cell bio exam 4

the protein containing lipid bilayer that surrounds a living cell

plasma membrane

all cells have a _______ membrane!

plasma

the plasma membrane separates that cell from its surrounding and allows the composition of cell to be ________ from its environment

different

cells are not in ___________ with the environment (fight against this)

equilibrium

membrane structure

• made of ___ layers of lipids into which proteins have been inserted

• the __________ of the membrane varies from cell type to cell type and depends on what a cell’s function is (form = function)

• the membrane also ____ allow nutrients in and waste out

• also functions to allow the cell to _____ and change shape

two, composition, must, move

common membrane components:

• protein ________

• protein ______

• molecular _______/receptors

• various types of ___________

channels, pumps, sensors, phospholipids

membrane structure

• the membrane is ____ healing (if it is pierced it quickly reseals)

• bacteria and archaea have a ______ membrane: the cell membrane/plasma membrane

• eukaryotes also have ________ membranes that surround organelles

• the internal membranes of eukaryotes act similarly to the plasma membrane but their _________ varies from organelle to organelle

self, single, internal, composition

what are the four parts that make up the endomembrane system?

ER smooth and rough, golgi aparatus, and nuclear envelope

all membranes are composed of ______ and form a bilayer

lipids

thin pair of closely positioned sheets composed mostly of phospholipids that forms the structured basis of all cell membranes

lipid bilayer

membrane lipids form bilayers in ______

• the ________ of the lipid bilayer is determined by the way lipids behave in water

• ___________ (dual nature) - having hydrophobic and hydrophilic regions

water, structure, amphipathic

interacts with water

hydrophilic

excludes water

hydrophobic

class of molecules that make up most of the lipids in the bilayer. composed of two fatty acid tails linked to a phosphate containing polar group

phospholipids

different phospholipids have ________ features and purposes in membranes

• examples:

  • ___ is often used for signaling

  • ___ used to start apoptosis

  • ___ creates curves in the membrane

different, PI, PS, PE

• phospholipids are ____ the only amphipathic molecules found in cell membrane

• many membranes contain sphingomyelin and/or _________, other types of lipids

• animal cell membranes contain _________

not, glycolipids, cholesterol

• the amphipathic nature of these molecules is why membranes assemble into ______

• the polar head groups will form electrostatic interactions with water (which is also polar) while hydrophobic regions will cluster away from water forcing water molecules around them to ________

bilayers, rearrange

single tail membrane lipid that forms into a spherical shape

micelle

• the same forces that make the bilayer form are also what makes membranes ____ healing

• any tear in the membrane will create a region where the __________ tails are exposed to water

• because this is a high energy, ________ arrangement the lipid bilayer will spontaneously seal driven by electrostatic interactions and hydrophobic forces

self, hydrophobic, unfavorable

the lipid bilayer is a ______ two dimensional fluid

flexible

electrostatic and hydrophobic interactions may keep the lipids from ________ the bilayer arrangement, but _______ stops them from moving around and changing places

escaping, nothing

common lipid movements:

• switching places _______ with other lipids

• ________ in place about an axis

laterally, spinning

rare lipid movements:

• ________ from one layer to the other layer

  • this requires ______, but it does occasionally happen and serves a purpose

flipping, enzymes

help lipids flip from the outer layer to the inner layer; requires ATP (has preference for phospatidylserine and phospatidylethanolamine)

flippases

helps lipids flop from the inner layer to the outer layer; requires ATP (has preference for phosphatidylcholine, sphingomyelin, and cholesterol)

floppases

an enzyme that can do either; no preferences (creates symmetrical membrane)

scramblases

the _______ of a lipid bilayer depends on its composition

fluidity

fluidity is important for function and must be maintained within certain limits

• allows membrane proteins to ______ rapidly through the membrane to get to where they need to be

• ensures that membrane molecules are distributed _____ between mother and daughter cells during division

• allows membranes to ____ with one another to mix and transport molecules

• allows membrane to ______

diffuse, evenly, fuse, reseal

the fluidity of a membrane at a given __________ depends on it’s composition

temperature

what are the two properties of phospholipid tails that affect how they pack?

length and number of double bonds

phospholipid tails

• ______ packed

  • longer tails

  • fewer double bonds

  • low temperature

• ______ packed

  • shorter tails

  • more double bonds

  • high temperature

tightly, loosely

contains 1 or more carbon double bonds (packed loosely)

unsaturated

only contains carbon single bonds (packed tightly)

saturated

temperature affects membrane _______. increasing temperature causes the membrane to be more ____. cells can counteract this by altering the composition of the membrane

• bacteria and yeast alter the length and saturation of fatty acid ____

• animals add ________ to increase rigidity

fluidity, fluid, tails, cholesterol

membrane assembly

• in eukaryotes, new phospholipids are made by ________ bound to the cytosolic surface of the smooth ER

• all new phospholipids are added to the ______ layer of the smooth ER membrane

• _________ moves phospholipids between layers of the ER to keep the composition of the inner and outer membrane the same (symmetry)

enzymes, outer, scramblase

membrane assembly

• although the ER maintains a constant and equalized composition of the inner and outer membranes, other organelles and the plasma membrane do ____

• the plasma membrane is extremely ________. this asymmetry is maintained by flippases and floppases

• other organelles have varying degrees of ________

not, asymmetric, asymmetry

membrane assembly

• membrane asymmetry begins in the _____ ________

• the golgi contains _________ that start the process of altering the membrane composition

golgi apparatus, flippases

• in the ____ membrane, phospholipids are randomly distributed

• in the golgi apparatus and other cell membranes, phospholipids distribution is _________

ER, asymmetric

• the nature of membrane assembly and asymmetry means that membranes have _______ inside and outside faces

• these faces are maintained even as pieces of the membrane bud off and/or fuse (the cytosolic face will always face the _______)

distinct, cytosol

any protein associated with the lipid bilayer of the cell membrane

membrane proteins

• most membrane functions are carried out by membrane ________

• cell membranes for different types of cells contain _________ proteins to support the specialized functions of cells

proteins, different

what functional class?

