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Lecture 5

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Department
Biology
Course
Biology 1002B
Professor
Tom Haffie
Semester
Winter

Description
Membrane Structure and Transport January, 21, 2013  The membrane is a phospholipid bilayer o It has a hydrophilic head and hydrophobic tail  Phospholipid bilayer can be formed spontaneous, no energy required  The membrane are more than 50% protein  Saturated vs. unsaturated o Unsaturated have lots of kinks in them, lots of movement  Physiological importance of unsaturation o Saturated ->(desaturase) -> Unsaturated o When you regulate desaturase, you can regulate unsaturation o Maintaining proper fluidity is very important, can’t be too lucid and can’t be too rigid  Membrane Permeability o The tail of the fatty acid is very hydrophobic o CO2, N2, O2 can move through the membrane, because they are very small o As size and charge increases, will be denied o So how to get other stuff across?  We use proteins to transport others across the membrane, the membrane protein  Membrane proteins o The protein interact with the membrane o They can form some kind of channels o For membrane protein, all one need is the primary sequence  Some sequences are rich in polar amino acids sequences and some sequences are non-polar amino acid, it takes about 17 to 20 amino acids made of predominantly of non-polar amino acid, then you’ll know it’s a membrane protein  Alpha helical structures o How can proteins interact with hydrophobic core?   Membrane transport o Diffusion: if the molecules are small and non-charged  Driven by energy change (change in free energy), concentration gradient o Facilitated: they leak from a high concentration to low concentration, there is a channel just for one specific molecule/ion, without it they can’t move o Active transport: (ABC transporter): moving molecules from low concentration to high concentration, endergonic process  Trans-membrane domain is going to be different, not the same (need 1000s of them)  They have a ATP binding site, ATP is the energy given to the transport  Modeling a Neuron o Ions diffuse along electrochemical (charged) gradients o In a neuron, there is a selective permeable membrane only permeable to potassium (K)  One side will have more K, so it will diffuse across from high to low concentration, but it the other side has a more
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