2.1.5 Flashcards
What is compartmentalisation?
The formation of separate membrane bound areas within a cell ; separate the contents of cells from their external environment and the different organelles within cells from the cytosol
Why is compartmentalisation important?
Metabolism includes many different and often incompatible reactions so containing these reactions allows specific conditions required for cellular reactions (chemical gradients) to be maintained
What is the plasma membrane?
The phospholipid bilayer that separates the cell from its external environment
Structure of phospholipid bilayer?
Hydrophilic phosphate heads form both the inner and outer surface of a membrane - sandwiching the fatty acid tails of the phospholipids to form a hydrophobic core inside the membrane
Where are aqueous environments found and how do they matter?
Inside of cells are usually aqueous and bilayer are perfectly suited because the outer surfaces of the hydrophilic phosphate heads can interact with water
When were cell membranes first seen?
Invention of electron microscope lead to images be taken with higher magnification and resolution ; images in 1950s show cell membrane as 2 black parallel lines
When was the fluid mosaic model proposed?
1972 - Singer and Nicolson built upon earlier lipid bilayer model
Describe fluid mosaic model
Phospholipids are free to move within the layer relative to each other (they are fluid) giving the membrane flexibility and because the proteins that occupy various positions in membrane vary in shape size and position (same as mosaic)
Glycoprotein
Branched carbohydrate portion of a proteins which acts as a recognition site for chemicals (hormones)
Glycolipids
Acts as a recognition site for cholera toxins
Cholesterol
Adds stability and flexibility
What are extrinsic proteins?
Lay on surface
What are intrinsic proteins?
Span the whole phospholipid layer
Examples of intrinsic proteins
Integral proteins that are embedded through both layers of a membrane - hydrophobic r groups of their amino acids interact with hydrophobic core keeping them intact
CHANNEL AND CARRIER - BOTH TRANSPORT PROTEINS
Channel proteins
Provide a hydrophilic channel that allows passive movement of polar molecules and ions DOWN a concentration gradient ; held in place by hydrophobic interactions
Carrier proteins
Passive AND Active transport - down and against concentration gradient into cells => shape of protein changes
What are glycoproteins?
They are intrinsic proteins that are embedded in cell surface membrane with attached sugars chains ; they help in cell adhesion and act as receptors for chemical signals
Cell signalling
When chemical bonds to receptor it elicits a response - binding of neurotransmitters triggers impulse to next neurone for example
Drugs act by attaching to cell receptors (beta blockers)
What are glycolipids?
Similar to glycoproteins as they are lipids with attached sugar chains - cell markers/antigens and can be recognised by cell as self (of the organism) or non-self (belonging to another organism)
What are extrinsic proteins?
Peripheral proteins only on one side of bilayer - normally have hydrophilic R-groups on their outer surfaces and interact with polar heads of phospholipids ; EITHER LAYER AND CAN MOVE BETWEEN
Structure of cholesterol
Lipid with a hydrophilic and hydrophobic end
Role of cholesterol
Regulates fluidity of membrane by positioning itself between phospholipids with hydrophilic end interacting with PO43- heads and hydrophobic with tails - this adds stability to membrane without making them too rigid. Also prevents membranes becoming too solid by stopping the phospholipid molecules from grouping together and crystallising
Membranes as sites of chemical reactions
Proteins in membrane forming organelles have to be in particular positions for chemical reactions to take place
Requirements for the production of ATP in respiration
Electron carriers and enzyme ATP synthase have to be in the correct positions within the cristae (inner membrane of mitochondrion)
What factors affect membrane structure?
Temperature and presence of solvents
Affect of temperature on cell membrane?
Phospholipids will have more KE and will move more making membrane more fluid and making membrane lose its structure. If temperature increases too much then cell breaks down completely. Loss of structure increases permeability of the membrane making it easier for particles to cross it
Affect of temperature on proteins
Carrier and channel proteins will be denatured at higher temperatures so permeability of cell membrane affected as unable to carry molecules across
How does the cell membrane interact with water?
Non-polar hydrophobic core orientated away from water and hydrophobic heads interact with water - keeping bilayer intact
What do organic solvents do?
They are less polar than water (or non-polar) - so they dissolve membranes by disrupting cells
Why is alcohol used in antiseptic wipes?
Alcohols dissolve the membranes of bacteria in a wound, killing them and reducing infection