Chapter 07 - Membrane Structure and Function

fluid mosaic model

a dynamic / active "fluid" membrane; three components: phospholipid bilayer, protein molecules, cholesterol

Which of the following factors would tend to increase membrane fluidity? a) a greater proportion of unsaturated phospholipids b) a greater proportion of saturated phospholipid c) a lower temperature d) a relatively high protein content in the membrane

a) a greater proportion of unsaturated phospholipids

proton pump

actively transports hydrogen ions (H⁺) out of cell; transfers positive charge to cytoplasm

ligands

any molecule that binds specifically to a receptor site on another molecule (LDLs, low density lipids)

All life forms currently have a cell membrane so we presume that the earliest forms of life had this "fence" isolating the internal organization from the external chaos. It is likely that the primordial environment was acidic. In such a case, the cell membrane would have to include a) a sodium (Na+) pump. b) a proton (H+) pump. c) mitochondria underneath in order to provide energy for active transport. d) an acid-proof cell wall. e) a totally non-permeable membrane.

b) a proton (H+) pump.

In what way do the membranes of a eukaryotic cell vary? a) phospholipids are found only in certain membranes b) certain proteins are unique to each cell membrane c) only certain membranes of the cell are selectively permeable d) only certain membranes are constructed from amphiphatic molecules

b) certain proteins are unique to each cell membrane

The current theory of the structure of the plasma membrane is best described by the____ model. a) sandwich b) fluid-mosaic c) unit membrane d) electrochemical e) unipermeable

b) fluid-mosaic

Which phrase does NOT describe one of the functions of proteins of the plasma membrane? a) forming a channel through the membrane b) initiating the replication of the genetic material c) binding to a substance to carry it through the membrane d) acting as a receptor for substances external to the cell e) increasing the rate of a chemical reaction

b) initiating the replication of the genetic material

Proteins within the phospholipid bilayer are different depending on the cell type or membrane type in question, but in general all proteins are restricted to lateral movement only in the plane of the membrane because a) proteins are amphipathic and resist changes in orientation b) phospholipids are amphipathic and resist protein reorientation c) membranes are a fluid mozaic d) non-polar amino acid side chains orient aqueous environment inside and outside the cell e) diglycerides with one hydrophilic phosphate group and two charged fatty acid groups are part of the membrane

b) phospholipids are amphipathic and resist protein reorientation

receptor protein

binds with messenger molecule; causes cell to respond to message

All of the following are part of a prokaryotic cell except a) DNA b) ribosomes c) an endoplasmic reticulum d) a plasma membrane e) a cell "wall" made of peptidoglycan

c) an endoplasmic reticulum

Which of the following protein functions is not correctly associated with its correct integral protein? a) carrier proteins; passage of molecules through the membrane b) enzymatic proteins; carry out metabolic reactions directly c) channel proteins; block the activity of carrier proteins d) cell recognition proteins; recognition of pathogens

c) channel proteins; block the activity of carrier proteins

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly a) spread in a continuous layer over the inner and outer surfaces of the membrane b) confined to the hydrophobic interior of the membrane c) embedded in the lipid bilayer d) randomly oriented in the membrane, with no fixed inside-outside polarity

c) embedded in the lipid bilayer

Which is the best definition of osmosis? a) movement of molecules from an area of their higher concentration to an area of their lower concentration b) movement of water across a semipermeable membrane from an area of high water concentration to an area of lower water concentration c) movement of molecules from an area of their lower concentration to an area of their higher concentration d) movement of water across a semipermeable membrane from an area of low water concentration to an area of higher water concentration e) movement of a substance against its concentration through the release of energy from ATP

c) movement of molecules from an area of their lower concentration to an area of their higher concentration

Which of the following processes includes all the others? a) osmosis b) diffusion of a solute across a membrane c) passive transport d) transport of an ion down its electrochemical gradient

c) passive transport

enzymatic protein

carry out metabolic reactions directly

endocytosis

cells engulf substances into pouch which becomes vesicle

hypertonic solution

concentration of solute higher than other side; cells shrink - plasmolysis (crenation)

hypotonic solution

concentration of solute lower than other side; cells swell; may cause break - lysis

cotransport

couple "downhill" diffusion of solute to "uphill" transport of second substance against concentration gradient; photosynthesis, respiration

If a cell is placed in a hypertonic solution, which will occur? a) Salts will move into the cell from the surrounding solution. b) Water will move into the cell from the surrounding solution. c) Salts will move out of the cell into the surrounding solution. d) Water will move out of the cell into the surrounding solution.

d) Water will move out of the cell into the surrounding solution.

Which of the following associations is NOT correct? a) Desmosomes---Structural junctions holding cells together in strong flexible sheet in an organ b) tight junctions---between cells serving as barriers c) plasmodesmata---porous junctions through cell walls of adjacent plant cells d) gap junctions---between differing types of plasma membranes

d) gap junctions---between differing types of plasma membranes

The highly folded nature of the specialized membrane known as the cristae is an evolutionary adaptation to a) increase survival of offspring b) keep the size of cells small c) increase surface area for exocytosis d) increase surface area for the electron transport chains e) allow for the formation of more lysozomes

d) increase surface area for the electron transport chains

The plasma membrane is capable of many different modes of moving molecules into and out of the cell. This includes facilitated transport which a) moves molecules against their concentration gradient b) allows for the movement of water through the membrane c) does not involve the use of membrane proteins d) is a form of diffusion e) requires energy in the form of ATP

d) is a form of diffusion

The manner by which cholesterol precursors are transported into the cell by binding of LDL to its receptor and the internalization of the receptor-LDL complex is a process of a) facilitated transport. b) active transport. c) cotransport. d) membrane mediated transport e) exocytosis