• protein example: Na+ pump

• specific function: actively pumps Na+ out of cells and K+ in

transporters

what functional class?

• protein example: K+ leak channel

• specific function: allows K+ ions to leave cells, thereby influencing cell excitability

ion channels

what functional class?

• protein example: integrins

• specific function: link intracellular actin filaments to extracellular matrix proteins

anchors

what functional class?

• protein example: platelet-derived growth factor (PDGF) receptor

• specific function: binds extracellular PDGF and, as a consequence, generates intracellular signals that direct the cell to grow and divide

receptors

what functional class?

• protein example: adenylyl cyclase

• specific function: catalyzes the production of the small intracellular signaling molecules cyclic AMP in response to extracellular signals

enzymes

membranes associate with the lipid bilayer in _________ ways

different

_________ ________ proteins

• transmembrane: go through the membrane fully

• monolayer-associated: only go through 1 layer

• lipid linked

integral membrane

___________ membrane proteins (not touching the lipid bilayer at all)

• protein attached (have covalent weak interactions)

peripheral

membrane proteins have a specific ___________ in the membrane that is critical for their function

orientation

transmembrane proteins face a unique challenge when crossing the membrane because the _______ bonds in the backbone of proteins is polar and hydrophilic

peptide

• in the transmembrane portions of transmembrane proteins the polar backbone is driven to form _______ bonds with itself creating an alpha helix

• in this structure __________ side chains extend off the exterior of the helix while the polar backbone H bonds with itself in the interior

• ______ _____ transmembrane proteins- pass through the lipid bilayer once

  • examples: ________ usually

hydrogen, hydrophobic, single pass, receptors

• many membrane proteins are channels, which can’t be formed if the peptide chain only crosses the membrane _____

• ________ transmembrane proteins- proteins whose polypeptide chains cross the membrane more than once

• unlike single pass proteins, multipass _______ the helices are made of hydrophobic and hydrophilic amino acids

• the __________ amino acids will be on the side of the helix that faces the aqueous environment (the inside of the channel)

• the _________ amino acids will be on the side of the helix that faces the membrane

once, multipass, proteins, hydrophilic, hydrophobic

some transmembrane proteins cross the membrane as a Beta sheet that is rolled into a barrel. we call these _____ _______

beta barrels

Beta barrels

• hydrophilic amino acids in these barrels face the _______ side (inside the channel)

• hydrophobic amino acids face the _______

aqueous, bilayer

the plasma membrane is reinforced by the underlying ____ ______

cell cortex

• a cell membrane alone is very ______

• membranes are therefore strengthened and supported by ______ structures

• in bacteria, yeast, and plants they are strengthened by a ____ wall

• in animals the plasma membrane is stabilized by a meshwork of filamentous proteins on the cytosolic side called the ____ ______

• in many, but not all, ________ cells the cell cortex is rich in actin and myosin

fragile, other, cell, cell cortex, animal

• animal cell example: _______ in red blood cells

• in RBCs the cell cortex is primarily made of a protein called spectrin. It forms a lattice and helps the RBC maintain it’s _______ shape

• ________ abnormalities that alter spectrin result in fragile, misshapen RBCs that are quickly destroyed resulting in anemia

spectrin, concave, genetic

a cell can _______ the movement of its membrane proteins

restrict

• the lipid bilayer is a fluid frequently allowing proteins to _______ freely through it

• but sometimes cells need to also ______ the movement of proteins in the bilayer

diffuse, restrict

ways cells can restrict protein movement

1. fusion to a molecule _______ the cell

2. fusion to a molecule _______ the cell

3. fusion to a molecule on ________ cell

4. erecting diffusion _______

inside, outside, another, barriers

the cell surface is coated with _________

carbohydrate

• many proteins in the plasma membrane have chains of _______ attached to them

• these are called _________ or proteoglycans (depending on how long the sugar chains)

• these molecules are located outside the cell membrane forming a layer of carbohydrates called the _________

• ________ of the glycocalyx: protection, mobility, cell signaling and recognition

sugars, glycoproteins, glycocalyx, function

solutes inside the cell are different from solutes outside the cell which is why equilibrium = ______

death

transport across cell membranes

• cells need to:

  • import ________

  • eliminate ______

  • regulate ___ concentrations

nutrients, waste, ion

most molecules cannot pass the membrane on their own, and so their transport is facilitated by ________ ________ _______

membrane transport proteins

the movement of molecules from an area where they are more concentrated to an area where they are less concentrated without help from any additional molecules

simple diffusion

movement of molecules across a membrane with assistance from a transport protein

facilitated transport

lipid bilayers are ________ to ions and most polar molecules

impermeable

• the ____ at which a molecule diffuses across a membrane depends on its size and solubility

• moves _______ across membranes:

  • large molecules, polar molecules, charged molecules, hydrophilic molecules

• moves more _______ across membranes:

  • small molecules, nonpolar molecules, neutral molecules, hydrophobic molecules

rate, slowly, rapidly