Topic 1 4 Membrane Transport Essential idea Membranes

Topic 1. 4 – Membrane Transport Essential idea: Membranes control the composition of cells by active and passive transport.

Types of Transport Some molecules pass through easily, and can therefore be moved through diffusion Other small molecules need energy (ATP) to move them through, and those are transported through by active transport Large molecules use their own membranes, and are moved past the cell membrane by endo/exocytosis Other molecules need a channel and utilize facilitated diffusion

Solutions – they’re not actually that confusing • A solution is a mixture of solutes dissolved in a solvent (i. e. oxygen in air, or kool-aid powder in water) • A concentration is all about the amount of solute dissolved in the solution Because a concentration refers to two different units, we can not use a single unit to refer to them. Solutions should always have a unit of mass on top of a unit of volume. Ex. g/ml or mg/ L

Brownian Motion • Brownian motion is the random movement of particles through a solution (liquid or gas). • This grumpy guy also discovered and named the nucleus as we see it in eukaryotic cells. Pretty amazing! • His original experiment involved pollen particles in water as the model particles.

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport. Diffusion • Diffusion involves the passive movement of molecules from regions of high concentration to low concentration • How would the salt molecules move in this scenario? Passive = no energy Net = overall movement Concentration gradient = the difference between concentration of two different compartments in a system High to low = down the concentration gradient Diffusion only occurs if a membrane is permeable to the substance

Difference in the rate of diffusion • Based on this diagram, which scenario would you see a higher rate of diffusion?

Difference in the rate of diffusion • Based on this diagram, which scenario would you see a higher rate of diffusion? • A higher concentration gradient leads to an increased rate of diffusion as molecules have more energy and move more quickly

Other Factors that affect the rate of diffusion • Surface Area • It is for this reason that cells can get only so big! • We see adaptations in biology to increase surface area in all parts of the body Length of the diffusion path Villi in the intestine Alveoli in Lungs

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport. Facilitated Diffusion is the movement of particles down the concentration gradient moving through channel proteins (type of integral proteins) • Requires a selectively permeable membrane – what types of molecules would require this type of transport? • Depends on the properties of the molecule • Each channel protein is specific to the molecule it allows through • Again – we are moving down the concentration gradient, so this is a type of passive transport

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport. Facilitated Diffusion is the movement of particles down the concentration gradient moving through channel proteins (type of integral proteins) Aquaporins – example of facilitated diffusion Voltage-gated ion channels

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport. Osmosis is the passive net movement of water molecules from regions of low solute concentration to high solute concentration, through a selectively permeable membrane Solvent moves from high to low concentration, due to the impermeability of the membrane to the solute.

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport. Comparing Diffusion and Osmosis • Osmosis vs. Diffusion Similar Both are Passive Both move down the concentration gradient Different Diffusion is of solutes Membrane not needed Osmosis only works with water Partially-permeable membrane essential

The ability of an extracellular solution to make water move into or out of a cell by osmosis is know as its tonicity Tonicity - Animal Cell

The ability of an extracellular solution to make water move into or out of a cell by osmosis is know as its tonicity Tonicity - Plants

Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2) Determining osmolarity of cells Based on this image: 1. Calculate the concentration (% solution) of the hypertonic solution. 2. Calculate the concentration of the Isotonic solution. 3. State the relationship between the environment inside the cell and outside the cell in the hypotonic scenario. 4. State the relationship between the inside and outside of the cell in the isotonic scenario. https: //www. youtube. com/watch? v=OYoa. Lzob. Qmk&feature=youtube_gdata_player

So what? Effect of transport of Acid on the body -Blood Vessels Act Much like cells Calcium from bones

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport. Passive Transport • Passive transport is made up of simple diffusion and facilitated diffusion • This is due to a net movement of particles from one side of the membrane to the other (Brownian movement) that goes down the concentration gradient Simple Diffusion Facilitated Diffusion Osmosis The rate is affected by: • Concentration gradient • SA: Volume Ratio • Length of diffusion Pathway The rate is affected by: • # of Channel proteins that allow molecules through the membrane • Everything to the left The rate is affected by: • Concentration gradient • SA: Volume Ratio • Length of Diffusion Pathway Occurs when a molecule’s properties allow it to cross the membrane Occurs if molecules cannot cross easily, but the cell still needs them often (i. e. polar molecules) Occurs when the membrane is permeable to the solvent, but not the solutes

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport. Active Transport – Uses energy, in the form of ATP, to move molecules against the concentration gradient. • Membrane is generally impermeable to the substance being transported • Active transport is the key in homeostasis in organisms, such as in the resetting of nerves after impulses have passed through

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport. Active Transport

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. • Neurons conduct impulses through chemical signals • The two elements involved are sodium (Na) and potassium (K) • Active transport causes these elements to be pumped against their concentration gradient • Each time the cell pumps ions against the concentration gradient, it uses ATP.

