E3: Intro to cell membranes Flashcards

1
Q

what does amphipathic mean

A

comprising hydrophilic and hydrophobic regions

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2
Q

what are the three major types of membrane lipids

A

-glycerophospholipids
-sphingolipids
-sterols

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3
Q

Describe glycerophospholipids (see structure on one note)

A
  • Phosphorylated head group, three-carbon glycerol backbone and 2
    hydrocarbon fatty acid chains
  • Polar group includes, choline or serine (other variations)
  • Amphipathic, various derivatives present in varying amounts in
    membranes of all cell
  • Fatty acid tail can be saturated or unsaturated (one or more double
    bonds – creates ‘kinks’ in the tail)
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4
Q

Describe sphingolipids (see structure on one note)

A
  • Phosphorylated head group, sphingosine backbone and 2
    hydrocarbon fatty acid chains, one of the fatty acid chains is
    contributed by sphingosine
  • Polar group includes choline or can be a sugar
  • Amphipathic, present in most cells, but most abundant in myelin
    sheath surrounding nerve cells
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5
Q

Describe sterols (see structure on one note)

A
  • Cholesterol in animals (ergosterol in fungi, hoponoids in bacteria)
  • Present in varying amounts and influences membrane
    fluidity/rigidity
  • Unsaturated, double bonds in fatty acid tails create space for
    sterols to sit in the membrane
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6
Q

Cell membrane is selectively permeable and maintains what?

A
  • Maintenance of pH and ionic composition
  • Regulation of cell volume
  • Concentration of metabolites and extrusion of waste substances and toxins
  • Generation of ion gradients for excitable tissues (muscle and nerve)
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7
Q

how do channels/ pores/ transporters allow compounds to enter or leave the cell?

A

-along their concentration gradients- passive or facilitated diffusion
-active transport
-membrane proteins allow movement of molecules by opening and closing of subunits

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8
Q

function of receptors and adhesion molecules

A

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

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9
Q

what small molecules can pass through the cell membrane unaided?

A

Water, gases (e.g., O2, CO2, NO), urea

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10
Q

what cannot pass through the membrane unaided?

A

Ions, sugars, amino acids

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11
Q

transport by diffusion can be…

A

-chemical
-electrical

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12
Q

Diffusion is influenced by…

A
  • Steepness of the concentration gradient
  • Temperature
  • Size or mass of the diffusing substance
  • Surface area
  • Diffusion distance
  • Numbers of channels / transporters on the surface of the cell
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13
Q

Describe membrane transport via active transport

A

-against a concentration gradient
* Usually highly specific for one molecule e.g., ions or class of molecules e.g., sugars, amino acids
* Require expenditure of energy and there are several key sources e.g.,
* ATP hydrolysis
* Dissipation of proton /sodium gradient

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14
Q

Describe facilitated transport proteins

A

Gated ion channels are highly selective for specific ions and open and close in response to a particular signal e.g ligand-gated, voltage-gated, mechanosensitive/gated

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15
Q

what are gap junctions

A

channels that connect directly with neighbouring cells

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16
Q

where can ATP hydrolysis take place

A
  • Sodium-potassium pump, calcium pump
  • Mitochondrial ATP synthase
  • ATP- Binding Cassette (ABC transporters)
17
Q

what do active transport proteins use ATP for

A

establish a proton or sodium gradient
* e.g., Na+ – K+ ATPase or Na+ pump is a membrane transporter that maintains gradients of Na+ and
K+ across the membrane.
* For each ATP hydrolyzed 3 Na+
ions are removed from the cell and 2 K+ are brought in; by keeping
this Na+ gradient, it creates a secondary ‘energy’ source to drive secondary active transport
-Proton gradients are also used to drive activity of mitochondrial ATP synthase and generation
of ATP

18
Q

what is a symport?

A

co-transporter that transfers two molecules in the same directions (e.g glucose and Na+ pump)

19
Q

what is secondary active transport

A

a process that moves molecules across a cell membrane by using energy stored in electrochemical gradient

20
Q

Describe the secondary active transport of glucose

A

-glucose is pumped from a low conc to a high conc using ATP stored in Na+ gradient
-glucose and Na+ is pumped together inside cell, conformational change
-Na+ is transported back outside the cell through sodium-potassium pump (primary active transport)
(process on one note)

21
Q

Describe what happens in the sodium potassium pump (electrogenic pump)

A

-3 Na+ ions bind to pump
-ATP undergoes hydrolysis, the phosphate transfers to carrier. Phosphorylation changes conformation and Na+ released
-2 K+ bind to pump
-de-phosphorylation occurs and conformation changes again so K+ enters cell

22
Q

what are antiporters?

A

co-transporters that transfer molecules in opposite directions
(look at one note for example)

23
Q

Describe the ATP-Binding Cassette (ABC) transporter

A

-present in pro- and eukaryotic cells
-transport best studied in gram negative bacteria
-requires energy generated by hydrolysis of ATP- active transport
(look at one note for structure)

24
Q

How do receptors work?

A

most don’t move across the membrane, but cause a change in the cytoplasmic domain of the receptor protein, either through
clustering of the receptors or through inducing a
conformational change of the receptor protein. usually initiate cascade of signalling molecules

25
Describe exocytosis
-secretion of proteins out -Packaged into secretory vesicles by Golgi apparatus -Vesicles fuse with cytoplasmic membrane and release their contents extracellularly; may involve clathrin-coated pits * Constitutive and active processes
26
Describe endocytosis
Uptake of macromolecules from extra-cellular space, across the cytoplasmic membrane
27
what is pinocytosis
a constitutive and continuous process involving uptake of extra-cellular fluid via small membrane vesicles
28
what is phagocytosis
a specialized form of endocytosis in 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 / added to help kill/destroy the phagocytosed bacteria or debris
29
what is receptor-mediated endocytosis
involves the protein clathrin forming clathrin-coated pits and vesicles; protein has a distinctive 3-legged structure called a triskelion, which assemble to form a basket-like structure to stabilize the endocytic vesicle
30
What are the different mechanisms of cell signalling?
-junction between cells (direct) -adhesion molecules (direct) -using intercellular chemical messenger and specific receptor molecule (indirect) look on one note for diagram
31
what drugs are used as receptor/ channel binding molecules
agonists and antagonists
32
what are agonists
drugs that activates receptor and produces biological effect e.g insulin
33
what are antagonists
drugs that block the activation of the target by ligand e.g., Beta blockers block the adrenaline receptor (treating hypertension and arrhythmia)
34
Describe a signal transduction blocker
Kinase inhibitors are being developed as cancer treatments