Transport Accross Membrane Flashcards
Factors influence the diffusion rate of substances across plasma membranes:
Steepness of the concentration gradient
Temperature
Mass of the diffusing substance
Surface area
Diffusion distance
Two sources of cellular energy can be used to drive active transport:
primary active transport and secondary active transport
Energy obtained from hydrolysisof adenosine triphosphate (ATP) is the source in
primary active transport
energy stored in an ionic concentration gradient is the source in
secondary active transport
The greater the difference in concentration between the two sides of the membrane, the higher the rate of
diffusion
energy source of primary active transport
atp
is a well-known primary active transport mechanism.
sodium-potassium pump
into the cell against their respective concentration gradients, using ATP as an energy source.
sodium-potassium pump
Secondary Active Transport also known as
cotransport or coupled transport
does not directly use ATP. Instead, it relies on the energy generated by primary active transport (usually the sodium gradient) to transport other molecules against their concentration gradients.
Secondary active transport
the transported molecule moves in the same direction as the ion
Symport (cotransport)
the transported molecule moves in the opposite direction to the ion
Antiport (exchanger):
of the PM allows a living cell to maintain different concentrations of certain substances on either side of the plasma membrane
selective permeability
is a difference in the concentration of a chemical from one place to another
concentration gradient
Many ions and molecules are more concentrated in either the
cytosol or the extracellular fluid
A difference in electrical charges between 2 regions constitutes an
electrical gradient
Because it occurs across the plasma membrane, this charge difference is termed the
membrane potential
Similarly, a positively charged substance will tend to move toward a
negatively charged area
A negatively charged substance will tend to move toward a
positively charged area
The combined influence of the concentration gradient and the electrical gradient on movement of a particular ion is referred to as its
electrochemical gradient
Substances generally move across membranes via transport processes that can be classified as
passive or active
a substance moves down its concentration or electrical gradient to cross the membrane using only its own kinetic energy
passive processes
Another way that some substances may enter and leave cells is an active process in w/c tiny, spherical membrane sacs called
vesicles
endocytosis, in which ___________________________________________ while bringing materials into a cell
vesicles detach from the plasma membrane
exocytosis, the_________________________________ to release materials from the cell
merging of vesicles with the plasma membrane
A passive process in w/c the random mixing of particles in a solution occurs because of the particles’
kinetic energy
Both the solutes, the dissolved substances, and the solvent, the liquid that does the dissolving, undergo
diffusion
If a particular solute is present in high concentration in one area of a solution and in low concentration in another area:
solute molecules will diffuse toward the area of lower concentration—they move down their concentration gradient
A passive process in which substances move freely through the lipid bilayer of the PM of cells without the help of membrane transport proteins
simple diffusion
Nonpolar, hydrophobic molecules move across the lipid bilayer through the process of
simple diffusion
also pass through the lipid bilayer by simple diffusion
Small, uncharged polar molecules such as water, urea, and small alcohols
Such molecules that can pass through the lipid bilayer through simple diffusion
oxygen, carbon dioxide, and nitrogen gases; fatty acids; steroids; and fat-soluble vitamins (A, D, E, and K)
Simple diffusion through the PM is important in the movement of
O & CO2bet. blood & body cells, and between blood & air w/in the lungs during breathing
It also is the route for absorption of some nutrients and excretion of some wastes by body cells
Simple Diffusion
Solutes that are too polar or highly charged to move through the lipid bilayer by simple diffusion can cross the PM by
facilatated diffusion
In this process, an integral membrane protein assists a specific substance across the membrane
facilatated diffusion
The integral membrane protein can be either a
membrane channel or a carrier
A solute moves down its concentration gradient across the lipid bilayer through a membrane channel
Channel-Mediated Facilitated Diffusion
These channels allow passage of small, inorganic ions
ion channels
Most membrane channels are
ion channels, integral transmembraneproteins
Diffusion of ions through channels is _________________ than free diffusion through the lipid bilayer
generally slower
A channel is said to be ____________ when part of the channel protein acts as a “plug” or “gate”
gated
Some gated channels randomly alternate between the
open and closed positions
is used to move a solute down its concentration gradient across the plasma membrane
carrier
Carrier also called a
transporter
The rate of carrier-mediated facilitated diffusion is determined by
the steepness of the concentration gradient across the membrane
The no. of carriers available in a PM places an upper limit, called the _________________________, on the rate at which facilitated diffusion can occur
transport maximum
Once all of the carriers are occupied, the ________________________ is reached
transport maximum
Substances that move across the plasma membrane by carrier-mediated facilitated diffusion include
glucose, fructose, galactose, and some vitamins
The selective permeability of the plasma membrane is often regulated to achieve
homeostasis
An inability to produce or utilize insulin is called
diabetes mellitus
A type of diffusion in which there is net movement of a solvent through a selectively permeable membrane
Osmosis
Like the other types of diffusion, osmosis is a
passive process
water moves through a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration
Osmosis
