Chapter 3 Flashcards
what are lipids
Any of a group of large biological molecules, including fats, phospholipids, and steroids, that mix
poorly, if at all, with water.
fatty acids are made of what components?
carboxylic acid,
long carbon chain
if a fatty acid link a glycerol it forms what molecule
triglyceride
2 types of fat and what distingues them?
saturated
unsaturated
unsaturated has double bonds
the main component of phospholipids is
fatty acids
the double bond has an impact on
fluidity of the plasma membrane
higher levels of unsaturation leads to
lower melting point
less viscous(oil)
est-ce que toutes les espèces ont le meme niveau d’insaturation?
non, their variations are due to the adaptations to specific environment conditions
is it possible to change the lipid composition of the plasma membrane depending on the temperature for some species?
yes
what is the fundamental role of the membrane?
to act as a selective permeable barrier, regulating the cell’s chemical composition
what is the main component of the plasma membrane?
phospholipids
it is a bilayer of phospholipids
what are the roles of the plasma membrane?
compartmentalization
site for biochemical activities
providing a selectively permeable barrier
transporting solutes
responding to external stimuli
intercellular interaction
energy transduction
phospholipid is made of what
lipid made up of glycerol joined to 2 fatty acids and a phosphate groupe and choline
which part of phospholipid is hydrophobic and hydrophilic?
head-hydrophilic
tail = hydrophobilc
if it has parts that are hydrophobic and hydrophilic then it is named as
amphipathic
(with both a hydrophilic
region and a hydrophobic region).
because of their amphipathic nature, the phospholipids do what when they assemble?
this causes phospholipids to assemble
into bilayers, exposing their hydrophilic
(polar) head to the polar water molecules.
can polar molecules cross the
bilayers membrane?
non
what means that amolecule is hydrophobic?
it means that it can not interact with water
phospholipids can differ based on what?
Phospholipids can differ based on the fatty acid chains (length, number and position of double bond),
the fatty acid linkage (ester versus ether)
the head group (Phosphatidyl choline, Phosphatidyl
ethanolamine, Phosphatidyl serine, Phosphatidyl inositol…)
if the fluidity is increased for the plasma memebrane
explain the impact on the permeability and protein functions?
it increases the membrane permeability and proteins functions
name the 3 possible movements of phospholipids?
lateral shift
transverse diffusion
flex
permeability of the membrane is higher for
• smaller molecules • less polar (charged) molecules • more hydrophobic molecules • highly lipid soluble substances • gas (ex: O 2 , CO 2
what means when a barrier is efficent?
it maintains the concentration of all the molecules inside the cell
what are transport proteins?
are transmembrane proteins that can modify temporarily the permeability
of the membrane by allowing only specific molecules to cross (enter or leave the cell).
explain the fick’s law of diffusion
The flux of molecules goes from regions of high concentration to
regions of low concentration
. The magnitude of this diffusion is proportional to the concentration gradient
between the two compartment (ex: across the plasma membrane).
the flux of molecules going from high to low concentration is du to
stochastic(random) movement of each molecule in all direction
net movement of a population of molecules towards…………(
lower concentrations (chemical gradient)
if the molecule is polar or charged, its net movement also depends on both
the chemical gradient
and
the electric gradient across the plasma membrane
what is an electric gradient?
it is a difference in the charges across the membrane(intern and extern) of the cell
passive (simple) diffusion across the phospholipids double layer, requiers energy(hydrolysis of ATP)?
NON
it does not require the energy(hydrolysis of ATP
it is a passive diffusion
c’est que les regles à suivre pour savoir quels molecules vont passer par simple diffusion(passive diffusion)
Substances follow their own concentration gradient (from high concentration to low concentration)
Gas follow their own partial pressure gradient (from high partial pressure to low partial pressure) CO2 and O2
At equilibrium there is an equal number of molecules passing in each direction
Note that diffusion can be facilitated by membrane transport proteins (channels) that are ………….
and give examples
highly selective and
let specific molecules go through
(ex: aquaporins in the kidney ducts)
what are aquaporins?
they are proteins that let molecules of water to pass through by simple diffusion(passive)
why there are transport proteins that can do passive diffusion?
because there are molecules who have difficulty to pass through the plasma membrane like sucrose, ions(Ca2+)
transport proteins are embedded where?
in the plasma membrane
The cell is able to modify (regulate) the entry/exit of molecules through…
the expression of genes that code for transport proteins (which are then inserted in the membrane)
•
the temporary opening and closing of some of these transport proteins (depending on a stimulus)
by regulating the entry/exit of molecules, the cell can maintain
•
a specific cellular concentration of each solute (ions, molecules)
•
a specific electric potential across the membrane (by keeping some ions outside and others inside)
what is the charge inside the cell normally and is due to what?
negative normally
due to the presence of phosphate groups and proteins that are both -ve charged and to the movements of ions in/out of the cell
what is a membrane potential?
also called
The charge difference (voltage) across the plasma membrane—. The attraction of opposite charges across the plasma membrane is a
source of potential energy.
electrical potential
the resting membrane potential has a value of
70 mV
If a molecule is not charged (or large), its diffusion across the membrane
only
depends on
depends on the chemical gradient concentration gradient