Topic 4 Cell membrane and signalling Flashcards
fluid mosaic model
membranes are not rigid with molecules locked into place but rather consist of proteins that move around within a mixture of lipid molecules that has the consistency of olive oil
the lipid molecules of the bilayer they are not stationary and…
vibrate, flex back and forth spin around their long axis, move sideways and exchange places within the same bilayer half.
What doesn’t move in cell membrane?
Membrane proteins that anchor cytoskeleton filaments to the membrane
An important of membranes is that proteins and other components of one half of the phospholipids are _____ from those that make up the other half. For ex____
different
a range of glycolipids and carbohydrates groups are attached to proteins on the external side of the plasma membrane while components of the cytoskeleton bind to proteins on the internal side of the plasma membrane.
freeze fracture technique: (3)
- block of cell is rapidly frozen by dipping it into liquid nitrogen
- Block is fractured by hitting it with a microscopically sharp knife edge. This splits the bilayers into inner and outer halfves exposing the membrane interior
- using electron microscopy, the split membrane appear as smooth layers in which the rise of proteins are embedded
lipid (3)
a group of water insoluble molecules that includes fats, phospholipids. and steroids
phospholipid long tail is composed of
carbon and hydrogen
phospholipid head is composed of
glycerol linked to one of several types of alcohol or amino acids by a phosphate group
a property that all phospholipids posses is that they are (word+definition)
amphipathic
molecule contains a region that is hydrophobic and a region that is hydrophilic.
Fully saturated
all the carbon are bound to the maximum number of hydrogen atoms
unsaturated
contain a carbon-carbon double bound
c-c double bond causes a ____ or ____ ion the fatty acid tail
kink/bend
when added to water, phospholipds self assemble into one of the three structure:
a micelle
a liposome
a bilayer
which structure forms depends on
the phospholipid concentration
The fluidity of a phospholipid bilayer is influenced by:
- type of fatty acids that make up the lipid molecules
- temperature
Which is more fluid and why? Unsat or sat
lipid molecules with unsaturated fatty acids are prevented from packing closely together because the c-c double bond forms a kink in the structure. As a result. the more unsaturated the fatty acids of the lipid molecules the more fluid (less viscous) the membrane
as temperature drops and the random molecular motion of lipid molecules slows down,
a point is reached where fluidity is lost and the phospholipid molecules form a semisolid gel.
the temperature at which the gelling occurs depends upon (2)
the fatty acid composition
the more unsaturated the lower the temperature at which gelling occurs
for most membrane system. the normal fluid state is achieved by
a mixed population of saturated and unsaturated fatty acids
at high temps the membrane may become too ____and as a result…
fluid
increased molecular motion associated with higher temp may cause membrane to be too “leaky.” The concentration of K, na and ca ions on either side of a membrane is strictly controlled. If membrane is too fluid these ions can start to freely diffuse across membrane. (distruption of cellular ion balance)
exposure of membrane at low temp is bad because
the resulting membrane gelling can decrease cell permeability and inhibit the function of protein complexes attached to or localized within the bilayer. For ex, the protein receptors need to change shape which can be inhibited if the membranes they are associated with is too rigid
Sterols +ex+influence of membrane
ex: chlosterol
found in the membranes of animal cells but not in those of plants or prokaryotes
membrane buffers
high temp=restrain movement the movement of lipid molecules thus reducing fluidity
lower temp= distrupt fatty acids from associating by occupying space between lipid molecules thus slowing the transition to the non fluid gel state.
what are the two major types of proteins that are associated with the membrane?
integral and peripheral membrane proteins
membrane proteins can be separated into four major functional categories______, all these functions may exist in a single membrane and one protein or protein complex may serve more than one of these functions
- transport (many proteins cannot diffuse freely through the membrane. instead a protein may provide a channel that allows movement of a specific molecule. Alternatively a membrane protein may change its shape and in so doing, shuttle specific molecules from one side of the membrane to the other.
- Enzyme activities (a number of enzymes are membrane proteins, the best examples are the enzymes associated with the respiratory and photosynthetic electron transport chain)
- signal transduction (Membranes often contain receptor proteins on their outer surface that bind to specific chemicals such as hormones. On binding, these receptors trigger changes on the inside surface of the membrane that lead to transduction of the signal through the cell.)
- Attachment/recognition (proteins exposed to both internal and external membrane surfaces act as attachment points for a range of cytoskeleton elements as well as components involved in cell-cell recognition)
integral membrane proteins (2)
proteins that are embedded in the phospholipid bilayer
- interact with both aqueous environment on either side of the membrane and the hydrophobic core, there have 2 distinct parts that differ markedly in polarity
domain of integral proteins that interact within the lipid bilayer/ outside
- consist predominantly of non polar amino acids and domains that are exposed on either side of the membrane are composed to primarily polar amino acids
peripheral membrane proteins+what made up of?
positioned on the surface of a membrane and do not interact with the hydrophobic core
mixture of polar and non polar amino acids
how are peripheral protein held to the membrane?
non covalent bond- ionic or hydrogen
diffusion of o2 and co2
diffuse rapidly due to vital role in cellular respiration and photosynthesis
passive transport+ex
movement of molecules across a membrane without the need to expend chemical energy
-diffusion
diffusion (2)
net movement from high concentration to low concentration
-primarily mechanism of solute movement within any particular cell
driving force of diffusion is:
increase in entropy
the rate of passive transport depends on
the concentration gradient that exist across membranes
the diffusion of molecules across a membrane releases
free energy which can be used to do work
there are ____ types of passive transport:__________
two
simple diffusion
facilitated diffusion
simple diffusion
the movement of molecules directly across a membrane without the involvement of a transporter
the rate of simple diffusion depends on (2)
- molecular size
- lipid solubility
Small non polar molecules/uncharged molecules and steroid hormones
move easy thru the membrane
membrane impermeable to
charged molecules
facilitated diffusion
the diffusion of molecules across a membrane through the aid of a transporter
the diffusion of charged and polar molecules such as (4) relies o specific transport complexes
water
amino acid
sugars
ions
facilitated diffusion is carried put by two types of transport proteins
channel proteins and carrier proteins
Channel proteins (2)
form hydrophilic pathways in the membrane
-transport of ions and water
aquaporins (3)
water specific transport proteins
has a positive charge in the centre of the change; that repel the transport of protons.
single file of water
gated channels (5)
found in all eukaryotes
type of channel protein
can switch between open closed and intermediate to allow the movement of ions (na, K and Ca, CL)
the opening and closing is influenced by changes in voltage across the membrane or by binding signal molecules
the opening and closing involves changes in the proteins three dimensional shape.
carrier proteins
the second type of transport protein under facilitated diffusion
binds a single specific solute such as a sugar molecule or amino acid and transport it across the lipid bilayer
single solute is transported (uniport transport)
osmosis
the passive transport of Peter
osmosis can occur by
simple diffusion through the lipid or facilitated by aquaphors
facilitated diffusion is much
– then simple diffusion
faster
