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Foundations of Medicine > The Cell Membrane > Flashcards

The Cell Membrane Flashcards

1
Q

What is another name for the cell membrane?

A

The plasma membrane

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2
Q

What is the function of the cell membrane?

A

Highly selectively permeable barrier – both around cells and intracellular compartments.

Control of an enclosed chemical environment – important to maintain ion gradients.

Communication – with extracellular and extra-organelle space.

Recognition of signalling molecules, adhesion proteins and other host cells (important in the immune system).

Signal generation – in response to a stimulus creating a change in membrane potential.

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3
Q

What are cell membranes made up of?

A

Lipids, proteins and carbohydrates

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4
Q

Discuss in simple terms a rough guide of dry weight of the cell membrane

A

1-10% carbohydrate
40% lipid
60% protein

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5
Q

What is the membrane bilayer and what is it made up of?

A

Thin polar membrane made of two layers of lipid molecules.

Also known as lipid bilayer

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6
Q

What make up phospholipids?

A

Head molecule which is a polar group meaning that the head end of the phospholipid is hydrophilic.

Tail of 2 fatty acid chains – normally consisting of between 14-24 carbons (but the most common carbon lengths are 16 and 18). As the tail is made of fatty acids, it does not form hydrogen bonds with water and therefore is hydrophobic and non-polar.

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7
Q

Phospholipid molecules are amphipathic, what does this mean?

A

They are both hydrophilic and hydrophobic.

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8
Q

What forces are between the fatty acid tails of the phospholipid?

A

In the bilayer, there are van der Waal forces between the fatty acid tails of the phospholipid, with electrostatic and hydrogen bonds between the hydrophilic groups and water.

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9
Q

Why is cholesterol important in the cell?

A

It is a major constituent of the cell membrane.

Cholesterol is important in the membrane as it helps to maintain cell membrane stability and fluidity at varying temperatures.

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10
Q

What does cholesterol consist of?

A

Cholesterol itself consists of a polar head, a planar steroid ring and a non-polar hydrocarbon tail.

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11
Q

How is cholesterol bound to neighbouring phospholipid molecules?

A

Via hydrogen bonds and therefore at low temperatures, reduces their packing.

Overall this means at low temperatures, when rate of movement is lowest, a fluid phase is maintained.

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12
Q

What happens with cholesterol at high temperatures?

A

Helps to stop the formation of crystalline structures and the rigid planar steroid ring prevents intrachain vibration and therefore making the membrane less fluid.

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13
Q

What are some of the functions of the membrane proteins in a typical cell membrane?

A

Catalysts – enzymes.
Transporters, pumps and ion channels.
Receptors for hormones, local mediators and neurotransmitters.
Energy transducers.

More active cells or organelles e.g. mitochondria, tend to contain more proteins, showing again that specialisation of function determines structure.

As part of the cell membrane, proteins can either be deeply embedded within the bilayer (integral) or be associated with the surface of the cell (peripheral).

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14
Q

What is pinocytosis?

A

When drops of water are ingested

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15
Q

What is endocytosis?

A

When the membrane invaginates forming a vesicle which separates on the inside surface of the membrane

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16
Q

What is exocytosis?

A

When a vesicle fuses with the membrane and releases its contents out the cell

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17
Q

What are the junction types in cell adhesion?

A

Occluding
Cell-Cell anchoring

Channel forming
Cell-Matrix anchoring

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18
Q

What is the function of a tight junction?

A

Seals gaps between epithelial cells
Limits the passage of ions and molecules through the intercellular space

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19
Q

What are the two types of cell-cell anchoring?

A

Adherens junction
Desmosome

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20
Q

What is connected in an adherens junction?

A

Actin filament bundle in one cell is connected with that in the other

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21
Q

What does a desmosome connect?

A

Intermediate filaments

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22
Q

What is the type of junction that is channel forming?

A

Gap junction

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23
Q

What is the function of a gap junction?

A

Links 2 cytoplasms together
Allows the passage of small water soluble molecules between cells

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24
Q

Describe the structure of cell-matrix anchoring

A

Actin filaments in the cell are linked to the extracellular matrix

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25
Q

What do hemidesmosomes do?

A

They anchor intermediate filaments in a cell to the extracellular matrix.

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26
Q

What are the methods of cell signalling?

A

Contact dependant
Paracrine
Synaptic
Endocrine

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27
Q

What is the difference between paracrine and endocrine signalling?

A

Paracrine signalling - produces paracrine factors that diffuse over a short distance - altering behaviour in nearby cells

Endocrine - Hormones are released from the cell into the bloodstream

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28
Q

What can pass through the capillary easily but not cell membranes

A

Ions

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29
Q

Why can membranes be described as dynamic?

A

They are always being formed and maintained

OR

Dismantled and metabolised

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30
Q

Why are membranes described as flexible?

A

Fatty acids in vivo behave like oil and can stretch

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31
Q

What does the membrane insulating against?

A

Electrical charges - so prevents the movement of electrical charges

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32
Q

What type of membrane protein are receptors?

A

Membrane spanning

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33
Q

What is meant by diffusion across membranes?

