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Biology > AOS 1.3: the plasma membrane > Flashcards

AOS 1.3: the plasma membrane Flashcards

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1
Q

Why does diffusion occur?

A

The kinetic energy stored inside each molecule, which causes them to randomly move around and bounce off each other. Overtime, this random movement leads to an even dispersion of particles in an area. Think of food dye spreading through water.
- food dye = solute
- water = solvent

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2
Q

What is diffusion?

A

when molecules move from an area of high concentration to an area of low concentration (or “down their concentration gradient”)

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3
Q

What molecules can’t diffuse?

A

polar, hydrophilic, large

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4
Q

What molecules can diffuse?

A

nonpolar, hydrophobic, small

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5
Q

What does a carbohydrate attached to a glycoprotein do on the plasma membrane?

A

Its function may be involved in receiving or sending signals and cell to cell adhesion

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6
Q

What is a phospholipid and its function?

A
  • the main molecule of which membranes are composed. They have a phosphate head and two fatty acid tails
  • regulating transport across membranes, and make up the structure in which proteins and carbohydrates are embedded.
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7
Q

What is osmosis?

A

The movement of water across a membrane from a .

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8
Q

What do carbohydrates do in the phospholipid bilayer?

A

Aid with cell communication, signalling, recognition of self or non-self (foreign) molecules, and adhesion

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9
Q

What does a protein do in the phospholipid bilayer?

A

All three kinds of protein (integral, transmembrane and peripheral) help with:
Transport - channels or pumps that control what enters and exits the cell, making the plasma membrane selectively permeable
Catalysis - speeding up chemical reactions with the help of a protein group called enzymes
Communication - receive signals or recognise cells and molecules. Often attached to the cytoskeleton to transmit signals into the cell
Adhesion - stick to other cells, the extracellular matrix, or the cytoskeleton

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10
Q

What does cholesterol do in the phospholipid bilayer?

A

Regulates fluidity of the membrane. At higher temperatures, the cholesterol keeps the phospholipids bound together. At lower temperatures, cholesterol disrupts the fatty acid tails, stopping phospholipids from becoming a solid boundary

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11
Q

what is an integral protein?

A

permanent parts of the membrane

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12
Q

What is the fluid mosaic model?

A

the plasma membrane is fluid because phospholipids continually move laterally (side to side) in the membrane. Occasionally, phospholipids may ‘flip-flop’ between two layers of the plasma membrane
the phospholipid bilayer is mosaic because it has many molecules embedded in it (these can also move fluidly around the bilayer)

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13
Q

what is a transmembrane protein?

A

integral proteins that span the entire bilayer

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14
Q

what is a peripheral protein?

A

temporarily attached to the plasma membrane

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15
Q

When is diffusion faster?

A
  • When the concentration gradient is steeper
  • At higher temperatures
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16
Q

What is facilitated diffusion?

A
  • involves moving down concentration gradients
  • transports large or polar substances (or hydrophilic)
  • doesn’t use energy (passive transport)
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17
Q

What is the plasma membrane?

A

All cells have a plasma membrane. It is the thin boundary of the cell made up of lipids that separates the intracellular and extracellular environments. It is selectively permeable, which means that only particular molecules can enter and exit the cell.

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18
Q

What does “selectively permeable” mean?

A

Only particular molecules can enter and exit the cell
Thanks to the plasma membrane, cells can have a specialised internal environment.

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19
Q

What is a phosphate head?

A

the hydrophilic subunit of a phospholipid
made of a glycerol and phosphate group
negatively charged, making it hydrophilic (‘water-loving’) and polar.

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20
Q

What is a fatty acid tail?

A

the hydrophobic subunit of a phospholipid
made of long chains of carbon and hydrogen
uncharged, hydrophobic (‘water-fearing’), and nonpolar.

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21
Q

Is water polar or nonpolar?

A

water is a polar substance

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22
Q

What does it mean for a molecule to be polar?

A

describes a molecule with both a positive end and negative end. These tend to be hydrophilic

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23
Q

What does it mean for a molecule to be nonpolar?

A

describes a molecule without a clearly positive or negative end. These tend to be hydrophobic

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24
Q

Why do the phosphate heads of a phospholipid face towards the intra and extra cellular environments?

