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