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Flashcards in chapter 7 Deck (106):
1

The plasma membrane is the boundary that

separates the living cell from its surroundings

2

The plasma membrane exhibits

selective permeability, allowing some substances to cross it more easily than others

-it chooses. its picky.

-not just anything gets in the cell. they decide what gets in cell. its like a bouncer at a club that decides who gets to go in or who doesnt.

3

Phospholipids are the most abundant

lipid in the plasma membrane

4

Phospholipids are

amphipathic molecules, containing hydrophobic and hydrophilic regions

-half like water, half doesnt like water

5

The fluid mosaic model states that

a membrane is a fluid structure with a “mosaic” of various proteins embedded in it

-fluid- dynamic, moving
-mosaic- a bunch of little pieces together
made of lots of different molecules/elements

6

Membranes have been chemically analyzed and found to be made of

proteins and lipids

7

Scientists studying the plasma membrane reasoned that it must be a

phospholipid bilayer

8

two main components of membranes

proteins and lipids (phospholipids)

9

In 1935, Hugh Davson and James Danielli proposed a sandwich model in which the phospholipid bilayer lies between two layers of globular proteins
Later studies found problems with this model, particularly the placement of membrane proteins, which have hydrophilic and hydrophobic regions
In 1972, S. J. Singer and G. Nicolson proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water

proteins are embedded across membrane

10

Freeze-fracture studies of the plasma membrane supported the fluid mosaic model.

Freeze-fracture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer.

11

Phospholipids in the plasma membrane can move within the bilayer. (constantly moving)

Most of the lipids, and some proteins, drift laterally.(move left to right)
Rarely does a molecule flip-flop transversely across the membrane.

12

As temperatures cool, membranes

switch from a fluid state to a solid state
-this is bad. dont want a membrane to freeze up.

13

The temperature at which a membrane solidifies depends on the types of lipids

Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids

(unsaturated fatty acids- double bonds with kinks)
(saturated fatty acids- will stack much better)

14

Membranes must be fluid to

work properly

15

The steroid cholesterol has different effects on membrane fluidity at different temperatures
(does different jobs at different times)

-At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids
-At cool temperatures, it maintains fluidity by preventing tight packing. and keeps things moving so it doesnt pack or go too slow.

normal body temperature- keep things moving but it restrains it so it doesnt go too fast

16

Some proteins in the plasma membrane can

drift within the bilayer

17

Proteins are much larger than lipids and

move more slowly

18

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.

19

A membrane is a

collage of different proteins, often grouped together, embedded in the fluid matrix of the lipid bilayer

20

Proteins determine

most of the membrane’s specific functions

21

The two sides of a membrane have

different protein and lipid compositions

22

phospholipids

most common lipid in a membrane

23

Peripheral proteins

are bound to the surface of the membrane

24

Integral proteins penetrate the hydrophobic core (across the membrane).

-Integral proteins that span the membrane are called transmembrane proteins
-The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into alpha helices

25

Six major functions of membrane proteins

1. Transport
2. Enzymatic activity (speed up reactions)
3. Signal transduction
4. Cell-cell recognition
5. Intercellular joining
6. Attachment to the cytoskeleton and extracellular matrix (ECM)

-Membranes are structural and functional mosaics

26

Cells recognize each other by

binding to surface molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane

27

Membrane carbohydrates may be covalently bonded to

lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)

28

Carbohydrates on the external side of the plasma membrane vary among

species, individuals, and even cell types in an individual
Example – Blood types

29

Membranes have

distinct inside and outside faces

30

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

the membrane is built by the ER and Golgi apparatus

31

Molecules that start out on the inside face of the ER end up

on the outside face of the plasma membrane

32

A cell must exchange materials with its surroundings, a process controlled by the

plasma membrane

33

Plasma membranes are selectively permeable, regulating the cell’s molecular traffic.
Three things that influence whether something will get in the membrane or not:

-Size of molecule
-Polarity of molecule (hydrophobic or hydrophilic)
-Presence/absence of transport proteins in the membrane

34

Hydrophobic (nonpolar) molecules, such as hydrocarbons, can

dissolve in the lipid bilayer and pass through the membrane rapidly
-Hydrocarbons, CO2 and O2

35

Polar molecules, such as sugars, do not

cross the membrane easily (hydrophilic molecules)
-C6H12O6, or charged molecules

36

its easy to get in the membrane if it is

hydrophobic

37

Transport proteins allow

passage of hydrophilic substances across the membrane

38

Some transport proteins, called channel proteins, have a

hydrophilic channel that certain molecules or ions can use as a tunnel

39

Channel proteins called aquaporins facilitate

the passage of water

40

Other transport proteins, called carrier proteins, bind to

molecules and change shape to shuttle them across the membrane

41

A transport protein is

specific for the substance it moves

42

Diffusion is

the tendency for molecules to spread out evenly into the available space

43

Although each molecule moves randomly, diffusion of a

population of molecules may be directional

44

At dynamic equilibrium,

as many molecules cross the membrane in one direction as in the other

45

Types of passive transport

diffusion
osmosis
facilitated diffusion

46

Substances diffuse down their

concentration gradient, the region along which the density of a chemical substance increases or decreases.

