Plasma Membrane Structure and Function
In animal cells, the carbohydrate chains attached to proteins give the cell a "sugar coat,
glycocalyx
Phospholipids and proteins that have attached carbohydrate (sugar) chains are called
glycolipids
Cell recognition proteins are
glycoproteins
concentration gradient
gradual change in chemical concentration between two areas of differing concentrations
Solutions that cause cells to shrink or shrivel due to loss of water are said to be
hypertonic solutions
Solutions that cause cells to swell, or even to burst, due to an intake of water are said to be
hypotonic
glycolipids and glycoproteins play an important role
in cellular identification
Collagen and elastin fibers are two well-known structural proteins
in extracellular matrix
active transport usually requires energy
in the form of ATP
as temperature increases the rate of diffusion
increases
Proteins that are embedded in the plasma membrane are called
integral proteins
Cells are flexible because the phospholipid bilayer
is fluid
The lipid content of the membrane is responsible for
its fluidity.
a gap junction is
junction between cells formed by the joining of two adjacent plasma membranes ; it leads strength and allows ions , sugars, and small molecules to pass between cells
tight junctions
junction between cells when adjacent plasma membrane proteins join to form an impermeable barrier
the substance that adds strength to the secondary walls of woody plants
lignin
Glycolipids
lipids in plasma membranes that contain an attached carbohydrate chain ; assembled in the golgi apparatus
Some plasma membrane proteins are enzymes that carry out
metabolic reactions directly
when a system reaches equilibrium
molecules are distributed equally
facilitated transport explains how
molecules such as glucose and amino acids are rapidly transported across the plasma membrane.
Without this carrier protein,
nerve impulse conduction would be impossible.
The hydrophilic heads of phospholipids are exposed to water
on the outside and inside surfaces of the membrane.
Receptor proteins have a shape that allows only
only a specific molecule to bind to it
The diffusion of water across a selectively permeable membrane from high to low concentration is called
osmosis
cholesterol helps modify the fluidity of the membrane
over a range of temperatures.
proteins that occur only on the cytoplasmic side of the membrane are called
peripheral proteins.
vesicles that enclose macromolecules during exocytosis are composed
phospholipid bilayers
Because similar substances associate with one another,
the hydrophilic polar heads of the phospholipid molecules naturally associate with the polar water molecules found on the outside and inside of the cell
why does the cytoplasm expand when placed in a hypotonic solution?
the large central vacuole gains water and the plasma membrane pushes againts the rigid cell wall
carbon dioxide molecules can not easily pass through
the membrane
The hydrophobic tails associate together and make up the interior of
the membrane.
The greater the concentration of unsaturated fatty acid residues
the more fluid the bilayer.
Receptor proteins: the binding of the receptor protein to a specific molecule causes
the protein to change its shape and thereby bring about a cellular response.
hemolysis
the rupturing or bursting of a red blood cell as the result of being placed in a hypotonic solution
things that are true about exocytosis and endocytosis
they occur at the cell membrane, involve membrane vesicles, and transport large molecules
what do carrier proteins do?
they receive a substance and change their shape , and this change moves the substance across the membrane
the hydrophobic nonpolar tails associate with each other because
they want to "get away" from the polar water.
Channel proteins are involved in passing molecules
through the membrane
Tight junction proteins actually connect plasma membranes between adjacent cells together,
, producing a zipperlike fastening
sodium-potassium pump (active transport)
Carrier protein in the plasma membrane that moves sodium ions out of and potassium ions into animal cells; important in nerve and muscle cells in animals
small non-charged molecules
Cross the cell membrane easily
Cell recognition proteins
Glycoproteins in the plasma membrane that identify self and help the body defend itself against pathogens.
hypertonic solution
Higher solute concentration (less water) than the cytoplasm of a cell; causes cell to lose water by osmosis.
adhesion junctions (flexible filaments between two cells)
Junction between cells in which the adjacent plasma membranes do not touch but are held together by intercellular filaments attached to buttonlike thickenings.
Exocytosis (Bulk Transport)
fusion of a vesicle with the plasma membrane moves a particle to outside the membrane.
fluid mosaic model
Model for the plasma membrane based on the changing location and pattern of protein molecules in a fluid phospholipid bilayer.
Bulk Transport
Movement of substances, usually large particles, across the plasma membrane using vesicles.
extracellular matrix
Nonliving substance secreted by some animal cells; is composed of protein and polysaccharides.
Proteins involved in active transport often are called
PUMPS
facilitated transport
Passive transfer of a substance into or out of a cell along a concentration gradient by a process that requires a protein carrier.
turgor pressure
Pressure of the cell contents against the cell wall; in plant cells, determined by the water content of the vacuole; provides internal support.
Carrier Proteins
Protein in the plasma membrane that combines with and transports a molecule or ion across the plasma membrane.
