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Lecture 5

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Biology 1002B
Tom Haffie

10. characteristics of trans membrane proteins that enable them to interact with hydrophobic core of membrane. • To be able to interact with hydrophobic core of a membrane, trans membrane proteins are composed of regions that consist of pre-dominantly non-polar amino acids that are usually coiled into alpha helices • Although proteins have hydrophobic groups, as well as hydrophilic groups, proteins can interact with the hydrophobic core. • This requires correct folding – the core of the protein will contain a channel through which the molecule can move – the parts of the protein that face the channel are hydrophilic and it's the hydrophobic parts that are exposed to the fatty acid core. • How the interact with the hydrophobic core> ✗ Alpha helix minimizes charges of the backbones ✗ Trans membrane can be identified because of the presence of stretches of the amino acids that are primarily non-polar. Non polar amino acids are present in the regions that interact with the core of the membrane. 11. factors influencing simple & facilitated diffusion. • Simple diffusion – if the molecules are small and uncharged, they can diffuse through the membrane through simple diffusion from one side to the other (high to low concentration). Diffusion is a free energy process, entropy -driven process. Membrane component responsible for transport: lipids • facilitated diffusion – involves specific transporter and what drives the movement of the molecules (polar and charged such as water, amino acids, sugars and ions) is diffusion based on a concentration gradient across the membrane. Membrane component responsible for transport: proteins. When the gradient falls to zero, transport stops. 12. Transport against a concentration gradient (active transport) • Many substances (sugar and amino acids) are pushed across membranes against their concentration gradients by active transport “pumps” which involves ABC transporter. (low concentration to high concentration). This requires Energy. Energy comes from ATP breakdown after ATP binds to the ATP-binding domain. 13. Role of electrochemical gradient in determining equilibrium concentration of ions. • Example: Na+/K+ pump located in the plasma membrane, pushes 3 NA+ out of the cell and 2 K+ into the cell in the same pumping cycle. As a result, outside membrane becomes more positive (more – ions than inner membrane) and inner membrane becomes more negative (less – ions). This creates an electrical potential difference (voltage) and it is called an electrochemical gradient. Electrochemical gradients store energy that is used for other transport mechanism such as nerve impulse transmis
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