Chapter 7-Lecture Notes

Question 1

_______________; is the boundary that separates the living cell from its surroundings; exhibits _____________________, allowing some substances to cross it more easily than others

Answer 1

The plasma membrane

selective permeability

Question 2

________________ are the most abundant lipid in the plasma membrane

Answer 2

Phospholipids

Question 3

Phospholipids are _________________ containing hydrophobic and hydrophilic regions

Answer 3

amphipathic molecules,

Question 4

A phospholipid bilayer can exists as a stable boundary between

Answer 4

two aqueous compartments

Question 5

_______________________ states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it; Proteins are not randomly distributed in the membrane

Answer 5

The fluid mosaic model

Question 6

_________________: in the plasma membrane can move within the bilayer

Answer 6

Phospholipids

Question 7

Most of the lipids, and some proteins, drift laterally

Rarely, a lipid ___________________________

Answer 7

may flip-flop transversely across

the membrane

Question 8

As temperatures cool, membranes switch from a fluid state to a solid state
The temperature at which a membrane solidifies depends on the types of lipids

Answer 8

Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids
Membranes must be fluid to work properly; they are usually about as fluid as salad oil

Question 9

The steroid cholesterol has different effects on membrane fluidity at different temperatures

Answer 9

At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids
At cool temperatures, it maintains fluidity by preventing tight packing

Question 10

Evolution of Differences in Membrane Lipid Composition
Variations in lipid composition of cell membranes of many species appear to be adaptations to specific environmental conditions
Ability to change the lipid compositions in response to temperature changes has evolved in organisms that live where temperatures vary

Answer 10

Membrane Proteins and Their Functions
A membrane is a collage of different proteins, often grouped together, embedded in the fluid matrix of the lipid bilayer
Proteins determine most of the membrane’s specific functions

Question 11

_____________: are bound to the surface of the membrane

_____________ penetrate the hydrophobic core

Answer 11

Peripheral proteins

Integral proteins

Question 12

Integral proteins that span the membrane are called

Answer 12

transmembrane proteins

Question 13

The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar
amino acids, often coiled into ______________

Answer 13

alpha helices

Question 14

Six major functions of membrane proteins

Answer 14

Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)

Question 15

HIV must bind to the immune cell surface protein CD4 and a “co-receptor” CCR5 in order to infect
a cell

Answer 15

HIV cannot enter the cells of resistant individuals that lack CCR5

Question 16

Cells recognize each other by binding to molecules, often containing carbohydrates, ___________________________________

Answer 16

on the extracellular surface of the plasma membrane

Question 17

Membrane carbohydrates may be covalently bonded to lipids (forming ________________) or more commonly to proteins (__________________)

Answer 17

glycolipids

forming glycoproteins

Question 18

_______________ on the external side of the plasma membrane vary among species, individuals, and even cell types in an individual

Answer 18

Carbohydrates

Question 19

The asymmetrical distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is

Answer 19

determined when the membrane is built by the ER and Golgi apparatus

Question 20

A cell must exchange materials with its surroundings, a ________________ control by _______

Answer 20

process controlled by the

plasma membrane

Question 21

Plasma membranes are ________________, regulating the cell’s molecular traffic

Answer 21

selectively permeable

Question 22

Hydrophobic (nonpolar) molecules, such as hydrocarbons, can

Answer 22

dissolve in the lipid bilayer and pass through the membrane rapidly

Question 23

Hydrophilic molecules including ions and polar molecules

Answer 23

do not cross the membrane easily

Question 24

allow passage of hydrophilic substances across the membrane

Answer 24

transport proteins
Some transport proteins, called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel

Question 25

Channel proteins called

——————————facilitate the passage of water

Answer 25

aquaporins

Question 26

Other transport proteins, called carrier proteins, bind to molecules and change shape to shuttle them across the membrane

Answer 26

A transport protein is specific for the substance

Question 27

_________________________ is the tendency for molecules to spread out evenly into the available space
Although each molecule moves randomly, diffusion of a population of molecules may be directional
At dynamic equilibrium, as many molecules cross the membrane in one direction as in the other

Answer 27

Diffusion

Question 28

Substances diffuse down their ______________________, the region along which the density of a chemical substance increases or decreases

Answer 28

concentration gradient

Question 29

No work must be done to move substances ________ the concentration gradient

Answer 29

down

Question 30

The diffusion of a substance across a biological membrane is _______________ because no energy is expended by the cell to make it happen