Enzymatic Proteins
Protein that catalyzes a specific reaction; may be found in the plasma membrane or the cytoplasm of the cell.
Receptor Proteins
Proteins located in the plasma membrane or within the cell; bind to a substance that alters some metabolic aspect of the cell.
isotonic solutions
Solution that is equal in solute concentration to that of the cytoplasm of a cell; causes cell to neither lose nor gain water by osmosis.
what is the plasma membrane composed of?
The membrane is composed of a phospholipid bilayer in which proteins are embedded (integral proteins) or associated with the cytoplasmic side (peripheral proteins).
tonicity
The solute concentration (osmolarity) of a solution compared to that of a cell. If the solution is isotonic to the cell, there is no net movement of water; if the solution is hypotonic, the cell gains water; and if the solution is hypertonic, the cell loses water.
active transport
Use of a plasma membrane carrier protein to move a molecule or ion from a region of lower concentration to one of higher concentration; it opposes equilibrium and requires energy.
without enzymatic proteins
a cell would never be able to perform the chemical reactions needed to maintain its metabolism.
extracellular matrix is
a meshwork of proteins and polysaccharides in close association with the cell that produced them
A carrier protein transports sodium and potassium ions
across the plasma membrane of a nerve cell.
proteins use energy to move a substance
against its concentration gradient
active transport moves molecules
against the concentration gradient
The plasma membrane is essential because it is selectively permeable
allowing only certain substances into the cell while keeping others out.
gap junction
allows cells to communicate; formed when two identical plasma membrane channels join
However, scientists have discovered that the majority of cells have channel proteins, called
aquaporins, that allow water to cross a membrane more quickly than expected.
these molecules follow their concentration gradient
as they move from an area where their concentration is high to an area where their concentration is low
Each cell within an individual has its own "fingerprint" because
because of these carbohydrate chains
Phospholipids are considered amphipathic molecules
because they possess both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region.
In general, small, noncharged molecules, such as carbon dioxide, oxygen, glycerol, and alcohol,
can freely cross the membrane.
the chemical responsible for opening the calcium channnels that result in the burning sensations associated with hot peppers
capcaisin
Note the plasma membrane's asymmetry
carbohydrate chains are attached to the outside surface and project into the extracellular matrix.
cytolysis
cells that have been disrupted.
the carbohydrate that can be found in both the primary and secondary cell wall of plants
cellulose `
When a plant cell is placed in a hypotonic solution, what expands?
cytoplasm
the adhesion junction that connects the cytoskeletons of adjacent animal cells creating a flexible sheet of cells called
desmosomes
movement of molecules from high to low concentration is called
diffusion
the adhesive protein in the extracellular matrix that binds integrin is called
fibronectin
Integrins ( cell signaling )are integral membrane proteins that connect to
fibronectin externally and to the actin cytoskeleton internally.
Fluid-Mosaic Model : Membranes are not rigid but rather are
flexible structures.
Membranes consist of a variety of molecules, including
phospholipids, cholesterol, and proteins
Receptor-mediated endocytosis is a special form of
pinocytosis.
things needed to complete active transport of molecules
plasma membrane, carrier proteins, energy
the intracellular junction with narrow membrane-lined that pass through the plant cell wall are
plasmodesmata
the loss of water from the central vacuole of a plant cell causing it to shrink is called
plasmolysis
phospholipid membranes form bilayers because their _______ heads are attracted to water, while their _______ tails face away from the water
polar, nonpolar
Channel Proteins
protein that forms a channel to allow a particular molecule or ion to cross the plasma membrane
The plasma membrane components that can function as channels, carriers, receptors, and enzymes are membrane
proteins
Glycoproteins (integral membrane proteins)
proteins in plasma membranes that contain an attached carbohydrate chain ; assembled in the golgi apparatus
Junction Protein
proteins in the cell membrane that assist in cell-to-cell communication
which type of molecule assists cell signaling by regulating the movement of molecules through the ECM to the plasma membrane?
proteoglycan
he prefix hypo means "less than" and refers to a solution with a lower concentration of solute (higher concentration of water)
than inside the cell
bulk transport is a way
that large particles can enter or exit a cell
Turgor pressure in plant cells is extremely important
to the maintenance of the plant's erect position
Phagocytosis
transports large substances, such as a virus
pinocytosis
transports small substances, such as a macromolecule, into a cell.
endocytosis (bulk transport)
vesicle formation moves a particle to inside the plasma membrane
. If a cell is placed in a hypotonic solution
water enters the cell, because the lower cellular concentration of water prompts a net movement of water from the outside to the inside of the cell
Aquaporins also allow cells to equalize
water pressure differences between their interior and exterior environments, so that their membranes don't burst from environmental pressure changes.
The amphipathic nature of phospholipids largely explains
why they form a bilayer in water