During osmosis, water molecules pass through a plasma membrane in two ways:
(1) by moving through the lipid bilayer via simple diffusion, as previously described, and
(2) by moving through aquaporins, integral membrane proteins that function as water channels
occurs only when a membrane is permeable to water but is not permeable to certain solutes
Osmosis
The solution with the impermeable solute also exerts a force, called the
osmotic pressure
is proportional to the concentration of the solute particles that cannot cross the membrane
osmotic pressure
The higher the solute concentration, the higher the solution’s
osmotic pressure
When body cells are placed in a solution having a different osmotic pressure than cytosol, however, the
shape and volume of the cells change
is a measure of the solution’s ability to change the volume of cells by altering their water content
tonicity
the concentrations of solutes that cannot cross the plasma membrane are the same on both sides of the membrane in this solution
Isotonic
a solution that has a lower concentration of solutes than the cytosol inside the cell
Hypotonic
The rupture of other types of cells due to placement in a hypotonic solution is referred to simply as
lysis
Pure water is very _____________ and causes rapid _____________
hypotonic; hemolysis
has a higher concentration of solutes than does the cytosol inside the cell
hypertonic solution
In such a solution, water molecules move out of the cells faster than they enter, causing the
cells to shrink
Such shrinkage of cells is called
crenation
Some polar or charged solutes that must enter or leave body cells cannot cross the plasma membrane through any form of passive transport
This is because they would need to move “uphill,” against their concentration gradients
Such solutes may be able to cross the membrane by a process called
active transport
is an active process because energy is required for carrier proteins to move solutes across the membrane against a concentration gradient
active transport
Two sources of cellular energy can be used to drive active transport:
(1) Energy obtained from hydrolysis of adenosine triphosphate (ATP) is the source in primary active transport;
(2) energy stored in an ionic concentration gradient is the source in secondary active transport
is the source in primary active transport
Energy obtained from hydrolysis of adenosine triphosphate (ATP)
is the source in secondary active transport
energy stored in an ionic concentration gradient
Like carrier-mediated facilitated diffusion, active transport processes exhibit a
transport maximum and saturation
carrier proteins that mediate primary active transport are often called
pumps
The most prevalent primary active transport mechanism expels sodium ions from cells and brings potassium ions Because of the specific ions it moves, this carrier is called the
sodium-potassium pump
If these transporters move two substances in the same direction they are called
symporters/symport
move two substances in opposite directions across the membrane
Antiporters/antiport
is a small, spherical sac
vesicle
materials move into a cell in a vesicle formed from the plasma membrane
endocytosis
materials move out of a cell by the fusion with the plasma membrane of vesicles formed inside the cell
exocytosis
Both endocytosis and exocytosis require
energy supplied by ATP
transport in vesicles is an
active process
Three types of endocytosis:
Receptor-mediated endocytosis, phagocytosis, and bulk-phase endocytosis
A highly selective type of endocytosis by which cells take up specific ligands
Receptor-mediated endocytosis
A vesicle forms after a receptor protein in the plasma membrane recognizes and binds to a particular particle in the extracellular fluid
Receptor-mediated endocytosis
Receptor-mediated endocytosis of LDLs (and other ligands) occurs as follows:
- Binding
- Vesicle formation
- Uncoating
- Fusion with endosome
- Recycling of receptors to plasma membrane
- Degradation in lysosomes
On the extracellular side of the PM, an LDL (low-density lipoprotein) cholesterol particle that contains cholesterol binds to a specific receptor in the PM to form a receptor,
LDL complex
The receptors are integral membrane proteins that are concentrated in regions of the plasma membrane called
clathrin-coated pits
a protein called ____________ attaches to the membrane on its cytoplasmic side
clathrin
The invaginatededges of the membrane around the clathrin-coated pit fuse, and a small piece of the membrane pinches off. The resulting vesicle, known as a
clathrin-coated vesicle
clathrin-coated vesicle, contains the receptor,
LDL complexes
Almost immediately after it is formed, the clathrin-coated vesicle loses its clathrincoat to become an
uncoated vesicle
A form of endocytosis in which the cell engulfs large solid particles, such as worn-out cells, whole bacteria, or viruses
Phagocytosis
Only a few body cells, termed _________________, are able to carry out phagocytosis
phagocytes
Two main types of phagocytes are
macrophages and neutrophils
located in many body tissues
macrophages
a type of white blood cell
neutrophils
In most cases, any undigested materials in the phagosomeremain indefinitely in a vesicle called a
residual body
a vital defense mechanism that helps protect the body from disease
phagocytosis
a form of endocytosis in which tiny droplets of extracellular fluid are taken up
bulk-phase endocytosis (pinocytosis)
No receptor proteins are involved; all solutes dissolved in the extracellular fluid are brought into the cell
bulk-phase endocytosis (pinocytosis)
releases materials from a cell
exocytosis
All cells carry out exocytosis, but it is especially important in two types of cells:
(1) secretory cells that liberate digestive enzymes, hormones, mucus, or other secretions
(2) nerve cells that release substances called neurotransmitters
liberate digestive enzymes, hormones, mucus, or other secretions
secretory cells
release substances called neurotransmitters
nerve cells
During exocytosis, membrane-enclosed vesicles called _________________________ form inside the cell, fuse with the plasma membrane
secretory vesicles
vesicles undergo endocytosis on one side of a cell, move across the cell
Transcytosis
