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Lecture 14

BIOL 1000 Lecture Notes - Lecture 14: Transmembrane Protein, Cell Membrane, Facilitated Diffusion

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BIOL 1000
Nicole Nivillac

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Biology February 7th : Lecture 13 Slides
Plasma Membrane: continuation
Transport across the Membrane
Selectively Permeable (slide 29)
Regulation between what can go through the membrane and what cant
Gases. Water can cross membrane freely
Other molecules (glucose, sucrose, ions) that are more difficult moving across membrane
due to size, so they need help
Composition: proteins and phospholipids mboth exist in the membrane
Integral membrane: have portions in both hydrophilic and hydrophobic parts of plasma
Integral membrane proteins, two major categories: polytopic and monotopic
Polytropic: both layers (transmembrane protein)
Monotopic: interact with just one membrane
All transmembrane are integral proteints but not all integral proteins are transmembrane
Predicting membrane protein structure (slide 31)
2 Categories of proteins: Transmembrane and Peripheral
Colour coded amino acids from their properties (green is hydrophobic, blue is
See long region of amnio acids = transmembrane because goes through both membranes
Transmembrane proteins: most integral proteins
Yellow segments: higher amounts of hydrophobic ends
Peripheral proteins: have no interaction with the hydrophobic region, interacting with
hydrophobic regions
How do they stay attached to the membrane: usually attached to transmembrane protein,
uses other ways to stay in close proximity with membrane
Find it in the intracellular portion of plasma membrane (cytoplasmic side) (look at it in
communications chapter)
4 ways of Transport:
First way: diffusion
High concentration to low concentration
Molecules start to side that has less molecules, they like to be spead out and end goal is
reach equilibrium
Molecules will go from being more localized to being more dispersed (Entropy increase)
Occurs spontaneously (lot of potential energy stored in gradient)
Once you start to move, end up in a balanced situation, no more change in concentration
on either side
Passive simple diffusion: high to low but don’t need any type of protein, they just move
across the membrane but don’t need any proteins to help, move with the gradient (no
energy required)
2nd way: Passive facilitated diffusion
facilitated by membrane proteins, in this case, passive facilitated, facilitiated means it
needs help with a protein
does not need energy, molecules move down concentration gradient (high to low) several
different proteints that can be involed
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