UNIT 2 - B 2.1 - Cell Membranes

Question 1

What are two ways scientists gathered evidence to find the model of a cell membrane?

Answer 1

Through using electron microscopes and studying cell/their actions in various environments

Question 2

What is the model of the cell membrane called?

Answer 2

The fluid mosaic model

Question 3

What is the “backbone” of the membrane?

Answer 3

the phospholipid bilayer

Question 4

What is each phospholipid composed of?

Answer 4

1 glycerol (3 carbons) 2 fatty acids and a highly polar alcohol attached to a phosphate group

Question 5

Why are fatty acids not soluble in water?

Answer 5

Because they are non-polar

Question 6

Why are phospholipids amphipathic?

Answer 6

Because their fatty acid tails are hydrophobic but the alcohol with the phosphate group is hydrophilic

Question 7

Why is the membrane typically fluid/flexible?

Answer 7

Because the fatty acid tails don’t attract each other strongly

Question 8

What maintains the overall structure of the membrane?

Answer 8

The relationship between the membrane’s chemical makeup and the chemical properties of water

Question 9

Why would hydrophilic molecules, even small ones, find it hard to move through the membrane?

Answer 9

Because of the hydrophobic region in the middle of the bilayer

Question 10

What is diffusion?

Answer 10

A type of transportation where particles move from a region of higher concentration to a region of lower concentration

Question 11

What is an example of diffusion through cell membranes?

Answer 11

Oxygen has a higher concentration on the outside so it diffuses into the cell while carbon dioxide has a higher concentration inside the cell so it diffuses to the outside (respiration)

Question 12

Where are proteins embedded in the membrane?

Answer 12

in the fluid matrix of the phospholipid bilayer

Question 13

What are the two main types of proteins in the membrane?

Answer 13

integral proteins and peripheral porteins

Question 14

Which type of membrane proteins shows an amphipathic character?

Answer 14

integral proteins

Question 15

Where are peripheral proteins located?

Answer 15

on the surface of the membrane, both inner and outer

Question 16

What are peripheral proteins often anchored to?

Answer 16

integral proteins

Question 17

What are the types of proteins typically present in a cell membrane?

Answer 17

Hormone-binding, enzymatic, cell adhesion, cell-to-cell communication, channel forming, and pumps for active transport

Question 18

What are hormone-binding proteins used for?

Answer 18

They have specific shapes to fit specific hormones which attach to the protein, then the protein changes shape resulting in a message being sent into the cell

Question 19

What are enzymatic proteins used for?

Answer 19

they are grouped together so that a sequence of metabolic reactions (metabolic pathway) is catalysed

Question 20

What are cell adhesion proteins used for?

Answer 20

They allow temporary or permanent connections (junctions) between cells

Question 21

What are the two types of junctions?

Answer 21

gap junctions and tight junctions

Question 22

What allows cell-to-cell communication proteins to distinguish between self and non-self material?

Answer 22

They have carbohydrate molecules attached which provides an identification label allowing for organisms to make these distinguishments

Question 23

What do channel forming proteins do?

Answer 23

they span the membrane, providing passageways for substances to be transported through

Question 24

What is involved in proteins acting as pumps for active transport?

Answer 24

the proteins shuttle a substance from one side of the membrane to the other by changing shape and they use energy in the form of ATP

Question 25

What are the two general types of cellular transport?

Answer 25

passive transport and active transport

Question 26

What is the main difference between active transport and passive transport?

Answer 26

active transport requires energy in the form of ATP but passive transport does not

Question 27

When is passive transport taking place?

Answer 27

when a substance moves from a high concentration to a low concentration (down the concentration gradient)

Question 28

Where does the source of energy for passive transport come from?

Answer 28

the kinetic energy of the molecules

Question 29

Why must energy be used in active transport?

Answer 29

Because the substance is usually moving against the concentration gradient

Question 30

What is an example of passive transport other than diffusion?

Answer 30

osmosis

Question 31

What does osmosis involve the movement of?

Answer 31

Water across a partially permeable membrane

Question 32

What is the concentration gradient allowing for osmosis a result of?

Answer 32

a difference in solute concentrations on either side of the membrane

Question 33

A hypotonic solution has a lower concentration than what kind of solution?

