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IB Biology > 1.3 Membrane Structure > Flashcards

1.3 Membrane Structure Flashcards

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1
Q

amphipathic

A

has hydrophobic and hydrophilic parts (ex. phospholipid)

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2
Q

what is the hydrophilic part of a phospholipid?

A

the head / phosphate group

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3
Q

what is the hydrophobic part of a phospholipid?

A

the hydrocarbon tails

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4
Q

what is the phospholipid bilayer

A

phospholipids arranged into double layers; hydrophobic tails facing each other inwards, hydrophilic heads facing water on either side

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5
Q

what did gorter & grendel do?

A
  • 1920s
  • figured out membrane contains a BILAYER
  • their model didn’t explain where proteins were located
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6
Q

what did davson & danielli propose?

A
  • 1930s
  • proposed layers of protein adjacent to both sides of bilayer
  • aka sandwich model
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7
Q

falsification of d&d

- freeze-etched electron microscopes

A
  • rapid freezing then fracturing of cells along membrane
  • globular structures scattered around centre of membrane
  • transmembrane proteins
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8
Q

falsification of d&d

- structure of membrane proteins

A
  • proteins extracted from membrane
  • varied in size, globular shapes
  • not like structural proteins that would be in continuous layers around bilayer
  • some parts of proteins= hydrophobic, therefore attracted to hydrocarbon tails
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9
Q

falsification of d&d

- fluorescent antibody tagging

A
  • fluorescent marks on antibodies that bind to membrane proteins used on 2 diff cells
  • when 2 cells fused, markers mixed throughout membrane
  • showed that proteins moved, not a static layer
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10
Q

3 evidences for falsifying d&d

A
  • freeze etched electron microscopes
  • structure of membrane proteins
  • fluorescent antibody tagging
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11
Q

what did singer & nicolson

A
  • 1966
  • made fluid mosaic model
  • proposed that proteins occupied many positions throughout membrane
  • peripheral proteins on inner/outer surface
  • integral proteins embedded in bilayer, some protrude
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12
Q

how do phospholipids / proteins appear on electron microscopes?

A
  • phospholipids appear light

- proteins appear dark

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13
Q

what’s the cell membrane’s primary function?

A

to serve as a barrier that ions & hydrophilic molecules can’t pass through

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14
Q

4 types of membrane proteins

A
  1. transporters
  2. anchors
  3. receptors
  4. enzymes
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15
Q

transporters

A
  • pumps for active transport (use ATP to move particles across membrane)
  • channels for passive transport (allow hydrophilic particles across by facilitated diffusion)
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16
Q

anchos

A
  • cell adhesion: form tight junctions b/ween cells

- cell-to-cell communication (glycoproteins serve as identification tags)

17
Q

receptros

A
  • hormone binding proteins

- bind to specific receptors on membrane to be released to interior of cell

18
Q

enzymes

A
  • proteins attached to membrane interior/exterior
  • catalyse chemical reactions
  • immobilised enzymes w/ active site on outside
19
Q

relation between membrane activity and protein content

A

the more active the membrane, the higher the protein content

20
Q

which membranes have the highest protein content?

A

chloroplasts and mitochondria membranes

21
Q

membranes outside the cell have _ protein content

A

50%

22
Q

integral proteins

A
  • partly hydrophobic (embedded in hydrocarbon chains)
  • many are transmembrane
  • hydrophilic parts project through phosphate head regions
23
Q

peripheral proteins

A
  • hydrophilic surface, not embedded
  • most are attached to surface of an integral protein
  • some have single hydrocarbon chain attached to them that’s inserted into membrane, anchoring protein into membrane surface
24
Q

protein channels

A

control entry and removal of specific molecules from cell

25
Q

carbohydrates

A
  • glycoproteins (cell recognition/immune responses) attached to proteins
  • glycolipids attached to lipids
26
Q

cholesterol

  • is found where?
  • what is it?
A
  • only in animal cell membranes, not plant cells
  • type of lipid specifically steroid
  • amphipathic (mostly hydrophobic, attracted to hydrocarbon chains
  • positioned b/ween phospholipids
27
Q

role of cholesterol in membrane

A
  • regulates fluidity of membrane by immobilising outer surface of membrane
  • separates phospholipid tails to prevent crystallisation & behaving as solid
  • reduces permeability to small water soluble molecules
  • secures peripheral proteins, forms high density lipid rafts to anchor the protein
  • due its shape, helps membrane curve into concave shape, helpful in formation of vesicles during endocytosis

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