1.3- Cell membranes and Transport Flashcards
What is the function of a cell membrane?
controls which substances can enter and exit the cells
controls the uptake of nutrients
allows waste products to pass out of the cell
cell recognition and signalling
What is the structure of a cell membrane?
selectively permeable membrane
composed of phospholipids and proteins
What are dietary lipids?
triglyceride
one glycerol 3 fatty acids
Phospholipids in the cell membrane
form bilayers, with one sheet of phospholipid forming over another
phosphate head is polar= hydrophilic, so its attracted to other polar molecules like water
fatty acid tails are non-polar= hydrophobic, so it repels water
one layer has its phosphate head pointing inwards, interacting with the water inside the cytoplasm
other layer has its phosphate head pointing outwards, interacting with the water that surrounds the cell
the bilayer forms the basis of the membrane structure
it allows lipid soluble molecules to enter and leave the cell but prevents water soluble molecules
What is the fluid mosaic model?
phospholipid bilayer is not a fixed structure
although the bilayer will always remain arranged in this configuration, the individual phospholipids are able to move (fluid) and the proteins embedded in the bilayer vary in shape and size, arranged randomly (mosaic)
phospholipids rotate on their axis
the movement increase the fluidity of the membrane
What are the types of proteins?
Intrinsic and extrinsic
How are the proteins arranged in the membrane?
randomly in contrast to the more regular patterns of phospholipids
What are extrinsic proteins?
occur on the surface of the bilayer, or partly embedded in it
they are polar and associate with hydrophilic heads of the phospholipids
provide structural support
also form recognition sites by identifying cells
many are receptor sites and binds with proteins such as hormones and neurotransmitters
What are intrinsic proteins?
span the phospholipid bilayer
they have polar and non-polar regions, which correspond with hydrophilic and hydrophobic regions of the bilayer
some act as channels or carriers to facilitate the diffusion of polar molecules, e.g ions, across the cell membrane
others form pumps and carry out active transport against a concentration gradient
What are glycolipids?
lipids which have combined with polysaccharide , they are found in the outer layer of the membrane and are involved in cell recognition
What are glycoproteins?
proteins combines with a polysaccharide
stick out of some membranes
What is cholesterol?
found in animal cells
fits between the phospholipid molecules
increasing the rigidity and stability of the membrane
membrane as a barrier
selectively permeable membrane
lipid soluble (non-polar) substances move through the membrane via the phospholipids
water soluble (polar) substances have to be transported via special protein molecules, which form water filled channels across the membrane
the hydrophobic core of the membrane impedes the transport of ions or polar molecules
ions and large molecules cannot diffuse across the non-polar centre of the phospholipid bilayer, because they are relatively insoluble in lipid
What are the passive processes?
diffusion
facilitated diffusion
osmosis
Which transport uses energy?
active transport
What does passive transport/diffusion mean?
the net movement of molecules or ions from a region of their high concentration to a region of their low concentration until they are equally distributed
What affects the rate of diffusion?
concentration gradient - the greater the difference in concentration of molecules in two areas, the greater the rate
distance of travel over which diffusion takes place- the shorter the distance between two areas, the greater the rate
surface area of membrane- larger the area the quicker the rate
thickness of surface- thinner the membrane the quicker the rate
an increase in temp- increase in rate due to kinetic energy
Particle size- smaller the particles, the quicker the rate
What is diffusion proportional to?
surface area x difference in conc / length of the diffusion path
What is facilitated diffusion?
ions and large molecules like glucose cannot pass through the cell membrane because they are insoluble in lipids
in the cell membrane intrinsic protein molecules span the membrane from one side to the other and help such particles to diffuse in or out of the cells
there are 2 types of proteins which facilitate diffusion- carrier and channel
What are channel proteins?
consist of pores lined with polar groups
this allows charged ions to pass though
each channel protein is specific for one type of ion
they can open and close depending on the needs of the cell, which are known as gated channels
What are carrier proteins?
allow facilitated diffusion across the membrane of larger polar molecules such as sugars and amino acids
a particular molecule attaches to a carrier protein at its binding site and causes the carrier protein to change shape or rotate within the membrane
this action releases the molecule on the other side of the membrane
What factors affect cell membrane permeability?
increasing temperature
increasing ethanol concentration
increasing sodium chloride concentration
increasing detergent concentration
How does increasing the temperature affect cell membrane permeability?
cell membrane and tonoplast are stable up to 40 degrees
temperatures above 40 degrees the cell membrane and tonoplast become increasingly unstable
increased heat energy leads to increased kinetic energy
the phospholipids vibrate more and move further apart, which increases the permeability of the membrane
the proteins within the membrane denature at high temperatures, this allows betalains to diffuse out of the cells more readily
therefore as temperature increases cell membrane and tonoplast permeability increases due to increased disruption of the membranes
How does increasing ethanol concentration affect cell membrane permeability?
ethanol dissolves phospholipids
greater the concentration of ethanol the more permeable the membranes become
