Membrane Dynamics (Ch. 5)

Fig 5.13 Facilitated diffusion of glucose into cells

*GLUT transporters *Insulin itself doesn't transport glucose into cells (binds to receptor that carries it into the cell)

Fig 5.25 The resting membrane potential of cells

*far fewer sodium channels compared to potassium *Sodium leak channel sends them into the cell

Fig 5.10 ESSENTIALS Membrane Transporters

*more gated than open channels *Glucose requires a carrier protein (3 types of carrier proteins)

The Body Is Mostly Water (Key Facts)

-adult women have less water per kilogram of body mass than men because women have more adipose tissue -age influences body water content -the distribution of water among body compartments is less variable i) intracellular compartment contains about 2/3 (67%) of the body's water ii) the remaining 1/3 (33%) is split between the interstitial fluid (which contains about 75% of the extracellular water) and the plasma (which contains about 25% of the extracellular water)

Competition

-closely related to specificity -A transporter may move several members of a related group of substates, but those substrates compete with one another for binding sites on the transporter

Saturation

-rate of substrate transport depends on the substrate concentration and the number of carrier molecules, a property that is shared by enzymes and other binding proteins

Specificity

-refers to the ability of a transporter to move only one molecule or only a group of closely related molecules ex. GLUT family of transporters

Transport Processes

-some require an outside source of energy, such as that stored in the high-energy bond of ATP -other transport processes use only the kinetic or potential energy already in the system Cell Membranes Are Selectively Permeable - Selectively permeable: which means that some molecules can cross the cell membranes but other molecules cannot. - Permeable: if a membrane allows a substance to pass through it, the membrane is said to be permeable to that substance - Impermeable: If a membrane does not allow a substance to pass, the membrane is said to impermeable to that substance

Vesicular Transport

-used to move macromolecules that are too large in and out of the cell with the aid of bubble-like vesicles created from the cell membrane. Two basic processes to import large molecules and particles: 1) Phagocytosis 2) Endocytosis

Secondary Active Transport (cotransporter)

-uses the kinetic energy of one molecule moving down its concentration gradient to push other molecules against their concentration gradient. -the cotransported molecules may go in the same direction across the membrane (symport) or in opposite direction (antiport). -the most common secondary active transport systems are driven by the sodium concentration gradient

Fig 5.2 1-3 further explained

1) In (1), compartments A and B contain equal volumes of glucose solution. Compartments B has more solute (glucose) per volume of solution and therefore is the more concentrated solution. A concentration gradient across the membrane exists for glucose. However, because the membrane is not permeable for glucose, glucose cannot move to equalize its distribution 2) Water, by contrast, can cross the membrane freely. It will move by osmosis from compartment A, which contains the dilute glucose solution, to compartment B, which contains the more concentrated glucose solution. Thus, water moves to dilute the more concentrated solution. 3) How can we make quantitative measurements of osmosis? One method is shown in (3). The solution to be measured is placed in compartment B with pure water in compartment A. Because compartment B has a higher solute concentration than compartment A, water will flow from A to B. However, by pushing down on the piston, you can keep water from entering compartment B. The pressure on the piston that exactly opposes the osmotic movement of water into compartments B is known as the "osmotic pressure" of solution B.

Fig 5.1 ESSENTIALS Body Fluid Compartments

2 Compartments: 1) Cells (intracellular fluid, ICF) - intracellular fluid is 2/3 of the total body water volume 2) Extracellular fluid (ECF) - extracellular fluid is 1/3 of the total body water volume. The ECF consists of: interstitial fluid [lies between the circulatory system and the cells] & blood plasma [is the liquid matrix of blood]

Chemical Disequilibrium

Although the overall concentrations of the ECF and intracellular fluid (ICF) are equal, some solutes are more concentrated in one of the body compartments than in the other. -this means the body is in a state of chemical disequilibrium

Fick's Law of Diffusion

An equation that describes the factors that determine the rate of diffusion of a molecule from an area of higher concentration to an area of lower concentration. Membrane permeability is the most complex of the terms in Fick's law because several factors influence it: 1) The size (and shape, for large molecules) of the diffusing molecule. As molecular size increases, membrane permeability decreases 2) The lipid-solubility of the molecule. As lipid solubility of the diffusing molecule increases, membrane permeability to the molecule increases 3) The composition of the lipid bilayer across which it is diffusing

The Resting Membrane Potential

Many of the body's solutes, including organic compounds such as pyruvate and lactate, are ions and, therefore, carry a net electrical charge -Potassium (K+) is the major cation within cells, and sodium (Na+) dominates the extracellular fluid -On the anion side, chloride ions (Cl-) mostly remain with Na+ in the extracellular fluid -Phosphate ions and negatively charged proteins are the major anions of the intracellular fluid -overall, the body is electrically neutral: for every cation, there is a matching anion (however ions are not distributed evenly between the ECF and the ICF Chemical & Electrical disequilibrium -70 mV resting membrane in human body

