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Lipids and Membranes Flashcards

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Organic Chemistry 101 flashcards
1
Q

What is the plasma membrane?

A

The plasma membrane is a complex mixture of lipid, protein and carbohydrate which is the boundary that separates the living cell from its surroundings

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2
Q

The plasma membrane exhibits selective permeability, what does this mean?

A

It allows some substances to cross it more easily than others

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3
Q

What are often responsible for controlling passage across cellular membranes

A

Transport proteins

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4
Q

Fats are constructed from two types of smaller molecules, what are they?

A

Glycerol and Fatty acids

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5
Q

What is glycerol?

A

Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon

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6
Q

What is a fatty acid?

A

A fatty acid consists of a carboxyl group attached to a long carbon skeleton

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7
Q

Why are fats hydrophobic?

A

Fats separate from water because water molecules hydrogen-bond to each other and exclude the fats

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8
Q

What determines the solubility of fatty acids?

A

Fatty acids have a polar end (the carboxylic acid group) and a non-polar hydrocarbon chain. The ratio of the polar group to the non-polar group is the factor which determines water solubility.

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9
Q

How can fatty acids vary?

A

Fatty acids vary in length (number of carbons) and in the number and locations of double bonds

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10
Q

What are saturated fatty acids?

A

Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds

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11
Q

What are unsaturated fatty acids?

A

Unsaturated fatty acids have one or more double bonds

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12
Q

What happens when phospholipids are in water?

A

When phospholipids are added to water, they self-assemble into double-layered sheetscalled bilayers. At the surface of a cell, phospholipids are also arranged in a bilayer, with the hydrophobic tails pointing toward the interior

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13
Q

What is the most abundant lipid in the plasma membrane?

A

Phospholipids are the most abundant lipid in the plasma membrane

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14
Q

What biomolecule increases stability of plasma membrane?

A

Cholesterol

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15
Q

Though cholesterol is present in plants, what do they use to stabilise the membrane?

A

They use related steroid lipids to buffer membrane fluidity

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16
Q

As temperatures cool, how do membranes change?

A

As temperatures cool, membranes switch from a fluid state to a solid state

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17
Q

The temperature at which a membrane solidifies depends on the types of lipids, how so?

A

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

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18
Q

What factors influence bilayer fluidity?

A
  1. The length of the fatty acid tail
  2. Temperature
  3. Cholesterol content of the bilayer
  4. The degree of saturation of fatty acids tails
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19
Q

How does the length of the fatty acid tail contribute to the membrane’s fluidity?

A

The length of the fatty acid tail impacts the fluidity of the membrane. This is because the intermolecular interactions between the phospholipid tails add rigidity to the membrane. As a result, the longer the phospholipid tails, the more interactions between the tails are possible and the less fluid the membrane will be.

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20
Q

How does the temperature contribute to the membrane’s fluidity?

A

As temperature increases, so does phospholipid bilayer fluidity. At lower temperatures, phospholipids in the bilayer do not have as much kinetic energy and they cluster together more closely, increasing intermolecular interactions and decreasing membrane fluidity. At high temperatures the opposite process occurs, phospholipids have enough kinetic energy to overcome the intermolecular forces holding the membrane together, which increases membrane fluidity.

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21
Q

How does the cholesterol contribute to the membrane’s fluidity?

A

Cholesterol has a somewhat more complicated relationship with membrane fluidity. You can think of it is a buffer that helps keep membrane fluidity from getting too high or too low at high and low temperatures.
At low temperatures, phospholipids tend to cluster together, but steroids in the phospholipid bilayer fill in between the phospholipids, disrupting their intermolecular interactions and increasing fluidity.
At high temperatures, the phospholipids are further apart. In this case, cholesterol in the membrane has the opposite effect and pulls phospholipids together, increasing intermolecular forces and decreasing fluidity.

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22
Q

How does the degree of saturation of fatty acids tails contribute to membrane’s fluidity?