Answer 33

hypertonic solution

Question 34

Which direction does water move from?

Answer 34

Hypotonic to hypertonic

Question 35

Why wouldn’t osmosis occur?

Answer 35

if isotonic solutions occur on either side of a partially permeable membrane

Question 36

What are aquaporins?

Answer 36

protein channels which allow water molecules to pass through them

Question 37

What is facilited diffusion?

Answer 37

a type of diffusion involving integral proteins

Question 38

Which two types of proteins are involved in facilitated diffusion?

Answer 38

carrier proteins and channel proteins

Question 39

How do carrier proteins transport substances from one side of the membrane to the other?

Answer 39

by changing shape

Question 40

Which direction(s) can carrier proteins transport substances?

Answer 40

with the concentration gradient (facilitated diffusion) or against the concentration gradient (active transport)

Question 41

What kinds of molecules can carrier proteins carry?

Answer 41

both water-soluble and insoluble molecules

Question 42

How are channel proteins different from carrier proteins?

Answer 42

they have pores through which molecules of the right size and charge can pass

Question 43

What allows channel proteins’ gates to open and close?

Answer 43

chemical or mechanical signals

Question 44

What molecules can channel proteins carry?

Answer 44

Only water-soluble molecules

Question 45

What allows cell membranes to be selectively permeable?

Answer 45

the presence of channel proteins and carrier proteins

Question 46

What do the factors which facilitate diffusion depend on?

Answer 46

the concentration difference across the membrane, the number of carrier proteins actively involved in transport, and the number of channel proteins open

Question 47

What does the transportation of molecules against a concentration gradient allow the cell to do?

Answer 47

to maintain interior concentrations of molecules that are different from exterior concentrations

Question 48

How can active transport take place?

Answer 48

because of the highly selective proteins in the membrane that bind with the substance to be transported

Question 49

What is an example of an active transport?

Answer 49

the sodium-potassium pump

Question 50

What are sodium-potassium pumps especially important for?

Answer 50

neurons so that animals can respond to stimuli

Question 51

What are the two major factors in how easily a substance can move passively across a membrane?

Answer 51

size and charge

Question 52

What sort of substances will move across a membrane easily?

Answer 52

small and non-polar substances

Question 53

What sort of substances do not move across a membrane easily?

Answer 53

polar or large or substances that are both

Question 54

What are examples of substances that move easily across a membrane?

Answer 54

oxygen, carbon dioxide and nitrogen

Question 55

What are examples of substances that have a hard time moving across a membrane?

Answer 55

chloride ions, potassium ions, sodium ions (due to charges), glucose, and sucrose (due to large size)

Question 56

Why is the cell membrane selectively permeable to large, charged molecules?

Answer 56

Because they must travel through integral proteins

Question 57

What are glycolipids in the cell membrane?

Answer 57

when a membrane phospholipids has a carbohydrate chain attached to it

Question 58

What are glycoproteins in the cell membrane?

Answer 58

cell membrane proteins that have carbogydrate chains attached to them

Question 59

Which side of the cell are carbohydrate chains found only?

Answer 59

the exterior, extracellular side

Question 60

What are glycolipids and glycoproteins important for?

Answer 60

cell identification and cell adhesion

Question 61

What are blood types A, B and O a result of?

Answer 61

carbohydrate chains

Question 62

What do carbohydrate chains allow the body to do?

Answer 62

work out which cell belong to the body (self) and which cells are from the outside (non-self)

Question 63

What would happen if the carbohydrate chains of a transplanted tissue or organ are not compatible?

Answer 63

rejection will occur- the reciever’s immune system will attack the foreign cells resulting in the transplant’s failure

Question 64

What is glycocalyx?

Answer 64

a thin sugar layer made up of carbohydrate chains attached to proteins that can cover a cell

Question 65

What are the functions of glycocalyx in animal cells?

Answer 65

cell to cell adhesion, cell to cell recognition and reception of various signalling chemicals

Question 66

What are the functions of glycocalyx in bacterial and fungal cells?

Answer 66

adhesion and protection

Question 67

What is the function of glycocalyx in plant cells?

