Cell Physiology Lecture 2 Flashcards
Vesicular Transport
A type of transport that uses vesicles to move substances across biological membranes
Endocytosis
The uptake of material into the cell using vesicles containing material that pinch off from the plasma membrane, and enter the cytoplasm of the cell.
-basically cell membrane wraps around and then pinches
What are the 3 types of endocytosis?
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
Exocytosis
release of material from the cell using vesicles containing material
that fuse with the plasma membrane and release their contents into the
extracellular fluid
-basically the vesicle fuses with the membrane and releases contents out to the ECF
Phagocytosis is also called _______
cell eating
How does phagocytosis bring things in the cell?
It uses extensions of the plasma membrane called pseudopodia to surround material being brought up into the cell.
Phagocytosis is used for bringing __________
large particles into the cell, such as bacteria or cell debris from nearby cells
(process used by white blood cells)
Pinocytosis is also called _______
Cell drinking
How does pinocytosis bring things in the cell?
-Plasma membrane simply ‘indents’ below the particles to be brought into the cell (does not use pseudopodia)
-Plasma membrane pinches together once it has indented and the vesicle containing particles brought into the cell is called an endocytic vesicle
Pinocytosis is as __________
Nonspecific process
Nonspecific process meaning in pinocytosis
Means it simply brings in extracellular fluid and substances dissolved in that fluid
-reason for why it is called “drinking”
Pinocytosis is used for ingesting ________
small molecules, ions, and nutrients (can not bring in large things into the cell such as bacteria or cell debris)
Steps of phagocytosis:
Once activated, the phagocytic cell moves to the material it will ingest
Steps of Phagocytosis:
- (Recognition) of substance to be ingested
- (Attachment) of phagocyte to the substance to be ingested
- (Pseuopodia) reach around the substance and come together to form a phagosome inside the phagocytic cell
- (Fusion) of the phagosome to a lysosome to form phagolysosome
- (Destruction) of ingested substance by lysosomal enzymes
- (Release) of end products into the cell or out of the cell by exocytosis
Receptor-mediated endocytosis is a ___________
Specific process as it involves receptors which bind specific ligands to be brought into the cell
What is the name of the cytoplasmic protein involved in receptor-mediated endocytosis?
Clathrin
Receptor-mediated endocytosis steps:
- The ligand binds to the receptor which causes it to change its shape. This causes clathrin to move to the membrane.
2.many receptors with ligands attached gather together in one small area on the cell’s surface, where clathrin is also present. By doing this, the cell can bring in more of the ligand at once, making the process more efficient
3.the part of the cell membrane where the clathrin and receptor-ligand complexes are gathered starts to bend inward, forming a small dip or pocket. This pocket, covered in clathrin and holding the receptors with their ligands, is called a clathrin-coated pit.
4.the indented part of the membrane, which contains the receptor-ligand complexes and is covered in clathrin, pinches off from the rest of the cell membrane to form a small bubble or vesicle. This vesicle is still lined with clathrin and carries the receptor-ligand complexes inside the cell.
5.
Once the vesicle is formed and inside the cell, the clathrin (the outer coating) is removed from the vesicle.
6.After the vesicle is inside the cell and the clathrin is removed, it has several options for what to do next: deposit contents into the lumen, travel across the cell and fuse with plasma membrane to releae conent, fuse with orghanellesd called endosomes, which then sort contents to the golgi or lysosomes.
Exocytosis Function
-Secrete specific substances like hormones
-release waste products
-add components of the membrane like lipdes and proteins to the plasma membrane when vesicles fuse with the membrane (balances portion removed by endocytosis).
Are there process that do not utilize vesicles to move substances across the membrane?
Yes
A difference in energy across a membrane acts as a __________
driving force to move a substance
Substances always move from a region of high energy to a region of ________
low energy
What are the 3 types of driving forces for non-vesicular transport?
- Chemical
- Electrical
- Electrochemical
When is there a chemical driving force?
When there is a difference in concentration between a substance on either side of a membrane.
How do molecules move in a chemical driving force?
They move passively from high to low concentration or “down” the concentration gradient.
What happens as the gradient gets more extreme in chemical driving force?
The rate of transport of the substance increases
What substances can be affected by the electrical driving force?
Any substance that is charged
Cells in our body have a membrane ________
potential
The electrical driving force exists due to the ___________
membrane potential
Membrane Potential meaning
the difference in electrical potential or voltage across a cell membrane
-also called a ‘seperation’ of charge across the membrane
Any charged substance experiences ____________ due to the membrane potential.
Attractive or Repulsive forces
Electrochemical Driving Force
The sum of the electrical and chemical driving forces acting on an ion.
Are neutral (not charged) substances affected by electrical driving force?
No
The direction of the electrochemical driving force depends on _________
the net direction of the electrical and chemical driving forces.
Simple Diffusion
The passive movement of a molecule through a biological membrane’s lipid bilayer
Simple diffusion does not require the __________
input of energy
Two factors affecting. the solubility of the substance in lipid
- Polarity
- Size
The plasma membrane has a __________ core
non-polar
Polar solubility
Soluble in water,
insoluble in lipids
Nonpolar solubility
water in-insoluble
soluble in lipids
Substances that move by simple diffusion move from _________
a region where they are found in high concentration to a region where they are found in a low concentration, or “down” their concentration gradient.
Which substances move across a phospholipid bilayer by simple diffusion?