A

The phosphate heads are hydrophilic so they are attracted to water which is a polar substance. Therefore, they are attracted to, and oriented towards, the aqueous intra- and extracellular environments. The fatty acid tails orient themselves away from the intra- and extracellular fluid to form the middle portion of the bilayer

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25
Q

Why is the phospholipid bilayer stable?

A

Because phospholipids have both hydrophilic and hydrophobic parts, they are amphipathic molecules. This amphipathic nature makes the plasma membrane stable:
the fatty acid tails are repelled from water whilst the phosphate heads are attracted to water, so a stable bilayer naturally forms.

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26
Q

What are polar and nonpolar molecules attracted to?

A
  • polar molecules are attracted to and dissolve in polar substances
  • nonpolar molecules are attracted to and dissolve in nonpolar substances
  • nonpolar molecules do not interact with polar molecules.
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27
Q

What does it mean if a molecule is amphipathic?

A

describes molecules with both hydrophilic and hydrophobic components.
Also known as amphiphilic

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28
Q

What is a protein?

A

a class of biomacromolecule made of amino acid monomers folded into a
3D shape, consisting of carbon, hydrogen, oxygen, nitrogen, and sometimes sulphur

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29
Q

What is a carbohydrate?

A

A class of biomacromolecule made from monosaccharide monomers consisting of carbon, hydrogen, and oxygen. Also known as saccharides or sugars

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30
Q

What molecules are embedded in the phospholipid bilayer?

A

Proteins, carbohydrates, and cholesterol are attached to and embedded in the phospholipid bilayer.

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31
Q

What is cholesterol?

A

a steroid-alcohol that regulates fluidity in plasma membranes

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32
Q

What is an integral protein?

A

proteins that are a permanent part of the membrane

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33
Q

What is a transmembrane protein?

A

integral proteins that span the entire bilayer

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34
Q

What is a peripheral protein?

A

are temporarily attached to the plasma membrane

35
Q

What are the functions of proteins embedded in the phospholipid bilayer?

A

Transport – channels or pumps that control what enters and exits the cell, making the plasma membrane selectively permeable
Catalysis – speeding up chemical reactions with the help of a protein group
called enzymes
Communication – receive signals or recognise cells and molecules. Often attached to the cytoskeleton to transmit signals into the cell
Adhesion – stick to other cells, the extracellular matrix, or the cytoskeleton

36
Q

What are the functions of carbohydrates embedded in the phospholipid bilayer?

A

Usually in chains that extend outside the cell, rooted in the membrane to lipids (glycolipids) or proteins (glycoproteins)

Aid with cell-cell communication, signalling, recognition of self or non-self (foreign) molecules, and adhesion

Carbohydrates attach to phospholipids

37
Q

What is cholesterol (in the phospholipid bilayer)?

A

A lipid steroid that embeds itself between the fatty acid tails of the phospholipid bilayer in animal cells. Cholesterol is replaced with similar molecules in other kingdoms, but all are functionally similar

38
Q

What are the functions of cholesterol embedded in the phospholipid bilayer?

A

Regulates the fluidity of the membrane.
At higher temperatures, the cholesterol
keeps phospholipids bound together. At lower temperatures, cholesterol disrupts the fatty acid tails, stopping phospholipids from becoming a solid boundary

39
Q

What is a glycolipid?

A

a phospholipid bound to a carbohydrate

40
Q

What is a glycoprotein?

A

a protein bound to a carbohydrate

41
Q

What is the mosaic component of the fluid mosaic model?

A

The ‘mosaic’ component of the model comes from the proteins and carbohydrates embedded in the membrane. These molecules can also move fluidly around the bilayer, like ice floating in a glass of water.

42
Q

What is meant by “passive transport”?

A

the movement of molecules through a semipermeable membrane and down the concentration gradient, without an input of energy

43
Q

What are methods of passive transport?

A

diffusion, facilitated diffusion, osmosis

44
Q

What is active transport?

A

movement of molecules across a semipermeable membrane that requires energy

45
Q

What are conditions of simple diffusion?

