Cell Physiology (Exam 1) Flashcards
Function of plasma membrane
- Helps maintain composition of intra- and extracellular fluids
- Regulates traffic in and out of the cell
- Forms a framework for protein components of the cell
- Proteins embedded in the membrane
- Detects chemical messengers at cell surface than can be transported through the membrane
- Links adjacent cells together
Tight junctions
- Impermeable barrier
- Occurs on apical (silica) side
Anchoring Junctions
- Desmosomes
- Composed of proteins with cell adhesion molecules
- Adherens junction
- Forms rings around cells
Gap junctions
- Composed of proteins that form channels between cell 1 and cell 2
- Connects their cytoplasm
Glycoproteins
- Membrane protein
- Have sugar chains attached
- Can be peripheral or integral
Integral proteins
- Membrane protein
- Tightly bound to the membrane
- Either embedded in or span the entire bilayer
- Involved in structural support, signaling, and transport
- Channel proteins do the transport and are integral proteins
Peripheral proteins
○ Membrane protein
○ Interact with the membrane surface or with integral proteins
○ Not embedding into the membrane
Relationship between membrane permeability and hydrophobic molecules
Pass through the membrane easily
Relationship between membrane permeability and small, uncharged, polar molecules
○ Glycerol, water, etc.
* Move slightly through the membrane by simple diffusion
Relationship between membrane permeability and large, uncharged, polar molecules
○ Not permeable
* Glucose, sucrose
Relationship between membrane permeability and ions
Impermeable
Relationship between membrane permeability and charged polar molecules
- Impermeable
- Amino acids, ATP
Simple Diffusion
Passive form of diffusion in which molecules move due to the intrinsic kinetic energy of their chemical gradients, flowing from an area of high concentration to one of low concentration (no ATP). This diffusion never stops, however the net becomes 0
Flux
The difference between two one-way fluxes
Net Flux depends on:
® Permeability
® Concentration gradient
® Temperature
® Surface area
® Size of molecule
* Distance
Facilitated Diffusion
Movements on molecules through trans-membrane proteins, molecules move down their electrochemical gradient, no ATP required (passive)
Channel Proteins
A tunnel through the membrane
Types of Channel Proteins
Ion channels, constitutive channels, and gated channels
Ion Channels
- Selective or non-selective
- Selective:
® Na+, K+, Cl_ - Non-selective
® Monovalent channels
* Allows Na+. K+, and Li+
- Selective:
Constitutive channels
Always open, includes aquaporins
Gated Channels
Only open under certain conditions (in response to stimulus)
Osmosis
- Passive transport of water
- The net diffusion of water from a region of high water concentration to a region of low water concentration
- Facilitated by aquaporins
How is water movement determined
Direction of water movement is determined only by a difference in total solute concentration and not by types of solute
Osmolarity
○ Total concentration of solute in solution in mols/L (OsM)
* Depends on the total number of molecules, not the individual type
Isoosmotic
Same osmolarity
Hyperosmotic
Higher OsM
Hypoosmotic
Lower OsM
Hydrostatic Pressure
○ Water above you pushed down (pressure) on you
* The pressure exerted by the standing column of water due to gravity
Osmotic Pressure
○ Pressure generated by water moving based on osmolarity
Ligand-Gated Channel
○ A signal molecule (ligand) binds to the receptor/channel regulating the opening and closing of the gates
○ Acetylcholine regulates entry of Na+ into muscle cells (selective channel)
* Less common, but some channels close with the binding of the ligand
Voltage-Gated Channels
○ Regulated by electrical state of the cell
* Voltage gated Na+ channels are activated by the membrane (when membrane potential is met)
Mechanically-gated channels
○ Regulated by a physical change
* Pressure is an example of such a change
Function of Permeases
- Carrier/permeases/transporters bind the substrate that they are moving across the membrane
- It goes through a conformational change, which then allows the molecule to be released inside
- ATP not needed
- Never open on both side
- Transport down the concentration gradient by carrier proteins instead of ATP
Active Transport
- Transported molecules must bind to a transporter
- Metabolic energy is required
- Directly in primary active transport
- Indirectly in secondary active transport
- Directly in primary active transport
- Metabolic energy is required
Primary Active Transport
- Requires ATP
- Moves solutes against their gradients
- Specific membrane bound transport proteins involved
- Are ATP-ases
- Breaks down ATP into its parts, allowing movement of molecules across the membrane
- Are ATP-ases
- Maintains electrochemical gradients
- Not equilibrium
Ca2+ Pump
- Hydrolysis of ATP directly required for the function of the carriers
- Molecule or ion binds to recognition site on one side of the carrier protein
- Binding stimulates phosphorylation (breakdown of ATP) of carrier
- Carrier protein undergoes conformational change
- Hinge-like motion releases transported molecules to opposite side of membrane
Primary active transport
Na+/K+ Pump
- Primary active transport
- ATPase pulls both Na+ and K+ against their gradients
- Na+ initially has sa high concentration outside of cell and low inside, K+ is the opposite
1. Na+ binds to the protein, stimulating phosphorylation of ATP
2. Phosphorylation of ATP causes the protein to change conformation
3. The conformational change expels Na+ and takes in K+
4. K+ binding gives you another phosphorylation of ATP
5. That changes the conformation again
6. K+ is released into the cell and the cycle repeats - ATP –> ADP and P
- Actively extrudes 3Na+ and transports 2k+ inward against the concentration gradient
- Changes osmolarity, and therefore flow of water
- Involved in setting up the gradients that allows electrochemical impulses to occur
- Provides energy for couples transport of other molecules
Secondary Active Transport
- No direct input of energy required, but it depends on the electrochemical gradient that is established by the primary active transport
- Coupled transport
- The energy required for uphill movement is obtained by the downhill transport of Na+
- Coupled transport
- Hydrolysis of ATP by Na+/K+ pump required indirectly to maintain Na+ gradient
Classifications of Transporters
Uniporter, symporter/cotransporter, antiporter/exchanges
Uniporter
The specific transport of a single substance in or out of cells
Symporter/cotransporter
carries two or more molecules across the cell membrane in the same direction
Antiporter/exchanges
Moves multiple cells in opposite directions across the cell membrane
Exocytosis
Fusion of the membrane-bound vesicles that contains cellular products with the plasma membrane
Endocytosis
Specific molecules can be taken into the cell because of the interaction of the molecule protein receptor
