Week 1.4 - Protein, lipid and vitamin digestion and absorption

Question 1

What are the 2 types of vitamins?

Answer 1

fat soluble and water soluble

Question 2

What is the structural makeup of a protein?

Answer 2

amino acids joined via condensation reactions by peptide bonds

Question 3

What may a post-translational transformation lead to?

Answer 3

lipoproteins or glycoproteins

Question 4

What is a peptide?

Answer 4

small amino acid chain - 3-10

Question 5

What breaks down proteins and what are the kinds?

Answer 5

peptidases.
exopeptidases break from one side - aminopeptidases or carboxypeptidases.
endopeptidases break chain from middle

Question 6

How do free amino acids transport through epithelium?

Answer 6

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

Question 7

What is the most common form that protein is found in a cell?

Answer 7

as dipeptides. 70% of the time. only 30% of the time they are found as monopeptides

Question 8

How do dipeptides exit the cell?

Answer 8

using PepT1 transporter, co-transporting di/tri peptides with protons, H+.

Question 9

What is the mechanism of the PepT1 transporter?

Answer 9

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

Question 10

What creates the acid micro climate?

Answer 10

NHE3 sodium proton exchanger 3. pumps H+ out and Na+ in. makes lumen next to microvilli acidic.

Question 11

What form are ingested fats in?

Answer 11

triacylglycerides

Question 12

Where does all fat digestion occur? By which enzyme?

Answer 12

in the small intestine by pancreatic lipase

Question 13

What is the speed of digestion of fats and why?

Answer 13

very slow because lipase is water soluble but triacylglycerols aren’t

Question 14

How does a large fat droplet convert into a smaller one?

Answer 14

mechanical digestion in GI wall and then bile salts emulsify them

Question 15

Why are bile salts able to act on fats?

Answer 15

they are amphipathic - attach via hydrophobic end. forms 1mm diameter droplets

Question 16

What does the emulsion of fat by bile salts form? why is this neccasary?

Answer 16

micelles. increases SA that lipase can work on

Question 17

What are the constituents of micelles?

Answer 17

monoglycerides and fatty acids, bile salts and phospholipids (present in bile)

Question 18

What size are micelles?

Answer 18

4-7μm
- still cant pass through epithelium alone.

Question 19

What is the journey of a micelle after is it formed?

Answer 19

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.

Question 20

What happens once a micelle enters the epithelial cell?

Answer 20

fatty acids and monoglycerol is free. goes to smooth ER, which reforms them back into TAG. Then golgi encloses it with membrane. forms chylomicron

Question 21

What happens once a chylomicron is formed?

Answer 21

released by exocytosis. enters lacteal - part of epithelial cell and lymphatic system.

Question 22

Why do chylomicrons transport in lacteal?

Answer 22

because they’re too large to enter blood capillary barrier

Question 23

what are some fat soluble vitamins?

Answer 23

ADEK

Question 24

what are some water soluble vitamins?

Answer 24

vitamin b, c and folic acid

Question 25

How is vitamin b12 absorbed?

Answer 25

must bind with intrinsic factor, which is synthesised in the stomach

Question 26

how do we treat a b12 deficiency?

Answer 26

oral if due to lack of intake.

intramuscular injection if due to lack of intrinsic factor

Question 27

What deficiency does lack of b12 lead to?

Answer 27

pernicious anaemia. has affect up to 3 years later. this is because we have a b12 storage in our liver

Question 28

How much iron do we absorb?

Answer 28

10% of daily intake. rest excreted with faeces

Question 29

How does iron transport across the brush border? What does it bind to?

Answer 29

DMT1 (di-metallic transporter 1 - H+ and iron) in duodenal enterocytes. binds to ferritin

Question 30

How does unbound iron transport in blood?

Answer 30

binds to transferrin

Question 31

How is ferritin expression regulated?

Answer 31

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

Question 32

Where is haem found and how can it be used?

Answer 32

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

Question 33

What state does the micelle have to be to enter the epithelium and why?

Answer 33

must be unionised which is achieved thanks to the acid microclimate. only unionised molecules can be absorped.