GRQ #2 - Membrane Potentials Flashcards
besides phospholipids the main components of the plasma membrane are
membrane proteins - they carry out many of the membrane’s functions
how are membrane proteins positioned
their hydrophobic amino acids are in the fatty acid tail portion of the phospholipid bilayer - the middle - and their hydrophilic amino acids are facing the water filled cytosol and/or ECF
What is an integral protein?
they typically span the entire width of the membrane and when they do reach both sides of the membrane they are known as transmembrane proteins
what are peripheral proteins>
they are found on only one side of the membrane
are all integral proteins static?
no - some are anchored in place by the cytoskeleton but many float freely within the plane of the PBL
are peripheral proteins static?
no - they are loosely bound to the membrane surface or to integral proteins and many can also move horizontally along the membrane surface
what is one structure/function of membrane proteins?
acting as channels. many transmembrane proteins serve as protein channels that allow certain substances to cross the membrane and pass into or out of the cell
what is another function of membrane proteins? acting as _
carriers. integral proteins called carrier proteins bind and directly transport substances into and out of the cell - ex. an ion from the ECF binds to a carrier protein which changes shape and releases the ion into the cytosol
another function of the membrane proteins is acting as __
receptors. a receptor is a membrane protein that binds to a chemical messenger called a ligand and when a ligand binds to its receptor then changes are triggered within the cell
receptor - ligand interactions are an example of __ and are responsible for __
cell-cell communication core principle. They are responsible for much of the physiology of the muscular, nervous, and endocrine systems
acting as ___ is another function of membrane proteins
acting as enzymes. enzymes are proteins that speed up chemical reactions and they are vital to plasma membrane structure and function and are often lodged within the membrane
enzymes can ___ metabolic reactions are are often found lodged within the ___
catalyze and are found lodged ex. enzymes can catalyze the formation or breakdown of bonds between substrates
providing ___ ____ is another function
structural support. membrane proteins may be bound to components of the cytoskeleton and other proteins in the ECF and cytosol which provides the cell with shape and help maintain structural integrity
___ ____ cells is another function of membrane proteins
linking adjacent cells. certain membrane proteins can attach to other membrane proteins in adjacent cells, holding the cells in a tissue together - known as “linker proteins” and they can strengthen a tissue or allow adjacent cells to communicate
what are other components of the plasma membrane? (4)
several kinds of lipids, glycolipids, glycoproteins (consist of carbohydrate chains called polysaccharides that are covalently attached to either membrane lipids or proteins) and carbohydrates
ex. cholesterol is a lipid
what does cholesterol do in the membrane?
it stabilizes the structure of the plasma membrane when the temperature changes - critical because the plasma membrane must maintain a certain state of fluidity to function
what is cell recognition?
the ability of our cells to tell one cell type from another - polysaccharides or polymers that are found on the outside of the membrane function in cell recognition
the glycoproteins and glycolipids produced by each cell are ___ to that cell type and that ___ and serve as a ___
each cell are unique to that cell type and that organism and serve as a sort of identification tag
the plasma membrane acts as a __ between the __ and the __ in our cells
fence between the extracellular fluid and the cytosol in our cells
the plasma membrane is ___ ___ and it is a property critical to the cell - it needs to pass things in and out like oxygen, nutrients etc.
selectively permeable - allows certain things to pass through but not others
the ECF and cytosol consist largely of ___ with dissolved __ and ____ of varying size & concentration
water with dissolved ions and organic compounds
The ECF contains substances the cell ___ while the cytosol contains substances that must ___
needs; leave the cell
ex: ECF = glucose, amino acids, fatty acids, water, oxygen, vitamins
cytosol = CO2, waste products
passive transport process
requires no net expenditure of energy from the cell
active transport process
do require the cell to expend energy usually in the form of ATP
what three variables does whether or not the process is active or passive depend on
- the type of substance crossing the membrane
- the membrane’s permeability
- the concentration of that substance both inside and outside the cell
what are the two basic types of passive transport?
osmosis and diffusion
diffusion is defined as
the movement of solute molecules (those that are dissolved) from an area of higher solute concentration to an area of lower solute concentration
what is the basic force that drives diffusion called?
