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FUN E > E3 Introduction to cell membrane structure and function > Flashcards

E3 Introduction to cell membrane structure and function Flashcards

1
Q

what does amphipathic mean?

A

comprising hydrophilic and hydrophobic regions

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2
Q

what are cytoplasmic membranes formed by?

A
  • lipid bilayers
  • the bilayer is made up from 2 leaflets
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3
Q

what are the 3 major types of membrane lipids?

A
  • glycerophospholipids
  • sphingolipids
  • sterols
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4
Q

describe the structure of glycerophospholipids

A
  • phosphorylated head group, 3-carbon glycerol backbone and 2 hydrocarbon fatty acid chains / tails
  • amphipathic
  • various derivatives present in varying amounts in membranes of all cells
  • fatty acids are around 20 carbons long
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5
Q

what do the polar group of a glycerophospholipid include?

A

choline or serine

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6
Q

what can the fatty acid tails in glycerophospholipids be?

A
  • saturated or unsaturated
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7
Q

what does it mean for a fatty acid to be unsaturated?

A
  • 1 or more carbon double bond within the chain
  • creates kinks in the tail and lessens the melting and boiling points as they can’t pack as close together
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8
Q

describe the structure of sphingolipids

A
  • phosphorylated head group, sphingosine backbone and 2 hydrocarbon fatty acid chains (1 of the fatty acid chains is contributed by sphingosine)
  • amphipathic
  • larger than glycerophospholipids
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9
Q

what does the polar group of a sphingolipid include / what can it be?

A

includes choline or can be a sugar

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10
Q

where are sphingolipids most abundant?

A

myelin sheath surrounding nerve cells

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11
Q

describe sterols in different organisms

A
  • cholesterol in animals
  • ergosterol in fungi
  • hopanoids in bacteria
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12
Q

what does more cholesterol do to cell membranes?

A

more rigid / stiff

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13
Q

what feature of cell membranes can be associated with cell signalling and transport across mmebranes?

A

clustering of lipid molecules to give domains or rafts

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14
Q

what can the composition of a membrane influence?

A
  • thickness, curvature and lateral freedom of movement of lipids in the bilayer
  • i.e. the fluidity
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15
Q

why are membranes self-sealing?

A
  • because they are dynamic structures
  • can self-seal due to amphipathic properties (ensure cell remains in tact - not damaged or killed)
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16
Q

what properties are the self-sealing property of membranes important for?

A
  • cell division
  • endocytosis and exocytosis
17
Q

what can cell membranes help to regulate and maintain?

A
  • pH and ionic concentration
  • cell volume
  • ion gradients for excitable tissues (muscles and nerves)
  • concentration of metabolites and extrusion of waste substances and toxins
18
Q

state some functions of membrane proteins

A
  • channels
  • pores
  • transporters
  • receptors
  • adhesion molecules
19
Q

describe the functions that channels, pores and transporters can perform

A
  • passive transport
  • diffusion
  • facilitated diffusion
  • active transport
20
Q

what do receptor and adhesion molecules allow for in membranes?

A
  • bind extracellular molecules without necessarily transporting them across the membrane
  • allow cells to sense their environment and to adhere to their tissue
21
Q

what main feature do membranes have?

A

selective permeability

22
Q

what molecules can pass through the bilayer unaided?

A
  • urea
  • water
  • gases

(however, rate of water movement may be insufficient for cell function)

23
Q

what are the 2 major classes of integral membrane proteins?

A
  • channels (pores)
  • transporters
24
Q

what is diffusion driven by?

A
  • differences on either side of a membrane
  • differences can be chemical or electrical
25
Q

what is diffusion rate influenced by?

A
  • steepness of concentration gradient
  • temperature
  • size or mass of the diffusing substance
  • surface area
  • diffusion distance
  • number of channels / transporters
26
Q

what are some examples of transporters?

A
  • uniporters
  • symporters
  • antiporters
  • ATP-binding cassette (ABC) system
27
Q

state 3 examples of gated ion channels

A
  • ligand-gated
  • voltage-gated
  • mechanosensitive
28
Q

what are gap junctions?

A
  • channels that connect directly with neighbouring cells
29
Q

what ratio of sodium and potassium ions are moved and how much ATP is required for this in active transport?

A
  • 3 sodium ions out of the cell
  • 2 potassium ions into the cell
  • 1 ATP hydrolysed for this above ratio
30
Q

what is the difference between a symport and antiport in co-transport?

A

symport:
- transports 2 different molecules in the same direction
- eg. sodium ion and glucose in active co-transport in the ileum

antiport:
- transports 2 different molecules in opposite directions (one into the cell and one out)

31
Q

describe the ATP-binding cassette transporter

A
  • over 200 different ABC systems
  • present in eukaryotes and prokaryotes
  • transport is best studied in Gram negative bacteria
  • in human cells, ABC transporters are involved in cystic fibrosis and multi-drug resistance
  • requires energy released by hydrolysis of ATP
32
Q

describe exocytosis

A
  • secretion of proteins out across the cytoplasmic membrane
  • packaged into secretory vesicles by Golgi and targeted to cytoplasmic membrane
  • vesicles fuse with cytoplasmic membranes and release their contents extracellularly
33
Q

what is the name for the dedicated transporter systems in bacteria? why are they necessary?

A
  • translocases
  • constraints of the cell wall means exocytosis and endocytosis might not be possible like in animal cells
34
Q

describe endocytosis in general

A
  • uptake of macromolecules from extracellular space across the cytoplasmic membrane
  • occurs continuously in animal cells
  • small portion of cytoplasmic membrane envelopes the molecule, invaginated and pinches off as an intracellular vesicle
35
Q

what are the 3 distinct mechanisms of endocytosis?

A
  • pinocytosis
  • phagocytosis
  • receptor-mediated endocytosis
36
Q

describe pinocytosis

A
  • bring small amounts of extracellular fluid in
  • a constitutive and continuous process involves uptakes of extracellular fluid via small membrane vesicles
37
Q

describe phagocytosis

A
  • endocytosis by macrophages and neutrophils to ingest bacteria and cell debris in a phagosome / phagolysosome
  • enzymes and reactive oxygen species like superoxide and nitric oxide are pumped in to help destroy the engulfed bacteria or debris
38
Q

describe receptor-mediated endocytosis

A
  • involves the protein ‘clathrin’ forming clathrin-coated pits and vesicles
  • ligand binds to receptor than causes pit to form vesicle
  • protein has a distinctive 3-legged structure called a triskelion which assemble to form a basket-like structure to stabilise the endocytic vesicle

FUN E (11 decks)

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