2.10 CELL MEMBRANES Flashcards
_____also commonly called plasma membranes because they separate the cytoplasm (aqueous contents) of a cell from its surroundings. It is also defined as a lipid-based structure that separates a cell’s aqueous-based interior from the aqueous environment surrounding the cell. It also controls the movement of substances into and out of the cell
(Cell membrane)
● Up to ____of the mass of a cell membrane is lipid material consisting primarily of the three types of membrane lipids just discussed: phospholipids, glycolipids, and cholesterol
80%
● The keys to understanding the structural basis for a cell membrane are
{(1) the virtually insoluble nature of membrane lipids in water and (2) the “head and two tails” structure of phospholipids and sphingoglycolipids.}
___ ● is a two-layer-thick structure of phospholipids and glycolipids in which the nonpolar tails of the lipids are in the middle of the structure and the polar heads are on the outside surfaces of the structure
LIPID BILAYER)
● How thick is the lipid bilayer?
(six-billionths to nine-billionths of a meter thick—that is, 6 to 9 nanometers thick)
● 3 DISTINCT PART OF THE LIPID BILAYER
( the exterior polar “heads,” the interior polar “heads,” and the central nonpolar “tails,”)
● A lipid bilayer is held together by________, not by covalent bonds. This means each phospholipid or sphingolipid is free to diffuse laterally within the lipid bilayer
( intermolecular interactions)
● Cholesterol molecules are also components of cell membranes. They regulate___________. Because of their compact shape. Within the membrane, the cholesterol molecule orientation is “______” to the outside
the hydroxyl group) and “______” to the inside (the steroid ring structure with its attached alkyl groups). [MEMBRANE RIGIDITY; head; TAIL]
● There are two general types of membrane proteins
integral and peripheral
● is a membrane protein that penetrates the cell membrane. Some membrane proteins penetrate only partially through the lipid bilayer, whereas others go completely from one side to the other side of the lipid bilayer
INTEGRAL MEMBRANE PROTEIN)
● a nonpenetrating membrane protein located on the surface of the cell membrane.
(PERIPHERAL MEMBRANE PROTEIN)
● _____________rather than chemical bonds govern the interactions between membrane proteins and the lipid bilayer
(Intermolecular forces)
● Three common transport mechanisms exist by which molecules can enter and leave cells. They are
passive transport, facilitated transport, and active transport)
● is the transport process in which a substance moves across a cell membrane by diffusion from a region of higher concentration to a region of lower concentration without the expenditure of any cellular energy. Only a few types of molecules, including O2, N2, H2O, urea, and ethanol, can cross membranes in this manner
(Passive transport)
● what molecules can cross the membrane in a passive transport
O2, N2, H2O, urea, and ethanol)
● is the transport process in which a substance moves across a cell membrane, with the aid of membrane proteins, from a region of higher concentration to a region of lower concentration without the expenditure of cellular energy. The specific protein molecules involved in the process are called carriers or transporters.
Facilitated Transport)
● What molecules can cross the membrane in facilitated transport
Glucose, chloride ion, and bicarbonate ion)
● Proteins involved in active transport are called “_______,” because they require energy much as a water pump requires energy in order to function
pumps
● is the transport process in which a substance moves across a cell membrane, with the aid of membrane proteins, against a concentration gradient with the expenditure of cellular energy
Active transport
● Why is there a need for energy in an active transport?
The need for energy expenditure is related to the molecules moving against a concentration gradient—from lower to higher concentration)
● Why is there a need for active transport?
It is essential to life processes to have some solutes “permanently” at different concentrations on the two sides of a membrane, a situation contrary to the natural tendency (osmosis) to establish equal concentrations on both sides of a membrane. Hence the need for active transport.)
● What molecules can cross the membrane during active transport
Sodium, potassium, and hydronium ion)
- The exterior surface positions in a lipid bilayer are occupied by?
- hydrophilic entities
- Which of the following polarity-based descriptions is correct for the interior of a lipid bilayer?
- contains nonpolar tails
- The biochemical function of the cholesterol present in cell membranes is?
- regulate membrane fluidity
- Which of the following membrane transport mechanism requires both the aid of proteins and the expenditure of energy?
- Active transport
