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Biology > Plasma membranes > Flashcards

Plasma membranes Flashcards

1
Q

Define compartmentalisation

A

the formation of separate membrane-bound areas in a cell

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2
Q

Why is compartmentalisation important to a cell?

A
  • metabolism includes many different and often incompatible reactions
  • containing reactions in separate parts of the cell allows the specific conditions required for cellular reactions (e.g. chemical gradients) to be maintained, and protects vital cell components
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3
Q

describe the structure of the phospholipid bilayer

A

made up of two layers of phospholipids
- hydrophilic phosphate heads form both the inner and outer surface of the membrane
- fatty acid tails are sandwiched in the middle of the membrane which form the hydrophobic core

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4
Q

describe the interaction of the membrane with the aqueous environment

A
  • the outer surface of the membrane is formed from hydrohphilic phosphate heads which can interact with the water
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5
Q

Describe the fluid mosaic model

A

Fluid: the phospholipids are free to move within the layer relative to each other, giving the membrane flexibility

Mosaic: proteins embedded in the bilayer vary in shape, size and position

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6
Q

what are intrinsic proteins

A

transmembrane proteins that are embedded through both layers of a membrane

they contain amino acids with hydrophobic R groups on their external surfaces, which can interact with the hydrophobic core of the membrane, keeping them in place

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7
Q

describe channel proteins

A
  • provides hydrophilic channel for passive movement of polar molecules/ions down a concentration gradient through membranes
  • held in position by interactions between hydrophobic core and hydrophobic R groups on proteins
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8
Q

describe carrier proteins

A
  • involves the shape of the protein changing
  • both active and passive transport
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9
Q

describe glycoproteins

A
  • intrinsic
  • embedded in cell-surface membrane with attached carbohydrate chains
  • cell adhesion
  • receptors for chemical signals
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10
Q

what is cell adhesion

A

when cells join together to form tight junctions in certain tissues

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11
Q

how are glycoproteins receptors?

A
  • chemical binds to receptors
  • elicits response from the cell
  • causes a direct response or a cascade of events inside the cell (cell communication/signalling)

some examples:
- receptors for neurotransmitters at nerve cell synapses- triggers or prevents impulses to next nerve
- receptors for peptide hormones which affect uptake/storage of glucose in cells

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12
Q

describe glycolipids

A
  • lipids with attached carbohydrate chains
  • they are cell markers/antigens which can be recognised by the immune system as self or non-self
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13
Q

describe cholesterol

A
  • lipid with hydrophilic end and hydrophobic end
  • regulates fluidity of membranes
  • positioned between phospholipids in the membrane layer
  • hydrophilic end interacting with the phospholipid heads, and hydrophobic end interacting with the phospholipid tails
  • this pulls the phospholipids together without making them too rigid or too solid by stopping them from grouping too closely together and crystallising
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14
Q

describe extrinsic proteins

A
  • present on one side of the bilayer
  • hydrophilic R groups on their outer surfaces which interact with the polar heads of phopholipids or intrinsic proteins
  • can be present in either layer, or move between them
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15
Q

effect of temperature on the membrane

A
  • phospholipids are constantly moving
  • if temp increases, phospholipids will have more K.E. so will move more
  • membrane is more fluid and loses structure
  • if temp continues to rise, cell will break down
  • loss of structure increases permeability, making it easier for particles to cross
  • carrier/channel proteins get denatured at higher temperatures
  • these proteins are involved in transport across membrane so as they denature, membrane permeability will be affected
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16
Q

how does water interact with the membrane

A
  • water is a polar solvent
  • essential in the formation of the phospholipid bilayer
  • charged hydrophilic heads interact with the water, keeping the bilayer intact
  • hydrophobic tails orientated away from the water- hydrophobic core
17
Q

definition of diffusion

A

the net movement of particles from a region of higher concentration to a region of lower concentration

  • happens when particles have K.E., move in random directions
  • passive process will continue until there is a concentration equilibrium, where the particles have equal movement in both directions
18
Q

factors affecting diffusion

A
  • temperature
  • concentration difference
  • diffusion distance
  • SA:V ratio
19
Q

simple diffusion

A

diffusion in the absence of a barrier or membrane

20
Q

diffusion across the plasma membrane

A
  • involves particles passing through the phospholipid bilayer
  • it can only happen if the membrane is permeable to particles
  • non polar molecules (oxygen) diffuse through freely by simple diffusion
21
Q

what particles can diffuse through the membrane?

A
  • hydrophobic core repels polar particles
  • polar molecules (such as water) with partial positive and negative charges can diffuse through membranes but only at a slow rate
  • small polar molecules pass through more easily than large polar molecules
  • membranes are partially permeable
22
Q

facilitated diffusion

A

diffusion across membrane through protein channels
- membranes with protein channels are selectively permeable as they are specific to one molecule/ion
- carrier proteins change shape when a specific molecule binds to them
- rate of diffusion is affected by number of channel proteins present

23
Q

active transport

A
  • the movement of molecules into/out of a cell from a region of lower concentration to a region of higher concentration. This process requires energy(ATP) as it is moving against the concentration gradient, and carrier proteins.
24
Q

process of active transport

A
  • molecule binds to receptors in the channel/carrier proteins outside of the cell
  • on the inside of the cell, ATP binds to carrier protein and is hydrolysed into ADP and PHOSPHATE
  • this causes protein to change shape
  • molecule released to inside cell
  • phosphate molecule released from carrier protein and recombines with ADP to form ATP
  • carrier protein returns to original shape
25
Q

Bulk transport definition

A
  • form of active transport
  • large molecules (e.g. enzymes,hormones) are too large to move through channel/carrier proteins so they are moved into and out of the cell by bulk transport
  • phagocytosis for solids
  • pinocytosis for liquids
26
Q

endocytosis

A
  • bulk transport of materials into cells
  • membrane bends inwards when it comes in contact with the material
  • membrane enfolds material until it closes, forming a vesicle
  • vesicle pinches off and moves into cytoplasm
27
Q

exocytosis

A
  • bulk transport of material out of cells
  • vesicles move towards membrane and fuse with it
  • contents are released outside of the cell
28
Q

what happens if an animal cell is placed in a solution with higher water potential

A
  • water will move into the cell by osmosis down the water potential gradient
  • increases the hydrostatic pressure
  • cell-surface membrane cannot stretch much/withstand the pressure
  • cell bursts- cytolysis
29
Q

what happens if an animal cell is placed into a solution with a lower water potential

A
  • cell will lose water by osmosis down the water potential gradient
  • reduction in volume of the cell
  • cell shrinks and is crenated
30
Q

what happens if a plant cell is placed in a solution with higher water potential

A
  • water enters cell by osmosis down the water potential gradient
  • cell membrane gets pushed against the cell wall
  • cell swells and becomes turgid
31
Q

what happens if a plant cell is placed in a solution with a lower water potential

A
  • water leaves cell by osmosis down the water potential gradient
  • cell membrane peels away from cell wall
  • cell shrivels and becomes plasmolysed

Biology (12 decks)

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