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Biology > Plasma membranes > Flashcards

Plasma membranes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Structure of phospholipid

A
  • Phosphate group (polar, hydrophillic head) bonded to glycerol molecule
  • 2 fatty acid tails (hydrophobic, non-polar)
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2
Q

function of plasma membranes

A
  • keep cellular components in cell
  • allow selected molecules to move in and out
  • isolating organelles from the rest of cytoplasm allowing cellular reactions to occur separately
  • allows cell to change shape
  • site of chemical reactions eg. respiration
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3
Q

fluid mosaic model

A
  • mosaic - proteins are scattered within 2 phospholipid layers (bilayer)
  • fluid because phospholipids can move around - flexible
  • hydrophobic fatty acid tail on inside
  • hydrophilic phosphate heads on outside
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4
Q

When exposed to water, what are the 2 structures phospholipds can form?

A

micelle - circular shape
bilayer - straight layer
- both have hydrophobic tails on inside and hydrphillic heads on outside

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5
Q

is it easier for hydrophobic or hydrophilic molecules to pass through the membrane?

A
  • hydrophobic because the centre (fatty acids) is hydrophobic
    eg. steroid hormones
  • prevents hydrophilic molecules passing through easily because they’re polar and can’t pass through non-polar membrane (apart from water because they’re small)
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6
Q

glycolipid function in membrane

A
  • recognition site for toxins eg. cholera
  • antigen - are recognised by immune system as one of their own cells
  • branched carbohydrate structure attached to head
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7
Q

glycoprotein function in membrane

A
  • presenting antigens
  • allow cells to attach to each other to form tissues such as nervous tissue
  • receptors for hormones
  • intrinsic protein
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8
Q

cholesterol function in membrane

A
  • stability, flexibility and fluidity - the more cholesterol the less fluidity and less permeability
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9
Q

cholesterol structure

A
  • hydrophobic region one end - attracts non-polar fatty acids in phospholipids
  • hydrophilic group other end - attracts the polar head of phospholipid
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10
Q

components of plasma membrane

A

glycolipid, glycoprotein, cholesterol, extrinsic and intrinsic proteins, hydrophobic tails, hydrophillic heads

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11
Q

extrinsic protein function in plasma membrane

A
  • structure
  • enzymes
  • receptors for molecules such as hormones
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12
Q

intrinsic protein function in membrane

A
  • carrier proteins - important in passive and active transport into cells - can change shape to allow molecules to pass through
  • channel proteins - lined with hydrophilic amino acids and filled with water molecules - allow water soluble molecules and ions to diffuse through
  • some are receptors for hormones, neurotransmitters etc.
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13
Q

What effect does heat have on the plasma membrane?

A
  • as temperature increases, kinetic energy of phospholipid increases
  • creates gap between bilayer
  • molecules can pass through gaps increasing permeability
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14
Q

effect of low pH on membrane

A
  • increases permeability
  • acidity changes tertiary structure of proteins in membrane
  • can cause them to denature
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15
Q

what effect do solvents (water / alcohol and benzene) have on the plasma membrane?

A
  • water is polar so creates stability with phospholipids
  • alcohols and benzene are less polar so can disrupt the bilayer structure - making it more permeable
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16
Q

method of investigating effect of temp. on membrane permeability

A
  • prepare beetroot cylinders by blotting and washing them until they’re free of pigment
  • put 5cm^3 distilled water into 6 test tubes of varying temps
  • put 3 beetroot discs in the first test tube and leave for 1 min
  • put water from test tube in a colourimeter
17
Q

what do temperatures below freezing do to the phospholipid bilayer?

A
  • phospholipids don’t have much kinetic energy so don’t move
  • they pack close together forming a rigid layer
  • channel proteins and carrier proteins denature
  • ice crystals may pierce the bilayer increasing permeability significantly
18
Q

what do temperatures 0-45 degrees do to the phospholipid bilayer?

A
  • phospholipids can move around and arent packed as closely together
  • membrane is partially permeable
  • temp gives lipids more energy
  • increases permeability
19
Q

what do temperatures above 45 degrees do to the phospholipid bilayer?

A
  • bilayer starts to melt and becomes more permeable
  • water inside cell puts pressure on membrane
  • channel and carrier proteins denature increasing permeability
20
Q

diffusion

A

net movement of particles down a concentration gradient from a high concentration to a low concentration

21
Q

what effect does the polarity of molecules have on the speed they diffuse across a membrane?

A
  • non-polar hydrophobic (eg. oxygen, co2) rapidly diffuse
  • small polar hydrophilic (eg. water, urea) diffuse slowly
  • polar charged particles - ions - cannot diffuse across a membrane (apart from water)
22
Q

facilitated diffusion definition

A
  • carrier or channel proteins allow polar, hydrophilic or large molecules to pass through the membrane
  • passive process - doesn’t require energy as particles have their own kinetic energy
23
Q

facilitated diffusion in carrier protein

A
  • carrier protein has binding site that specific chemical binds to
  • when chemical binds it changes tertiary structure bringing the chemical across the membrane
24
Q

facilitated diffusion in channel proteins

A
  • lined with hydrophilic amino acids and contains water
  • hydrophilic substances can pass through the channel
  • they are selective - only certain chemicals can pass through each type of protein channel
  • some are always open, some open as response to trigger eg. chemical binding to it
25
Q

where does active transport occur in membranes?

A

carrier proteins

26
Q

how does active transport work?

A
  • molecule being transported attaches to receptor site on carrier protein
  • ATP molecule binds to carrier protein and undergoes hydrolysis producing a phosphate and ADP molecule
  • phosphate attaches to carrier protein and causes a change in shape transporting the molecule to the other side of the membrane
  • phosphate detaches and carrier protein returns to original shape
27
Q

partially permeable membrane

A
  • water molecules can pass freely across membrane
  • solute molecule cannot
28
Q

osmosis definition

A

movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane

29
Q

units for water potential

A

kilopascals

30
Q

what happens when both sides of the membrane have the same water potential?

A
  • reached equilibrium and osmosis stops
  • same no. water molecules moving in each direction so net movement is 0
31
Q

what happens when water pot. outside cell is higher than inside? (animal cells)

A
  • water moves in cell via osmosis and hydrostatic pressure increases
  • cell may burst (lyse)
32
Q

what happens when water pot. inside cell is higher than outside? (animal cells)

A
  • water moves out by osmosis
  • cell shrinks
33
Q

what happens when water pot. outside cell is higher than inside? (plant cell)

A
  • water moves into cell by osmosis
  • protoplast pushes against cell wall as hydrostatic pressure increases
  • cell wall is strong so doesn’t burst, cell just becomes turgid
34
Q

what happens when water pot. inside cell is higher than outside? (plant cell)

A
  • water moves out cell by osmosis
  • protoplast pulls away from cell wall - shrivels
  • plasmolysis - there is a gap between protoplast and cell wall which is filled with solution surrounding cell
35
Q

2 processes involved in bulk transport

A

endocytosis
exocystosis
(both require energy to move vesicles)

36
Q

endocytosis

A
  • cell membrane folds inwards forming cavity around particles (invagination)
  • membrane forms vesicle around particles and vesicle moves into cell
  • next depends on what’s in the vesicle (eg. bacteria digested, particles transported to somewhere in cell)
37
Q

2 types of endocytosis

A
  • phagocytosis - solid materials taken into cell
  • pinocytosis - liquid brought into the cell
38
Q

exocytosis

A
  • proteins found in Golgi apparatus
  • vesicles bud off Golgi containing proteins and move towards cell membrane
  • vesicle fuses with membrane and proteins secreted

Biology (13 decks)

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