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OCR A-level Biology Module 2: Foundations in Biology > Biological Membranes > Flashcards

Biological Membranes Flashcards

The seemingly insignificant cell boundaries? Not even close!

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1
Q

What are the main roles of extracellular plasma membranes?

A
  1. Forming a partially permeable membrane between cell internal and external
  2. Providing a site for chemical reactions (e.g. mitochondrion’s “CRISTAE”)
  3. Site for cell-cell signalling + recognition (via glycolax receptors and surface antigens)
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2
Q

What are the main roles of intracellular membranes?

A
  • Compartmentilisation = separating cell organelles / reactions from rest of the cell
  • Creating a concentration gradient = allowing important molecules to diffuse in cell
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3
Q

List and explain the 4 main components of plasma cell membrane

A
  1. PHOSPHOLIPIDS - mantains the bilayer as amphilphilic layer repels/attracts regions
  2. THE GLYCOLAX - Acts as the cell receptors for hormones, cell adhesion and neurotransmission
  3. TRANSPORT PROTIENS - Allows ions / large molecules / water solubles to enter bilayer
  4. CHOLESTEROL - A sterol molecule regulating cell membrane fluidity
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4
Q

What is the structure of the phospholipids in the cell membrane?

A
  • Contains hydrophilic charged phosphate head with 2 hydrophobic fatty acid tails
  • Contains a central glycerol backbone
    *
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5
Q

How does the phospholipids function in the plasme membrane?

A
  • The hydrophilic head will attract towards aqueous environment, while hydrophobic tails will repel
  • This will mean a stable bilayer will form!
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6
Q

What is the structure of the glycolax in the cell membrane?

A
  1. Contains glycoprotiens and glycoprotiens binded to their corresponding molecule
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7
Q

How does the the glycolax function in the plasme membrane?

A
  1. These will detect variable changed in cell environment, as well as detecting for hormones and neurotransmitters
  2. Allows for cell adhesion to occur with other cell’s plasma membrane
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8
Q

What is the structure of transport protiens in the cell membrane?

A
  1. CHANNEL= water-filled pores, lined to suit hydrophilic molecules
  2. CARRIER = Shape-changing molecules that are also lined with a hydrophilic tertiary structre
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9
Q

How does the transport protiens function in the plasme membrane?

A
  • CHANNEL = will allow polar/charge/water-soluble molecules to diffuse into the lipid bilayer, having a hydrophilic region internally (aquaporins)
  • CARRIER = will change shape to facilitate moleucules against the concentration gradient (A.T.) into bilayer, USING ENERGY!!!
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10
Q

What is the structure of cholesterol in the cell membrane?

A
  1. This molecule will act as a phospholipid buffer, REGULATING MEMBRANE FLUIDITY.
  2. Hot = prevents phospholipids becoming too fluid by packing them closer together
  3. Cold = prevents phospholipids becoming to stiff by stimulating more phospholipid movement!
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11
Q

What does the fluid-mosaic modell mean in the plasma membrane?

A
  1. fluid = phospholipids are free to move SIDEWAYS in the membrane
  2. mosaic = protiens are RANDOMLY SCATTERED across the membrane, within!
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12
Q

Explain the differences in polar and non-polar molecule entry…..

A
  1. POLAR = will need to undergo facilitated diffusion due to hydrophobic inner layer, meaning that they will be repelled
  2. NON-POLAR = small molecules (e.g Carbon Dioxide) can undergo simple diffusion straight through this bilayer…..
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13
Q

Define facilitated diffusion

and list examples!!

A
  • This is the moevement of molecules from a high to low concentration across a semi-permeable membrane via channel proitens, without the use of ATP energy!!!

used in transporting polar/ionic/large molecules

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14
Q

Define simple diffusion

and list examples!!

A
  • This is the movement of molecules from a high to low concentration without the use of ATP energy across a medium with the molecules’ OWN KINETIC ENERGY!!!
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15
Q

Define active transport

and list examples!!

A
  • This is the movement of molecules from a low to high conc agaoinst the concentration gradient using ATP and CARRIER PROTIENS

used in the Small Intestine to absorb glucose molecule into blood

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16
Q

What other porcesses require energy from ATP??

and what does ATP acually stand for!

