Chapter 7 - "Membrane Structure and Function"

amphipathic nature (distinct hydrophobic and hydrophilic regions)

characteristics of phospholipids molecules

transport

allows polar molecules through the bilayer

enzymatic activity

anchors the enzymes of a metabolic pathway together

signal transduction

receives molecules outside cell, releases different molecule inside cell

cell-cell recognition

a glycoprotein indicates the cell is in the proper position relative to its neighbors

intercellular joining

cell-cell anchorage, as in a desmosome or tight junction

attachment to cytoskeleton or ECM

actin filaments attach to plasma membrane

dispersion of molecules from an area of high concentration to an area of low concentration

diffusion means:

across a membrane towards higher solute concentration

in osmosis:

burst

if a red blood cell is put in a hypotonic solution, it will:

pinocytosis

a cell forms a vesicle that contains a volumes of extracellular fluid

phagocytosis

a cell envelops a particle/other cell to form a food vesicle

receptor-mediated endocytosis

binding ligands which trigger vesicle formation

exocytosis

moving large molecules/particles out of the cell

active transport

which of the following could describe a process that allows protons (H+) to move against their concentration gradient across a biological membrane using a protein channel?

O2, H2O, N2, and CO2

which of these substances is likely to cross a cellular membrane by simple diffusion?

peripheral proteins

which of these are associated with membranes but are not embedded in the lipid bilayer at all?

• they rarely flip from one side of the membrane to the other

• they often move laterally along the plane of the membrane

Select all of the TRUE statements about membrane phospholipids, assuming that the fluid mosaic model of cell membranes is true.

plasmodesmata and gap junctions

small molecules can travel directly from the cytoplasm of one cell to the cytoplasm of an adjacent cell through ____________

aqueous environments

membranes separate ______________, so that differences can be maintained

plasma membrane

the _____________ surrounds the cell and separates the interior of the cell from the external environment

membrane-bound organelles

______________ have their interior region separated from the rest of the cell

border guarding

controlling what gets in and out

border guarding

passage of substances across membranes is generally regulated by ___________

border guarding

___________ helps to establish and maintain appropriate environments in the cell even as the outside environment changes

membranes

what is a surface for chemistry

enzymes

many _______ are embedded in membranes

membranes

________ helps make reactions easier to control

membranes

__________ help in getting reactants together and in getting catalysts and “reaction chains” together

membrane

sometimes, reactants on one side of a ________ and products are released on the other side, helping cells avoid equilibrium

raising flags and sending or receiving messages

for membranes, more surface chemistry:

chemical recognition and signaling

proteins and glycoproteins embedded in membranes are used for ______________

fluid mosaic model

in the ___________, the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

lipid bilayers

biological membranes are ________ with associated proteins and glycoproteins

phospholipids

most of the lipid involved in lipid bilayers are _________, although others like cholesterol and various glycolipids are also present

membrane

proteins are not randomly distributed in the ___________

spontaneously

phospholipid molecules _________ form bilayers in aqueous environments and requires no energy

• amphipathic nature (distinct hydrophobic and hydrophilic regions)

• overall cylindrical structure

• phosphate group to glycerol is water loving part

• fatty acid tails are water fearing

two reasons no energy is required from cells for phospholipid molecules to spontaneously form bilayers in aqueous environments:

two chains of fatty acids

recall the hydrophilic “head” and hydrophobic “tails” of phospholipids, tails come from ________ linked to glycerol

a polar organic molecule

recall the hydrophilic “head” and hydrophobic “tails” of phospholipids, head come from ___________ linked via a phosphate group to the glycerol backbone

detergents

there are other amphipathic molecules, such as __________ that come to a point at their single hydrophobic tail, thus tending to form spheres instead of bilayers

detergents

____________ can “solubilize” lipids to varying degrees; high enough concentrations of detergents will disrupt cell membranes

fluid mosaic model

the ___________ describes the structure and properties of cell membranes

isolated membrane proteins

____________________ were often found to have a globular nature

sandwich model and singer Nicholson model

two fluid mosaic models:

fluid mosaic model

______________ has some proteins imbedded in lipid bilayers that act as two-dimensional fluids

membranes

___________ are held together by mainly weak hydrophobic interactions

fluid mosaic model

this ______________ explained the existing date and made two key predictions that have been verified

materials, including embedded proteins, can be moved along the membrane due to its fluid properties

1st key prediction about the fluid mosaic model that has been verified:

digestion of certain “transmembrane” proteins applied to one side of a membrane will produce protein fragments that differ from those found if digestion is done only one the other side