A

Polarity – nonpolar, uncharged, or hydrophobic molecules (e.g. O2, H2, CO2, lipids) can cross the membrane because most of the plasma membrane is nonpolar (in the form of fatty acid tails), and nonpolar molecules have an affinity for each other.
* Size – small molecules like water are able to slip through the lipids in the phospholipid bilayer. However, if a small molecule is highly charged – like an ion (e.g. H+, K+, Cl–) – then it still can’t cross the membrane by simple diffusion.

46
Q

What happens to molecules that cant undergo simple diffusion?

A

only small, nonpolar molecules can freely diffuse across the phospholipid bilayer. Large and hydrophilic molecules, such as ions, amino acids, proteins, glucose, or nucleic acids however, will simply bounce off the membrane and be unable to diffuse through. This leads to a higher concentration of these molecules on one side.

47
Q

When will diffusion “speed up”?

A

Diffusion is faster when the concentration gradient is steeper – that is, when there is a greater difference in concentration between the intra- and extra-cellular environments. It will also speed up at higher temperatures.

48
Q

What is facilitated diffusion?

A

Molecules that are too large or too charged to freely cross the plasma membrane can use a membrane protein, such as a protein channel, to move down their concentration gradient into or out of the cell.

The passive movement of molecules down their concentration gradient through a membrane-bound protein.

49
Q

What is a protein chanel?

A

pores or holes in the membrane that let a specific substance through.
a transmembrane protein pore in a phospholipid bilayer that selectively enables transport of large or polar molecules

50
Q

How do carrier proteins transport molecules across the membrane?

A

bind to the substance that is being transported and undergo a conformational change to push the substance down its concentration gradient through to the other side of the membrane. They return to their original shape once the molecule has been transported.

51
Q

What is a carrier protein?

A

a membrane protein that undergoes conformational change to transport molecules across a membrane

52
Q

How does facilitated diffusion contribute to the selective permeability of the membrane?

A

Both channels and carrier proteins are specific to the molecule they transport.
Because facilitated diffusion can be faster than simple diffusion, some small and/or nonpolar molecules that can diffuse (like water) also have dedicated protein channels.

53
Q

What is osmosis?

A

the diffusion of water across a selectively permeable membrane from areas
of low solute concentration to areas of high solute concentration.

54
Q

Why can water diffuse across the membrane despite being hydrophilic?

A

extremely small

55
Q

How can water movement across the membrane be increased?

A

water movement can be increased by protein channels known as aquaporins.

56
Q

what is tonicity?

A

a measure of the relative concentration of solutes on either side of a semipermeable membrane, described as hypertonic, hypotonic, or isotonic

57
Q

What does hypertonic mean?

A

describes a solution with a higher solute concentration when compared to another solution

58
Q

What does isotonic mean?

A

describes a solution with the same solute concentration as another solution

59
Q

What does hypotonic mean?

A

describes a solution with a lower solute concentration when compared to another solution

60
Q

What does turgid mean?

A

escribes plant cells that are swollen and firm from water uptake

61
Q

What does lyse mean?

A

To cause a cell plasma membrane to burst or break

62
Q

What does plasmolysed mean?

A

Describes plant cells with weak and sagging plasma membranes from water loss

63
Q

How does a cell become turgid?

A

If a plant cell cytosol is hypertonic compared to extracellular fluid, water will move into the cell and cause it to swell and become turgid. The cell will stay turgid (rather than burst) due to the presence of a cell wall.

64
Q

How does a cell become plasmolysed?

A

When water moves out of a plant cell, which happens if the cell is hypotonic compared to the extracellular fluid, the cell shrinks and becomes plasmolysed.

65
Q

What is the importance of regulating tonicity?

A

high turgor pressure in plant stems prevents the plant from wilting. Additionally, if you have ever been placed on a drip in hospital, you are given a saline solution to stay hydrated – not pure water. This saline solution is isotonic to our cells, ensuring that the cells in your blood do not shrivel or lyse.

66
Q

What is active transport?

A

movement of molecules across a semipermeable membrane that requires energy

67
Q

What is protein-mediated active transport?

A

a type of active transport which involves using membrane proteins to move molecules across a membrane against their concentration gradient. Also known as active transport

68
Q

What is bulk transport?

