9 Ions, Vitamins and Minerals Flashcards
Q: mM µM nM pM fM
A: Millimolar (mM) 10-3 Micromolar (µM) 10-6 Nanomolar (nM) 10-9 Picomolar (pM) 10-12 Femtomolar (fM) 10-15
Q: What is diffusion? How does speed vary? (2) How have multicellular organisms evolved? to?
A: The process whereby atoms or molecules intermingle because of their random thermal motion
Diffusion occurs rapidly over microscopic distances, but slowly over macroscopic distances.
Multicellular organisms evolve circulatory systems to bring individual cells within diffusion range
Q: What does the cell membrane act as in terms of diffusion? allowing? Which molecules can cross easily?
A: The cell membrane acts as a diffusion barrier, enabling cells to maintain cytoplasmic concentrations of substances different from their extracellular concentrations
Lipid soluble (non-polar) molecules can cross more easily than water soluble (polar) molecules
Q: What is osmosis?
A: water movement from hypotonic -> isotonic -> hypertonic ACROSS semipermeable membrane
Q: How does the epithelium of the gut form a continuous layer? What else does this structure do? What determines the molecules that can cross the epithelium to enter the bloodstream?
A: tight junctions form between enterocytes- different proteins that connect cells together
allows differentiation between apical and basolateral membrane as proteins can’t move freely between the regions
depends on ‘tightness’- not consistent throughout the gut -> have varying leakiness/selectivity on what can pass between cells
Q: What are the 2 ways molecules can cross the epithelium to enter the blood?
A: Paracellular Transport
through tight junctions and lateral intercellular spaces.
Transcellular Transport through the epithelial cells (absorbed at apical side of cell and exocytosed on other (basolateral))
Q: What are the 3 ways that solutes can cross cell membranes? What are the 2 types of protein involved? Speed comparison? Control comparison?
A: simple diffusion, facilitated transport or active transport. Two types of transport proteins involved.
1) Channel proteins form aqueous pores allowing specific solutes to pass across the membrane. 2) Carrier proteins bind to the solute and undergo a conformational change to transport it across the membrane. Channel proteins allow much faster transport than carrier proteins but channel proteins allow much less control - only allow things to move DOWN electrochemical gradient
Q: What are the 4 types of ion channel?
A: can be gated to some degree- can be open or closed
- voltage gated
- ligand-gated (extracellular ligand) eg H binding
- ligand-gated (intracellular ligand) - secondary intracellular signals eg cAMP or Ca2+
- mechanically gated eg pressure transducers and stretch receptors
Q: What are the 3 types of carrier mediated transport?
A: uniport- allows the movement of 1 molecule in 1 direction
coupled transport:
symport- allows the movement of 2 molecules in one direction
antiport=counter transport: allows movement of 2 molecules in opposite directions (often of molecules with same charge= prevent disturbance of electrochemical equilibrium)
Q: What are the 3 types of membrane transport in terms of energy? Describe.
A: Active transport requires energy:
- Primary active transport is linked directly to cellular metabolism (uses ATP to power the transport).
- Secondary active transport derives energy from the concentration gradient of another substance that is actively transported = currency is often Na+
Facilitated transport /facilitated diffusion:
-enhances the rate a substance can flow down its concentration gradient. This tends to equilibrate the substance across the membrane and does not require energy
Q: Give 2 examples of Primary active transporters.
A: Na+/K+ ATPase
H+/K+ ATPase (in stomach- H+ put into gastric fluid)
Give 3 examples of Secondary active transporters.
A: SGLT-1 co-transport (sodium/glucose)
HCO3-/Cl- counter transport (in pancreas)
Na+/H+ counter transport (in pancreas)
Q: Give 2 examples of Facilitated transport /facilitated diffusion transporters. we have already covered in the course.
A: GLUT-5, GLUT-2
Q: By which process are glucose and galactose absorbed by enterocyte? Via? When is this effective? why?
A: by secondary active transport (carrier protein and electrochemical gradient)
Carrier protein = SGLT-1 on apical membrane
SGLT1 can transport glucose uphill against its concentration gradient (so effective when glucose at levels in the lumen are below those in the enterocyte)
- energy is being inputted in form of Na+ coming down its electrochemical gradient
Q: By which process is fructose absorbed by enterocyte? Via? When is this effective? why?
A: Absorption of fructose is by facilitated diffusion
Carrier protein = GLUT-5 on apical membrane
Effective at relatively low concentrations of fructose in the lumen as tissue and plasma levels are low
Q: By which process does glucose exit an enterocyte? Via? How does glucose vary between plasma and tissue/enterocyte?
A: Exit of glucose at the basolateral membrane is by facilitated diffusion. Carrier protein = GLUT-2, a high-capacity, low-affinity facilitative transporter.
Glucose between plasma and tissue/enterocyte generally equilibrated.
