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Alevel Bio > 5 - plasma membrane > Flashcards

5 - plasma membrane Flashcards

1
Q

Define compartmentalisation.

A

Formation of separate membrane-bound areas

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2
Q

What occurs during compartmentalisation?

A
  • Membranes separate contents of a cell from its environment
  • Membranes separate organelles from one another
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3
Q

Why is compartmentalisation important?

A

Metabolism in a cell includes different and incompatible reactions so different regions need to be split.

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4
Q

State the components of a plasma membrane.

A

Phospholipid bilayer
Intrinsic proteins
Extrinsic proteins
Glycolipids
Glycoproteins
Cholesterol

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5
Q

Describe the features of intrinsic proteins.

A

aka - integral, transmembrane proteins
- Embedded through both layers of the bilayer
- Have amino acids with hydrophobic R-groups on the external surface, this keeps them in place as the interact with the hydrophobic core of the membrane

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6
Q

What are the 2 types of intrinsic proteins?

A

Channel proteins
Carrier proteins

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7
Q

What are the features and functions of channel proteins?

A
  • Hydrophilic channel allowing passive movement of polar molecules and ions down the concentration gradient
  • They would usually pass through the membrane very slowly as the centre of the bilayer is hydrophobic.
  • Held in place by hydrophobic R-groups on the external surface of the protein interacting with the hydrophobic centre of the bilayer.
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8
Q

What are the features and functions of carrier proteins?

A

Role in passive & active transport.
This involves the shape of the protein changing

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9
Q

What is the structure of a glycoprotein?

A
  • Embedded in cell surface proteins
  • They are extrinsic proteins
  • Consist of carbohydrate chains of varying lengths attached to proteins
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10
Q

Describe the functions of glycoproteins.

A
  • Cell adhesion - when cells join to form tight junctions in cell tissues
  • Act as receptors for chemical signals - chemicals bind to receptors and causes a direct effect or series of events
  • Cell signalling (communication)
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11
Q

What is cell signalling?

A
  • Neurotransmitter receptors at nerve cell synapses have neurotransmitters such as acetylcholine which bind and trigger an impulse in the next neurone
  • Receptors for peptide hormones such as insulin and glucagon
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12
Q

What are the features and functions of glycolipids?

A
  • Lipids attached to carbohydrate chains
  • Cell markers (antigens) recognised by the immune system as self (part of the organism) or non-self (not part of the organism), triggering an appropriate response.

E.g. antibody production

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13
Q

What is the structure and function of cholesterol?

A
  • Is an amphipathic (dual hydrophilic and hydrophobic ability) lipid
  • Regulates membrane fluidity
  • Positioned between phospholipid in the bilayer
  • The hydrophilic end interacts with the phosphate ends and the hydrophobic ends interact with the fatty acid tails
  • Stops phospholipids from getting too close and crystallising
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14
Q

What is the effect of temperature increase on plasma membranes?

A
  • Increased temperature > increased kinetic energy in the plasma membrane
  • More movement of the phospholipids making the bilayer more fluid - structure is lost and the cell breaks down
  • Makes easier for particles to pass in and out of the cell
  • This disrupts cell processes.
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15
Q

What is the effect of carrier and channel proteins?

A

They denature at high temperature affecting membrane permeability

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16
Q

Why are polar solvents important in bilayers?

A

Important in lipid bilayer formation as it keeps phosphate heads in water and fatty acid tails in the centre - keeps membranes intact.

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17
Q

What are the effects of organic solvents?

A
  • Less polar (alcohols, benzene) > they dissolve membranes and disrupt the cells
  • Pure alcohol solutions are toxic = destroy cells
  • Less concentrated alcohol (e.g. drinks) cause damage (don’t dissolve)
  • Membrane becomes more fluid and permeable
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18
Q

Why is it important to keep membranes intact?

A

Vital for specific functions such as nerve impulse transmissions

19
Q

State what can be used for a practical used to investigate membrane permeability and why

A

Use beetroot, contains betalain - red pigment released when membrane is disrupted.

20
Q

Define passive transport

A

A passive (non-energy requiring) energy process and doesn’t use energy from cellular respiration, uses energy from natural motion of the cell.