No work must be done to move substances down the concentration gradient
-Oxygen gets into cells this way for cellular respiration

47

The diffusion of a substance across a biological membrane is

passive transport because no energy is expended by the cell to make it happen

48

in diffusion, the concentration of one molecule has

no effect on the movement of other molecules

49

passive transport-

requires no energy to do anything to make it happen. it just happens

50

diffusion

movement of molecules from an area of [high mol (high concentration)] to---> [low mol (low concentration)]
"down" the concentration gradient

51

osmosis

movement of water across a selectively permeable membrane
water will move from an area of [low solute] to ---> an area of [high solute]

52

Osmosis is the

diffusion of water across a selectively permeable membrane.

Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides

-water moves from where there is less stuff to more stuff.

53

Tonicity is the

ability of a surrounding solution to cause a cell to gain or lose water
(its always a comparison)
(how cells gain or lose water)

54

Isotonic solution:

Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
its the exact same thing
water vs. water
x vs. x

55

Hypertonic solution:

Solute concentration is greater than that inside the cell; cell loses water
have more solute than what it is being compared to

56

Hypotonic solution:

Solute concentration is less than that inside the cell; cell gains water
have less solute than what comparing it to

57

Hypertonic or hypotonic environments create

osmotic problems for organisms

58

Osmoregulation,

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

(Adapt H2O concentrations)

59

The protist Paramecium,

which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump

60

in a hypotonic solution in animal cells

it fills with water until it lyses (explodes)

61

in a isotonic solution in animal cells

its normal
an equal amount of water goes in and out
we want cells in isotonic enviornemnt

62

in a hypertonic solution in animal cells

it becomes crenate/shriveled

63

in a hypotonic solution in a plant cell

it is turgid, normal.
plant cells love to be turgid in hypotonic solution

64

in a isotonic solution in a plant cell

it is flaccid, water goes in and out

65

in a hypertonic solution in a plant cell

it is plasmolyzed, the plasma membrane rips off edges of plasma membrane, this is bad

66

Cell walls help

maintain water balance

67

plant cells like to be in

hypotonic solutions

68

animal cells like to be in

isotonic solutions

69

A plant cell in a hypotonic solution

swells until the wall opposes uptake; the cell is now turgid (firm)

70

If a plant cell and its surroundings are

isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt

71

In a hypertonic environment, plant cells

lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis

-cant be fixed. bad.

72

In facilitated diffusion,

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

-Most transport proteins are very specific
-2 types of transport proteins:
--Channel proteins and carrier proteins

73

Channel proteins provide

corridors that allow a specific molecule or ion to cross the membrane

74

Channel proteins include

-Aquaporins for facilitated diffusion of water (help move water)
-Ion channels that open or close in response to a stimulus (gated channels)

75

Carrier proteins undergo a

subtle change in shape that translocates the solute-binding site across the membrane

(move things down concentration gradient)

76

Some diseases are caused by

malfunctions in specific transport systems, for example the kidney disease cystinuria

77

Facilitated diffusion is still passive

because the solute moves down its concentration gradient, and the transport requires no energy
-Channel proteins and carrier proteins

78

Some transport proteins, however, can move

solutes against their concentration gradients
-this requires energy

79

Active transport

moves substances against their concentration gradients

80

Active transport requires

energy, usually in the form of ATP

81

Active transport is performed by

specific proteins embedded in the membranes

82

Active transport allows

cells to maintain concentration gradients that differ from their surroundings

83

The sodium-potassium pump

is one type of active transport system

84

Membrane potential is the

voltage difference across a membrane

85

Voltage is created by

differences in the distribution of positive and negative ions across a membrane

86

Cells have a

net negative internal charge

87

Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane:

-A chemical force (the ion’s concentration gradient)
-An electrical force (the effect of the membrane potential on the ion’s movement)

88

An electrogenic pump is a

transport protein that generates voltage across a membrane
(ex. sodium potassium pump)

89

The sodium-potassium pump is the major electrogenic pump of animals

3 Na+ out, 2K+ in = overall 1 positive charge to the extracellular fluid

90

The main electrogenic pump of plants, fungi, and bacteria is a

proton pump

91

Electrogenic pumps help

store energy that can be used for cellular work

92

Cotransport occurs when

active transport of a solute indirectly drives transport of other solutes

93

Plants commonly use

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

94

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

95

Bulk transport requires energy

-exocytosis
-endocytosis

96

In exocytosis,

transport vesicles migrate to the membrane, fuse with it, and release their contents

97

Many secretory cells use exocytosis to export their products

-Pancreatic beta cells releasing insulin
-Neurons releasing neurotransmitters
-Plants making cell walls

98

exocytosis

taking things out of the cell

99

In endocytosis,

the cell takes in macromolecules by forming vesicles from the plasma membrane

100

Endocytosis is a

reversal of exocytosis, involving different proteins

101

There are three types of endocytosis

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

102

endocytosis

bring things into the cell

103

In phagocytosis a cell engulfs a particle in a vacuole

The vacuole fuses with a lysosome to digest the particle

104

In pinocytosis,

molecules are taken up when extracellular fluid is “gulped” into tiny vesicles

105

In receptor-mediated endocytosis,

binding of ligands to receptors triggers vesicle formation

106

A ligand is

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