B2.1 Membranes Flashcards
what are cell membranes made of
phospholipids in a bilayer
what is the structure of phospholipids and how do they react to water
they have a hydrophilic head that points outwards, and a hydrophobic tail( made of fatty acids) which move away from water
why is the plasma membrane fluid
because the phospholipids dont have bonds and are held together through attraction
what is the function of the phospholipid bilayer
they create a strong, stable barrier between aqueous solutions that allow substances to leave or enter the cell
what is diffusion
the passive movement of particles from a higher to lower concentration, down a concentration gradient, using kinetic energy of the molecules
when does diffusion across the cell membrane occur
the plasma membrane is fully permeable to the solute.
The lipid bilayer is permeable to non polar substances
what are peripheral proteins
proteins attached to the outer surface of the bilayer or the inner surface
functions of peripheral proteins
shuttles between integral proteins
scaffold proteins that hold shape
receptors for extra cellular signals
what are integral proteins
proteins embedded in one or both layers of the membrane.
They can act as channels, receptors or antigens
what is osmosis
the diffusion of water molecules across a membrane that is permeable to water(partially permeable) down a concentration gradient
what happens to dissolved substances in water
they attract a group of polar water molecules around it
what happens when the solution is more concentrated( in terms of water potential)
the greater the number of water molecules that are held almost stationary
what are aquaporins
a water channel pore in a membrane that allow water to diffuse through the plasma membrane
is a protein
what is facilitated diffusion
particles of a substance that cannot diffuse across the plasma membrane are helped across the membrane by integral proteins that span the membrane
is facilitated diffusion passive or active
passive diffusion
what do channel proteins transport
through facilitated diffusion, they provide hydrophilic channels for polar and charged molecules to pass through,
only specific charged particles
what is active transport
movement of particles from lower to higher concentration, using energy from ATP that has been created during respiration
How is active transport facilitated
through carrier proteins
what are pump proteins
used for active transport across membranes that is used selectively to move one or two specific substances across
characteristic features of active transport
occurs against a concentration gradient
active uptake is highly selective
involves pump molecules
How is permeability determined in the case of simple diffusion
not selective and depends only on the size and hydrophilic or hydrophobic properties
what creates selective permeability in membranes
facilitated diffusion and active transport
what cannot pass through the hydrophobic interior of membranes
Large polar molecules or charged molecules
What are glycoproteins and glycolipids
carbohydrates that are on the surface of the plasma membrane which are attached to proteins or lipids
what is the glycocalyx
glycoproteins and glycolipids together
what do carbohydrates do in membranes
help with cell recognition and cell adhesion
highly hydrophilic and attracts large amounts of watedr
Explain fluid mosaic model of membrane structure
described as fluid because the components are on the move
mosaic because the proteins are scattered about in patterns
what is the effect of unsaturated fatty acids on the phospholipid bilayer
because unsaturated fatty acids have lower melting points, an excess makes the membrane more fluid
what do saturated fatty acids do to the phospholipid bilayer
they make the membrane stronger at higher temperatures
why must membranes be sufficiently fluid
they must be fluid for proteins to move around and function
what does a decrease in temperature lead to in the membrane
temperature falling leads to less fluidity and the membrane can even solidify
what is homeo-viscous adaptation
adaptation that allows some organisms to vary the balance between saturated and unsaturated fatty acids in response to ambient temperatures
what is the structure of cholesterol
a steroid, made of hydrophilic hydroxyl and hydrophobic hydrocarbon on either side of a carbon ring
what is the role of cholesterol in the phospholipid bilayer
stabilises the membrane at higher temperatures and prevents stiffening at lower temperatures
has the effect of disturbing the packing of the phospholipids, increasing the flexibility of the membrane
what does cholesterol do to the bilayer in low temperatures
maintains the fluidity of the membrane by forcing apart the phospholipids and maintaining distance between them
what does cholesterol do to the bilayer in high temperatures
bonds between the cholesterol and phospholipids maintain the structural integrity of the membrane and prevent them from becoming too fluid
what is uptake into a cell called
endocytosis
what is export out of a cell called
exocytosis
How is endocytosis done
through the formation of vesicles as the plasma membrane pinches inwards, taking material into cell
how is exocytosis done
vesicles fuse with the membrane and material is exported
what is phagocytosis
bulk transport of solid matter being taken in
what is pinocytosis
the bulk transport of fluids
how are nerve impulses transmitted along the axon of a nerve cell
through momentary reversal in electric potential difference in the membrane , brought by rapid movements of sodium and potassium ions
what are voltage gated channels/gated ion channels
channel proteins that are exclusively permeable for one type of ion
what is a neurotransmitter gated ion channel
opens temporarily when a specific neurotransmitter bonds with it
steps of a voltage gated channel
When theres a stimulus, sodium channels open and let sodium in
The interior of axon depolarises, nerve pulse initiated
more positive charge leads to more potassium channels open, sodium channels close
potassium ions exit down the axon down an electrochemical gradient
interior becomes less positive, so potassium channels close through ‘ball and chain’ protein
when there is more positive charge outside, the channel returns to fully closed
what are exchange transporters
used in active transport of sodium and potassium ions
used to help generate membrane potentials
what are the steps in exchange transporters
3 sodium ions loaded into binding sities
ATP reactions cause pump proteins to close to the interior and open to the exterior
3 sodium ions released and 2 potassium ions loaded
reversal of shape of pump protein and potassium ions are released
what is indirect active transport
cotransporters move sodium in one direction and move glucose as well
example of indirect active transport( glucose and sodium)
2 sodium ions moved for each glucose
what is movement of sodium in terms of cotransporter protein
build up of concentration gradient allowing sodium to enter cotransporter protein down its concentration gradient
what is the result of indirect active transport in terms of glucose
allows glucose to be transferred against it concentration gradient
what are Cell Adhesion molecules and where are they located
they help maintain tissue structure/function, and help glue cells together
located on the cell surface
What is the Extra-Cellular Matrix
a network of proteins and molecules that surround, support and give structure to cells and tissues
How are CAM’s related to ECM
some are used to bind cells to the ECM, forming a cohesive unit
what proteins are used for cell-cell junction
cadherin proteins
what proteins are used for cell-ECM junctions
done through integrin proteins
what are the 4 types of cell junctions
anchoring junctions( strengthens contact)
tight junctions (seal gaps between cells)
gap junctions (links cytoplasm)
signal relaying junctions ( synapses)
