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Wong_Justin_block2_MM3 (Synthesis and Sidedness of Membranes (Inside the…
Wong_Justin_block2_MM3
Membrane Proteins
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Integral Proteins
Transport: Proteins that spans the whole membrane with a hydrophilic channel running through it that is selective to a certain solute. Other transport proteins shuttle a substance from one side to another by changing shape. There are some that hydrolyze ATP as an energy source to actively pump substances across the membrane.
Cell- Cell Recognition: Some glycoproteins serve as identification tags that are specifically recognized by other cells
Signal Transduction: Has binding site with specific shape of a chemical messenger, such as a hormone. The external messenger may cause a conformational change in the protein receptor that relays the message to the inside of the cell
Attachment to Cytoskeleton and ECM: Microfilaments and other parts of the cytoskeleton bonding to membrane proteins, a function that maintains cell shape and stabilizes the location of certain membrane proteins.
Intercellular Joining: Membrane proteins of adjacent cells may hook together in different types of junction(gap/tight/etc.)
Enzymatic Activity: A protein built into the membrane could be an enzyme with its active site exposed to substances in the adjacent solution. There are some cases where several enzymes in a membrane are organized as a team that carries out sequential steps of a metabolic pathway.
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Endocytosis: cell takes in macromolecules and particular matter by forming new vesicles from the plasma membrane
Active Transport: to pump a molecule across a membrane against its gradient requires a form of "work"; the cell must expend energy
Electrogenic pump: Proton pumps are the main electogenic pumps of plants, fungi, and bacteria; tehy are membrane proteins that store energy by generating voltage across membranes by using ATP for power, a proton pump trans locate positive charge in the form of hydrogen ions, The voltage and H+ concentration gradient represents a dual energy source that can drive other processes, such as the uptake of nutrients.
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Facilitated Diffusion
Polar molecules and ions impeded by the lip bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane. Channel protein has channel where water molecules or a specific solute can pass. Carrier protein alternate between two conformations, move solute across membrane.
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Lipids
Phospholipids
Movement: Lipids move laterally in a membrane, but flip-flopping across the membrane could occur although quite rare
Membrane Fluidity: Unsaturated hydrocarbon tails of phospholipids have kinks that keep the molecule s from packing together, enhancing membrane fluidity
Cholesterol within the animal cell membrane: Cholesterol reduces membrane fluidly at moderate temperatures by reducing phospholipid movement , but at a low temperature, it hinders solidification by disrupting the regular packing of phospholipids
Bilayer: Outer heads are hydrophilic, hydrophobic middle region