MEMBRANE TRANSPORT & TISSUE STRUCTURE/FUNCTION Flashcards
Cell membrane
Surrounds the cell to separate internal contents with the extracellular environment and regulates passage of molecules through
Why must cell membrane be dynamic and constantly in flux
Because cells exclude some substances, take in others, and excrete others, all in controlled quantities which requires the membrane to be dynamic and constantly in flux
Singer & Nicolson 1972
Proposed the fluid mosaic model which sought to explain the microscopic observations and the functions of the cell membrane
Mosaic of components of the membrane (4)
Phospholipids, cholesterol, proteins, and carbohydrates
Phospholipid backbone
Primarily made up of a bilayer of phospholipids. The hydrophilic head of the phospholipids are in contact with the water-based intracellular and extracellular fluid while the hydrophobic fatty acid tails point towards each other at the interior of the membrane
Cholesterol in cell membrane
Contributes to the fluidity of the membrane
Amphipathic
Molecule that contains both a hydrophilic and hydrophobic region (eg. Soap)
Integral proteins
Proteins embedded in the plasma membrane and may span all of parts of the membrane to sere as channels, gates, or pumps to move materials into or out of cells
Peripheral proteins
Found on exterior or interior surfaces of the membrane, attached either to the integral proteins or phospholipid molecules. Stabilizes and gives shape to membrane
Carbohydrates
Found on the exterior surface of cells and are bound to either proteins as GLYCOPROTEINS or lipids as GLYCOLIPIDS
Glycoprotein
Protein that has a carbohydrate molecule attached which extends to the extracellular matrix
Glycocalyx
Fuzzy appearing coating around cell formed from glycoproteins and other carbohydrates that surrounds the other most cellular membrane of cells. Glycocalyx consist of 2-60 units that may be either straight or branches
Glycocalyx functions (4):
- Can have molecules that allow cell to bind to another cell
- Can contain receptors for hormones
- Can have enzymes to break down nutrients
- Gives identity of belonging in the person’s body. Knows the body’s own cells (reason for organ donor rejection)
Selective permeability
Ability to differentiate between different types of molecules, only allowing some molecules through while blocking others assisted by the hydrophobic and hydrophilic characteristics of the membrane
Things that can/cannot pass through selective permeable membrane (4):
- Lipid-soluble material can easily slip through the hydrophobic lipid core
- Molecules like CO2 and O2 have no charge and pass through easily
- Substances that are polar (water) cannot pass easily
- Ions or molecules cannot pass easily or at all through the hydrophobic core
Diffusion (4):
- Passive process requiring NO energy
- Movement from an area of high concentration to an area of low concentration until equilibrium is reached
- Can occur across the selectively permeable membrane of living cells if molecules can pass through the hydrophobic core
- In a system with more than one substance, each separate substance has its own concentration gradient
Simple diffusion
When molecules make their way across the cell membrane without any assistance
Factors affecting diffusion (4):
- Concentration gradient: Greater the difference in concentration, the more rapid the diffusion
- Mass of molecules that are diffusing: Larger molecules move more slowly because it is more difficult for them to move in substance when there are little to no space between molecules they are moving through
- Temperature: High temperature increases energy and the movement of molecules = increased rate of diffusion
- Solvent density: As the density of the solvent increases, the rate of diffusion decreases because the molecules have a difficult time getting through the denser solvent
Facilitated diffusion
Assists molecules that cannot pass through the cell membrane by simple diffusion (polar molecules, ions, large compounds) with the help of specific integral proteins called transmembrane integral proteins
Transmembrane integral protein
Specific integral proteins that span the membrane that assist this movement of facilitated diffusion to occur
Two types of transmembrane integral protein:
- Channel proteins
- Carrier proteins
- Both of these are examples of diffusion thus NO ENERGY NEEDED
Channel proteins
Selectively allows particular materials, like certain ions to pass in and out of cell
Carrier proteins
Interact with the substance and shuttle it across the membrane
Osmosis
Diffusion of water across a selectively permeable membrane; only water is transported and follows the concentration gradient of low concentration to high concentration
Why is osmosis even a thing
Because a selectively permeable membrane will limit the passage of solutes, but rarely limit the passage of water
Tonicity
Describes the amount of solute in a solution
Osmolarity
The measure of the total amount of solute dissolved in the solution
3 terms used to relate the osmolarity of a cell:
- Hypotonic
- Hypertonic
- Isotonic
Hypotonic solution
Has a lower concentration of solutes than the fluid inside the cell; net movement of water INTO cell via osmosis (eg. RBC swelling and bursting)
Hypertonic solution
Has a higher concentration of solutes than the fluid inside the cell; net movement of water OUT the cell via osmosis (eg. RBC shrivelling)
Isotonic solution
Has the same concentration of solutes as the fluid inside the cell; no net movement of water into or out of cell (eg. RBC no change)
Active transport
Mechanism that requires the use of the cell’s energy (ATP) when substances must move into a cell AGAINST its concentration gradient
2 classifications of active transport mechanisms:
- Movement of solute molecules across membrane using ATP
- Expulsion of substances out of cell by exocytosis
-Primary active transport
-Secondary active transport
- Directly uses a source of chemical energy (e.g., ATP) to move molecules across a membrane against their gradient
- Uses an electrochemical gradient – generated by active transport – as an energy source to move molecules against their gradient, and thus does not directly require a chemical source of energy such as ATP
Secondary active transport
Movement of a substance across the cell membrane using the energy invested in the active transport of a different substance (active transport powers the movement of another substance)
Endocytosis
Ingestion of large particles like bacteria and the uptake of fluids or macromolecules in small vesicles from outside the cell
Phagocytosis
“Cell eating” Cell engulfing large particles; important for removing pathogens and cell debris
Pinocytosis
“Cell drinking” Cells engulfs droplets of extracellular fluid along with dissolved small molecules