Membranes Flashcards
Functions of membrane proteins (5)
Receptors, transport, enzymes, maintenance of cell structure, communication
What do receptor proteins do
Allow communication of an extracellular signal to the intracellular space to create a cellular response
Types of transporters
Channels and carrier mediated transport proteins
How does water cross the membrane
Aquaporins
Function of carrier mediated transport proteins
Open to ECF or ICF, never both at the same time. Open and close. Move large molecules like glucose
Glucose transporters permanently present in cell membranes are what
Insulin independent. These cells have glucose transporters in their membrane all the time. Insulin is only required for glucose uptake in muscle and adipose tissue.
Membrane enzymes do what
Catalyse chemical reactions on the cell membrane. Ligand binding to a receptor enzyme activates an intracellular enzyme which catalyses an intracellular response
Structural proteins do what
Anchor the cell membrane to the intracellular skeleton, extracellular matrix and or to other cells. Dysfunction or loss can cause serious debility
What are G proteins
Peripheral proteins that relay a signal along the membrane from an integral receptor protein to an integral enzyme protein. Moves along the internal layer of the protein, can’t move across.
Protein content of myelin
Low content of protein (18%), major component is lipid, very good insulator so ideal for function which is insulating myelinated nerve fibres
Plasma membranes protein content
Greater activity so protein content is 50%
Membranes involved in energy transduction such as mitochondria protein content
Roughly 75%
To pass passively and rapidly through the lipid bilayer, molecules need to be
Small, uncharged and lipophilic (hydrophobic)
Gases pass readily
What uses facilitated diffusion
Ions and nutrients like glucose which are large and charged
What is used in facilitated diffusion
Protein channels and mediated transport proteins
Sodium concentration is higher ____ the cell
Outside the cell
Pumps out ___ sodium ions and in ___ potassium ions
3 , 2
Electrogenic pump does what
Produces net movement of positive charge out of the cell. Creates a charge difference across the membrane
How much of the resting energy if the body is used by Na/K ATPase
40%
Endocytosis
Invagination of cell membrane to form a vesicle that eventually disintegrates on the cytoplasmic surface of the membrane which then releases the content into the cell to get to their destination. Common mechanisms for terminating signals from extracellular ligands
Exocytosis
The reverse of endocytosis. proteins manufactured in cells are released from the cells by the process of exocytosis. Some hormones are released this way
What is required to prevent movement of water across a membrane
Osmotic pressure
Osmosis is
Movement of water molecules across a membrane to create equal concentrations at either side. Not equal volume
Why is osmosis without diffusion clinically important
This is when there is a change in cell volume. This can be a problem as the cells can shrivel up or they can swell and burst
What determines the osmotic effect on water
The number of solute particles, not molecules
Osmolarity
Number of particles per litre of solution. Determines concentration of biologocial solutions in terms of osmoles
Normal human plasma has osmolarity of
300 mOsmol/l
Tonicity
Number of non penetrating particles in solution
Non penetrating (Na and Cl in ECF and K in ICF)
Isoosmotic
Same total number of solute particles as the normal ECF
Isotonic
Same total number of non penetrating solute particles as the normal ECF
Haemolysis
Bursting of red blood cells
Urea
CO(NH2)2
Organic compound with chemical formulae
What happens if a cell goes into a hyperosmotic urea solution (in vitro)
swell and burst because urea is penetrating and is in aqueous hypotonic solution. Urea equilibrates by diffusion and as the urea goes in the water goes out. The cell is still full of non penetrating species. So the extracellular fluid has lots of water ( more than the intracellular fluid) so the water tries to go inside the cell to find osmotic equilibrium and this causes cell to swell and burst
What happens to NaCl when it is put in solution
Na and Cl split up so if there’s a solution of NaCl that is 150mM then u have 150mM of Na and 150mM of cl so altogether u have osmolarity of 300mOsmols
What causes changes in cell volume
Tonicity Only
1 mol of sodium chloride solution has an osmolarity of
2osmoles/litre
