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
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