transport across membranes Flashcards
explain why a cell surface membrane is often called as a fluid mosaic model?
- bilayer membrane
- position of molecules within membrane is fluid = are able to move around in the membrane
- membrane made up of many different molecules arranged in a mosaic
explain the arrangement of the phospholipids in the cell surface membrane
bilayer
- hydrophobic fatty acid tails face away from water and hydrophilic heads attract water
what is the function of the phospholipids in the cell surface membrane
- hydrophobic tails repel water and hydrophilic head attracts water, forming a bilayer
- allows LIPID SOLUBLE (NON-POLAR) molecules to pass
- via SIMPLE DIFFUSION
- prevents small POLAR molecules like ions to pass
what is the function of cholesterol in the cell surface membrane?
- decreases permeability AND
- increases stability of the membrane
(more cholesterol = less fluidity of the membrane)
what is the function of the channel proteins in the cell surface membrane?
- have specific 3 structure only transporting specifically complementary molecules
- only allow SPECIFIC IONS/POLAR or SMALL molecules to move across membrane
- via FACILIATED DIFFUSION
- can be open or closed or intrinsic (allow ions to move straight through)
what is the function of the carrier proteins in the cell surface membrane?
- transport ions and LARGE molecules (eg: glucose, amino acids)
- via faciliated diffusion AND active transport
what is the function of the receptor proteins in the cell surface membrane?
- specific cells have specific receptors, only specific molecules can bind to specific receptors
- protein molecules act as specific receptiors for complementary molecules (ie: hormones like insulin, which cell responds by increasing the cell permeability to glucose).
what is the function of the glycoproteins in the cell surface membrane?
glycoprotein = carb + protein
- used in cell recognition, act as antigens
- on outer surface membrane
- produced in golgi body
- immune cells detect shape of glycoproteins to detect if SELF or NON SELF
what is the function of aquaporins in the cell surface membrane?
- specific type of channel proteins specific to water
more aquaporins = more permeable to water = easier osmosis
diffusion
- passive process = no ATP from respiration
- net movement of non-polar, small molecules (eg: 02, CO2 and oestrogen) from an area of highER concentration to an area of lowER concentration
- across a partially permeable membrane
ficks law
rate of diffusion = (SA x CG) divided by diffusion distance
factors affecting rate of diffusion
- temperature = increased kinetic energy, faster rate of diffusion of molecules
- Surface Area = larger surface area allows more space for molecules to move through, alows more proteins to be present (eg: microvilli)
- concentration gradient = as concentration difference increases, rate of diffusion increases
- diffusion distance = shorter distance/ fewer membranes to cross means faster diffusion
faciliated diffusion
- channel and carrier proteins have a specific shape that are compkementry to a specific ions
- passive, no ATP
- proteins have binding sites
faciliated diffusion graph
- levels off when carrier proteins are saturated/ binding sites are full
- B plateaues at a lower rate because less specific carrier proteins
- number of proteins is a limiting factor
many different substances enter and leave the cell by crossing its cell surface membrane. describe how substances can cross via a CSM
- diffusion from a higher concentration to a lower concentration
- small, non-polar molecules pass via phospholipid bilayer
- water moves by osmosis from a high water potential to a lower water potential
- active transport is movement of substances from low concentration to a higher concentration, against a concentration gradient
- active transport requires energy
- glucose cotransported
- active transport and faciliated diffusion involves proteins
