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Cell Biology > Chapter 4: The Structure and Function of the Plasma Membrane > Flashcards

Chapter 4: The Structure and Function of the Plasma Membrane Flashcards

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1
Q

What are the 7 roles of the Plasma Membrane?

A

1) Compartmentalization
2) Scaffold for biochemical activities
3) Providing a selectively permeable barrier
4) Transporting Solutes
5) Responding to external stimuli
6) Intercellular interaction
7) Energy transduction (converting energy/message into another form)

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2
Q

What does Compartmentalization do for the cell?

A

2 things:

1) It allows for specialized activities to happen without external interference
2) It enables cellular activities to be regulated independently of one another (for ex: lysosome’s pH is 2 to degrade waste but the cell’s pH must be 7 in order to function)

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3
Q

How is the Plasma Membrane the Scaffold for biochemical activities? What does this mean?

A

The Plasma Membrane provided the cell with an extensive framework where components can be ordered for effective interaction.
Ex: the structure of the plant cell allows the chloroplast to interact quickly with the cell membrane.

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4
Q

Why is providing a selectively permeable barrier important?

A

It promotes movement of selected elements into and out of cells; allows small molecules, like H20, to move freely between the inside and outside of the cell.

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5
Q

How does the Plasma Membrane respond to external stimuli?

A

Via Signal transduction.

  • What this means is that the Plasma Membrane uses Receptors (proteins that respond to and recognize signals).
  • they also use other stimuli; like light or mechanical tension
  • The interactions between receptor and external stimuli cause activation or inhibition of intracellular activities
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6
Q

How does the Plasma Membrane allow for Intercellular interactions?

A

The Membranes (both extracellular and intercellular) mediate, recognize, and interact with adjacent cells. They do this too:

1) recognize and signal one another
2) adhere to each other
3) exchange materials and signals

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7
Q

What is energy transduction? Why is it needed?

A

Energy Transduction is the conversion of energy from sunlight to chemical energy.
It’s needed to transfer chemical energy to ATP.

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8
Q

Whom proposed the Lipid Bilayer Theory? When? What was the procedure?

A

It was proposed by Gorter and Grendel in 1925. They extracted lipids from red blood cells

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9
Q

What does the Lipid Bilayer Theory state?

A

that the ratio of the surface of the extracted lipids compared to red blood cells were 1:8:1 to 2.2:1

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10
Q

What are the components of phospholipids?

A
  • Polar head groups (glycerol) that face the aqueous compartments outside of the bilayer
  • Hydrophobic fatty acyl chains that face inward (in the intermembrane space)
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11
Q

Whom proposed the Fluid Mosaic Model and when?

A

Singer and Nicolson proposed the Fluid Mosaic model in 1972.

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12
Q

What did the Fluid Mosaic Model state?

A

It stated the CENTRAL DOGMA of membrane biology: that the lipid bilayer exists in a fluid state. This includes:

  • Individual lipid molecules can move laterally within the plane of the membrane.
  • membrane proteins occur as a “mosaic” of discontinuous particles that penetrate the lipid sheet.
  • the cellular membranes are mobile and capable of coming together to engage in various transient or semipermanent interactions.
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13
Q

What are the components of the plasma membrane itself?

A
  • Glycoproteins (both Integral and peripheral)
  • Phospholipids
  • Glycolipids
  • Cholesterols
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14
Q

Explain the Chemical Composition of Membranes.

A
  • Structural backbone: the Lipid Bilayer
  • Specificity is determinded by: Proteins (i.e. a unique set of membrane proteins determine the specialize activities of a cell type)
  • the lipid and protein components are bounded toheter by non-covalent bonds
  • Membarnes also contain carbohydrates
  • Protein/lipid ratios vary amond membrane types
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15
Q

Explain Membrane lipids. What are the 3 main types of them?

