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