A

Phospholipid tails can be saturated or unsaturated. The terms saturated and unsaturated refer to whether or not double bonds are present between the carbons in the fatty acid tails. Saturated tails have no double bonds and as a result have straight, unkinked tails. Unsaturated tails have double bonds and, as a result, have crooked, kinked tails

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23
Q

Variations in lipid composition of cell membranes of many species appear to be what?

A

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

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24
Q

What are Peripheral proteins?

A

Peripheral proteins are bound to the surface of the membrane. The ability to attach to the membrane but not be locked to it allows peripheral proteins to work on the surface of the cell membrane

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25
Q

Give examples of peripheral proteins

A

Some act as receptors, some as enzymes, catalyzing the reaction and since many are cytoskeletons, they give a cell its shape, offers support, and facilitates movement through three main components: micro filaments, intermediate filaments, and micro tubule

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26
Q

What are Integral proteins?

A

Integral proteins penetrate the hydrophobic core

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27
Q

What is the function of Integral proteins?

A

Integral membrane proteins function as transporters, channels (see Potassium Channel), linkers, receptors, proteins involved in accumulation energy, and proteins responsible for cell adhesion. Examples, insulin receptors, Integrins, Cadherins.

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28
Q

What are transmembrane proteins?

A

Integral proteins that span the membrane

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29
Q

What is the function of transmembrane proteins?

A

Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane

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30
Q

The hydrophobic regions of an integral protein consist of what?

A

One or more stretches of nonpolar amino acids, often coiled into α helices

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31
Q

What is the fluid mosaic model?

A

In the fluid mosaic model, the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

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32
Q

How are proteins held in the membrane?

A

Proteins are not randomly distributed in the membrane

Membranes are held together mainly by weak hydrophobic interactions

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33
Q

How do lipids and proteins move within the membrane

A

Most of the lipids and some proteins can move sideways (laterally) within the membrane

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34
Q

What determines most of the membrane’s functions?

A

Proteins

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35
Q

What functions can the membrane carry out?

A

i. Transport
ii. Enzymatic activity
iii. Signal transduction
iv. Cell-cell recognition
v. Intercellular joining
vi. Attachment to the cytoskeleton and extracellular matrix (ECM)

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36
Q

What determines the structure of the membrane?

A

The lipid bilayer

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37
Q

How are cell-surface proteins important in the medical field?

A

HIV must bind to the immune cell-surface protein CD4 and a “co-receptor” CCR5 in order to infect a cell
HIV cannot enter the cells of resistant individuals who lack CCR5
Drugs are now being developed to mask the CCR5 protein

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38
Q

What are the three major components of cell membranes?

A

Lipids, proteins, and carbohydrates.

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39
Q

Membranes have distinct inside and outside faces, how?

A

When vesicles fuse with the plasma membrane, and becomes continuous with the cytoplasmic layer of the plasma membrane (opposite). Molecules that begin on the inside face of the ER end on the outside face of the plasma membrane

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40
Q

What controlls the cell exchange with it’s surroundings

A

Controlled by the plasma membrane (selectively permeable, regulating the cell’s molecular traffic)

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41
Q

How does the plasma membrane regulate what comes in and out

A

Hydrophobic (nonpolar) molecules, such as hydrocarbons or oxygen and carbon dioxide, can dissolve in the lipid bilayer and pass through the membrane rapidly
Hydrophilic molecules including ions and polar molecules do not cross the membrane easily

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42
Q

How do proteins built into the membrane play key roles in regulating transport?

A

Transport proteins allow passage of hydrophilic substances across the membrane
Some transport proteins, called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel

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43
Q

What are channel proteins and what are their function?

A

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

44
Q

What is the function of channel proteins called aquaporins?

A

Greatly facilitate the passage of water molecules

45
Q

What are carrier proteins?

A

Other transport proteins, called carrier proteins, bind to molecules and change shape to shuttle

46
Q

What is dynamic equilibrium involving molecules passing through the membrane

A

At dynamic equilibrium, as many molecules cross the membrane in one direction as in the other

47
Q

What kind of transport is the diffusion of a substance across a biological membrane?

