1.3 Cell Membranes and Transports Flashcards
(42 cards)
What is a phospholipid made of?
2 Fatty acids and 1 phosphate attached to a glycerol
Why are phospholipids used to make membranes?
because they have special properties including:
-phosphate head attracted to water (HYDROPHILIC)
-tails repel water (HYDROPHOBIC)
these factors mean that when they are placed in water they will arrange themselves in a specific way so that both parts of the molecule are satisfied.
Hydrophilic
attract water and allow water soluble and non-polar molecules through
Hydrophobic
repel water and allow lipid soluble and polar molecules through
Polar and Non polar
-the phosphate ‘head’ is charged = polar
-the fatty acid ‘tail’ isn’t charger = non-polar
Width of phospholipid bilayer
7-8nm
The other main components of the phospholipid bilayer are:
PROTEINS
What do proteins do?
-They can form channels to allow certain molecules to pass through.
-They can have carbohydrates attached to them to act as signal molecules for cell recognition.
-They can act as receptors for hormones and other signal molecules to bind to.
When was the Fluid Mosaic Model developed?
-was developed by Singer and Nicolson in 1972.
-It built upon the work by Davson and Danielli in 1935 who thought there was a phospholipid bilayer between two layers of globular proteins. They thought it was trilaminar and made of lipids and proteins
Why is it fluid?
because the lipid layer of the membrane isn’t fixed in one place, the phospholipids can move about freely.the membrane actually has the consistency of cooking oil
Why is it mosaic?
because of the patchwork pattern produced by the scattered proteins when membrane is viewed from above
Intrinsic proteins
or Integral proteins are embedded in the bilayer, if they span it from one side to the other they can also be called TRANSMEMBRANE Proteins. They can form channels or act as carriers
Extrinsic proteins
or Peripheral proteins are loosely attached to one side of the membrane. These are often enzymes or receptor molecules
Controlling the position of proteins in membranes:
The non-polar amino acids cause proteins to be embedded in membranes while polar amino acids cause portions of the proteins to protrude from the membrane.
Creating hydrophilic channels through membranes:
Polar amino acids are found inside membrane proteins and create a channel through which hydrophilic molecules can pass through.
Where are hydrophilic parts with polar/ charged R groups?
located around the phospholipid heads or on the outside
Where are hydrophobic portions with non polar R groups?
near/ between the hydrophobic tails
What charge do channel proteins have?
charged/ polar R groups lining the channel
What affects how fluid the phospholipid membrane is?
-There is also some cholesterol which makes the membrane more structured.
-You can also have different proportions of unsaturated and saturated fatty acids in the phospholipids to control how fluid the membrane is. The more unsaturated fatty acids the more fluid.
What are glycoproteins and their function?
-proteins with carbs attached
-Cell to cell recognition
-Cell to cell communication
-Immunity
-Recognition of hormones
-Binding of molecules (adhesion) and crosslinking cells for strength and stability
Cholesterol
-Cholesterol helps prevent extremes…
It both stabilises (makes more rigid) the membrane AND also helps maintain the fluidity.
-It integrates between the phospholipids, and without it the membrane would be too fluid AND it helps to separate the phospholipids so that the fatty chains can’t come together and crystallise.
-It is present in Animal cell membranes but absent in bacteria and most plants – because they have cell walls to provide stability
Glycocalyx
-Is the covering of glycoproteins and glycolipids that surrounds a cell membrane
-The glycocalyx is involved in immunity, compatibility, inflammation regulation, fertilisation, embryonic development etc.
-It helps molecules with cell recognition, cell-to-cell communication and intercellular adhesion.
-The word literally means ’sugar-coat’, and this network of glycoproteins and glycolipids is often very obvious in bacteria or as a layer of slime on fish etc.
What affects permeability of a membrane?
1- Temperature
2- Ethanol
3- pH
Temperature affecting permeability
-the higher the temperature, the more kinetic energy the phospholipid and protein molecules have.
-That creates gaps or pores in the phospholipid bilayer. Over 40°C proteins will lose their tertiary structure because the H-bonds break and they become denatured. These will get larger and larger.
-Smaller molecules will have more energy than larger ones when heated up.
-Diffusion happens more rapidly when the molecules have more energy
