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APS 138: Molecular and cell biology > Lecture 17: Transport > Flashcards

Lecture 17: Transport Flashcards

1
Q

The necessity for transport in eukaryotic cells

A
  • Metabolism needs fuel, produces waste products.
  • Transport between cytosol and organelles.
  • Proteins secreted via the secretory system.
  • Signalling within and between cells.
  • Proteins targeted to different organelles.
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2
Q

Physical communication between animal cells:

A

Gap junctions

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3
Q

Gap junctions:

A
  • exchange of metabolites and signalling between cells.
  • channel proteins: connexins in vertebrates, innexins in invertebrates.
  • rapid exchange of ions and metabolites < ~1 kDa.
  • ~ 20 connexins in human genome, mutations lead to muscular dystrophy, deafness, skin diseases, cataracts.
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4
Q

connexins vs innexins

A

connexin in vertebrates

innexin in invertebrates

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5
Q

Physical communication between plant cells:

A

Plasmodesmata

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6
Q

Plasmodesmata :

A
  • Exclusion limit (~1 KDa), but can dilate to allow passage of molecules >20 kDa, (proteins and RNA)
  • Enable cytoplasmically interconnected fields of cells known as symplasm
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7
Q

Membrane structure:

A

Phospholipid bilayer:

  • phospholipid molecules (hydrophobic tails, hydrophilic heads)
  • integral proteins
  • carbohydrates
  • surface proteins
  • glycoprotein
  • glycolipid
  • peripheral protein
  • cholesterol
  • protein channel (transport protein)
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8
Q

The lipid bilayer :

—WHO

A

Gorter + Grendel 1925.
noticed must be a ‘bi’ layer because surface area occupied by lipids of erythrocytes was double that of total surface area of erythrocytes.

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9
Q

Gorter + grendel how did they test:

A

erythrocytes –> extraction of membrane lipid in solvent –> lipid film on water

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10
Q

Inherent transport properties of lipid membranes: Hydrophobic molecules

A

O2, CO2, N2, steroid hormones.

All pass through lipid bilayer.

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11
Q

Inherent transport properties of lipid membranes: Small uncharged polar molecules

A

H2O, urea, glycerol

Some passes through, more rejected to pass through lipid bilayer

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12
Q

Inherent transport properties of lipid membranes: Large uncharged polar molecules

A

glucose, sucrose

little passes through, majority rejected

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13
Q

Inherent transport properties of lipid membranes: ions

A

e.g. H+, Na+, HCO-3, K+, Ca2+, Cl-, Mg2+

ALL REJECTED

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14
Q

Time taken for 1 ml water to pass through 1 cm2 of membrane under 1 atm pressure: Red blood cell

A

2 days

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15
Q

Time taken for 1 ml water to pass through 1 cm2 of membrane under 1 atm pressure: Zoothamnium (a colonial protist)

A

6 weeks

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16
Q

Time taken for 1 ml water to pass through 1 cm2 of membrane under 1 atm pressure: Amoeba

A

9 months

17
Q

Aquaporins

A

membrane channels for transport of water, glycerol CO2 etc

18
Q

Aquaporins what do they carry out:

A

Facilitate diffusion of small uncharged molecules (water, glycerol, urea, CO2)

19
Q

occurrence of aquaporins:

A

correlates with high water fluxes (e.g. kidney, eye)

20
Q

how man aquaporins genes in man and in Arabidopsis

A

10 genes in man

30 genes in Arabidopsis

21
Q

What can aquaporins activity be regulated by/

A

by PTMs (phosphorylation)

22
Q

Passive transport:

A

of an ion or molecule facilitated by favourable concentration gradient.

23
Q

Active Transport::

A

Active transport against a concentration gradient requires energy.

24
Q

Passive transport uses which channels?

A

channel protein and transporter protein

25
Q

active transport uses

A

just transporter proteins & requires energy

26
Q

Passive and active transport:

A

Transport of a charged ion or molecule is facilitated by a favourable membrane potential.
Transport against an unfavourable membrane potential requires energy.

27
Q

Three ways of driving active transport:

A
  • coupled transporter
  • ATP-driven pump
  • Light-driven pump

All go against electrochemical gradient

28
Q

ATP-driven membrane transport in cells: P-type pump

A

P-ATPases: transport specific ions e.g. H+, Na+, K+, Mg2+, Ca2+. One or two polypeptides (< than rotary ATPases).

29
Q

ATP-driven membrane transport in cells: H+-PPases

A

In plants (not animals and fungi) H+-PPAses also couple PPi hydrolysis to H+ movement
ATP –> ADP + Pi
Pi used in pump

30
Q

ATP-driven membrane transport in cells: ATP-Binding Cassette transporters

A

(ABC) transporters. Substrates include lipids and sterols, ions and small molecules, drugs and large polypeptides. Cystic fibrosis transmembrane conductance regulator (CFTR) is an ABC Cl‐ transporter.
ATP –> Pi + ADP

31
Q

ATP-driven membrane transport in cells: Rotary ATPases family of membrane protein complexes

A

(F‐ATPase, V‐ATPase and A‐ATPase) are H+ pumps with role in energy conversion.
Pi + ADP –> ATP

32
Q

ion channels

A
  • Ions pass down their electrochemical gradient (a function of ion concentration and membrane potential) without input of metabolic energy.
  • Water‐filled pores allow only ions of a certain size and/or charge to pass.
33
Q

how many genes for ion channels cloned in man?

A

>

  1. Opened by different stimuli, including voltage, temperature, pH, stretch and ligands
34
Q

patch clamping:

A

used to study small patch of membrane. Glass pipette (v.small) touches cell membrane, causes tight seel to form between pipette &membrane. Ions that flow through when single ion channel opens must flow through pipette. Resulting electrical current can be measured. Record of current can show whether channels open/closed

35
Q

Patch clamping once collected:

A
  • alter voltage across patch

- measure current (ions) which flows

36
Q

connexins are arranged into

A

connexons

37
Q

Transporters are often linked: Two types of glucose carriers and Na+/K+ ATPase enable…

A

epithelial cells to transport glucose from the gut

38
Q

Transporters often linked: HCl secretion in gastric parietal cells:

A
  • The H+/K+‐ATPase in luminal membrane drives H+ ions into lumen in exchange for K+, raising [H+] against a concentration gradient of about 3 million to 1 (pH 1.5 to 3.5, 100 mM HCl).
    +
  • K+ taken cycles via K+ channels.
  • For each H+ ion secreted, one HCO3- ion (from CO2 & OH- catalyzed by carbonic anhydrase, CA) enters the blood in exchange for a Cl– ion via a coupled anion antiporter. Intracellular Cl– enters lumen via Cl– channels.
    + Immunolocalisation of H /K ATPase in
    COUPLED TRANSPORTER (e.g. Na+/H+; Cl‐/HCO3‐)
  • H+/K+‐ATPase inhibitors (benzimidazole derivatives) act as ant‐acids (ulcers, heartburn).
39
Q

Transporters often linked: Sucrose + sieve tube elements

A

Sucrose enters sieve‐tube elements of phloem by active transport (SUT1; sucrose/H+ symporter)

APS 138: Molecular and cell biology (15 decks)

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