lecture 1 part b Flashcards

1
Q

what mucin genes are secreted in the stomach?

A
  • 5a,c and 6
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2
Q

what are mucins secreted in small intestine for?

A
  • absorption
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3
Q

what are mucins secreted in stomach for?

A
  • doesnt want absorption
  • only absorbs aspirin (becomes uncharged in acid so can be absorbed)
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4
Q

what does the N terminal allow?

A
  • globular
  • polymerisation
  • form large complexes
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5
Q

what are VNTRs?

A
  • variable number tandem repeats
  • sequence of a.acids that repeats multiple times
  • contains serine, threonine and proline (STP region)
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6
Q

what is the structure of serine and threonine?

A
  • have OH group
  • can attach carbohydrates
  • highly glycosylated
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7
Q

what are regions between molecules susceptible to?

A
  • proteolytic enzymes
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8
Q

why does the stomach need secretion of acid?

A
  • to balance with the erosion
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9
Q

why do the mucins need to be polymerised?

A
  • to form gel
  • can then be degraded by pepsin
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10
Q

what is pepsin?

A
  • stomach enzyme
  • used for food digestion
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11
Q

where should pepsin have no activity?

A
  • at surface
  • not correct pH
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12
Q

which pepsin is the most negatively charged?

A
  • pepsin 1
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13
Q

which pepsin is the least negatively charged?

A
  • pepsin 5
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14
Q

what can pepsin isoenzymes be separated by?

A
  • agar gel electrophoresis at ph5
  • anion exchange
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15
Q

what is the mechanism of activation of pepsin?

A
  • 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
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16
Q

what happens at a pH above 5?

A
  • held up away from active site
  • by salt bridges of charge charge interactions
17
Q

what are the positively charged amino acids?

A
  • histone
  • lysine
  • arginine
18
Q

what are the negatively charged amino acids?

A
  • aspartate
  • glutamate
19
Q

what happens at pH below 5?

A
  • 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
20
Q

what is the structure of pepsin?

A
  • 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
21
Q

why cant pepsin be made from pepsinogen?

A
  • part of N terminal in pepsin is missing
22
Q

how stable is pepsin?

A
  • active pepsin is in a metastable condition (pH 5)
  • if pH increases becomes denatured and extended
  • if pH then decreases its stable but misfolded
23
Q

what is the role for pepsinogen in antimicrobial peptides?

A
  • activation peptide is cleaved off in 2 cleavages
24
Q

how long is human pepsin?

A
  • 47 amino acids long
25
Q

what happened when pepsin peptides were tested against bacteria?

A
  • full length peptide showed to be effective
  • shorter less effective but at higher concentrations
26
Q

what was the 1-25 peptide effective in?

A
  • preventing biofilm formation of p.aerunginosa and s.aureus
27
Q

what is the best conditions for bacterial killing with pepsin activation?

A
  • pH 3.5
  • incubated