A
  • They are amphipathic (has both hydrophilic region and hydrophobic region)
  • The 3 types of membrane lipids are:
    1) Phosphoglyceries: diacylglyceried with small funcitonal head groups linked to the glycerol backbone by phosphate ester bonds
    2) Sphingolipids: ceramides formed by the attachment of sphingosine to fatty acids
    3) Cholesterol: a smaller and less amphipathic lipid that is only found in animals
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16
Q

How do Lipid Bilayer composition differ among types of cellular membranes, cells, and organisms?

A

Via the lipids in/on the Bilayer. The lipids can be different in…

  • types of lipids
  • nauture of the head groups
  • particular species of fatty acyl chains
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17
Q

Why is the Lipid Bilayer so important?

A

For many reasons…

  • it has many structural elements
  • it determines the physical state of the membrane
  • it infulence the acitvity of particualr membrane proteins
  • it provides the precursors for highly active chemical messengers that regualte cellular functions
  • it provides dynamic properties for the plasma membrane
  • it maintains proper internal compositon of a cell by forming a barrier
  • it seperates electric charges across the plasma membrane
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18
Q

What are liposomes? What are they used for?

A

Liposomes are artifically prepared spherical vesicles made of a lipid bilayer that can self-assemble themselves.
Scienticst used them for drugs or DNA delivery

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19
Q

How are the Membrane Lipids Asymmetrical? Why is this important?

A
  • Both the inner and outer membrane leaflets (sheets) have different lipid compostitions.
  • This provides different physico-chemical properties appropriate for different interactions
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20
Q

What is the percent composition of carbohydrates in the membrane? Of the percentage, describe the two types that exist in the plasma membrane and the percentage of them there.

A

10% of the plasma membrane is carbs in eukaryotics cells. These carbs covelently link to lipids and proteins on the extracellular surface of the bilayer. Of that 10%:

  • 90% are glycoporteins( short, branched carbs that interact with other cells and structures outside the cell)
  • 10% are glycolipids (Longer carb chains that may be cell-to-cell recognition sites)
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21
Q

What is membrane “sideness”? Why is it important to the Plasma Membrane?

A

1) membrane “sideness”: this refers to the asymmetry of the membrane bilayer resulted from different lipid composition and different membrane proteins attached to the bilayer.
2) It renders distinct properties and functions to each individual layer of the membrane. (i.e. the membrane proteins responsible for cell interaction are exposed to the extracellular space; membrane proteins interacting with cytoplasmic molecules are exposed to cytoplasm)

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22
Q

What are the 3 Membrane Proteins?

A

1) Integral Proteins (transmembrane)
2) Peripheral Proteins
3) Lipid-anchored proteins

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23
Q

What are Integral Proteins? What are their characteristics? Where are they located within the membrane?

A
  • They are transmembrane proteins that penetrate the entire lipid bilayer.
  • They’re amphipathic (have both hydrophilic and hydrophobic regions).
  • The transmembrane domain is hydrophobic.
  • Amino acids in the transmembrane domain form van der Walls interaction with fatty acyl chain of a lipid bilayer
    1) Protein is anchored in the lipid bilayer
    2) Permeability barrier is preserved
    3) Protein and surrounding lipids form direct close contact and allow important functional interactions to happen
  • they form functional domains outside and inside of the bilayer to interact with water-soluble substances
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24
Q

What is the function of Integral Proteins?

A
  • They function as receptors and respond to stimuli.
  • They function as channels/transporters (i.e. they move ions and solutes). Channel proteins have hydrophilic cores that form aqueous channels in the membrane-spanning region
  • They function as agents by transferring electrons
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25
Q

What are the characteristics of Peripheral proteins? Where are they located?

A
  • they are located entirely outside of bilayer on either the extracellular or cytoplasmic side
  • they are associated with membrane surface by noncovalent bonds
26
Q

What are the Functions of Peripheral proteins?

A

Functions:

  • mechanical support for the membrane
  • anchor for integral proteins
  • enzymes
  • specialized coats
  • factors to transmit transmembrane signals
27
Q

What are the characteristics of Lipid-anchored membrane proteins? Where are they located?

A
  • located outside of the bilayer, on either extracellular or cytoplasmic surface
  • they’re covalently linked to a lipid molecule in the lipid bilayer
  • they are distinguished both by the types of lipid anchor and their orientation
28
Q

What are GPI-linked proteins?