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. Facilitated Diffusion of potassium • Nerve impulses are conducted all the time, and as such, the body needs to reuse the same ions over again • This process is done by voltage gated channels

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. Step one – Channel closed • When potassium ions dissociate in water, they are surrounded by water molecules. • These water molecules make potassium much larger, and unable to pass through the channel • To pass through, the potassium breaks its bonds with the water molecules and forms temporary bonds with the amino acids of the proteins that make up the pore

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. Step two – Channel opens briefly • Potassium can then move freely through the pump for a brief amount of time. • Once this has occurred, the potassium will once again be surrounded by water molecules.

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. Step three – Channel closed again • The channel stops too much potassium from leaving using a ball and chain globular protein. • Once enough potassium has left, the ball and chain stops the flow of K+ ions out, until the channel protein changes its conformation back to the original form

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. ep St 1 -2 Facilitated transport of these potassium ions allow for a change in charge to come with them. This is a major mechanism by which the body can send a message. St e p Re se Now lets see how active transport works in this process! t 23

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. The active transport in maintaining resting concentrations of ions is maintained by a Sodium-Potassium Pump protein. Notice how this pump protein is fully integral throughout the membrane, and can change conformation through the use of cellular energy in order to move molecules against their concentration gradients.

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. STEP ONE Interior of the pump protein is open to the inside of the axon. This allows three sodium ions to enter the pump and attach to the binding sites STEP TWO ATP transfers a phosphate group from itself to the pump; this causes the pump to change shape and the interior is closed.

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. STEP THREE The interior of the pump opens to the outside of the axon and the three sodium ions are released. STEP FOUR Two potassium ions can then enter and attach to their binding sites

Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. STEP FIVE Binding of the potassium causes release of the phosphate group; this causes the pump to change shape again so that it is again only open to the inside of the axon. STEP SIX The interior of the pump opens to the inside of the axon and the two potassium ions are released; sodium ions can then enter and bind to the pump again.

Summary Diagram Can you come up with a one word description for what is happening in each stage of a Sodium. Potassium pump’s function? 1. 2. 3. 4. 5. 6. Try creating a mnemonic from the words you use.

The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells. Vesicle Transport • Vesicles transport macromolecules (those that are too large for diffusion or protein channels) and newly formed molecules such as proteins • Vesicles are formed from the phospholipid bilayer of the organelle, and serve to protect it as it moves through the cytoplasm Budding Fusing

The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells. Two Processes of vesicle transport – Endocytosis and Exocytosis Endocytosis Involves the intake of large, or bulk molecules (i. e. glucose) Extracellular materials interact with the cellular membrane and are brought into the cell in a vesicle. Exocytosis Involves the process of secretion (i. e. waste, protein) Intracellular vesicles fuse with the cell membrane to allow materials being carried within to be expelled into the ECM.

The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells. Vesicle Transport Vesicle transport is the mechanism of all interneuron communication It is also important in the releasing of hormones in to the blood stream

The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells. Vesicle Fusing Two vesicles come close together to begin to interact. This is where like dissolves like comes into play. Since both membranes are made of the same material, they can begin to interact.

The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells. Vesicle Fusing Given that the membranes are made of phospholipids, they can begin to fuse together The phospholipids from one membrane meld with the other membrane, and so an intermediate membrane is formed for a brief moment

The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells. Vesicle Fusing The two vesicles fuse together further, and the intermediate membrane gets wider.

The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells. Vesicle Fusing Finally the membranes are fully fused. This allows contents from both to be integrated into each other. In the case of intracellular vesicle transport, this would be the fusing of the vesicle with another organelle For extracellular transport, this would be the fusing of a vesicle with the cell membrane

How Vesicles Fuse Step 1 Step 2 Step 3 Step 4 NOTICE! There is never a broken section of the bilayer throughout this whole process.

Applications of Phospholipids in medicine • Pharmacists are constantly using liposomes to transport drugs around the body and deliver them to cells. The $$ question to be able to answer: How do you deliver it to the right cells? Tons of potential cancer treatments b/c of the “slack” structure of cancer cell colonies.

Membranes control the composition of cells by active and passive transport. Using the following animation, see if you can identify the type of transport for each of these substances: Active – Pump Active – Vesicle Passive – Facilitated Osmosis https: //www. pbslearningmedia. org/asset/tdc 0 2_int_membraneweb/