Nucleotide kinases phosphorylate gemcitabine to gemcitabine-monophosphate and then to its active metabolites Gemcitabine diphosphate and Gemcitabine triphosphate
What is the Rate limiting step in the transformation of Gemcitabine?
The first phosphorylation of Gemcitabine
What happens once Gemcitabine is converted to Gemcitabine Triphosphate?
It is incorporated into the DNA and protected from base pair excision with the addition of another natural nucleotide
What are the mechanisms of cancer control that Gemcitabine can do?
- Mass chain termination of DNA
- Apoptosis by Gemcitabine monophosphate
- Blocking de novo DNA synthesis by Gemcitabine by diphosphate
- Lowering the pool of opposing deoxycytidine triphosphate by Gemcitabine Triphosphate
How does Gemcitabine monophosphate fight cancer?
By inducing Apoptosis
How does Gemcitabine Diphosphate fight cancer?
By blocking de novo DNA synthesis
How does Gemcitabine Triphosphate fight cancer?
By lowering the pool of opposing deoxycytidine triphosphate by Gemcitabine Triphosphate
How does Gemcitabine kill cancer undergoing DNA synthesis?
By not allowing the cell to copy its DNA to properly divide
