Chapter 3: Diffusion-Osmosis-Transport

Secondary active transport -how does it move -energy use

transport mechanism that does not require energy from ATP and moves substrates down concentration gradient, which is where it gets its energy from: gives second substrate a ride. May involve symport/antiport

Carrier mediated transport: directional terms and associated carrier proteins

•Symport/cotransport moves 2 substances in the same direction Carrier protein: symporter • Antiport/counter transport moves them in opposite direction Carrier protein: antiporter

Diffusion: what is it? water vs. solutes

Diffusion is a passive transport mechanism that assists membrane passage of solutes and water. *movement of solutes* passive and active diffusion *movement of water* osmosis

Sodium-potassium exchange pump -Why activates pump -What is carried in/out -Associated carrier protein -energy demand

exchanges intracellular sodium ions for extracellular potassium ions o For each ATP converted/hydrolyzed to ADP and P this carrier protein pump carriers 3 Na+ out and 2 K+ into cell o High energy demand : sodium-potassium ATPase may use up to 40% of the ATP produced by a resting cell . o Rate of transport depends on the concentration of sodium ions in the cytoplasm. When concentration rises, the pump becomes more active . Carrier proteinsodium-potassium ATPase

-Osmotic pressue -Hydrostatic pressure -Aquaporin

o Osmotic pressure: of a solution is the force of water movement into that solution resulting from its solute concentration o Hydrostatic pressure: opposes osmotic pressure oAquaporins: What makes osmosis so efficient: abundant water channels that allow water molecules to cross a membrane. They exceed the # of solute channels which water can also pass through so osmosis becomes doubly efficient.

Active transport: primary vs. secondary -how does it move -exchange pump -energy use

requires carrier proteins that move specific substance across a membrane against their concentration gradient. If the carrier moves one solute in one direction and another solute in the opposite direction, it is called an exchange pump. Active transport consumes ATP and is *NOT* dependent on the concentration gradient.

Exocytosis

Intracellular vesicles fuse with the plasma membrane to release fluids and or solids from cells

Diffusion across plasma membrane: simple vs. channel mediated diffusion, leak channels

Most lipid soluble materials, water, gases freely diffuse across the phospholipid bi-layer of the plasma membrane Small water-soluble molecules/ions rely on channel-mediated diffusion through a passage w/in a transmembrane. Leak channels> membrane channels that are always open and allow ions to pass across the plasma membrane

Osmosis : Define: 3 important things -osmotic pressure -hydrostatic pressure -aquaporin

Osmosis is the net flow of water across a selectively permeable membrane in response to differences in solute concentrations. 1. The diffusion of water molecules across a selectively permeable membrane 2. Osmosis takes place across a selectively permeable membrane that is freely permeable to all solutes 3. In osmosis, water flows across a selectively permeable membrane toward the solution that has higher concentration of solutes because that is where the concentration of water is slower

Permeability: define -impermeable -freely permeable -selectively permeable

Permeability: the properties of the plasma membrane that determines precisely which substances can leave the cytoplasm *Impermeable:* nothing can pass through an impermeable membrane *Freely permeable:* anything can pass through a freely permeable membrane *Selectively permeable* permits the free passage of some materials and restricts the passage of others depending on a host of factors.

Primary active transport -example

Process of pumping solutes against a concentration gradient using energy from ATP. Sodium-potassium exchange pump

5 Important factors that influence diffusion rates of substances in the body?

*1. Distance:* the shorter the distance, the more quickly concentration gradients are eliminated *2. Ion/Molecule size:* the smaller the ion/molecule size the faster its rate of diffusion. Ions & small organic molecules like glucose diffuse more rapidly than do large proteins. *3. Temperature: * the higher the temperature, the faster the diffusion rate. Diffusion proceeds somewhat more quickly at human body temperature than cooler environmental temperature *4. Concentration gradient: * the steeper the gradient the faster diffusion proceeds *5. Electrical forces:* opposite electrical charges +/- attract and like electrical charges -/- or +/+ repel each other. The cytoplasm -inner-surface of the plasma membrane has a net negative charge relative to the extracellular =outer-surface. The negative charge tends to attract positive ions from extracellular fluid into the cell while repelling the entry of negative ions.