A

Passive transport because no energy is expended by the cell

48
Q

Water diffuses (osmosis) until when?

A

Until the solute concentration is equal on both sides

49
Q

What is tonicity?

A

Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water

50
Q

The tonicity of a solution depends on what?

A

Its concentration of solutes that cannot cross the membrane relative to that inside the cell

51
Q

What is an isotonic solution?

A

Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane

52
Q

What is a Hypertonic solution?

A

Solute concentration is greater than inside the cell; cell loses water

53
Q

What is a Hypotonic solution?

A

Solute concentration is less than inside the cell; cell gains water

54
Q

What happens to cells without cell walls in a hypertonic solution?

A

Shrivel in hypertonic solution

55
Q

What happens to cells without cell walls in a hypotonic solution?

A

Lyse (burst) in a hypotonic solution

56
Q

What is a turgid cell?

A

A plant cell in a hypotonic solution swells until the wall opposes uptake

57
Q

What is a ‘‘flaccid cell’’ (limp)?

A

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

58
Q

What is plasmolysis?

A

In a hypertonic environment, plant cells lose water

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

59
Q

What is facilitated diffusion?

A

Where transport proteins (Transport proteins include channel proteins and carrier proteins) speed the passive movement of molecules across the plasma membrane

60
Q

How do channel proteins faciliate transport across membranes?

A

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

61
Q

How do ion proteins faciliate transport across membranes?

A

Ion channels facilitate the transport of ions

62
Q

Give an example of an ion channel and what it does

A

Some ion channels, called gated channels, open or close in response to a stimulus. For example, in nerve cells, ion channels open in response to electrical stimulus

63
Q

Is faciliated diffusion passive or active?

A

Facilitated diffusion is still passive because the solute moves down its concentration gradient i.e. no energy required

64
Q

What is active transport?

A

Active transport requires energy, usually in the form of ATP hydrolysis, to move substances against their concentration gradients

65
Q

What are the proteins involved in active transport?

A

All proteins involved in active transport are carrier proteins

66
Q

Give an example of active transport, how its controlled and its function

A

Active transport allows cells to maintain concentration gradients that differ from their surroundings
For example, an animal cell has a much higher potassium (K+) and a much lower sodium (Na+) concentration compared to its surroundings
This is controlled by the sodium-potassium pump, a transport protein that is energized by transfer of a phosphate group from the hydrolysis of ATP

67
Q

Describe the sodium-potassium pump: a specific case of active transport

A

i. Cytoplasmic Na+ binds to the sodium-potassium pump. The affinity for Na+ is high when the protein has this shape.
ii. Na+ binding stimulates phosphorylation by ATP.
iii. Phosphorylation leads to a change in protein shape, reducing its affinity for Na+, which is released outside.
iv. The new shape has a high affinity for K+, which binds on the extracellular side and triggers release of the phosphate group.
v. Loss of the phosphate group restores the protein’s original shape, which has a lower affinity for K+.
vi. K+ is released; affinity for Na+ is high again, and the cycle repeats.

68
Q

What is membrane potential?

A

It is the voltage across a membrane

69
Q

How is the voltage created in the membrane potential?

A

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

70
Q

What is the electrochemical gradient?

A

Two combined forces 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)

71
Q

What is an electrogenic pump?

A

An electrogenic pump is a transport protein that generates voltage across a membrane.

72
Q

What is the mahor electrogenic pump of animal cells?

A

The sodium-potassium pump is the major electrogenic pump of animal cells

73
Q

What is the mahor electrogenic pump of plants, fungi, and bacteria?

A

A proton pump, which actively transports hydrogen ions (H+) out of the cell

74
Q

What is cotransport?