A

Dissolved or gaseous substances have to pass through the cell membrane to get into or out of a cell.

Diffusion is one of the processes that allows this to happen.

Diffusion occurs when particles spread.

They move from a region where they are in high concentration to a region where they are in low concentration.

34
Q

Briefly, outline the difference in active and passive diffusion

A

Passive mechanisms like diffusion use no energy, while active transport requires energy to get done.

35
Q

What is active diffusion?

A

Active diffusion refers to the movement of molecules or ions from an area of lower concentration to a higher concentration with the assistant of carrier proteins in the cell membrane, utilizing cellular energy.

36
Q

What are the two types of active diffusion?

A

Primary active diffusion
Secondary active diffusion

37
Q

What is primary active diffusion?

A

Primary active diffusion refers to the transport of molecules against the concentration gradient by utilizing cellular energy in the form of ATP.

The primary active transport is most obvious in the sodium/potassium pump (Na+/K+ ATPase), which maintains the resting potential of the cell.

38
Q

What is secondary active diffusion?

A

Secondary active diffusion refers to the transport of molecules against the concentration gradient by the energy released from an electrochemical gradient.

Here, the transmembrane proteins are made by channel proteins (pore-forming proteins).

A simultaneous movement of another substance against the concentration gradient is observed with the secondary active transport.

Hence, the channel proteins involved in the secondary active diffusion can be identified as cotransporters.

The two types of cotransporters are antiporters and symporters.

39
Q

What are the four main types of passive diffusion?

A

Osmosis
Simple diffusion
Facilitated diffusion
Filtration

40
Q

What is osmosis?

A

Osmosis is the movement of water across a selectively permeable membrane. It occurs from a high water potential to a low water potential.

41
Q

What is filtration?

A

The movement of water and solutes from an area of high hydrostatic pressure to an area of low hydrostatic pressure.

This is due to the hydrostatic pressure generated by the cardiovascular system. It occurs in Bowman’s capsule in the kidney.

42
Q

What is facilitated diffusion?

A

Facilitated diffusion is the passive movement of substances, such as biological molecules or ions, across a plasma membrane by means of a transport protein located in the plasma membrane.

Since the movement of substances is from greater to lesser concentrations, chemical energy is neither used nor required.

The three types of transport proteins involved in the facilitated diffusion are channel proteins, aquaporins, and carrier proteins.

Channel proteins make hydrophobic tunnels across the membrane, allowing the selected hydrophobic molecules to pass through the membrane. Some channel proteins are opened at all times, and some are gated like ion channel proteins.

Aquaporins allow water to cross the membrane quickly.

Carrier proteins change their shape, transporting target molecules across the membrane.

43
Q

What is simple diffusion?

A

The simple movement of molecules across a permeable membrane is called simple diffusion.

Small, non-polar molecules use simple diffusion.

The diffusion distance should be less in order to maintain a better flow.

44
Q

List the factors which favour diffusion through the lipid bilayer

A

Small, hydrophobic/lipophilic, uncharged

45
Q

What are the two sub categories of membrane proteins?

A

Integral proteins
Peripheral proteins

46
Q

What are integral proteins?

A

An integral, or intrinsic, membrane protein is a type of membrane protein that is permanently attached to the biological membrane.

47
Q

What are the two types of integral proteins?

A

Integral polytopic protein
Integral monotropic protein

48
Q

What are examples of integral proteins?

A

Insulin receptor
Glycoprotein
Ion channels and gates
Gap junction proteins
G protein coupled receptors
Some types of receptor proteins
Cell adhesion proteins/molecules

49
Q

What is the difference between integral polytopic proteins and integral monotopic proteins.

A

Integral polytopic proteins are transmembrane proteins that that span across the membrane more than once.
Single-pass membrane proteins cross the membrane only once, while multi-pass membrane proteins weave in and out, crossing several times.

Integral monotropic proteins are are permanently attached to the cell membrane from one side.

50
Q

What are peripheral membrane proteins?

A

Peripheral membrane proteins (PMPs) are a class of membrane proteins that attach to the lipid bilayer, acting on the lipid-water interface, in contrast to transmembrane proteins, which are fully embedded in the cell membrane

Attached temporarily.

51
Q

What are examples of peripheral membrane proteins?

A

Enzymes such as alpha/beta hydrolase fold
Proteins are proteins involved in electron transport chains, such as cytochrome c
Membrane - targeting proteins

52
Q

What are the functions of peripheral proteins?

A

Anchor the membrane to the intracellular cytoskeleton

They connect the cell to the extracellular matrix

Performs signalling functions within the cell

53
Q

Define electrochemical gradient

A

It is the combination of the difference in ion concentration and the difference in charge across a membrane.

It drives passive movement

54
Q

How do you calculate the magnitude of diffusion (F)?

A

Kp x A x (C1-C2)

Where Kp is the permeability coefficient (measuring the ease at which a molecule can pass through a given membrane)

55
Q

What are protein channels used for?

A

Channel proteins span the membrane and make hydrophilic tunnels across it, allowing their target molecules to pass through by diffusion. Channels are very selective and will accept only one type of molecule (or a few closely related molecules) for transport.