A

inner-leaflet proteins that are anchored to membrane lipids by long hydrocarbon chains

29
Q

What is Membrane Fluidity used for?

A

Fluidity or Viscosity is used to describe the physical state of lipid molecules

30
Q

What phases can membrane lipid molecules exist in?

A

They can exist in either:
1) liquid-crystal phase: individual lipid molecule that can rotate or move laterally

2) solid-crystal(gel) phase: movement of the lipid molecules is greatly restricted

31
Q

What is the determinant for the fluidity of lipid molecules?

A

TEMPERATURE

32
Q

Define transition temperature. How does it relate to the fluidity of the cell membrane lipids?

A

the temperature that lipid molecules changes from liquid-crystal phase to gel phase

  • If the temp is higher than the transition temp: then they’ll be in the liquid phase
  • If the temp is lower than the transition temp: then they’ll be in the gel phase
33
Q

What are the determinants for the transition temps of the membrane lipids?

A

1) Saturation of fatty acid chains: the more unsaturated they are, the lower the transition temp
2) Length of the fatty acid chains: the shorter the chains, the lower the transition temp
3) Presence of cholesterol: the more cholesterol, the lower the transition temp.

34
Q

What is the importance of Membrane Fluidity?

A
  • The fluidity of membranes is a compormise between structural rigidity and complete fluidity.
  • The fluidity allows interactions to occur within the membrane.
  • It plays a key role in membrane assembly, allowing proteins and lipids to move into the preexisting membrane and for membranes to grow.
35
Q

How do organisms(besides birds and mammals) maintain membrane fluidity?

A

By altering the composition of membrane lipids. They remodle lipid bilayers involved the saturation or desauration of fatty acyl chains

36
Q

What is an example of membrane alteration?

A

Ex: if the temp gets colder.

  • desaturating single bonds form double bonds
  • reshuffling the chains between lipid molecules will produce ones that contain two unsaturated fatty acids
37
Q

Explain the Dynamic Nature of the Plasma Membrane: Phospholipids.

A
  • Phospholipids can move laterally within the same leaflet(bilayer) with considerable ease
  • In contrast, it takes a phospholipid molecule hours to days to move across to the other leaflet (to flip-flop)
  • The physical state of the lipid is an important determinant of the mobility of integral proteins.
38
Q

What is Cell Fusion?

A

a technique whereby two different types of cells, or cells from two different species, can be fused to produce one cell with a common cytoplasm and a single, continuous plasma membrane

39
Q

What limits protein movements in the cell membrane?

A

Protein movements are limited by interations with cytoskeleton, other proeins, and extracellular materials.

40
Q

How can substances move across the Cell Membranes?

A
  • Simple Diffusion
  • Facilitated Diffusion
  • Active Transport
41
Q

What is Diffusion?

A
  • the spontaneous movement of material from a region of high concentration to low concentraion
  • depeds on the random thermal motion of solutes and is an exergonic process acompanied with increased entropy
42
Q

What does the free-energy change during diffuion of both nonelectrolytes and electrolytes repsectively depend on?

A
  • For nonelectrolytes: it depends on the concetration gradient
  • For electrolytes: it depends on electrochemical gradient
43
Q

What does simple diffusion of nonelectorlytes require?

A
  • a concentration gradient
  • membrane permeability
    1) directly via the lipid bilayer
    2) traverse an aqueous pore across the membrane
44
Q

What are the determinats of diffusion rates?

A

1) Polarity

2) Molecular Size

45
Q

How to measure polarity?

A

1) Partiton coefficient: ratio of solubility of a substance in octanol(a nonpolar solvent) to that in water.
- Less polar = less partition coefficient
- Larger partition coefficient = faster penetration of cell membrane

2) Size
- the smaller the size, the faster the penetration
- small inorganinc molecules: 02, CO2, NO, and H2O are faster
- large polar molecules: sugars, amino acids, and phosphorylated intermediates are poorly permeable

46
Q

Explain the Diffusion of H2O through the membrane.

