lecture 1 part b

Question 1

what mucin genes are secreted in the stomach?

Answer 1

• 5a,c and 6

Question 2

what are mucins secreted in small intestine for?

Answer 2

• absorption

Question 3

what are mucins secreted in stomach for?

Answer 3

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

Question 4

what does the N terminal allow?

Answer 4

• globular
• polymerisation
• form large complexes

Question 5

what are VNTRs?

Answer 5

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

Question 6

what is the structure of serine and threonine?

Answer 6

• have OH group
• can attach carbohydrates
• highly glycosylated

Question 7

what are regions between molecules susceptible to?

Answer 7

• proteolytic enzymes

Question 8

why does the stomach need secretion of acid?

Answer 8

• to balance with the erosion

Question 9

why do the mucins need to be polymerised?

Answer 9

• to form gel
• can then be degraded by pepsin

Question 10

what is pepsin?

Answer 10

• stomach enzyme
• used for food digestion

Question 11

where should pepsin have no activity?

Answer 11

• at surface
• not correct pH

Question 12

which pepsin is the most negatively charged?

Answer 12

• pepsin 1

Question 13

which pepsin is the least negatively charged?

Answer 13

• pepsin 5

Question 14

what can pepsin isoenzymes be separated by?

Answer 14

• agar gel electrophoresis at ph5
• anion exchange

Question 15

what is the mechanism of activation of pepsin?

Answer 15

• 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

Question 16

what happens at a pH above 5?

Answer 16

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

Question 17

what are the positively charged amino acids?

Answer 17

• histone
• lysine
• arginine

Question 18

what are the negatively charged amino acids?

Answer 18

• aspartate
• glutamate

Question 19

what happens at pH below 5?

Answer 19

• 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

Question 20

what is the structure of pepsin?

Answer 20

• 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

Question 21

why cant pepsin be made from pepsinogen?

Answer 21

• part of N terminal in pepsin is missing

Question 22

how stable is pepsin?

Answer 22

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

Question 23

what is the role for pepsinogen in antimicrobial peptides?

Answer 23

• activation peptide is cleaved off in 2 cleavages

Question 24

how long is human pepsin?

Answer 24

• 47 amino acids long

Question 25

what happened when pepsin peptides were tested against bacteria?

Answer 25

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

Question 26

what was the 1-25 peptide effective in?

Answer 26

• preventing biofilm formation of p.aerunginosa and s.aureus

Question 27

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

Answer 27

• pH 3.5
• incubated