lecture 1 part b Flashcards
what mucin genes are secreted in the stomach?
- 5a,c and 6
what are mucins secreted in small intestine for?
- absorption
what are mucins secreted in stomach for?
- doesnt want absorption
- only absorbs aspirin (becomes uncharged in acid so can be absorbed)
what does the N terminal allow?
- globular
- polymerisation
- form large complexes
what are VNTRs?
- variable number tandem repeats
- sequence of a.acids that repeats multiple times
- contains serine, threonine and proline (STP region)
what is the structure of serine and threonine?
- have OH group
- can attach carbohydrates
- highly glycosylated
what are regions between molecules susceptible to?
- proteolytic enzymes
why does the stomach need secretion of acid?
- to balance with the erosion
why do the mucins need to be polymerised?
- to form gel
- can then be degraded by pepsin
what is pepsin?
- stomach enzyme
- used for food digestion
where should pepsin have no activity?
- at surface
- not correct pH
which pepsin is the most negatively charged?
- pepsin 1
which pepsin is the least negatively charged?
- pepsin 5
what can pepsin isoenzymes be separated by?
- agar gel electrophoresis at ph5
- anion exchange
what is the mechanism of activation of pepsin?
- lid over active site formed by N terminal of molecule
- 2 points of cleavage (16&17, 44&45)
- hydrophobic amino acids present at cleavage points
- ## pepsin cleaves between the 2 hydrophobic amino acids
what happens at a pH above 5?
- held up away from active site
- by salt bridges of charge charge interactions
what are the positively charged amino acids?
- histone
- lysine
- arginine
what are the negatively charged amino acids?
- aspartate
- glutamate
what happens at pH below 5?
- salt bridges no longer hold due to loss of charge of negative ions
- active site becomes active
- cleaves part of N terminal off
- forms propepsin
- interacts with other pro pepsin or pepsin to form active pepsin
what is the structure of pepsin?
- symmetrical
- N terminal lobe and C terminal lobe
-2 lobes and central Valle y(active site) - relies on Asp32 ad Asp215 for binding of COO- and HOOC
why cant pepsin be made from pepsinogen?
- part of N terminal in pepsin is missing
how stable is pepsin?
- active pepsin is in a metastable condition (pH 5)
- if pH increases becomes denatured and extended
- if pH then decreases its stable but misfolded
what is the role for pepsinogen in antimicrobial peptides?
- activation peptide is cleaved off in 2 cleavages
how long is human pepsin?
- 47 amino acids long
