Cell Surface Membranes+ Flashcards
How do phospholipids act as a barrier
The tails form a hydrophobic core comprising the innermost part of both the outer and inner layer of the membrane
Act as a barrier to most water-soluble substances (the non-polar fatty acid tails prevent polar molecules or ions from passing across the membrane)
What do the phospholipid tails keep in and keep out
This ensures water-soluble molecules such as sugars, amino acids and proteins cannot leak out of the cell and unwanted water-soluble molecules cannot get in
How can phospholipids be chemically modified and to do what
Can be chemically modified to act as signalling molecules by:
Moving within the bilayer to activate other molecules (eg. enzymes)
Being hydrolysed which releases smaller water-soluble molecules that bind to specific receptors in the cytoplasm
What is cholesterols function
Cholesterol regulates the fluidity of the membrane
How does cholesterol act at low temperatures
Cholesterol molecules sit in between the phospholipids, preventing them from packing too closely together when temperatures are low; this prevents membranes from freezing and fracturing.
How does cholesterol act at high temperature
Interaction between cholesterol and phospholipid tails also stabilises the cell membrane at higher temperatures by stopping the membrane from becoming too fluid
Cholesterol molecules bind to the hydrophobic tails of phospholipids, stabilising them and causing phospholipids to pack more closely together
How does cholesterol contribute to impermeability and strenghth
Cholesterol also contributes to the impermeably of the membrane to ions and increases mechanical strength and stability of membranes; without it membranes would break down and cells burst
Cholesterol stabilizes the cell membrane by forming interactions with the phospholipid tails and heads.
Glycolipids & glycoproteins how does there structure /location allow them to carry out function r
Glycolipids and glycoproteins contain carbohydrate chains that exist on the surface (the periphery/extrinsically), which enables them to act as receptor molecules
This allows glycolipids and glycoproteins to bind with certain substances at the cell’s surface
Glycolipids & glycoproteins receptor types
signalling receptors for hormones and neurotransmitters
receptors involved in endocytosis
receptors involved in cell adhesion and stabilisation (as the carbohydrate part can form hydrogen bonds with water molecules surrounding the cell
Some act as cell markers or antigens, for cell-to-cell recognition
What do transport proteins create and what does this allow
Transport proteins create hydrophilic channels to allow ions and polar molecules to travel through the membrane.
Transport proteins allow the cell to control which substances enter or leave
What are the types of transport proteins
channel (pore) proteins
carrier proteins
Each transport protein is specific to
specific to a particular ion or molecule
Transport proteins allow the cell to control which substances enter or leave
Membranes become less fluid when there is:
An increased proportion of saturated fatty acid chains as the chains pack together tightly and therefore there is a high number of intermolecular forces between the chains
A lower temperature as the molecules have less energy and therefore are not moving as freely which causes the structure to be more closely packed
Membranes become more fluid when there is:
An increased proportion of unsaturated fatty acid chains as these chains are bent, which means the chains are less tightly packed together and there are less intermolecular forces
At higher temperatures, the molecules have more energy and therefore move more freely, which increasing membrane fluidity