A
  1. ENDOCYTOCIS and EXOCYTOSIS both require intermidiate source of energy from ATP

ATP = Adenosine Triphosphate!

17
Q

Define osmosis

and list examples!!

A
  • This is the net movement of water molecules from a high to low water potential, across a semi-permeable membrane
18
Q

Define water potential

A
  • This is the measure of the tendancy for water molecules to diffuse from one region to another
19
Q

How can we measure water potential?

A
  1. 0Kpa = GREATEST WATER POTENTIAL
  2. -900Kpa = VERY, VERY LOW WATER POTENTIAL
  3. A lower water potential: more solute dissolved in the solution

works the same vice versa (0Kpa = pure water only = max water potential = WATER GONNA WANT TO MOVE ALOT!!

20
Q

Define the following “osmotic words”:
Hypertonic,Hypotonic,Isotonic

A
  1. Hypertonic = a high solute concentration
  2. Hypotonic = a low solute concentration
  3. Isotonic = water molecules entering and leaving the cell at the exact same rate = equal concentration of water and solute!
21
Q

Define the following “osmotic words”:
Plasmolysed,Crenated,Flaccid

A
  1. Plasmolysed = a single plant cell shrinks, being pulled away from cell wall = low w.potential
  2. Crenated = animal cell shrivels and shrinks
  3. Flaccid = ENTIRE PLANT TISSUE becoming “plasmolysed”, losing its original SHAPE and STRUCTURE
22
Q

How would a cell mantain its concentration gradient in general?

A
  1. A cell would normally have molecules diffusin cellular organnelles after diffusing into the cell itself.
  2. This will mean rate of molecular consumption will cause a steady gradient difference.
23
Q

Explain the 5factors that **affects the rate of diffusion*

A
  1. TEMPRATURE = warmer will mean more KE of particles - faster rate
  2. MOLECULAR SIZE = smaller will mean faster movement of KE - faster rate
  3. GRADIENT DIFFERENCE = steeper will mean much more rate of molecule to move - faster rate
  4. SURFACE AREA = greater will mean more particles able to cross the membrane per unit time - faster rate
  5. T.O.E.S = thinner will mean less distance to travel the membrane to destination - faster rate

notice how they ALL end in “faster rate” in particular ……..

24
Q

What are the main factors affecting plasma membrane permeability??

A
  1. Solvent concentration! (organic….)
  2. Temprature! (hotter or colder….)
25
Q

Explain how ORGANIC SOLVENTS can INCREASE membrane permeablility

A
  1. Substances like ethanol can cause membrane disentigration, due to being lipid-solubles and phosphate tempoarily bonding to OH- group.
  2. This will cause phospholpiids to losse stability and form larger gaps in this membrane
  3. PLUS!!!!, cholesterol is also lipid-soluble, meaning that this will further enlarge these gaps!!!!
26
Q

Explain how TEMPRATURES can INCREASE membrane permeablility

A
  1. Warmer tempratures will cause phospholipids to have more kinetic energy
  2. This will mean more movemet, meaning larger gaps will start to form as a result!!!!!!!!!
27
Q

What kind of structures can form when the bilayer dissolves in an organic substance (e.g. Ethanol) ?

A
  • Turns from a PHOSPHOLIPID BILAYER into a MICELLE structure!!!
  • Due to the hydrophobic fatty acid tails constantly reppeling agains aquaeous solutions whiles the phosphate head will attract towards
  • Therfore, the tails will face inwards and away, while the phospholipids will face outwards and towards
28
Q

How can we investigate permeability of the cell plasma membrane?

A
  • The Beetroot Practical!!!!
  • Consists of heating beetroot samples of equal SA and masses in different tempratures
  • Consists of using a COLORIMETER to measure ABSORBANCE OF GREEN LIGHT (in A.U.)

Green light wavelength = 540micrometers

amount of betalin substance leaskage DIRECTLY PROPORTIONAL too the degree of membrange damege/permeability

29
Q

Why is “green light” used in colorimeter in absorbance of light practical with beetroot

A
  • This is the BEST ABSORBED WAVELENGTH in as compared to RED / GREEN contrasting, giving the most accurate results!!!
  • They are at oppposite eends of the colour spectrum

OCR A-level Biology Module 2: Foundations in Biology (5 decks)

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