A

a type of active transport that uses vesicles to move large molecules or groups of molecules into or out of the cell. Also known as cytosis

69
Q

What is a protein pump?

A

a polypeptide that transports molecules across a membrane against its concentration gradient with the aid of ATP

70
Q

When do cells need to use protein-mediated active transport?

A

Sometimes, there is a big difference in the concentration of substances inside the cell compared to outside the cell. Take Figure 2a, for example. In this instance, there is a higher concentration of potassium ions (K+) inside the cell compared to the extracellular fluid. Despite this, the cell may still require more K+ to function optimally – so it must somehow draw the K+ into the cytosol, against its concentration gradient. To make matters more difficult, K+ cannot simply diffuse across the plasma membrane as it is a charged molecule. Furthermore, the cell cannot use facilitated diffusion either, as K+ ions need to move against its concentration gradient. In this scenario, the cell must use energy and protein pumps to move the ions against their concentration gradient and into the cytoplasm

71
Q

What does a molecule being transported against its concentration gradient require?

A

energy, usually in the form of adenosine triphosphate (ATP)
membrane proteins, typically protein pumps and carrier proteins.

72
Q

What is the process of active transport?

A

Binding – the target molecule for transport binds to a specific protein pump
Conformational change – energy released from the reaction ATP _ ADP + P causes a
i conformational change in the protein pump. This energy comes from breaking the bond between the second and third phosphate ions in the ATP molecule
3
Release – the target molecule is pushed through the protein and released to the other side of the membrane.

73
Q

What is ATP?

A

a high energy molecule that, when broken down, provides energy for cellular processes

74
Q

What is bulk transport?

A

Bulk transport is a type of active transport that moves large molecules or groups of molecules – such as amino acids, proteins, signalling molecules, or pathogens – into or out of the cell using vesicles.

75
Q

What is exocytosis?

A

the process by which the contents of a vesicle are released from a cell.

76
Q

How are proteins created and moved out of the cell?

A

Often, proteins are made at ribosomes located on the surface of the rough endoplasmic reticulum, sorted, packaged, and modified at the Golgi apparatus, and then transported by vesicles to the plasma membrane for exocytosis. This is an important process because cells often need to release products such as hormones, neurotransmitters, and antibodies in large amounts.

77
Q

What are the steps of exocytosis?

A
  1. Vesicular transport – a vesicle containing secretory products is transported to the plasma membrane
  2. Fusion – the membranes of the vesicle and cell fuse
  3. Release – the secretory products are released from the vesicle and out of the cell.
78
Q

Why is exocytosis possible?

A

because the plasma membrane is fluid and can fuse with the phospholipid bilayers of a vesicle. When a vesicle fuses with the plasma membrane, it adds phospholipids to the bilayer and makes the plasma membrane surface area slightly bigger.

79
Q

What is endocytosis?

A

Endocytosis involves transporting large molecules or groups of molecules into the cell.

80
Q

Why is endocytosis important?

A

many of the molecules that cells require to survive are too large to take in through protein channels in the plasma membrane. Once inside the cell, these substances can be broken down, used for metabolic processes, or become structural elements of the cell. Endocytosis can also be an effective defence mechanism. If a cell engulfs an invader or toxin, a lysosome can fuse with the vesicle to digest its contents.

81
Q

What are the three steps in endocytosis?

A
  1. Fold – the plasma membrane folds inwards to form a cavity that fills with extracellular fluid and the target molecules.
  2. Trap – the plasma membrane continues folding back on itself until the two ends of the membrane meet and fuse. This traps the target molecules inside the vesicle.
  3. Bud – the vesicle (or endosome) pinches off from the membrane. It can then be transported to the appropriate cellular location or fused with a lysosome for digestion.
82
Q

How can endocytosis make the cell shrink?

A

endocytosis takes phospholipids away from the plasma membrane, so if large amounts of endocytosis occur the cell could shrink.

83
Q

What is phagocytosis?

A

endocytosis of solid material or food particles
This is what occurs when immune cells like macrophages engulf invading microorganisms.

84
Q

What is pinocytosis?

A

(‘cell drinking’) is the process of engulfing molecules dissolved in extracellular fluid.

Biology (8 decks)

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