a concentration gradient - it involves a difference in concentration of a substance from one area to another
diffusion allows solutes to move into and out of the cell using the ___ ____ of a concentration gradient
potential energy
moving from a higher to a lower concentration during the process of diffusion is known as
moving down/with the concentration gradient
why do the molecules scatter when the divider is removed>
they move due to their own kinetic energy, which all molecules have as long as thermal energy or heat is present
the movement continues until ___ is reached because there is no more __ ___
equilibrium because there is no more potential energy from a gradient to drive it
no “net” movement refers to the fact that there is no further change taking place in the solution’s concentration, but the molecules are __ even at ___ because of their __ ___
the molecules are moving even at equilibrium because of their kinetic energy
rate of diffusion depends on several factors which include
size and phase of the diffusing particles, temperature, size of the concentration gradient
___ particles, particles in ___ phase, ___ temperatures and ___ concentration gradients ___ the rate of diffusion
smaller, gaseous phase, higher temps, steeper concentration gradients, increase the rate
raising the particles’ __ __ will cause them to move __
kinetic energy; move faster
the ___ which the particles diffuse and the __ of a barrier are other factors
medium; presence
when a barrier exists, the rate of diffusion depends on the properties of the barrier such as __, ___, and ___ to the ___
thickness, surface area and permeability to the particles
the barrier to diffusion in and out of the cell is the ___ ___
plasma membrane
what are the two types of basic diffusion
facilitated and simple
what is simple diffusion
it mostly involves nonpolar solutes (such as hydrocarbons and lipids and gases like O2 and CO2) that pass straight through the phospholipid bilayer without assistance from a membrane protein
facilitated diffusion involves:
charged or polar solutes (such as ions and glucose) that cross the bilayer with the help of a membrane protein
nonpolar molecules in simple diffusion have properties similar to those of the nonpolar fatty acid tail region therefore they can ___
easily cross into or out of the cell with their concentration gradients
fatty acid tails don’t want to react with the polar solutes and ions making it ___ for them to cross the membrane unassisted
difficult
what two types of membrane proteins do the polar solutes rely on to transport in and out of the cell?
channels and carriers
when using the protein channels,
the hydrophilic amino acids in the protein are orientate toward the interior of the channel which forms the passageway through which charged polar solutes can pass ; most channels are specific for an individual solute
facilitated diffusion using carrier proteins works in that …
the carriers bind one or two specific solutes and “carry” them into or out of the cell - when a solute binds to the carrier protein, the protein changes shape allowing the solute to move across the membrane
three types of carrier proteins are:
- uniporter
- antiporter
- symporter
a uniporter:
transports a single solute
a antiporter:
transports two different solutes in opposite directions - one in the cell and one out
a symporter:
moves two solutes in the same direction
facilitated diffusion is a type of ___ transport even though it requires the ___
passive; requires the help of membrane proteins
both facilitated and simple diffusion rely on the __ __ of the __ __ to drive each solute’s movement
potential energy of the concentration gradient to drive the solute’s movement
active transport requires ___ because solutes are moving ___
cells to expend energy in the form of ATP because solutes are moving against their concentration gradient
they move from ___ concentration to ___
low to high concentration
energy must be supplied from the ___ of ___ because the gradient does not provide ___ to drive the movement
hydrolysis of ATP because gradient doesn’t provide energy to drive movement
active transport requires carrier proteins called __
pumps - they bind and transport a solute across the membrane
pumps can be __ , ___, or ___ and they are all ___ so they are also enzymes that catalyze the reaction that breaks down ATP into ADP and a phosphate
uniporter, antiporter or symporters and they are all ATPases
what are the two types of active transport that move substances across the plasma membrane?
primary active transport and secondary active transport
in the process of primary active transport:
a pump binds a solute and transports it against its concentration gradient using energy from the hydrolysis of ATP
the major primary active transport pump in the body is the ___ pump known as the ___
the antiport pump known as the sodium-potassium pump
critical to maintain the concentration gradients of sodium and potassium ions as they are required for __ __
skeletal muscles to contract, the heart to beat, nerves to send impulses, cells to maintain their osmotic balance and more
the pump maintains this steep concentration gradient by transporting __ sodium ions ___ of the cell for every __ potassium ions it moves __ the cell
3 sodium ions out of the cell for every 2 potassium ions it moves into the cell - both against their concentration gradient
sequence of events of the sodium potassium pump:
- the pump binds 3 sodium ions from the cytosol
- ATP is hydrolyzed, phosphate binds to pump and pump changes shape
- the pump releases the three sodium ions into the ECF and binds 2 potassium ions
- the phosphate detaches and the pump changes back to original shape
- the pump releases the two potassium ions into the cytosol
secondary active transport is the process of:
using ATP indirectly. the cell first uses ATP to create a concentration gradient by pumping one substance across the plasma membrane and then once the first gradient is established the cell harnesses that potential energy to power the active transport another substance against its gradient ; the active transport of one substance is coupled with the passive transport of a second substance
