Week 1.4 - Protein, lipid and vitamin digestion and absorption Flashcards
What are the 2 types of vitamins?
fat soluble and water soluble
What is the structural makeup of a protein?
amino acids joined via condensation reactions by peptide bonds
What may a post-translational transformation lead to?
lipoproteins or glycoproteins
What is a peptide?
small amino acid chain - 3-10
What breaks down proteins and what are the kinds?
peptidases.
exopeptidases break from one side - aminopeptidases or carboxypeptidases.
endopeptidases break chain from middle
How do free amino acids transport through epithelium?
NaK pump.
SAAT1 sodium amino acid transporter 1 co-transports amino acid and sodium.
amino acid then exits passive transportation via baso-lateral membrane to blood
What is the most common form that protein is found in a cell?
as dipeptides. 70% of the time. only 30% of the time they are found as monopeptides
How do dipeptides exit the cell?
using PepT1 transporter, co-transporting di/tri peptides with protons, H+.
What is the mechanism of the PepT1 transporter?
in intestine, pH is over 7. next to border it is about 6. this is an acid micro-climate. this allows PepT1 to work as it relies on proton motive force - 1 proton in 1 dipeptide in
What creates the acid micro climate?
NHE3 sodium proton exchanger 3. pumps H+ out and Na+ in. makes lumen next to microvilli acidic.
What form are ingested fats in?
triacylglycerides
Where does all fat digestion occur? By which enzyme?
in the small intestine by pancreatic lipase
What is the speed of digestion of fats and why?
very slow because lipase is water soluble but triacylglycerols aren’t
How does a large fat droplet convert into a smaller one?
mechanical digestion in GI wall and then bile salts emulsify them
Why are bile salts able to act on fats?
they are amphipathic - attach via hydrophobic end. forms 1mm diameter droplets
What does the emulsion of fat by bile salts form? why is this neccasary?
micelles. increases SA that lipase can work on
What are the constituents of micelles?
monoglycerides and fatty acids, bile salts and phospholipids (present in bile)
What size are micelles?
4-7μm
- still cant pass through epithelium alone.
What is the journey of a micelle after is it formed?
swim through lumen, before reaching brush border. acid micro climate allows micelle to be coated in protons so it becomes uncharged and can be absorbed.
What happens once a micelle enters the epithelial cell?
fatty acids and monoglycerol is free. goes to smooth ER, which reforms them back into TAG. Then golgi encloses it with membrane. forms chylomicron
What happens once a chylomicron is formed?
released by exocytosis. enters lacteal - part of epithelial cell and lymphatic system.
Why do chylomicrons transport in lacteal?
because they’re too large to enter blood capillary barrier
what are some fat soluble vitamins?
ADEK
what are some water soluble vitamins?
vitamin b, c and folic acid
How is vitamin b12 absorbed?
must bind with intrinsic factor, which is synthesised in the stomach
how do we treat a b12 deficiency?
oral if due to lack of intake.
intramuscular injection if due to lack of intrinsic factor
What deficiency does lack of b12 lead to?
pernicious anaemia. has affect up to 3 years later. this is because we have a b12 storage in our liver
How much iron do we absorb?
10% of daily intake. rest excreted with faeces
How does iron transport across the brush border? What does it bind to?
DMT1 (di-metallic transporter 1 - H+ and iron) in duodenal enterocytes. binds to ferritin
How does unbound iron transport in blood?
binds to transferrin
How is ferritin expression regulated?
if lots of blood, hyperaemia, more iron present so more expression, so more iron is stored in enterocytes bound to ferritin.
in anaemia, less iron leads to less ferritin, so iron can be released into blood and bind to transferrin
Where is haem found and how can it be used?
found in meat. complex iron form. can directly absorb into enterocyte by endocytosis. then haem oxygenate releases iron and it goes on to bind to ferritin, or leave in blood and bind to transferrin
What state does the micelle have to be to enter the epithelium and why?
must be unionised which is achieved thanks to the acid microclimate. only unionised molecules can be absorped.
