Chapter 5: Membranes Flashcards
Membrane
also called plasma membrane, is found in all cells and separates the cell from the outside environment
The lipid layer forming the foundation of a cell’s membrane is a bilayer of ?
Phospholipid
Phospholipids include ___,
___, ___
glycerol phospholipids, sphingolipids, and sphingomyelin
Cell membranes are assembled from four components:
Phospholipid bilayer, Transmembrane proteins, Interior Protein Network, and Cell-Surface Markers
What is the function of the phospholipid bilayer?
Provides permeability barrier, matrix for proteins
What does spectrins do?
Determine the shape of the cell
What do Clathrins do?
Anchor certain proteins to specific sites, expecially on the exterior plasma
Transmembrane proteins
The proteins has a variety of functions like transportation and communication
Interior Protein Network
Membranes are structurally supported by intracellular proteins, reinforcing the shape
Cell-Surface Markers
Different cell type exhibit various glycoproteins + glycolipids on their surface acting as a cell identity marker
Why do phospholipids spontaneously form bilayers?
The amphipathic structure
What part of the phospholipid is hydrophilic?
the polar head group
What part of the phospholipid is hydrophobic?
the nonpolar hydrocarbon tails
Why is a lipid bilayer stable?
because water has an affinity for hydrogen bonding, and doesn’t stop.
What changes the degree of membrane fluidity?
the composition of the membrane itself
How does changes in the environment effect the plasma membrane of a single-celled organism?
Increasing temperature makes a membrane more fluid and decreasing makes it less fluid
What are the six key classes of membrane proteins?
Transporters, enzymes, cell-surface receptors, cell-surface identity markers, cell-to-cell adhesion proteins, attachments to the cytoskeleton, proteins that affect membrane structure
Proteins that affect membrane structure
Membranes tend to form spheres or sheets in aqueous solutions. Wedge-shaped proteins can cause membranes to bend allowing the formation of tubes and folded sheets.
Enzymes
Cells carry out many chemical reaction on the interior surface of the plasma membrane, using enzymes attached to the membrane.
Cell-to-cell adhesion proteins
Cells use specific proteins to glue themselves to one another. Some act forming temporary interactions and other more permanent bond.
How membrane proteins attach to the surface of membranes, how do they do this?
Transmembrane domain
Hydrophobic region of a transmembrane protein that anchors it in the membrane
Passive transport
The movement of substances across a cell’s membrane without the expenditure of energy
Diffusion
A net movement of dissolved molecule or other particles from a region where they are more concentrated to a region where they are less concentrated
Facilitated Diffusion
The diffusion of molecules or ions through carrier proteins or ion channels, which require a concentration gradient but no energy required.
Channel protein
A transmembrane protein with a hydrophilic interior that provides an aqueous channel allowing diffusion of species that can not cross the membrane.
What types of ions use a channel protein?
K+, Na+, or Ca2+
Carrier Protein
A membrane protein that binds to a specific molecule that can not cross the membrane and allows passage through the membrane.
Ion channel
Membrane proteins that allow the passage of ions through a phospholipid bilayer used specific for a single ion, and may be found in the plasma membrane or in internal membrane.
Three conditions that determine the direction of net movement of the ions include:
- relative concentration on either side of membrane
- voltage difference across the membrane
the state of the gate (opened or closed)
How do water molecules interact with dissolved solutes?
They form hydration shells around the charged solute molecule
Osmosis
The diffusion of water across a selectively permeable membrane
If two solutions have unequal osmotic concentrations, the solution with the higher concentration is
Hypertonic
the solution with the lower concentration is
Hypotonic
When two solutions have the same osmotic concentration, the solutions are
Isotonic
Aquaporin
A membrane channel that allows water to cross the membrane more easily than by diffusion through the membrane.
Aquaporins fall into two general categories including:
those that are specifically for only water and those that are allow other small hydrophilic molecules
Osmotic Pressure
The potential pressure developed by a solution separated from pure water by a differentially permeable membrane.
- Higher the solute concentration = higher osmotic pressure
Extrusion
Some single-celled eukaryotes like protist, use organelles called contractile vacuoles to remove water
Isosmotic Regulation
Some organisms that live in the ocean adjust their internal concentration of solutes to match that of the surrounding seawater
Turgor
Most plant cells are hypertonic to their environment, contain high concentration of solutes in their central vacuoles. This results in hydrostatic pressure, known as turgor pressure, where the plasma membrane presses against the interior of the cell making the cell rigid
Active Transport
The pumping of ions and other molecules across a cellular membrane from a region of lower concentration to a higher concentration; this transport requiring energy
Uniporters
Carrier proteins that transport a single type of molecule
Symporter
A carrier protein in a cell’s membrane that transports two molecules or ions in the same direction across the membrane
Antiporter
A carrier protein in a cell’s membrane that transports two molecules in opposite directions across the membrane
Sodium-Potassium Pump
Transmembrane channels engaged in the active transport of Na+, exchanging them for K+, where both ions are being moved against their concentration gradients
Bulk transport
Transport of large amounts of substances across plasma membrane by utilizing energy
What are the two processes involved in bulk transport?
endocytosis, and exocytosis
Endocytosis
The uptake of materials into cells by inclusion within an invagination of the plasma membrane; the uptake of solid material in phagocytosis and that of dissolved material in pinocytosis
What are three types of endocytosis?
phagocytosis, pinocytosis, and receptor-mediated endocytosis
Phagocytosis
Endocytosis of a solid particle
Pinocytosis
The process of fluid uptake by endocytosis in a cell
Receptor-mediated endocytosis
Process by which specific macromolecules are transported into eukaryotic cells at clathrin-coated pits, after binding to specific cell-surface receptors
Exocytosis
The discharge of material from vesicles at the cell surface
Why is exocytosis important in plant cells?
It’s a mean of exporting the materials needed to construct the cell wall through the plasma membrane
How is exocytosis used in animal cells?
It provides a mechanism for secreting many hormones, neurotransmitters, digestive enzymes, and other substances
Coupled Transport
Molecules are transported across a membrane against their concentration gradients by the cotransport of sodium ions or protons down their concentration gradients
The fluid mosaic model of the membrane describes the membrane as
made of proteins and lipids that can freely move
How are active transport and coupled transport related?
Coupled transport uses the concentration gradient established by active transport
What variable(s) influence(s) whether a nonpolar molecule can move across a membrane by passive diffusion?
The difference in concentration of the molecule across the membrane