Answer 67

to help anchor the plant’s cell membrane to the cell wall

Question 68

What may the membrane’s consistancy be compared to?

Answer 68

the consistancy of olive oil

Question 69

Where may cholesterol be found in animal cells’ membranes?

Answer 69

in the hydrophobic regions

Question 70

What does cholesterol have a role in with the membrane?

Answer 70

determining the membrane’s fluidity

Question 71

What would happen if cholesterol was not in the cell membrane?

Answer 71

The membrane wouldn’t be able to function at such a wide temperature range

Question 72

How do cholesterol molecules help the membrane’s fluidity?

Answer 72

by interacting with the tails in the phospholipid bilayer

Question 73

Since plant cells do not have cholesterol molecules, what do they depend on to have a proper membrane fluidity?

Answer 73

saturated or unsaturated fatty acids

Question 74

What allows fluidity for the cell membrane?

Answer 74

because the heads of the phospholipids are the only things that can create hydrogen bonds with water and because hydrogen bonds are relatively weak, individual phospholipids and unanchored proteins are relatively free to move around

Question 75

What do the double bonds within the fatty acid tails cause the molecules to become?

Answer 75

bent and less tightly packed and lower melting points

Question 76

When do the cell membrane fatty acids have mostly saturated bonds?

Answer 76

when the surrounding temperatures are higher

Question 77

What allows a denser arrangement of the phospholipid layer?

Answer 77

higher temps= more saturated bonds= straighter shape= denser arrangement of phospholipid layer

Question 78

What does the membrane’s increased density allow for?

Answer 78

a stronger membrane and more able to be effective at higher temperatures

Question 79

What types of organisms are more vulnerable to temperature changes?

Answer 79

single-celled organisms like bacteria

Question 80

What are fatty acid desaturases?

Answer 80

a type of enzyme in bacterial membranes

Question 81

What do fatty acid desaturases do?

Answer 81

speed up reactions that result in an increase in double bonds within the fatty acid tails

Question 82

What does cholesterol in the membrane act to do at high temperatures vs low temperatures?

Answer 82

at high temperatures: stabilize membranes
at low temperatures: maintain membrane flexibility

Question 83

Why is there more cholesterol in the plasma membrane than the endoplasmic reticulum membrane?

Answer 83

Because the plasma membrane is subjected to more extreme temperatures

Question 84

How may large molecules and large amounts of material move across the plasma membrane?

Answer 84

through endocytosis and exocytosis

Question 85

What’s the difference between endocytosis and exocytosis?

Answer 85

endocytosis allows macromolecules to enter the cell while exocytosis allows them to leave

Question 86

What is the process of endocytosis?

Answer 86

When a portion of the plasma membrane is pinched off to enclose the material within a vesicle in the cell

Question 87

Why do the ends of the membrane reattach after endocytosis?

Answer 87

Because of the hydrophobic and hydrophilic properties of phospholipids and the presence of water

Question 88

What is exocytosis?

Answer 88

The process of endocytosis, but backwards

Question 89

What is the first step of protein exocytosis?

Answer 89

protein produced by the ribosomes of the rough ER enters the lumen of the ER and is packed into a vesicle

Question 90

What is the lumen?

Answer 90

The inner space of the ER

Question 91

What is the second step of protein exocytosis?

Answer 91

the vesicle carrying the protein fuses with the cis side of the golgi apparatus

Question 92

What is the third step of protein exocytosis?

Answer 92

The protein is modified as it moves through the golgi apparatus and exits on the trans face inside another vesicle

Question 93

What is the fourth step of protein exocytosis?

Answer 93

the vesicle with the modified protein moves towards and fuses with the plasma membrane resulting in the secretion of the contents from the cell

Question 94

What are gated channels?

Answer 94

channels which allow ions to pass through the cell membrane which open and close in response to chemical and electrical stimuli

Question 95

What does movement of ions through channels control?

Answer 95

The electrical potential across the membranes

Question 96

What types of cells especially have their electrical potentials controled by ions movement through channels?

Answer 96

nerve cells and muscle cells

Question 97

What is an example of a neurotransmitter-gated ion channel?

Answer 97

nicotinic acetylcholine receptors

Question 98

What are neurotransmitters?

