Cell processes. Flashcards
What does amphipathic mean?
Has both polar and non polar regions
Cell membrane controls the passage of substances into and out of the cell; this allows for (4)
Concentration gradients
Spatial organisation of chemical and physical processes within the cell
Controlled uptake of nutrients and discharge of waste
Development of a membrane potential
The two basic classes of membrane proteins
Intergral (transmembrane): Extend into or completely across the cell membrane.
Peripheral: Attached to either the inner or outer surface of the membrane, easily removed.
Functions of membrane proteins (6)
Receptors Cell identity markers linkers Enzymes Channels Transporters
Cell membrane is permeable to?
Impermeable to?
Permeable:
nonpolar uncharged molecules (O2, N2, benzene)
Small uncharged polar molecules (H2O, urea, glycerol, O2)
Impermeable:
Large uncharged polar molecules (glucose, amino acids)
Ions (Na+, K+. Cl-, Ca2+, H+)
Factors influencing diffusion
Concentration Temperature Surface area Size of molecule Distance
Membrane potential is influenced by…?
Concentration and electrical gradients; electrochemical gradient.
Describe osmotic pressure
The hydrostatic pressure applied to oppose osmosis. A colligative property, i.e. depends on the numbers and not the types of particles in solution.
Osmolarity depends on…?
Concentration and ionisation properties of solutes
Define tonicity
The effect a solution has on cell volume (thus includes membrane permeability of the solute)
Describe ion channels
Water filled pore that span lipid bilayer
Rapid transfer rate (~1 million ions/sec)
Exhibit ion selectivity
What opens and closes ion channels
Voltage Ligands Phosphorylation Cell volume (stretch) pH
Two classes of carrier proteins and common features
Passive or active
Exhibit: Specificity, saturation, inhibition, and competition
Describe passive carriers
Substrates move down their concentration gradients via the transport protein which undergoes a conformational change as the substrate move through.
Eg GLUT which move glucose into the cell down it’s concentration gradient.
Describe primary active transport
Energy used by hydrolysis of ATP to move a substrate against its concentration gradient.
How much of the cells energy is used in primary active transport?
30%
Describe the features of the Na+/K+ ATPase
Primary active transport that maintains low Na+ and high K+ inside the cell. Three Na+ are pumped out of the cell for every 2 K+ pumped in.
What does the Na+K+ ATPase facilitate (6)?
Resting membrane potential
Electrical excitability
Contraction of muscle
Maintenance of steady state cell volume
Uptake of nutrients via secondary active transporters
Maintenance of intracellular pH by secondary active transport.
Describe secondary active transport
Uses the energy stored in the ion gradient to facilitate movement of substrate against their concentration gradient through substrates moving though channels alongside ions moving down their conc. gradients. Eg. glucose and aa move into the cell alongside Na+ ions.
Describe three forms of endocytosis
Phagocytosis- Carried out primarily by macrophages and neutrophils, foreign particle binds with the membrane receptor protein. Pseudopods extend and form a vesicle around it (phagosome); phagosome binds with lysosome and foreign particle degraded.
Pinocytosis- same as phagocytosis but not pseudopod
Receptor mediated endocytosis. Substance binds to receptor protein in specific clathrin coated region. Cathrin comes off and vesicle binds with endosome. Ligands digested by lysosomal enzymes or transported across cell.
Exocytosis
Substances exit the cell through fusion of their carrier vesicles with the cell membrane
Process of glucose absorption
1) Na+K+ATPase located in basolateral membrane creates electrochemical gradient
2) Na+ glucose cotransporter moves glucose from the lumen into the cell via secondary active transport
3) glucose moves out of the cell into the blood via passive facilitated diffusion through the GLUT transport protein
4) movement of ions and glucose across the cell induces H2O and Cl- movement across the paracellular pathway into the blood.
5) Na+ exits cell via the Na+K+ ATPase pump
What is the maximum transport rate of glucose
375 mg/min
Steps of chloride secretion
1) Na+K+ATPase located in basolateral membrane creates electrochemical gradient
2) NaKCl simperer uses energy of Na gradient to move Cl into the cell actively accumulating it above its concentration gradient.
3) Cl- leaves the cell in apical membrane through facilitated passive diffusion via the CFTR gated channel
4) Na exits via NaK ATPase pump and K exits through K channel
5) Transport of Cl across the epithelium induces paracellular H2O and Na fluxes
Describe 2 steps of CFTR channel gating
1) phosphorylation of the regulatory domain
2) Results in binding of ATP to the nucleotide binding site channel opened.
3) hydrolysis of ATP is required for the closing of the CFTR channel
Describe pathology in sweat secretion in CF patients
In sweat gland there is primary secretion of isotonic solution; there is then secondary reabsorption to create a hypotonic solution. The reabsorption is affected in CF as CFTR channels not working
What is the fluidity of the membrane determined by?
The amount of cholesterol and the number of double bonds in the fatty acid tails (each puts a kink in the tail which increase fluidity by preventing lipid molecules from packing too tightly).
Relating to intra and extracellular ion concentrations which ion wants to move into the cell
Na+
Describe the three kinds of endocytosis
1) Phagocytosis carried out mainly by phagocytes uses pseudopods
2) Pinocytosis cell drinking a vesicle forms and substance ingested
3) Receptor mediated endocytosis. For specific substances substance binds to receptor protein in clathrin coated region, vesicle forms and becomes uncoated and binds with endosome