2nd key prediction about the fluid mosaic model that has been verified:

two-dimensional fluids

biological membranes act a ________________, or liquid crystals

biological membranes

_____________ are free to move in two dimensions, but not in third, the molecule of the membrane can rotate or move laterally (movement occurs sideways)

“flip”

molecules rarely ______ from one side of the membrane to the other (that would be movement in the third dimension)

temperature and the molecules

the fluidity of a membrane is a function of both __________________ in the membrane

fluidity

cells need membranes to be within a reasonable range of _________ - too fluid and they are too weak, too viscous and they are more like solid gels

salad oil

cells are usually as fluid as _______

unsaturated fatty acids

membranes rich in _____________ are more fluid than those rich in saturated fatty acids

phospholipids

at a given temperature, ___________ with saturated fats are less fluid than those with unsaturated fats

“bend”

in an unsaturated fat, a carbon-carbon double bond produces a ________ that causes the phospholipids to be spaced further away from its neighbors, thus retaining more freedom of motion

cholesterol

other lipids, such as _________, can stabilize membrane fluidity

colder temperatures

at ________________, unsaturated fats are preferred in cell membranes (makes them more fluid)

fluidity

at cool temperatures, unsaturated fats maintain ________ by preventing tight packing

higher temperatures

at ______________, saturated fats are preferred (make them less fluid)

cholesterol

___________ restrains movement of phospholipids

plants

___________ use related steroid lipids to buffer membrane fluidity

membranes with high proportion of unsaturated hydrocarbon tails

Fishes in extreme cold have ____________________, enabling their membrane to remain fluid in spite of low temperature

organisms

in the fluid mosaic model, __________ control membrane fluidity by several means (3)

• by regulating their temp (fastest method)

• by changing the fatty acid profile of their membranes (slow process)

• By adding fluidity modifiers or stabilizers like cholesterol (“fluidity buffer” usually always present)

The means that organisms control membrane fluidity in the fluid mosaic model:

open ends

in the fluid mosaic model, biological membranes resist having __________

“self-seal”

a lipid bilayer will spontaneously __________

lumen

usually, “self-sealing” results in nearly spherical vesicles with an internal aqueous __________

structural elements, such as structural proteins

in the fluid mosaic model, the spherical tendency can be modified with _______________________

self-sealing

in the fluid mosaic model, winding membrane surfaces must be kept far enough apart and structurally supported to prevent them from _______________

protein contractile rings

vesicle formation take advantage of self-sealing as regions of membrane are pinched off by _______________

membrane surfaces

in the fluid mosaic model, fusion of ________________ can occur when they are in close proximity (spontaneously; no energy cost)

fusion

in the fluid mosaic model, ________ is common between vesicles and various organelles

two separate membrane-bound lumens

the the fluid mosaic model, contents of ________________ are mixed when fusion occurs

fusion of vesicles with the plasma membrane

in the fluid mosaic model, ___________________________-delivers the material in the vesicle lumen to the outside of the cell

different proteins, often grouped together

a membrane is a collage of __________________, embedded in the fluid matrix of the lipid bilayer

50

more than _____ kinds of proteins have been found in plasma membrane of RBC

proteins

________ determine most of the membrane’s specific functions

• transmembrane proteins

• peripheral proteins

2 membrane proteins:

2 ; 50

membrane proteins:

__% of the molecules in plasma membrane

__% of its weight

peripheral proteins

____________ are bound to the surface of the membrane

intergral proteins

____________ penetrate the hydrophobic core

transmembrane proteins

________________ span the membrane

hydrophobic regions

_________________ of and integral protein are stretches of non polar amino acids coiled into alpha helices

intergal or peripheral

membrane proteins are classified as either ___________________

intergral proteins

_________________ are amphipathic proteins that are firmly bound to the membrane, and can only be released from the membrane by detergents

transmembrane proteins

integral proteins that span the membrane are called ______________

hydrophobic helices

______________ are common in the membrane spanning domains of transmembrane proteins

hydrophobic helices

some _______________ wind back and forth across the membrane

peripheral proteins

__________________ are not embedded in the membrane

peripheral proteins

___________ usually bound ionically or by hydrogen bonds to a hydrophilic portion of an integral protein

from species to species

the carbohydrates on the extracellular side of the plasma membrane vary__________, among individuals of the same species, and even from one cell type to another in a single individual

diversity of the molecules and their location on the cell’s surface

the _____________________________ enable membrane carbohydrates to function as markers that distinguish one cell from another

membranes

______________ have distinct inside and outside faces

protein profile

the ____________ of one membrane side typically differs from that of the other side

cytoplasmic side

many more proteins are on the _____________ of the plasma membrane as revealed by freeze-fracturing plasma membranes

depending on the target side

the types of processing that a protein receives differs _______________, or if it is integral