A & P Chapter 3 - How things get into and out of cells

tonicity

term used instead of osmolarity when describing the effects of various osmotic solutions on cells

concentration gradient

the difference between the high and low concentrations

secondary active transport

the transport mechanism itself does not require energy, but the cell often needs to expend ATP at a later time to preserve homeostasis moves a substrate down its concentration gradient, but can also move another substrate at the same time, without regard to its concentration gradient the concentration gradient for one substance provides the driving force needed by the carrier protein and the second substance gets a "free ride"

the higher the solute concentration, the __________ the water concentration

lower

2 ways an ion or a molecule can diffuse across a cell membrane

1. crossing the lipid portion of the membrane 2. passing through a membrane channel

3 major categories of transport processes

1. diffusion - results from the random motion and collisions of ions and molecules (passive) 2. carrier-mediated transport - requires the presence of specialized integral membrane proteins. (active or passive) 3. vesicular transport - involves the movement of materials within small membranous sacs, or vesicles (active)

three major types of endocytosis

1. receptor-mediated endocytosis 2. pinocytosis 3. phagocytosis

sodium-potassium ATPase may use up to _________ percent of the ATP produced by a resting cell

40

which substances can cross the cell membrane by simple diffusion?

alcohol fatty acids steroids dissolved gases (oxygen and carbon dioxide) lipid-soluble drugs

diffusion

as a result of continuous random motion, over time, the molecules in any given space will tend to become evenly distributed. as the molecules move around, there will be a net movement of material from areas of higher concentration to areas of lower concentration

exchange pump

carrier protein that performs countertransport (antiport) of ions

If a red blood cell is in a __________ solution, water will flow into the cell, causing it to swell up like a bllon

hypotonic

carrier-mediated transport

integral proteins bind specific ions or organic substrates and carry them across the cell membrane

receptor-mediated endocytosis

involves the formation of small vesicles at the surface of the membrane; produces vesicles that contain a specific target molecule in high concentrations

vesicular transport (bulk transport)

materials move into or out of the cell in vesicles, small membranous sacs that form at, or fuse with, the cell membrane

selectively permeable

permits the free passage of some materials and restricts the passage of others

In ____________, cytoplasmic extensions called pseudopodia surround the object, and their membranes fuse to form a phagosome. This vesicle then fuses with many lysosomes, whereupon its contents are digested by lysosomal enzymes.

phagocytosis

________________ is a form of vesicular transport that is performed only by specialized cells, such as macrophages

phagocytosis

in ___________, a deep grove or pocket forms in the cell membrane and then pinches off

pinocytosis

phagocytosis "cell eating"

produces phagosomes containing solid objects that may be as large as the cell itself.

Some solutes diffuse into the cytoplasm, other diffuse out, and a few (such as ________) are unable to diffuse across the cell membrane at all

proteins

osmosis eliminates solute concentration differences much more _________ than solute diffusion

quickly

many important substances, including cholesterol and iron ions are distributed through the body attached to special transport proteins. These proteins are too large to pass through membrane pores, but they can and do enter cells by __________-_________ ______________.

receptor-mediated endocytosis

factors that influence whether something will pass through the cell lmembrane

size, electrical charge, molecular shape, lipid solubility

if ATP is readily available, the rate of transport across the sodium-potassium exchange pump depends on the concentration of ________ ions in the _________

sodium cytoplasm

the concentration gradient for _________ ions most often provides the driving force for cotransport mechanisms that move materials into the cell. Although the initial transport activity proceeds without direct energy expenditure, the cell must expend ATP to pump the arriving _________ ions out of the cell by using the sodium -potassium exchange pump

sodium sodium

simple diffusion

substances diffuse through the lipid portions of the membrane

channel-mediated diffusion

substances diffuse through transmembrane proteins

facilitated diffusion

substances that are insoluble in lipids and too large to fit through membrane channels are passively transported across the membrane by carrier proteins substances move from an area of higher concentration to an area of lower concentration

hemolysis

the bursting of red blood cells

countertransport (antiport)

the carrier protein transports two substances in opposite directions simultaneously, one substance moves into the cell and one substance moves out of the cell

cotransport (symport)

the carrier protein transports two substances in the same direction simultaneously, either into or out of the cell

osmosis

the net diffusion of water across a membrane

crenation

the shrinking of red blood cells

osmolarity (or osmotic concentration)

the total solute concentration in an aqueous solution

the _________ concentration of dissolved ions and molecules on either side of the cell membrane stays the same

total

which substances can cross the cell-membrane by channel-mediated diffusion?

