Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Cytoplasmic streaming wikipedia , lookup
Cell growth wikipedia , lookup
Cell nucleus wikipedia , lookup
Extracellular matrix wikipedia , lookup
Membrane potential wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Cytokinesis wikipedia , lookup
Signal transduction wikipedia , lookup
Cell membrane wikipedia , lookup
Cell Transport Overview of Passive Transport • Cell membrane is selectively permeable as CM can regulate what comes in and out • Passive transport: movement of particles across a semi-permeable membrane without an input of energy from the cell • 3 types: – Simple Diffusion – Facilitated Diffusion – Osmosis Simple Diffusion • Random movement of particles from an area of high concentration to an area of low concentration • Movement of particles from [high] to [low] is called movement down a concentration gradient Factors that affect Rate of Diffusion 1. Size of molecule – Rate of diffusion ↓ with ↑ molecule size 2. Polarity of molecule – Some substances can diffuse easily than others (eg. Small non-polar molecules like lipids & steroid hormones can diffuse across CM compared to large polar molecules like glucose which cannot get across). 3. Charge of ions & molecules – Charged ions/molecules cannot get across. Factors that affect Rate of Diffusion 4. Temperature – ↑ T = ↑ rate of diffusion (particles have more energy and move faster) 5. Pressure – ↑ P = ↑ rate of diffusion (more force on particles, pushing them across membrane) Diffusion through Phospholipid Bilayer What molecules can get through directly? – fats & other lipids – water & small polar molecules inside cell lipid H2O salt What molecules can NOT get through directly? Large polar molecules glucose, amino acids Ions salts NH3 outside cell sugar aa Large molecules starches, proteins Channels through Cell Membrane • Membrane becomes semi-permeable with protein channels – specific channels allow specific material across cell membrane inside cell H+ H2O salt aa sugar outside cell Facilitated Diffusion • Diffusion of ions or molecules across CM from [high] to [low] by using a membrane protein (channel proteins & carrier proteins). • Proteins must be specialized to aid the diffusion of these molecules as it has a specific fit. Channel Proteins • Highly specific as structure of channel protein determines what molecules can move through it • Some channel proteins are open 24/7, others have gates that open/close in response to signals • Allow passage of charged ions (eg. Na+) and polar molecules (that cannot simply diffuse across CM) Carrier Proteins • In comparison to channel proteins, can transport larger molecules (eg. glucose, AAs) • Because they can only bind to a few at a time, CPs have lower rate of diffusion compared to channel proteins CARRIER PROTEINS high concentration outside cell lower concentration inside cell a) molecule bounces b) carrier protein into a specific binds molecule carrier protein d) carrier protein resumes its shape, as seen in (a) c) carrier changes shape & flips over, bringing molecule into cell Osmosis • Diffusion of water molecules across a selectively permeable membrane • Cells are ideally bathed in isotonic solutions (where conc. inside cell equals conc. outside cell) • H2O molecules move from a side with [high] to a side with [low] across a selectively permeable membrane to obtain equilibrium – SP membrane allows water to go through, but not other molecules Osmosis happens when there is a difference in solute conc. SP membrane keeps solutes molecules from moving to other side! (impermeable to them) Result: Equal conc. of solution on BOTH sides 1. Isotonic – solution has the same solute conc. as another solution. Nothing happens to cell size. 2. Hypertonic – solution has higher solute conc. than another solution Water moves OUT to adjust conc. = cell SHRINKS 3. Hypotonic – solution has lower solute conc. than another solution Water moves IN to adjust conc. = cell SWELLS & may burst isotonic 1. hyper 2. hypo hypo hyper 3. Hyper = more solute, less water Hypo = less solute, more water Note: the solution with the higher concentration is designated “hypertonic” .05 M Note: the solution with the lower concentration is designated “hypotonic” Osmosis .03 M Cell (compared to beaker) hypertonic or hypotonic Beaker (compared to cell) hypertonic or hypotonic Which way does the water flow? in or out of cell Active Transport • As living beings, we NEED energy to sustain life processes. • Active transport is the transport of a molecule across a membrane AGAINST its concentration gradient and requires energy. • We eat food containing nutrients for energy, glucose being one of them. – Recall: glucose cannot be stored inside body as it is water-soluble, so it must be converted into glycogen. This conversion MAKES energy in the form of adenosine triphosphate (ATP) = main source of energy for cells – ATP reacts with certain compounds to release energy to drive life processes ATP Molecule • Derived from an adenosine nucleotide • Has 3 phosphate groups • Breaking of end phosphate group from ATP molecule releases energy, which can be used by the cell 1. CM Carrier Protein Pump • Bit similar to facilitated diffusion, but… • Cell energy (ATP) is used to move substance across CM against concentration gradient (low high) 1. Substance (eg. protein, vitamin, molecule) binds to carrier protein. 2. Carrier protein uses energy (ATP) to flip over & “pumps” (releases) substance to other side of the membrane. 3. Carrier protein flips back to get another substance. HIGH CONCENTRATION DIFFUSION LOW CONCENTRATION • Ion pumps are CM carrier proteins that use ATP to pump ions from [low] to [high]. • An example of this is the Na+-K+ pump (plays role in nervous system) 1. [Na+] low & [K+] high inside cell. Na+ ions bind to pump. 2. ATP molecule binds to pump. ATP hydrolyzed, releasing energy. One phosphate group stays attached to pump. 3. Energy allows pump to change shape. Na+ ions exit cell. 4. K+ ions bind to pump. This causes the phosphate group to detach from pump. 5. & 6. Pump changes shape to release K+ ions into cell.