BIO130H1 Lecture Notes - Lecture 2: Uniporter, Chemical Polarity, Conformational Change

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Published on 21 Apr 2013
School
UTSG
Department
Biology
Course
BIO130H1
Professor
Lecture 2 Crossing the Membrane
Permeability of the Membrane
Very permeable to Hydrophobic Molecules
Semi-permeable to small uncharged polar molecules
Impermeable to large uncharged polar molecules or Ions
Proteins for transport
All are multipass transmembrane proteins
Proteins are selective to either a class or maybe an individual molecule
Different cell membranes have different transport proteins
Proteins of Passive Transport
Channel Mediated Facilitated Diffusion
o The ion or large uncharged polar molecule enters/exits the cell via a (gated) channel
o When the gate is opened, a lot of the molecule can cross at the same time
Transporter Mediated Facilitated Diffusion
o A proteins undergoes conformational shifts to allow a few molecules to move in or out
Channel Proteins
Create a hydrophilic “pore” across the membrane
May be highly selective
Much faster transportation than a transporter; like a “highway
o May be gated or non-gated
o Non-gated = always open
o Gated = opening & closing is regulated via electrical, mechanical, or chemical signals
Electrical: When receiving an electrical charge, the gate opens
Mechanical: A force (eg. Stretching) occurs on the membrane, the gate opens
Chemical: A ligand binds on the outside/inside of membrane, and channel opens
Uniporters
Glut Uniporter
o One molecule attaches to the porter
o The porter bring the molecule through the membrane into the area of low concentration
o Occurs by conformational change
o Goes along the concentration gradient
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Document Summary

Impermeable to large uncharged polar molecules or ions. Proteins are selective to either a class or maybe an individual molecule. Different cell membranes have different transport proteins. Channel mediated facilitated diffusion: the ion or large uncharged polar molecule enters/exits the cell via a (gated) channel, when the gate is opened, a lot of the molecule can cross at the same time. Transporter mediated facilitated diffusion: a proteins undergoes conformational shifts to allow a few molecules to move in or out. Create a hydrophilic pore across the membrane. Much faster transportation than a transporter; like a highway : may be gated or non-gated, non-gated = always open, gated = opening & closing is regulated via electrical, mechanical, or chemical signals. Electrical: when receiving an electrical charge, the gate opens. Mechanical: a force (eg. stretching) occurs on the membrane, the gate opens. Chemical: a ligand binds on the outside/inside of membrane, and channel opens.

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