SfM - Forces Acting Across Membranes Flashcards
what is the function of membrane receptors?
most signalling occurs via hydrophilic signals (can’t cross membrane - neurotransmitters/hormones). Need to use receptors to relay their message to the cell. Once bound, this triggers a conformational change of the receptor. This triggers intracellular signalling pathways
are membrane receptors specific?
receptors are v.specific to ligands. the ligands can only have an effect on a receptor if the receptor possesses the corresponding binding site
what are membrane transporters?
transported are proteins that allow the moment of ions or other molecules across the membrane.
- channel proteins create a pore through the membrane so water (open) or ions (gated) can flow
what are enzymes role in the cell membrane?
membrane enzymes catalyse chemical reactions on the cell membrane
structural proteins and their role?
these proteins are associated with the cell membrane but not incorporated into it. they can anchor the membrane to intracellular skeleton and to the ECM (collagen).
- maintains integrity and normal function of the cell (dysfunction can cause problems i.e duchenne’s muscular dystrophy)
how do different membranes differ in protein content?
- nerve fibres are surrounded by myelin (only 18% protein so excellent insulator)
- mitochondria membrane is high in protein (75%) as they are involved in energy transduction
what happens in endocytosis?
invagination of the membrane to form a vesicle which eventually disintegrates on the cytoplasmic (inside) surface of the membrane, releasing contents which then migrate within the cell to their destination (tends to STOP signalling as the receptor is endocytosed)
what is exocytosis?
Molecules are put into a vesicle by organelles inside the cell and moves towards the membrane to be expelled into the extracellular fluid
what is diffusion?
Process by which a gas or substance in solution expands to fill all the available volume. Therefore, molecules spread from regions of high concentration to regions of low concentration, until the concentration is uniform throughout the volume.
examples of channels
- voltage gated channels = open/close in response to electrical potential (charge difference on either side of the membrane)
- ligand gated channels = open/close when they bind a specific molecule
what is active transport?
movement of molecules through transport proteins against their electrochemical gradients
- requires energy (ATP)
- carries protein also functions as an enzyme (ATPase)
what are active transporters?
often referred to as pumps (Na+/K+/ATPase)
Na high outside cell, K high inside cell
3Na+ out 2K+ in
Produces net movement of positive charge OUT of cells
how does Na+K+ATPase work>
- when channel open to intracellular fluid, binding sites have high affinity for Na+.
- when Na+ binds it triggers a conformational change i.e ATPase phosphorylated
- Na+ released into ECF
- when pump is open to the ECF it has a high affinity for K+
- K+ moves into pump and binds (ATPase dephosphorylated) and K+ released into ICF
what is osmosis?
net movement of H2O from regions of high to low concentration
how is water and solute concentration related?
H2O concentration is inversely related to the concentration of solute (more solute dissolved = less water)