A

Cotransport occurs when active transport of a solute indirectly drives transport of other substances
The diffusion of an actively transported solute down its concentration gradient is coupled with the transport of a second substance against its own concentration gradient (an energetically favorable transport is coupled to an energetically unfavorable transport to move molecules across membranes)
Glucose will not easily move across the cell membrane. But the cell wants glucose and also has a lot of glucose within it already. So even if you have a simple passive transporter for glucose on the membrane, there is not much glucose that will get in.

75
Q

How do small molecules and water enter or leave the cell?

A

through the lipid bilayer or via transport proteins

76
Q

How do large molecules enter or leave the cell?

A

Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles (requires energy)

77
Q

What are the three types of endocytosis?

A

i. Phagocytosis-cellular eating
ii. Pinocytosis-cellular drinking
iii. Receptor-mediated endocytosis

78
Q

What is Phagocytosis-cellular eating and give an example?

A

Phagocytosis, or “cell eating”, is the process by which a cell engulfs a particle and digests it.
Cells in the immune systems of organisms use phagocytosis to devour bodily intruders such as bacteria, and they also engulf and get rid of cell debris.

79
Q

What is Pinocytosis?

A

Pinocytosis is a cellular process by which fluids and nutrients are ingested by cells. Also called cell drinking, pinocytosis is a type of endocytosis that involves the inward folding of the cell membrane (plasma membrane) and the formation of membrane-bound, fluid-filled vesicles

80
Q

What is Receptor-mediated endocytosis?

A

binding of specific solutes to receptors triggers vesicle formation

81
Q

Give an example of receptor mediated endocytosis

A

Cholesterol intake - Human cells use receptor-mediated endocytosis to take in cholesterol, which is carried in particles called low-density lipoproteins (LDLs)
Individuals with the disease familial hypercholesterolemia have missing or defective LDL receptor proteins

82
Q

Which makes up more of the membranes in a cell - internal or plasma membranes?

A

The internal membranes make up more of the membranes in a cell than the plasma membranes

83
Q

What are the compartmentalization functions of membranes?

A

Separate outside from inside as well as separating within the cell, allow localization of enzymes, allow filtration to occur (selective permeability)

84
Q

How do membranes function in storing energy?

A

Across a membrane you can build up a concentration gradient and harness the potential energy created by the gradient

85
Q

fats and oils (are/are not) in membranes

A

are not

86
Q

Membrane proteins that do not directly cross the cell membrane but rather are on the surface or associated with another protein are what?

A

Peripheral

87
Q

How do peripheral proteins attach?

A

Electrostatic interactions and hydrogen bonding interactions

88
Q

Is removing peripheral proteins easy or hard and why?

A

Fairly easy since high salt solutions or extreme pH’s will disrupt their electrostatic interactions

89
Q

Is removing integral proteins easy or hard and why?

A

Hard because you cannot remove an integral membrane protein without destroying membrane integrity with strong detergents of organic solvents, often denaturing the protein as well

90
Q

What is the statement that all components of a membrane are not in a set position but more relative is what?

A

The fluid mosaic model

91
Q

The temperature that defines when the bilayer will lose fluidity is known as?

A

The transition temperature

92
Q

Why does the type and amount of phospholipids affect fluidity of the membrane?

A

Each different phospholipid has a different transition state (sphingomyelin generally makes the membrane less fluid)

93
Q

Why do fish make oils?

A

To keep their membranes fluid instead of freezing up

94
Q

Cholesterol is only present in what kind of cells?

A

Animal cells

95
Q

Besides functioning to affect membrane fluidity, cholesterol also

A

May decrease the permeability of the membrane

96
Q

Which molecule will diffuse most quickly across a lipid bilayer membrane?

a) H2O
b) O2
c) H2PO4–
d) glucose
e) Na+

A

B)Polar molecules and large ions dissolved in water cannot diffuse freely across the plasma membrane due to the hydrophobic nature of the fatty acid tails of the phospholipids that make up the lipid bilayer. Only small, non-polar molecules, such as oxygen and carbon dioxide, can diffuse easily across the membrane.