56
Q

What are carrier proteins used for?

A

Carrier protein is a type of cell membrane protein involved in facilitated diffusion and active transport of substances out of or into the cell. Carrier proteins are responsible for the diffusion of sugars, amino acids, and nucleosides.

An example of a carrier protein is the sodium potassium pump.

57
Q

What are the three types of gated channels?

A

Ion gated channels
Ligand gated channels (aka chemically gated)
Voltage gated channels

58
Q

What are the three types of gated channels?

A

Ligand gated (aka chemically gated)
Mechanical gated
Voltage gated

59
Q

What is a ligand gated channel?

A
60
Q

What is the difference between osmosis and diffusion?

A

O
Only water or another solvent moves from a region of high energy or concentration to a region of lower energy or concentration.
Osmosis occurs only in a liquid medium.
Osmosis requires a semipermeable membrane.
The concentration of the solvent does not become equal on both sides of the membrane.
Osmosis mainly depends on the number of solute particles dissolved in the solvent.
The movement in osmosis seeks to equalize solvent concentration, although it does not achieve this.

D

Any type of substance moves from an area of highest energy or concentration to a region of lowest energy or concentration.
Diffusion can occur in any medium, whether it is liquid, solid, or gas.
Diffusion does not require a semipermeable membrane.
The concentration of the diffusion substance equalizes to fill the available space.
The movement in diffusion is to equalize concentration (energy) throughout the system.

61
Q

What is tonicity?

A

Tonicity is the capability of a solution to modify the volume of cells by altering their water content. The movement of water into a cell can lead to hypotonicity or hypertonicity when water moves out of the cell.

62
Q

What is osmolarity?

A

Osmolarity describes the total number of particles in solution.

63
Q

What is osmolarity measured in?

A

Osmolarity measures the concentration of biological solutions in specific units called, osmoles.

64
Q

What is the osmolarity of normal human plasma?

A

The normal human plasma has an osmolarity of 285mOsmol/l which is the same as within cells (usually rounded to 300) as there is no water barrier, so they have to be the same inside and outside the cell.

65
Q

What is an osmotic flux?

A

An osmotic flux is when a solute can’t cross the membrane causing the net movement in water in one direct, change the concentration to the solute to make equilibrium but also change in the volume will differ greatly.

66
Q

What are non-penetrating solutes?

A

The non- penetrating solutes include sodium and chlorine ions in the extracellular fluid and potassium ions in the intercellular fluid.

67
Q

What is the volume of a cell dependant on?

A

The volume of a cell at an time is dependant on the concentration of non-penetrating solutes on either side of the membrane.

68
Q

What is endocytosis?

A

Taking in of matter by a living cell by invagination of its membrane to form a vacuole

69
Q

Steps of endocytosis

A
  1. Plasma membrane fold inwards (invaginates)
  2. Plasma membrane folds back on itself until the ends of the in-folded membrane meet, trapping the fluid inside the vesicle
  3. Vesicle is pinched off from the membrane as the ends of the in-folded membrane fuse together. Internalised vesicle is then processed by the cell.
70
Q

What is exocytosis?

A

Exocytosis is the process of moving materials from within a cell to the exterior of the cell.

This process requires energy and is therefore a type of active transport.

71
Q

Steps of exocytosis

A
  1. Vesicles containing molecules are transported from within the cell to the cell membrane.
  2. The vesicle membrane attaches to the cell membrane.
  3. Fusion of the vesicle membrane with the cell membrane releases the vesicle contents outside the cell.
72
Q

What are carrier mediated transport systems?

A

Carrier-mediated transport is an energy-dependent pathway generally used by small hydrophilic molecules.

There are specific receptors on the membrane of carriers that recognize the target molecules and transport them across the cell.

73
Q

Why are membranes described as flexible?

A

Fatty acids in vivo behave like oil and can stretch

74
Q

What does the membrane insulate against?

A

Electrical changes - prevents the movement of electrical charges

75
Q

What are extracellular glycoproteins and glycolipids responsible for?

A

Self vs non-self regonition

76
Q

What makes a molecule diffuse across a membrane easily?

A

Small
Hydrophobic/lipophilic
Uncharged

77
Q

What does h2o pass through in the cells?

A

Aquaporins

78
Q

What are the different types of ion channels?

A

Voltage gated ion channels
Ligand gated ion channels (aka ionotropic receptors)
Mechanosensitive ion channels

79
Q

What are voltage gated channels?

A

Voltage-gated ion channels typically are closed at the resting membrane potential but open upon membrane depolarization. These channels detect changes in electric potential across the membrane through a domain responsible for sensing voltage.

80
Q

What are ligand gated channels?

A

Ligand-gated ion channels open when a chemical ligand such as a neurotransmitter binds to the protein which triggers a conformational change that results in the conducting state.

81
Q

What opens and closes mechanically gated ligand channels?

A

Mechanically-gated channels open in response to physical deformation of the receptor, as in sensory receptors of touch and pressure

Foundations of Medicine (56 decks)

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