membranes and membrane transport Flashcards

1
Q

lipid is bilayer is …. + ….. …..

A

dynamic
selectively permeable

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2
Q

what do the proteins in the lipid bilayer enable

A

signalling, communication + selective permeability

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3
Q

what are the cell membranes a mix of

A

glycolipids
phospholipids
sphingolipids
cholesterol

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4
Q

what are phospholipids made from

A

glycerol
phosphate
head group
hydrocarbon tail

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5
Q

phospholipids are ……….

A

amphipathic

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6
Q

why are phospholipids amphipathic

A

hydrophilic head = face towards fluid
hydrophobic tail = face each other

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7
Q

where do the hydrophobic tails face

A

towards each other

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8
Q

where do the hydrophilic heads face

A

towards fluid

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9
Q

what are the tails described as

A

hydrophilic

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10
Q

what are the heads described as

A

hydrophobic

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11
Q

what determines the fluidity of the membrane

A

fatty acid chains

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12
Q

what do fatty acid chains determine

A

the fluidity of the membrane

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13
Q

what are phosphoglycerides derived from

A

glycerol

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14
Q

what are sphingolipids derived from

A

sphingosine

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15
Q

what is functionally important

A

lipid symmetry

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16
Q

describe glycolipids

A

found in the non cytosolic layer only
contain sugar
made from sphingosine
glycosylation occurs in lumen of golgi

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17
Q

what do the inner and outer monolayers have

A

different compositions

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18
Q

describe cholesterol

A

modulates the properties of lipid bilayers
inserts between membrane phospholipids
tightens packing in bilayer
decreases membrane permeability to small molecules
increases rigidity
different cells have different lipid compositions

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19
Q

what does the hydrophobic nature of fatty acids derive

A

the structure formed by phospholipids

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20
Q

what do lipid bilayers spontaneously do

A

close to form sealed compartments

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21
Q

describe biological membranes

A

fluid structures
allows lipids and membrane proteins to rapidly diffuse in lateral plane + interact with one another
ensures membranes are equally shared between daughter cells during cell division
allows cells to change shape (cell motility)allows membranes to fuse with other membranes - eg. in exocytosis or secretion of proteins

22
Q

what are the 4 types of integral and peripheral membrane proteins

A

single-pass
multipass transmembrane proteins
beta-barrel
lipid-linked
peripheral membrane protein

23
Q

what do both single-pass and multipass transmembrane proteins have

A

hydrophobic amino acids with side chains interacting with lipid monolayer

24
Q

describe membrane protein function

A

transport
enzymatic activity
signal transduction
cell-cell recognition
intracellular joining
attachment to the cytoskeleton + extra-cellular matrix

25
Q

what are the 2 types of membranes

A

active
passive

26
Q

what does active transport require

A

ATP

27
Q

passive transport doesn’t require ….

A

ATP

28
Q

describe simple diffusion

A

non membrane proteins involved
driven by conc gradients
down a conc gradient
ability of a solute to cross membrane by simple diffusion depends on:
-conc gradient - hydrophobicity/charge , size
-membranes are highly impermeable to ions

29
Q

what relationship do membranes have with ions

A

highly impermeable

30
Q

what does the ability of a solute to cross the membrane by simple diffusion depend on

A

-conc gradient - hydrophobicity/charge , size
-membranes are highly impermeable to ions

31
Q

describe facilitated diffusion

A

membrane proteins involved
driven by conc gradients
no energy input - ATP not needed

32
Q

describe the transport of inorganic ions + small molecules across the membrane

A

required for intracellular ion concs
uptake of nutrients
excretion of metabolic waste products
- are different mechanisms for transport of large macromolecules across membranes

33
Q

what are the 2 classes of proteins involved in facilitated diffusion

A

channels
uniporter or carrier proteins

34
Q

describe channel proteins

A

discrimates mainly on size and charge

35
Q

describe uniporter carrier proteins

A

involves binding site for solutes
-transport inorganic ions/small molecules across the membrane passively along their conc gradient/electrochemical gradients

36
Q

what is another word for conc gradients

A

electrochemical gradients

37
Q

describe ion channels

A
  • membranes are impermeable to ions
  • channels transport them across the membrane
  • exhibit ion selectivity
  • driven by conc/electrochemical gradient
  • fast : transport up to 10 molecules per sec
  • may be regulated - eg. open and close in response to a stimulus
38
Q

describe K+ channels

A
  • most common ion channels - present in all cells
  • important subsrt (K+ leak channels) are continuously open (not gated)
  • selective: conduct K+ 10,000-fold more effectively than Na+
39
Q

describe uniporter carrier proteins

A
  • glucose transporter (Glut2) in gut epithelia (solute=glucose)
  • highly selective - transported molecule bound to carrier
  • relatively slow (<1000 molecules per second)
40
Q

describe the transport of glucose into erythrocytes by GLUT 1

A

glucose = higher conc in blood than erythocte
tasnported into cell by GLUT 1
along conc gradient
GLUT 1 - works in both directions
= conc gradient maintain -> converting glucose into glucose-6-phosphate
glucose-6-phosphate isn’t recognised by GLUT 1 = one-directional transport

41
Q

why is it important for GLUT 1 to work in both directions

A

conc gradient is maintained
achieved by converting glucose to glucose-6-phosphate

42
Q

why is the transport 1 directional

A

as glucose-6-phosphate isn’t recognised by Glut1

43
Q

describe active transport

A

energy required - ATP
solutes move against conc gradient

44
Q

what are the 3 ways that cells carry out active transport

A

ATP-driven pumps
coupled transporters
light driven pumps

45
Q

describe ATP-driven pumps

A
  • couple the transport of solute against its gradient to the hydrolysis of ATP
  • primary active transport
46
Q

describe coupled transporters

A
  • couple the transport of one solute with the gradient to another against the gradient
  • secondary active transport
47
Q

describe light driven pumps

A

couple the transport of a solute against its gradient to the input of energy from light

48
Q

what do ATP driven pumps do

A
  • move solutes against the gradient by expending energy
  • eg. na+ / k+ gradient
  • in absence of na+ / k+ ATPase ions would flow down their gradients disturbing osmotic balance and preventing ‘secondary’ active transport
49
Q

what do couple transporters do

A
  • move solutes against conc gradient by coupling transport to Na+ gradient created by Na+/K+ ATPase
  • don’t directly depend on the hydrolysis of ATP
  • eg. secondary active transport
50
Q

summary

A
  • Membranes consist of lipids (mainly phospholipid) and protein.
  • Membranes are fluid (fluid mosaic model).
  • Transmembrane proteins are inserted into the membrane during synthesis.
  • Lipid nature of membrane prevents passage of ionised molecules
  • Therefore need channels/ carriers to allow ions and ionic substances to cross the membrane
  • Passive- diffusion, Active- against concentration gradient
51
Q

describe Na+ / K+ pump action

A
  1. 3 x Na+ ions bind. Pump hydrolyses ATP and is phosphorylated
  2. Na+ dependent phosphorylation causes pump to undergo conformational change, Na+ is transferred across the membrane and released
  3. 2 K+ ions bind and pump is dephosphorylated
  4. K+ dependent dephosphorylation causes the pump to return to its original conformation. K+ is transferred across the membrane and released