Answer 30

passive transport

Question 31

________________ is the diffusion of water across a selectively permeable membrane

Answer 31

Osmosis

Question 32

______________________ solution: Solute concentration is greater than that inside the cell; cell loses water

Answer 32

Hypertonic

In a hypertonic environment, plant cells lose water

Question 33

____________ solution: Solute concentration is less than that inside the cell; cell gains water

Answer 33

Hypotonic

In a hypertonic environment, plant cells take water

Question 34

Hypertonic or hypotonic environments create

Answer 34

osmotic problems for organisms

Question 35

—————————the control of solute concentrations and water balance, is a necessary adaptation for life in such environments

Answer 35

Osmoregulation,

Question 36

The protist Paramecium, which is hypertonic to its pond water environment, has a

Answer 36

contractile vacuole that acts as a pump

Question 37

A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now _________________

Answer 37

turgid

Question 38

If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell;
the cell becomes

Answer 38

flaccid

Question 39

The membrane pulls away from the cell wall causing the plant to wilt, a usually lethal effect called

Answer 39

plasmolysis

Question 40

In_________________ transport proteins speed the passive movement of molecules across the plasma membrane

Answer 40

facilitated diffusion,

Question 41

the solute concentration is equal both in and outside the cell. No water leaves or exits

Answer 41

Isotonic

Question 42

______________ facilitate the diffusion of ions

Answer 42

Ion channels

Question 43

Some ion channels, called gated channels, _____________________

Answer 43

open or close in response to a stimulus

Question 44

_____________________ moves substances against their concentration gradient; requires energy, usually in the form of ATP; is performed by specific proteins embedded in the membranes

Answer 44

Active transport

Question 45

Some ion channels, called _________________, open or close in response to a stimulus

Answer 45

gated channels

Question 46

Carrier proteins undergo a subtle change in shape that

Answer 46

translocates the solute-binding site across the membrane

Question 47

—————— is still passive because the solute moves down its concentration gradient, and the transport requires no energy

Answer 47

Facilitated diffusion

Question 48

Some transport proteins, however,

Answer 48

can move solutes against their concentration gradients

Question 49

moves substances against their concentration gradients

Answer 49

Active transport

Question 50

____________________: requires energy, usually in the form of ATP; is performed by specific proteins embedded in the membrane

Answer 50

Active transport

Question 51

Active transport allows cells to maintain concentration gradients that differ from their surroundings
The _________________ is one type of active transport system

Answer 51

sodium-potassium pump

Question 52

______________________ is the voltage difference across a membrane

Answer 52

Membrane potential

Question 53

__________ is created by differences in the distribution of positive and negative ions across a membrane

Answer 53

Voltage

Question 54

___________________ collectively called the electrochemical gradient, drive the diffusion of ions across a membrane

Answer 54

Two combined forces,
A chemical force (the ion’s concentration gradient)
An electrical force (the effect of the membrane potential on the ion’s movement)

Question 55

__________________ is a transport protein that generates voltage across a membrane
The sodium-potassium pump is the major electrogenic pump of animal cells

Answer 55

An electrogenic pump

Question 56

The main electrogenic pump of plants, fungi, and bacteria is a ____________ This Electrogenic pumps help store energy that can be used for cellular work

Answer 56

proton pump

Question 57

__________________ occurs when active transport of a solute indirectly drives transport of other substances

Answer 57

Cotransport

Question 58

Plants commonly use the

Answer 58

gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell

Question 59

______________: across the
plasma membrane occurs by exocytosis and endocytosis
Small molecules and water enter or leave the cell through the lipid bilayer or via transport proteins
Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles

Answer 59

Bulk transport

Bulk transport requires energy

Question 60

______________: transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell
Many secretory cells use exocytosis to export
their products

Answer 60

exocytosis,

Question 61

____________: the cell takes in macromolecules by forming vesicles from the plasma membrane
Endocytosis is a reversal of exocytosis, involving different proteins

Answer 61

endocytosis,

Question 62

There are three types of endocytosis

Answer 62

Phagocytosis (“cellular eating”)
Pinocytosis (“cellular drinking”)
Receptor-mediated endocytosis

Question 63

___________________: a cell engulfs a particle in a vacuole

The vacuole fuses with a lysosome to digest the particle

Answer 63

phagocytosis

Question 64

_______________: molecules dissolved in droplets are taken up when extracellular fluid is “gulped” into tiny vesicles

Answer 64

pinocytosis,

Question 65

_________________: , binding of ligands to receptors triggers vesicle formation

Answer 65

receptor-mediated endocytosis

Question 66

________________________ is any molecule that binds specifically to a receptor site of another molecule

Answer 66

A ligand