21
Q

Define equilibrium

A

Balance/no difference in concentration

22
Q

Define diffusion

A

Net movement of particles from a region of higher concentration to a region of lower concentration DOWN the concentration gradient.

It is a passive process

23
Q

What happens to the rate of diffusion as distance increases?

A

As distance increases, rate of diffusion decreases
- At high speeds particles are colliding more and more so they lose their energy over long distances.

24
Q

What factors affect rate of diffusion?

A

Temperature
- Higher temp, more kinetic energy, faster particle movement

Concentration gradient (difference)
- Overall movement is greater from high conc. to low

25
Q

What is simple diffusion?

A

Diffusion in the absence of a barrier or membrane

26
Q

What happens during diffusion across a membrane?

A
  • Must cross phospholipid bilayer
  • Non-polar molecules (e.g. O2) diffuse freely down concentration gradient
  • Hydrophobic interior of bilayer repels ions (due to charge) and polar molecules pass slowly
  • Small polar molecules pass easier than large ones

THIS MAKING MEMBRANES PARTIALLY PERMEABLE.

27
Q

What factors affect the rate of membrane diffusion?

A

Surface area: Larger SA of exchange surface = greater R.o.D

Membrane thickness - thinner membrane = greater R.o.D

28
Q

Define facilliated diffusion

A

Diffusion across a membrane whereby polar molecules & ions travel through a channel/carrier protein

(down conc. gradient, no energy requires)

Membranes with protein channels are SELECTIVELY PERMEABLE

29
Q

What factors affect the rate of facilitated diffusion?

A
  • Temp
  • Membrane thickness
  • Surface area
  • No. of channel/carrier proteins
30
Q

Define active transport.

A

Energy and carrier protein requiring process - molecules move from area of low conc to area of high conc up/against the conc gradient.

31
Q

Where is the energy required obtained from?

A

Metabolic energy supplied from ATP
- Carrier protein acts as pump

32
Q

Describe the process involved in a membrane pump.

A
  1. Molecule binds to receptor
  2. ATP hydrolysed, Pi binds to carrier protein changing its shape (ADP released)
  3. CP shape is open so molecule can be released
  4. Pi released from CP to bind with ADP to from ATP
  5. CP returns to original shape
33
Q

Define solute

A

Substance dissolved in a solvent (e.g. water)

34
Q

Define concentration

A

Amount of solute in a certain volume of aqueous solution

35
Q

Define water potential

A

Pressure exerted by molecules as they collide with membrane or barrier

36
Q

What is the water potential of PURE water?

A
  • Has the highest w.p. of 0
  • Every solution has a -ve water potential
  • Higher concentration = lower water potential
  • Pure water at 25 degrees and 100kPa is 0 w.p.
37
Q

What happens when 2 solutions of different concentrations are separated by a partially permeable membrane?

A
  • Water moves between the solutions
  • Water moves from an area of high w.p. (low solute concentration) to an area of low w.p. (high solute concentration) until equilibrium is reached.
38
Q

What is hydrostatic pressure?

A

Pressure exerted by water
- If water diffuses into a solution in a closed system the volume increases, increasing hydrostatic pressure.

39
Q

What is cytolysis?

A

When a cell is paced in a solution of higher w.p. of its cytoplasm, water diffuses in, increasing hydrostatic pressure causing cell to burst.

40
Q

How is cytolysis and crenation prevented?

A

Multicellular organisms have control mechanisms to ensure they remain isotonic (equal water potential).

41
Q

What is crenation?

A

Cell placed in solution of lower w.p. than the cytoplasm, water leaves via osmosis (cell shrivels)

42
Q

How do plant cells become turgid?

A
  • They cannot control the water potential of surrounding fluids as roots are surrounded by pure water
  • Water enters plant cell - turgor pressure increases as water pushes against walls
  • Cells resist entry of water meaning the cell is turgid
43
Q

What is plasmolysis?

A

When water leaves the plant cell, volume of cytoplasm falls pulling plasma membrane from cell wall leading to cell collapsing

Alevel Bio (9 decks)

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