water molecules ions, such as sodium, potassium, and chloride

osmotic pressure

is an indication of the force with which pure water moves into that solution as a result of its solute concentration

pinocytosis "cell drinking"

is the formation of endosomes filled with extracelluar fluid is not as selective as receptor-mediated endocytosis, because no receptor proteins are involved. the target appears to be the fluid contents in general, rather than specific bound ligands

exocytosis

is the functional reverse of endocytosis

permeability of the cell membrane

is the property of the cell membrane that determines precisely which substances can enter or leave the cytoplasm

_________ refers to the solute concentration of the solution, while ________ is a description of how the solution affects a cell

osmolarity tonicity

_________ processes move ions or molecules across the cell membrane with no expenditure of energy by the cell

passive

________ processes require that the cell expend energy, generally in the form of ATP

active

ion pumps

carrier proteins that actively transport the cations sodium, potassium, calcium, and magnesium across their cell membranes. Specialized cells can transport additional ions such as iodide, chloride, and iron

factors that influence diffusion rates

distance - the shorter the distance, the more quickly concentration gradients are eliminated; few cells are farther than 125 um from a blood vessel molecule size - ions ans mall organic molecules such as glucose diffuse more rapidly than do large proteins temperature - the higher the temperature, the faster the diffusion rate gradient size - the larger the concentration gradient, the faster diffusion proceeds electrical forces - opposite electrical charges attract each other; like charges repel each other

diffusion tends to _________ the concentration gradient

eliminate

___________ involves relatively large volumes of extracellular material and requires energy in the form of ATP

endocytosis

two major categories or vesicular transport

endocytosis exocytosis

sodium-potassium exchange pump

exchanges intracellular sodium for extracellular potassium one average for each ATP molecule consumed, 3 sodium ions are ejected and 2 potassium ions are reclaimed by the cell

In ___________, a vesicle created inside the cell fuses with the cell membrane and discharges its contents into the extracellular environment

exocytosis

endocytosis

extracellular materials can be packaged in vesicles at the cell surface and imported into the cell

all cells move glucose across their membranes through ___________ ___________

facilitated diffusion

most receptor molecules are ___________, and each binds to a specific ligand, or target, such as a transport protein or a hormone

glycoproteins

water tends to flow across a membrane toward the solution containing the ________ solute concentration

higher

diffusion tends to spread materials from a region of _______ concentration to one of ________ concentration

higher lower

a cell in a ________ solution will lose water by osmosis

hypertonic

3 characteristics of osmosis

1. osmosis is the movement of water molecules across a membrane 2. osmosis occurs across a selectively permeable membrane that is freely permeable to water, but not freely permeable to solutes 3. in osmosis, water flows across a membrane toward the solution that has the higher concentration of solutes, because that is where the concentration of water is lower

characteristics of carrier-mediated transport

1. specificity - each carrier protein in the cell membrane will bind and transport only certain 2. saturation limits - the availability of substrate molecules and carrier proteins limits the rate of transport into or out of the cell 3. regulation - the binding of other molecules, such as hormones, can affect the activity of carrier proteins

active transport

a high-energy bond (such as from ATP) provides the energy needed to move ions or molecules across the membrane does not depend on a concentration gradient

freely permeable

a membrane through which any substance can pass without difficulty

impermeable

a membrane through which nothing can pass

isotonic

a solution that does not cause an osmotic flow of water into or out of a cell

Inside the cell, the ________ vesicles fuse with primary lysosomes filled with digestive enzymes, creating secondary lysosomes. The lysosomal enzymes then free the ligands from their receptors, and the ligands enter the cytosol by diffusion or active transport. The vesicle membrane detaches from the secondary lysosome and returns to the cell surface, where its receptors are available to bind more ligands.

coated

receptors bound to ligands cluster together. Once an area of the cell membrane has become covered with ligands, it forms groves or pockets that move to one area of the cell and then pinch off to form an endosome. The endosomes formed in this way are called _____________ vesicles because they are surrounded by a protein-fiber network that originally carpeted the inner membrane surface beneath the receptor-ligand clusters.

coated

despite its energy cost, active transport has one great advantage; it does not depend on a _____________ __________

concentration gradient

each solute diffuses as though it were the ______ material in solution

only

hydrostatic pressure

opposes osmotic pressure