d) membrane mediated transport

Which of the following is a major cause of the size limits for certain types of cells? a) the evolution of larger cells after the evolution of smaller cells b) the difference in plasma membranes between prokaryotes and eukaryotes c) the need for a surface area of sufficient area to allow the cell's function d) a volume that is small enough to allow for diffusion to exchange nutrients and gasses from the center of the cell e) Both selections 'C' and 'D' are applicable

e) Both selections 'C' and 'D' are applicable

Having similar ____________ would allow tissues and organs to be transplanted easily. a) cell recognition proteins b) major histocompatibility complex proteins c) carbohydrate modified components of the cell membrane. d) glycoproteins e) all of the choices are involved in tissue transplantation

e) all of the choices are involved in tissue transplantation

Which of the following is the reason plants wilt on a hot summer day? a) loss of water b) lack of turgor pressure c) heat weakens the plant cell walls d) failure of evaporative transpiration due to a lack of water around the plants root system e) both loss of water and therefore lack of turgor pressure

e) both loss of water and therefore lack of turgor pressure

carrier proteins

hold onto their passengers and change shape in a way that shuttles them across the membrane; facilitated (passive)

phagocytosis

large, solid material into vesicle

pinocytosis

liquid or small solid particles go into vesicle

diffusion

movement of solute molecules down a concentration gradient; molecules move both ways; high to low and vice versa

osmosis

movement of water to equalize solute concentrations on either side of a semi-permeable membrane

active transport

moves a substance against their concentration gradient w/help of a protein carrier molecule; requires ATP

plant cell walls

permeable cell wall; cellulose main component

gap junctions

plasma membrane channels are joined

sodium-potassium pump

protein changes shape when activated by ATP; releases sodium out or releases potassium in; against gradient; active transport; electrogenic pump for animals

concentration gradient

region along which the density of chemical substances increases or decreases

osmoregulation

regulation of osmotic pressure of cell determined by the relative concentration of solutes and water

isotonic solution

solute and water concentrations equal on both sides of membrane

receptor-mediated

specific form of pinocytosis using a coated pit

FMM: cholesterol

stiffen and stabilize phospholipid bilayer

channel proteins

take ions and a variety of polar molecules and hydrophilic substances and avoid contact with lipid bilayer; facilitated (passive)

passive transport

transport of a molecule without using energy; diffusion and facilitated diffusion

facilitated diffusion

transport of a substance across a cell membrane with the aid of carrier molecules along the substrates concentration gradient; passive transport

FMM: cholesterol and fluid

unsaturated versus saturated hydrocarbon tails; cholesterol within animal cell membrane

exocytosis

vesicles fuse with plasma membrane and secrete contents

How do you think a cell performing cellular respiration rids itself of the resulting CO₂?

CO₂ is a nonpolar molecule that can diffuse through the plasma membrane. As long as it diffuses away so that the concentration remain low outside the cell, it will continue to exit the cell in this way.

What property allows O₂ and CO₂ to cross a lipid bilayer without the help of membrane proteins?

O₂ and CO₂ are both nonpolar molecules that can easily pass through the hydrophobic interior of a membrane.

Why is a transport protein needed to move many water molecules rapid across a membrane?

Water is a polar molecule, so it cannot pass very rapidly through the hydrophobic region in the middle of a phospholipid bilayer.

extracellular matrix

external meshwork of polysaccharides and proteins; close association with cell that produced them

FMM: proteins

float around; hormone receptors and transporters; water and ion transporters; glycoproteins

tight junctions

form impermeable barriers

desmosomes

intercellular filaments between cells; adhesion

equilibrium

net change stops; solute concentration uniform; no gradient

plasmodesmata

penetrate plant cell wall; contains strand of cytoplasm; allows passage of materials

recognition protein

provides unique chemical ID for cells; helps body recognize foreign substances

As a cell grows, its plasma membrane expands. Does this involve endocytosis or exocytosis?

Exocytosis. When a transport vesicle fuses with the plasma membrane, the vesicle membrane becomes part of the plasma membrane.

Sodium-potassium pumps help nerve cells establish a voltage across their plasma membranes. Do these pumps use ATP or produce ATP?

The pump uses ATP. To establish a voltage, ions have to be pumped against their gradients, which requires energy.

Plasma membrane proteins have carbohydrates attached to them in the ER and the Golgi apparatus, then are transported in vesicles to the cell surface. On which side of the vesicle membrane are the carbohydrates?

They are on the inner side of transport vesicle membrane.

Which is the best definition of active transport? a) movement of molecules from an area of their higher concentration to an area of their lower concentration b) movement of water across a semipermeable membrane from an area of high water concentration to an area of lower water concentration c) movement of molecules from an area of their lower concentration to an area of their higher concentration d) movement of water across a semipermeable membrane from an area of low water concentration to an area of higher water concentration e) movement of a substance against its concentration through the release of energy from ATP

e) movement of a substance against its concentration through the release of energy from ATP

In a phospholipid bilayer, the a) phosphate groups are hydrophobic. b) fatty acid tails are ionized. c) fatty acid tails are hydrophilic. d) proteins are located only between the two layers. e) phosphate heads are oriented toward the exterior or toward the cytoplasm.

e) phosphate heads are oriented toward the exterior or toward the cytoplasm.

The major functions of the plasma membrane do NOT include: a) separation of the fluid environments inside and outside the cell. b) regulation of molecules and ions that pass into and out of the cell. c) recognition and communication between different cells and tissues. d) maintaining connections between adjacent cells. e) production of proteins used in construction of the cell wall.

e) production of proteins used in construction of the cell wall.

FFM: phospholipid bilayer

external surface with hydrophilic heads; cytoplasmic surface lined with hydrophilic polar heads; nonpolar, hydrophobic fatty acids in between; separates cytoplasm (internal) from external