Chapter 5 The Structure Of Plasma Membranes Flashcards
What is the structure of a phospholipid?
Contains a charged hydrophilic head and non-polar hydrophobic tails
When exposed to water the hydrophilic phosphate head will always face towards the water forming the inner and outer surface, while the hydrophobic tails will point inwards away from the water forming the core.
What structures can phospholipids form when exposed to water?
A Micelle or a Bilayer
What is Cell Membrane theory?
1972 Singer and Nicolson proposed Fluid-Mosaic model
-Phospholipids are free to move (fluid)
-Embedded proteins vary in shape, size and position
What components make up a cell membrane?
Cholesterol
Glycolipids
Membrane Proteins - Consisting of intrinsic and extrinsic proteins
Intrinsic proteins include: Carrier proteins, Channel proteins, Glycoproteins
What are Intrinsic proteins?
Transmembrane proteins embedded through both phospholipid layers.
They contain amino acid groups with hydrophobic-R groups which interact with the hydrophobic membranes core to keep them in place. Eg, Channel and Carrier proteins.
What are the function of Channel proteins?
Provide a hydrophobic channel for passive movement of polar molecules down a concentration gradient by diffusion.
What are the function of Carrier proteins?
Involved in passive and active transport which often involves change in the protein configuration.
What is the structure of Glycoproteins?
Embedded intrinsic proteins which have attached carbohydrate chains
What is the function of Glycoproteins?
Play a role as receptors and in cell adhesion.
When chemicals bind to these receptors this causes a direct response or chemical cascade known as cell signalling.
For example,
Receptors for neurotransmitters
Receptors for peptide hormones like insulin
What are Extrinsic proteins?
Proteins free on the membrane surface or bound to an intrinsic protein.
They are only bound to one side of the bilayer, but can be present on either side.
They contain hydrophilic R-groups on the outer surfaces and they interact with the polar heads of phospholipids or intrinsic proteins.
What is the structure of Glycolipids?
Lipids with attached carbohydrate chains
What is the function of Glycolipids?
Act as cell markers or antigens for cell recognition
What is the structure of cholesterol?
Lipids with hydrophilic and hydrophobic ends. They are positioned between phospholipids in a membrane bilayer, with the hydrophilic end interacting with the polar heads and the hydrophobic end interacting with the tails of the phospholipid.
What is the function of Cholesterol?
Important in controlling membrane fluidity
Affects stability of membranes without rigidity- prevents lysis.
Regulates the fluidity of membranes as the more cholesterol there is, the less fluid that can pass through therefore making it less permeable.
What is the function of Actin Microfilaments in a membrane?
Give mechanical strength
Determines the cell shape
Allows movement of the cell surface
What are chemical reaction sites?
The membranes of organelles often carry proteins in fixed positions in order for chemical reactions to take place.
What is the function of the phospholipids?
They act as a barrier to control what enters and exits the cell
The smaller and less polar the molecule the faster it can diffuse across the membrane.
Why is membrane fluidity necessary?
Diffusion of substances
Membranes to fuse
Cells to move and change shape
What are the factors that can affect membrane structure?
Temperature
Solvents
How does temperature affect membrane structure?
As the temperature increases, the kinetic energy of the phospholipids increases, this therefore makes the membrane more fluid and structure is lost.
Consequently, this creates a gap between the bilayer, where molecules can pass through so the permeability of the membrane increases. At higher temperatures carrier and channel proteins can denature also affecting membrane permeability.
Why is water important for the membrane structure of a phospholipid bilayer?
Water, a polar solvent, is important in keeping the phospholipid bilayer intact by interacting with the charged hydrophilic heads.
What types of organic solvents are there?
Less polar than water- alcohols
Non-polar - Benzene
What is the effect organic solvents on cell membranes?
Organic solvents dissolve membranes and disrupt cells
What is the effect of pure or strong alcohol solutions?
They destroy body cells as they are toxic.
What is the effect of weaker solutions of alcohol?
Weaker solutions of alcohol can’t dissolve membranes, but can still damage cells.
What is the impact of non-polar alcohols entering the cell membrane?
The membrane will be disrupted which causes it to become more fluid and permeable
What is diffusion?
Passive net movement of particles down a concentration gradient from an area of high concentration to an area of low concentration.
Diffusion will occur until equilibrium has been reached.