3. Cell Membranes and Transport Flashcards
phospholipid
describe phospholipid head
charged
hydrophillic
micelle
how are phospholipids held together in bilayers
weak hydrophobic interactions between the hydrocarbon tails allowing some membrane fluidity
Fluid Mosaic Model of Membrane Structure
Singer and Nicholson - 1972
-fluid, components of the membrane, particularly phospholipids can move between the two layers of membrane
-mosaic, looked at freeze fracture electron microscopy
-cell membrane is fractured along the line of least resistance – the centre of the bilayer. The images produced have a speckled effect caused by the proteins exposed, looked like a mosaic
why is it called the fluid mosaic model 2 marks
mosaic of protein molecules, randomly arranged
lipid layer is fluid - can move
fluid mosaic model membrane diagram
two types of membrane proteins
extrinsic
intrinsic
extrinsic proteins
on or in one side of the bilayer
eg receptors
intrinsic proteins
runs through both sides of the bilayer
eg transport proteins
eg of intrinsic protein and where it is found
ATP synthase
embedded on cristae of mitochondria
diagram of intrinsic and extrinsic proteins
characteristics of intrinsic proteins
hydrophilic and hydrophobic parts
span the membrane
some are channel proteins
channel protein
have hydrophilic R groups lining the space down the middle of the protein. These channels are specific to particular charged or polar particles and allow them to diffuse across the membrane in facilitated diffusion.
have hydrophilic groups lining the pore
protein carriers
involved in active transport and facilitated diffusion across the membrane; these are specific to the polar or charged molecules carrier
channel and carrier
cell membranes
selectively permeable
hydrophobic layer in middle of bilayer is impermeable to polar and charged particles
function of cell membrane
Taking up nutrients/other requirements/reference to selective permeability;
phagocytosis/secreting chemicals; cell recognition;
adhesion; receptor sites.
How do non polar molecules get through cell membrane
Non-polar molecules like oxygen, carbon dioxide and fat-soluble vitamins (A, D, E and K) dissolve in the hydrophobic layer and can cross the membrane by simple diffusion.
glycoprotein
These are proteins with carbohydrate chains attached
These carbohydrate chains also project out into whatever fluid is surrounding the cell (they are found on the outer phospholipid monolayer)
glycolipid
These are lipids with carbohydrate chains attached
These carbohydrate chains project out into whatever fluid is surrounding the cell (they are found on the outer phospholipid monolayer)
glycocalyx
All of the carbohydrates projecting outside of the cell
glycocalyx is mainly involved in cell to cell recognition
only found on the side of the bilayer that faces out of the cell
act as antigens in cell recognition
cell membrane - carbohydrates
act as specific antigens.
-An individual’s specific antigens are unique to themselves
- are involved in cell recognition and signaling, playing a critical role in immune responses
-If the carbohydrate structures on a cell are recognized as foreign, they trigger an immune response.
providing energy needed by the cell to survive
cell membrane - hydrophobic region, molecules of cholesterol
regulate the fluidity of the membrane and are found between fatty acid tails.
If there is not enough cholesterol, the membrane becomes too fluid
if there is too much cholesterol, the membrane becomes too rigid.
label
A - Hydrophilic heads
B - Hydrophobic tail
C - Intrinsic protein
D - Oligosaccharide/ glycoprotein
explain at temp below 40 degrees celcius effect on pigment in cell
the increased kinetic energy of the phospholipids and proteins in the membrane causes them to move more. This creates gaps between the phospholipids. The pigment will also have more kinetic energy so will move more and diffuse out of the cell into the water through these gaps.