Cellular Level of Organization Part 2 PDF

Cellular Level of Organizati on Part 2 Membrane Transport  Membrane Transport The cell membrane is a barrier, but: nutrients must get in products and wastes must get out  Permeability Permeability determines what moves in and out of a cell: A membrane that: le...

Cellular Level of Organizati on Part 2 Membrane Transport  Membrane Transport The cell membrane is a barrier, but: nutrients must get in products and wastes must get out  Permeability Permeability determines what moves in and out of a cell: A membrane that: lets nothing in or out is impermeable lets anything pass is freely permeable ‘chooses’ what moves across is selectively permeable Selective Permeabilit y Cell membrane is selectively permeable: allows some materials to move freely restricts other materials  Restricted Materials Selective permeability restricts materials based on: – size – electrical charge – molecular shape – lipid solubility  Transport Transport through a cell membrane can be: – passive (no energy required) – active (requiring energy and ATP) Membran e Transport Diffusion (passive) a) Simple b) Facilitated a) Channel- mediated b) Carrier- mediated (Facilitated diffusion) Active transport c) Carrier- mediated (active) Vesicular transport Diffusion: – molecules mix randomly – solute spreads through solvent – eliminates concentration gradient – I.E perfume – Substances always move down their concentration gradients From areas of high to areas of low concentration  Simple Diffusion Materials which diffuse through cell membrane: – lipid-soluble compounds (alcohols, fatty acids, and steroids) – dissolved gases (oxygen and carbon dioxide) Channel-Mediated Diffusion Small materials which pass through transmembrane proteins (channels): – are water soluble compounds – are ions Carrier-Mediated Transport Carrier-mediated transport of ions and organic substrates: – Facilitated diffusion – Active transport  Specificity: 1 transport protein, 1 set Characteristi of substrates cs of Carrier- Saturation limits: Mediated Transport rate depends on transport proteins, not substrate Regulation: cofactors such as hormones  Carrier-Mediated Transport Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids): molecule binds to receptor site on carrier protein protein changes shape, molecules pass through receptor site is specific to certain molecules  Carrier-Mediated Transport Counter- Co-transport 2 substances move 1 transport substance in the same moves in while direction at the another moves out same time  Simple Types Diffusio n Of Channe Diffusio l Mediat n ed Diffusio n Facilitate d Transport  Active Transport Carrier-mediated – needs a protein to move molecules Active transport proteins: – move substrates AGAINST CONCENTRATION GRADIENT – require energy, such as ATP – ion pumps - move ions (Na+, K+, Ca+, Mg2+) – exchange pump - countertransports 2 ions at the same time  Sodium-Potassium Exchange Pump 321 NOKIA 3 Na out, 2 K into, 1 ATP Simple  Also called bulk transport Vesicles: endocytosis (endo = Vesicular into) 3 types Transport active transport using ATP: receptor-mediated pinocytosis phagocytosis exocytosis (exo = out of)  Receptors (glycoproteins) bind target Receptor- molecules (ligands) – Mediated This is like a lock and key. Only the specific ligand will work on a receptor. Coated vesicle (endosome) carries Endocytosis ligands and receptors into the cell  Pinocytosis (cell drinking) Pinocytosis Endosomes “drink” extracellular fluid Non-specific  Phagocytosis “cell eating” pseudopodia (psuedo = false, podia = feet) engulf large objects in vesicles called phagosomes  Exocytosis Is the reverse of endocytosis – Discharges material from the cell – A form of secretion  Osmosis Osmosis is the diffusion of WATER across the cell membrane. – Water ALWAYS flows from areas of low solute concentration to areas of high solute concentration – For osmosis to occur the membrane must be freely permeable to the water, but only selectively permeable to solutes. – WATER FOLLOWS THE HIGHER CONCENTRATION OF SOLUTES!!! (Osmolarity)  Osmolarity Osmolarity is the concentration of solutes in a solution – If a solution has Low Osmolarity = little bit of solute + lots bit of water – If a solution has High osmolarity = lots of solute + little bit of water  Clinical Relevance: Different Types of Pressures Osmotic Pressure - pressure within capillaries due to proteins in the blood – Causes fluid to return to the blood vessel Hydrostatic Pressure – outward pressure by fluid pressing against the walls of its container – Pushes fluid out of the blood  Tonicity The osmotic effect of a solute on a cell: Think muscle ‘tone’  Isotonic Solutions A solution that does not cause osmotic flow of water in or out of a cell iso = same, tonos = tension  Hypotonic Solutions hypo = below The solution has less solutes than the cells The solution loses water through osmosis Cells placed in a hypotonic solution gain water. Cells swell then ruptures (hemolysis of red blood cells)  Hypertonic Solutions hyper = above Solution has more solutes than inside the cell The solution gains water by osmosis Cells placed in a hypertonic solution lose water. The cells shrink (crenation of red blood cells)