Membrane Structure and Function Flashcards
Plasma membrane
Made up primarily of phospholypids, it separates the internal environment of the cell from the external environment. Fluidity regulated by steroids (ex. Cholesterol). Membrane studded with proteins.
Peripheral proteins (plasma membrane)
Associated with only one side of the plasma membrane, usually the inside, and held in place by cytoskeletal filaments.
Integral proteins (plasma membrane)
Span the plasma membrane, and can protrude from either side. Embedded in the membrane but can move laterally.
Fluid-mosaic model
The combination of proteins, steroids, and phospholipids that form a mosaic pattern on the plasma membrane structure.
Glycolipids
Phospholipids that have a carbohydrate chain attached to them; occur only on the outside of plasma membrane. Play an important role in cellular identification.
Glycoproteins
Proteins with carbohydrate chains attached. Play an important role in cellular identification
Channel Proteins
An integral protein involved in the passage of molecules through the membrane. May contain a gate requiring the binding of specific molecules in the channel.
Carrier Proteins
Involved in the passage of molecules through the membrane. Combine with a substance to help it move across the membrane.
Cell recognition Proteins
Glycoproteins that help the body recognize when it is being invaded by pathogens
Receptor Proteins
Have a shape that allows a specific molecule to bind to them. Binding changes the shape of the protein, allowing a cellular response. (ex: liver stores glucose after being signaled to by insulin)
Enzymatic Proteins
Carry out metabolic reactions directly.
Cell Signaling
Cells “talking” to one another by means of signaling molecules, called chemical messengers. (ex: pancreas releases insulin, transported to liver, signals liver to store glucose as glycogen)
Selectively permeable (membrane)
Certain substances can move across the plasma membrane. Small, noncharged molecules can freely cross the membrane and are said to go “down” their concentration gradient moving from high concentration to low concentration. Molecules moving “up” the gradient require energy.
Aquaporins
Special channel proteins that allow water to quickly cross the membrane (despite it being a polar molecule).
Diffusion
The movement of molecules from a higher to a lower concentration until equilibrium is achieved and they are distributed evenly. The rate of diffusion is influenced by temperature, pressure, electrical currents, molecular size.
Osmosis
The diffusion of water across a selectively permeable membrane due to concentration differences.
Isotonic solution
The solute concentration and the water concentration both inside and outside the cell are equal. There is no net gain or loss of water.
Hypotonic solution
A solution with a lower concentration of solute (higher concentration of water) than inside the cell. Net movement of water is from the outside to the inside of the cell, causing cell to swell.
Turgor Pressure
Created by the swelling of a plant cell in a hypotonic solution. Large central vacuole gains water, causing the cytoplasm to expand and the plasma membrane to push against the cell wall. Helps to maintain rigidity of plant structure.
Hypertonic solution
Solutions that cause the cells to shrivel/shrink due to water loss. A solution with a higher concentration of solute than the cell. The net movement of water is from inside to outside the cell.
Crenation
The shriveling of a cell in a hypertonic solution.
Plasmolysis
Shrinking of the cytoplasm due to osmosis (ex: a plant cell placed in a hypertonic solution)
Facilitated Transport
Passage of molecules across the plasma membrane, facilitated by their reversible combination with carrier proteins. (ex: glucose and amino acids, even though they are not water-soluble) Does not require energy expenditure, as these molecules are moving down the concentration gradient.
Active Transport
Molecules or ions move through the plasma membrane, accumulating inside or outside the cell. Molecules move to the region of higher concentration. Chemical energy required for the carrier to combine with the substance to be transported.
Sodium-Potassium Pump
Sodium ions moved to the outside of the cell and potassium ions moved to the inside of the cell by pump proteins. Results in a solute concentration gradient and an electrical gradient.
Bulk Transport
Macromolecules that are too large to be transported by carrier proteins (ex: polysaccharides) are transported by vesicle formation. Vesicle formation is called membrane-assisted transport because membrane is needed to form the vesicle.
Exocytosis
Vesicle fuses with the plasma membrane and cells secrete substance. Hormones, neurotransmitters, and digestive enzymes are secreted in this manner. The membrane of the vesicle becomes part of the plasma membrane, which enlarges it.
Endocytosis
Cells take in substances by vesicle formation. A portion of the plasma membrane invaginates to envelop the substance, and then the membrane pinches off to form an intracellular vesicle. Happens in 3 different ways.
Phagocytosis
Transports large substances, like viruses, as a form of endocytosis. Common in amoebas, but also happens in humans. When an endocytic vesicle fuses with a lysosome, digestion occurs.
Pinocytosis
Vesicles form around small substances, such as macromolecules and liquid, into cells as a form of endocytosis. “Cell drinking”
Receptor-mediated endocytosis
A form of endocytosis that uses a receptor protein shaped so that a specific molecule can bind to it. Selective and more efficient than pinocytosis