97
Q

Singer and Nicolson’s fluid mosaic model of the membrane proposed that
A) membranes are a phospholipid bilayer.
B) membranes are a phospholipid bilayer between two layers of hydrophilic proteins.
C) membranes are a single layer of phospholipids and proteins.
D) membranes consist of protein molecules embedded in a fluid bilayer of phospholipids.
E) membranes consist of a mosaic of polysaccharides and proteins.

A

D)

98
Q

An animal cell membrane will be more fluid at room temperature if it contains
A) more cholesterol.
B) longer chain fatty acids.
C) more cis-unsaturated and polyunsaturated fatty acids.
D) more trans-unsaturated fatty acids.
E) any of the above

A

C)

99
Q 
Which of these processes can move a solute against its concentration gradient?
A) osmosis 
B) passive transport 
C) facilitated diffusion 
D) active transport
A

D)

100
Q 
Which of the following proteins is not necessarily associated with the plasma membrane?
A) recognition protein 
B) plasma protein 
C) receptor protein 
D) channel protein
A

B) (synthesised in liver)

101
Q

Which of the following affects the rate of diffusion through a selectively permeable membrane?
I. concentration gradient
II. temperature
III. molecular size
A).I only B) II only C) I and II D) I, II, and III

A

D) I, II, III

102
Q

The movement of potassium into an animal cell requires
A) low cellular concentrations of sodium.
B) high cellular concentrations of potassium.
C) an energy source such as ATP.
D) a cotransport protein.
E) a potassium channel protein.

A

C) an energy source such as ATP.

103
Q

Which best describes a biological membrane?

a) two layers of phospholipids with proteins embedded between the two layers
b) a mixture of covalently linked phospholipids and proteins that determines which solutes can cross the membrane and which cannot
c) two layers of phospholipids with proteins either spanning the layers or on the surface of the layers
d) a fluid structure in which phospholipids and proteins move freely between sides of the membrane
e) two layers of phospholipids (with opposite orientations of the phospholipids in each layer) with each layer covered on the outside with proteins

A

c) two layers of phospholipids with proteins either spanning the layers or on the surface of the layers

104
Q

Which amino acid would most likely be present in the outer side of a transmembrane domain of an integral membrane protein?

a) a charged amino acid like lysine
b) a polar amino acid like serine
c) a special amino acid like proline
d) a hydrophobic amino acid like valine
e) any of the above, with no preference

A

d) Transmembrane domains need hydrophobic amino acids to interact with the hydrophobic interior of a membrane

105
Q

Based on our model of the membrane, which statement would lose points on an exam?

a) Glycoproteins tend to have oligosaccharides on their outward-facing side.
b) Transmembrane proteins often bind with cytoplasmic proteins, but not with extracellular molecules.
c) The combinations of phospholipids in the two faces of the membrane often differ.
d) Phospholipids tend to move faster laterally along the membrane than do the proteins.
e) Some transmembrane proteins function as active transport systems.

A

b) Transmembrane proteins often bind with cytoplasmic proteins, but not with extracellular molecules.

106
Q

A correct distinction between facilitated diffusion and active transport is that

a) active transport requires conformational changes in the transport protein associated with the transport process, and facilitated diffusion does not.
b) active transport requires an integral membrane protein to carry out the transport, and facilitated diffusion does not.
c) facilitated diffusion requires a protein-lined pore in the membrane, and active transport does not.
d) facilitated diffusion depends on an existing energy gradient acting on the transported substance, while active transport makes such a gradient.
e) facilitated diffusion requires cellular energy (often from ATP hydrolysis), but active transport does not.

A

d) facilitated diffusion depends on an existing energy gradient acting on the transported substance, while active transport makes such a gradient.

107
Q

Which part of the cell is most crucial for getting membrane proteins to their proper location?

a) plasma membrane
b) mitochondrion
c) chloroplast
d) Golgi apparatus
e) lysosome

A

d) Golgi apparatus

From Molecules to Cells (9 decks)

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