Answer 98

chemicals that allow signals to pass between two nerves at junctions

Question 99

What are the junctions called where signals pass between two nerves?

Answer 99

synapses

Question 100

Where do neurotransmitters also function?

Answer 100

At the junctions between nerves and muscles

Question 101

When do neurotransmitter-gated ion channels open?

Answer 101

When acetylcholine attaches to a nicotinic acetylcholine receptor

Question 102

What are some of the positive ions that can pass through the neurotransmitter-gated ion channels when they are opened?

Answer 102

Na, K, and Ca

Question 103

What do the positive ions passing through the neurotransmitter-gated ion channel cause?

Answer 103

the membrane potential to change so that an impulse is generated

Question 104

How are our bodies’ responses possible?

Answer 104

nerve impulses carried along multiple connected neurons within the body

Question 105

What can cause muscle movement?

Answer 105

When the neurotransmitter is released at the junction between a nerve and a muscle, the receptor opens and positive ions move allowing for muscle movement

Question 106

What produces antibodies to nicotinic acetylcholine receptors?

Answer 106

The autoimmune disorder known as mysathenia gravis

Question 107

What do the antibodies produced by mysathenia gravis do which makes incomplete muscle movement more common?

Answer 107

They bind to the receptors which reduces the person’s response to the neurotransmitter, acetylcholine

Question 108

What are voltage-gated channel proteins opened by?

Answer 108

changes in membrane polarity

Question 109

What are examples of voltage-gated protein carriers?

Answer 109

Positive sodium and potassium channels

Question 110

Which channel in sodium and potassium channels opens first?

Answer 110

the sodium channel

Question 111

What depolarizes the membrane of a neuron?

Answer 111

When the sodium channel opens and sodium ions move from the outside of the neuron to the inside

Question 112

What happens after the potassium channels opens (slowly) and potassium ions move from the inside of the cell to the outside?

Answer 112

The membrane returns to its normal potential

Question 113

What is the process of re-establishing membrane potential after depolarization?

Answer 113

Repolarization

Question 114

What is the sodium-potassium pump an important example of?

Answer 114

Active transport

Question 115

Where do animal cells have a higher concentration of potassium ions?

Answer 115

Inside the cells

Question 116

Where do animal cells have a higher concentration of sodium ions?

Answer 116

Outside the cells

Question 117

What does the higher concentration of positive sodium ions outside the cells than positive potssium ions inside the cell create?

Answer 117

A difference in charge across the membrane

Question 118

What is a difference in charge across a membrane also called?

Answer 118

the membrane potential

Question 119

What kind of cells is the membrane potential especially important to?

Answer 119

nerve cells

Question 120

What does a nerve impulse take place as a result of?

Answer 120

sodium ions diffusing into the cell through specialized channels creating a change in charge

Question 121

What is depolarization?

Answer 121

a change in charge

Question 122

What repolarizes the cell?

Answer 122

potassium ions diffusing out of the cell

Question 123

What does the sodium-potassium pumps maintain?

Answer 123

the membrane potential

Question 124

What is the first stage of the sodium-potassium pump?

Answer 124

The pump protein with an attached ATP molcule binds to three sodium ions in the cell

Question 125

What is the second stage of the sodium-potassium pump?

Answer 125

ATP is split after the binding of sodium ions which provides energy and leaves a phosphate attached to the carrier

Question 126

What is the addition of phosphate called?

Answer 126

phosphorylation

Question 127

When does ATP become adenosine diphosphate (ADP)?

Answer 127

When ATP carries out phosphorylation of the sodium-potassium pump and loses a phosphate

Question 128

What is the third stage of the sodium-potassium pump?

Answer 128

The protein changes shape due to the phosphorylation and expells sodium ions out of the cell

Question 129

What is the fourth stage of the sodium-potassium pump?

Answer 129

Two potassium ions from outside the cells bind to different regions of the protein which causes the release of the phosphate group

Question 130

What is the fifth stage of the sodium-potassium pump?

Answer 130

The protein’s original shape is restored after it loses the phosphate group and the potassium ions are released inside the cell

Question 131

How many of each ion enter/exit the cell during each cycle of the sodium-potassium pump?

Answer 131

three sodium ions leave, two potassium ions enter