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Transcript
Cell Transport: moving things in and out of the cell Plasma membrane: Material that surrounds all cells and certain organelles within the cell - location of plasma membrane gives it more specialized name like cell membrane, nuclear membrane etc. Cell Transport Phospholipid – primary molecule in the cell membrane consisting of two parts Phosphate Group (POLAR) Fatty Acid Tails (NON POLAR) Remember the Triglycerides? What’s the difference between them and a phospholipid? Phospholipids and Polarity • Fatty acid tails are non-polar. – Hydrophobic (water-haters) • Phosphate heads are polar – Hydrophilic (water-lovers) Phospholipids Bi-layer Plasma Membrane Structure • 1. Phospholipid Bi-layer – makes up most of membrane structure • 2. Proteins – many different roles • 3. Carbohydrate Chains – cell identification Role of Proteins Membrane Model • Membrane as a whole is often described as a fluid mosaic – two-dimensional fluid of freely diffusing lipids, dotted or embedded with proteins – Think of the lipid bi-layer as a body of water with various proteins and associated carbohydrate chains moving around. - Proteins can change location by moving through the phospolipids. Figure 8.5 Evidence for the drifting of membrane proteins Movement of substances through the membrane May be • PASSIVE– requires no energy expenditure by cell. – Diffusion and Osmosis – Facilitated diffusion • ACTIVE– does require energy expenditure – Why? – Ex. Transport Proteins, Bulk Transport Diffusion - Molecules will move from areas of high concentration to areas of lesser concentration (concentration gradient) - Due to random collisions of molecules – If occurs across a membrane, the membrane must be permeable to the substance. • Size is a major factor • Electrical charges • Polar vs non-polar Factors that affect permeability: Diffusion (cont.) • Movement of particles (solute) from high to low concentration will continue until there is an even distribution of particles. • This is called equilibrium. • Particles move across the membrane randomly at equilibrium. (In other words, movement still happens, just no NET MOVEMENT!) Special Type of Diffusion - Osmosis • Diffusion of water across a selectively permeable membrane • Water moves from a high concentration of water (less salt or sugar dissolved in it) to a low concentration of water (more salt or sugar dissolved in it) Figure 8.11 Osmosis Tonicity • When comparing the concentrations of 2 solutions: • Isotonic – same concentration of solute • Hypertonic – higher concentration of solute • Hypotonic – lower concentration of solute Osmotic Pressure Effects on Cells • Inside of cells are usually hypertonic to fresh water (hypotonic) • Animals cells tend to be surrounded by isotonic solutions (blood, saliva, etc) • Plant cells have tough cellulose cell walls that protect them from over-expanding Facilitated Diffusion • Charged particles and some molecules can move passively through protein channels. Glucose is a great example of a molecule that enters cells via facilitated diffusion • Important to note that this is still happening through the process of diffusion using the concentration gradient to move molecules in/out of cell. – Energy Not Needed! Facilitated Diffusion • Those molecules which cannot move freely through the membrane have to diffuse through special integral membrane proteins ACTIVE TRANSPORT Small molecules and ions can be “pumped” in/out of cell using energy (ATP). We will look at a couple really important examples of these when we look at cell respiration and photosynthesis. Also key in neuron function! Active Transport • Two main categories – Small Stuff – Transport Proteins • Molecules can move in/out of cell using transport proteins. – Big Stuff – Vesicle Transport • Large materials (ie. chunks or food, complex molecules, liquid and even cells) that cannot pass through a protein channel need to be brought in through complex movement of membrane vesicles – Exocytosis – Endocytosis The three types of endocytosis in animal cells SUMMARY OF WAYS TO MOVE STUFF IN AND OUT: Passive Transport: Requires no energy - simple diffusion - facilitated diffusion (via proteins) Active Transport: Requires energy in the form of ATP (energy molecule) - transport proteins - endo/exocytosis