Vesicular transport Passive or active

*Vesicular transport:* involves moving materials within small membranous sacs called vesicles. Always active

Carrier mediated transport: 2 examples?

1) facilitated diffusion 2) active transport

Carrier mediated transport: 3 characteristics they share with enzymes

1. *Specificity:* each protein in the plasma membrane binds and transports only certain substances 2. *Saturation limit:* the availability of substrate molecules and carrier proteins limits the rate of transport into or out of the cell just as the availability of substrates and enzymes limits its enzymatic reaction rate. When all the available carrier proteins are operating at max speed they are said to be saturated *3. Regulation:* just as enzyme activity often depends on the presence of cofactors, the binding of other molecules such as hormones can affect the activity of carrier proteins for this reason, hormones provide an important means of coordinating carrier protein activity throughout body

Concentration gradient: define -how long does diffusion last -energy and the concentration gradient

Concentration gradient: diffusion is the net movement of a substance from an area of high concentration to an area of lower concentration. Diffusion occurs until the concentration gradient is eliminated. The concentration gradient is also called the potential energy gradient.

Endocytosis: 3 major types what are their vesicles called?

The packaging of extracellular materials into a vesicle for transport into cell. There are 3 major types are: *1) Receptor mediated endocytosis:* is a highly selective process, where specific molecules are ingested into the cell. The specificity results from a receptor-ligand interaction. Receptors on the plasma membrane of the target tissue will specifically bind to ligands on the outside of the cell. *2) Pinocytosis:* 'cell drinking' vesicles form at the plasma membrane and bring fluids and small molecules into the cell. *3) Phagocytosis:* 'cell eating' vesicles form at the plasma membrane to bring in particles into cell. In this process cytoplasmic extensions called pseudopodia surround the object and their membrane fuse to form phagosome. It then fuses with lysosomes, and lysosomal enzymes digest its contacts. Only specialized cells such as *Macrophages* that protect tissues by engulfing bacteria, cell debris, abnormal material perform phagocytocisis. *Endocytosis vesicles are called endosomes*

Carrier mediated transport: define What does it require? Passive or active?

They assist membrane Integral proteins bind specific ions or organic substrates and carry them across the plasma membrane. It can be passive or active depending on the substance being transported

Transcytosis: few specialized cells endocytosis produces vesicles on one side of cell and discharged through exocytosis on opposite side. Bulk transport

a method of bulk transport. In a few specialized cells, endocytosis produces vesicles on one side of cell and discharged through exocytosis on opposite side

Facilitated diffusion: -how does it move -energy use

compounds are transported across a membrane after binding to a receptor site w/in the channel of a carrier protein. Can move in either direction. Follows concentration gradient. No ATP used

Membrane potential Potential difference Resting membrane potential

o Charge on cytoplasmic side of membrane has slight negative charge, cytoplasm is neutral, exterior plasma membrane slightly positive due to sodium ions. They would normally rush together, but plasma membrane keeps them apart. When positive and negative charges are held apart, a *potential difference* exists between them as in stored energy. *Potential difference across a plasma membrane is called the membrane potential* The membrane potential of a cell results from the unequal distribution of positive/negative charges across the plasma membrane. The membrane potential in an unstimulated or undistributed cell is the *resting membrane potential*

-Osmolarity -Tonicity -Isotonic -Hypotonic -Hypertonic Example: red blood cell: hypo/hyper state

o Osmotic concentration: total solute concentration (dissolved substances) in an aqueous solution oTonicity: describes effects of osmotic solutions on cells o Isotonic: a solution that does not cause an osmotic flow. Iso means even o Hypotonic: a solution that causes water flow into the cell o Hypertonic: a solution that causes water flow out of the cel o Example: Red blood cell: Hemolysis-hypotonic - Crenation -Hypertonic-