A
  • the plasma membranes are semipermeable
  • H2O penetrate much more rapidly than other solutes
  • Osmosis: diffusion of H2O through a semipermeable membrane from areas of lower soute concentration to areas of higher solute concentration
  • there are Hypotonic, Hypertonic, and Isotonic solutions
47
Q

How does a cell react in these solutions?

A

Temporarily:

  • In hypotonic solution’s, the cell swells; this happens because the cell loses ions to this environment
  • In hypertonic solution’s, the cell shrinks; this happens because the cell gains ions from the environment
  • In isotonic solution’s, the cells remain unchanged
48
Q

What are the effects of osmosis on a plant cell?

A
  • Plants are hypertonic vs environment: they develop turgor pressure because cell walls prevent swelling
  • In hypertonic solutions the plant cell undergoes plasmolysis.
  • H2O penetrates plasma membrane through specialized protein channels
  • plants use Aquaporins
    1) small integral membrane proteins
    2) form specialized protein channels to allow passive movement of H2O
    3) Not permeable to hydrogen ions
49
Q

Explain the Diffusion of Ions through Membranes

A
  • the plasma membrane is Not permeable to charged substances (i.e. Na+, K+, Ca2+, and Cl-)
  • So they have to use Ion Channels
  • this provieds openings for specific ions on plasma membranes
  • Enables the rapid conductance of specific ions for critical biolgical funtions
50
Q

What is the Nature of ion channels?

A
  • Highly selective: only permeable to one particular type of ion
  • diffusion of ions always go from higher energy to lower energy
  • can exist in either “open” or “close” conformation, thus it called “gated”
51
Q

What are the 3 types of ion channels?

A

1) voltage-gated channels: ionic charge
2) ligand-gated channels: binding of a ligand
3) mechano-gated channels

52
Q

How is Facilitated Diffusion similar to Simple Diffusion?

A
  • has two comon features with simple diffusion
    1) diffusion of substances is passive (follows concetation or charge gradient)
    2) activity can be regualted
53
Q

What are the distinct features of Facilitated Diffusion?

A
  • Facilitative transporter
    1) highly specific: distinguishes between stereoisomers
    2) exhibits saturation-type kinetics: moves only 100’s to 1000’s of solute per seconds
  • works equally well for transportation of both directions
54
Q

What are the feature of Active Transport?

A
  • maintains the gradients for potassium (K+), sodium (Na+), calcium (Ca2+)
55
Q

What isthe common feature between Facilitated Diffusion and Active Transport?

A

Transport proteins: pumps

56
Q

What are the distinct features of active transport?

A
  • substancesare transported against concentration gradient (i.e.: from lower region to higher region)
  • its coupled with an exergonic process
  • hydrolysis of ATP
  • Absorbance of light
  • Transport of electrons
  • Flow of other substances following gradient
57
Q

What is Primary Active transport? Describe its characteristics.

A

Primary Active Transport is a coupling transport to ATP hydrolysis.
- Cells require higher Na+ outside and higher K+ inside for normal function

58
Q

Describe Na+/K+ ATPase(Pump). And it’s orginal discovery.

A
  • In 1957, Dr. Skou discovered the Na+/K+ ATPase and proposed this enzyme is the sodium-potassium pump.
  • The ATPase is a phosphorylation(P)- type pump, in which phosporylation causes chane in pump conformation and ion affinity that allow transport against gradients
59
Q

What is the ratio of Na+:K+ pumped through the membrane?

A

the raito of Na+:K+ pumped is 3:2

60
Q

What are the other primary ion transport systems?

A

Other P-type pumps are:

  • H+ and Ca2+ ATPase
  • H+/K+ ATPase
61
Q

Define the Secondary Active Transport(Co-transport)

A

Secondary Active Transport is a coupling transport to Existing Ion Gradients

  • it is the use of energy stored in an ionic gradient, which is generated by primary active transportation, to transport other solutes
  • not directly coupled with ATP hydrolysis

Cell Biology (8 decks)

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