- If a substance is small, non-polar and uncharged
- If a substance is polar and uncharged, it may cross by SD if small enough
When will you not be able to move across a phospholipid bilayer by simple diffusion?
-Any substance that has a charge, regardless of size, polarity because their charge will not allow them to interact with the non-polar tails of the phospholipids.
-If a substance is large, uncharged, and polar
3 other factors affecting the rate of simple diffusion:
- Magnitude of the driving force
- Membrane surface area
- Membrane Permeability
Factor affecting rate of simple diffusion - Magnitude of the driving force
The greater the concentration difference of a substance on either side of the membrane, the greater the driving force, and the greater the rate of SD
Factor affecting rate of simple diffusion - Membrane Surface Area
The amount of membrane available for cells to cross matters. A larger cell has a bigger surface area for membranes and thus more molecules can cross at once.
Factor affecting rate of simple diffusion - Membrane Permeability
The permeability of the membrane to a specific substance depends on the membrane, and the substance.
Depends on:
- The lipid solubility of the diffusing substance (non-polar substances cross more easily)
- Size and shape of the diffusing substance (small and more regularly shaped cross the membrane more easily)
- Temperature of the substance, at high temperature substances move around more helping them diffuse faster across the membrane
- Diffusing Distance, if a substance has to cross more layers of cells it will diffuse slower than if it had to only cross one layer (referring to the membrane cells)
What is osmosis
The net movement of water across a selectively permeable membrane driven by a difference in solute concentration on both sides of the membrane.
In osmosis water flows from:
A region of high water concentration to low water concentration
or
a region of low solute concentration to a region of high solute concentration
How do you change the concentration of water?
By adding solute
Pure water
water with no solute added
Water can move across membrane through _________
simple diffusion
Why can water flow across membranes through simple diffusion?
Because water molecules are polar but small, the simple diffusion of water is limited but finite.
Certain tissues have a larger permeability to water such as the _________ because ________-
- Kidneys
- there are water channels called aquaporins
Mediated transport is ________
The use of a protein to cross a cell
What are the two forms of mediated transport?
-Facilitated Diffusion
-Active Transport
Facilitated Diffusion is a type of _______
passive transport
Passive Transport
Energy is not required, as substances move passively down their concentration gradient
In facilitated diffusion, types of proteins are involved as _______
carriers or channels
Facilitated Diffusion is a ___________ transport process
specific
Facilitated Diffusion selectivity
-Carriers are proteins with specific binding sites for the substance to be transported across the membrane
-Channels are selective for a specific ion (ie: sodium ion) or a type of ion (ie: cation or anion)
Channel-mediated facilitated diffusion:
-Channels may be selective for a specific ion or type of ion that moves through them
-Channels do not just allow ions to pass through. For example, aquaporins are water channels that are specific for water molecules
-The direction and magnitude of ion flux through a channel depends on the
electrochemical gradient of that ion
-Channels exist in an open or closed state and may be gated. Gating refers to the opening
(activation) or closing (by deactivation or inactivation) of ion channels. Gating is the process of an ion channel transforming between any of its conducting and non- conducting states.
Carrier-mediated facilitated diffusion:
-Uses proteins called carriers which have a specific binding site
-Carrier proteins bind the substance and move it across the plasma membrane from a region of high concentration to a region of low concentration (diffusion)
-Does not require energy such as ATP
Example of Carrier-mediated facilitated diffusion
The GLUT family of proteins, which are carriers move glucose across the membrane from a region of high concentration to a region of low concentration (glucose is non-polar and uncharged but it is too big to move across the membrane by simple diffusion).
Channel gates may be:
voltage-gated (changes in voltage cause the channel to open or close)
ligand-gating (the binding of a substance or ligand to a binding site on the channel causes it to open or close)
mechanically-gated (mechanical stimuli such as swelling or stretching of a cell causes the channel to open or close)
Active transport proteins are often called:
pumps
Active transport:
-Involves transport proteins with specific binding sites for the substance to be transported
-Capable of uphill transport, or moving a substance against an gradient from low to high
-utilize energy to do uphill transport
Primary or secondary active transport obtain energy from __________
Different sources
Example of Primary Active Transport
Na+/K+ Pump
Na/K pump at rest
At rest, a cell has a high Na+, outside the cell, and a high K+ inside the cell
What does the Na/K pump do for every molecule of ATP hydrolyzed?
It moves 3 Na+ ions out of the cell, and 2 K+ into the cell, against their concentration gradients
Function of Na+/K+ pump
contributes to establishing and maintaining the membrane potential of the cell and maintains the Na+ and K+ concentration gradients
Secondary Active Transport
Uses electrochemical gradient established by primary active transport to move ions
Secondary Active Transport Example
Na+/glucose transporter, moves glucose same direction (against its gradient)
Na+/H+ exchanges, moves Hydrogen in opposite direction of Sodium (both against their gradient)
Simple Diffusion is a _______________
unsaturable transport process
Mediated Transport is a _____________
saturable transport process
Why is Simple Diffusion an unsaturable transport process?
Because it does not involve proteins and binding sites. As you increase the concentration of the substance you increase the movement of the substance across the membrane
Why is mediated transport a saturable transport process?
Because it involves proteins and binding sites, each cell has a limited amount of proteins and each protein has a limited number of binding sites for a substance.
As the concentration of substance increases, an increased number of binding sites are occupied. The transport rate will plateau once all site are occupied, and increasing the concentration would not do anything.