Simple Diffusion

Passive transport -diffusion directly across the phospholipid bilayer of a membrane -has the following properties in addition to the properties of diffusion listed earlier: 1) The rate of diffusion depends on the ability of the diffusing molecule to dissolve in the lipid bilayer of the membrane 2) The rate of diffusion across a membrane is directly proportional to the surface area of the membrane

Electrical Disequilibrium

The body as a whole is electrically neutral, but a few extra negative ions are found in the intracellular fluid, while their matching positive ions are located in the extracellular fluid -as a result, the inside of the cells is slightly negative relative to the extracellular fluid -this ionic imbalance results in a state of electrical disequillibrium

Tonicity Describes the Volume Change of a Cell

Tonicity: is a physiological term used to describe a solution and how that solution would affect cell volume if the cell were placed in the solution and allowed to come to equilibrium i) describing the movement of water and change in cell volume when a cell is placed in a solution) -If a cell placed in the solution gains water at equilibrium and swells, we say that the solution is "hypotonic" to the cell. -If the cell loses water and shrinks at equilibrium, the solution is said to be "hypertonic". -If the cell in the solution does not change size at equilibrium, the solution is "isotonic".

Membrane enzymes

catalyze chemical reactions that take place either on the cell's external surface or just inside the cell ex. enzymes on the external surface of cells lining the small intestine are responsible for digesting peptides and carbohydrates.

Passive Transport

does not require the input of energy other than the potential energy stored in a concentration gradient

Structural proteins

have 3 major roles: 1) they help create cell junctions that hold tissues together, such as tight junction and gap junction 2) they connect the membrane to the cytoskeleton to maintain the shape of the cell. The microvilli of transporting epithelia are one example of membrane shaping by the cytoskeleton 3) they attach cells to the extracellular matrix by linking cytoskeleton fibers to extracellular collagens and other protein fibers

Facilitated diffusion

if mediated transport is passive and moves molecules down their concentration gradient, and if net transport stops when concentrations are equal on both sides of the membrane, the process is facilitated diffusion

Osmotic Equilibrium

in which the fluid concentration are equal on the two sides of the cell membrane *concentration is expressed as amount of solute per volume of solution

Osmolality

is concentration expressed as osmoles of solute per kilogram of water -usually used in clinical situations because it is easy to estimate people's body water content by weighing them. -clinicians estimate a person's fluid loss in dehydration by equating weight loss to fluid loss ex. Because 1 liter of pure water weight weighs 1 kilogram, a decrease in body weight of 1 kg (or 2.2 lbs) is considered equivalent to the loss of 1 liter of body fluid

Diffusion

may be defined as the movement of molecules from an area of higher concentration of the molecules to an area of lower concentration of the molecules. (ex. open cologne bottle in room) Diffusion has the following 7 properties: 1) Diffusion is a passive process 2) Molecules move from an area of higher concentration to an area of lower concentration (a difference in the concentration of a substance between two places is called a concentration gradient or chemical gradient) 3) Net movement of molecules occurs until the concentration is equal everywhere 4) Diffusion is rapid over short distances but much slower over long distances 5) Diffusion is directly related to temperature (higher temp, molecules move faster) 6) Diffusion rate is inversely related to molecular weight and size (smaller molecules require less energy to move over a distance and therefore diffuse faster) 7) Diffusion can take place in an open system or across a partition that separates two compartments (ex. ECF & ICF)

Transport proteins (membrane transport)

moves molecules across membranes Two main types of transport proteins: 1) Channel proteins - creates water-filled passageways that directly link the intracellular and extracellular compartments 2) Carrier proteins - also just called transporters, bind to the substrates that they carry but nerve from nerve from a direct connection between the intracellular fluid and extracellular fluid.

Membrane receptors

part of the body's chemical signaling system the binding of a receptor with its ligand usually triggers another event at the membrane. also play an important role in some forms of vesicular transport

Active Transport

requires the input of energy from some outside source, such as the high-energy phosphate bond of ATP

Osmosis

the movement of water across a membrane in response to a solute concentration gradient -in osmosis, water moves to dilute the more concentrated solution

Osmolarity

the number of osmotically active particles (ions or intact molecules) per liter of solution expressed in osmoles per liter (osmol/L or OsM) -the normal osmolarity of the human body ranges from 280-296 milliosmoles per liter (mOsM)

Primary Active Transport

uses ATP as its energy source, many primary active transporters are known as ATPases The sodium-potassium pump is probably the single most important transport protein in animal cells because it maintains the concentration gradients of Na and K across the cell membrane i) transporter is arranged in the cell membrane so that it pumps 3 Na out of the cell and 2 K into the cell for each ATP consumed.

Mediated transport

when solutes cross membranes with the help of membrane proteins