Proteins 2

Question 1

What important non-protein biomolecules do amino acids form?

Answer 1

Hormones, coenzymes, porphyrins

Question 2

What are porphyrins, and give an example?

Answer 2

Water-soluble, nitrogenous pigments with a cylindrical structure - haem.

Question 3

Describe the process by which haem forms bilirubin.

Answer 3

Heme -> Biliverdin (using heme oxygenase, losing CO and Fe3+)

Biliverdin -> Bilirubin (using biliverdin reductase, and NADPH+ + H+ -> NADP+)

Question 4

Describe the transport of bilirubin through the body.

Answer 4

Bilirubin in blood -> bilirubin diglucuronide in liver (glucuronyl-bilirubin transferase)

-> bilirubin in bile (transport to intestine)

-> Urobilinogen -> Stercobilin
OR -> Urobilinogen -> (transport to kidney) Urobilin

Question 5

What are the three protein testing techniques?

Answer 5

Colorimetric assays, SDS-PAGE and Western blotting, Enzyme-linked immunosorbent assay (ELISA)

Question 6

Describe a colorimetric assay and give an example.

Answer 6

Semi-quantitative measure of protein presence or activity - colour change visually assessed. E.g. bromophenol blue.

Question 7

What does SDS-PAGE stand for?

Answer 7

Sodium dodecyl sulphate polyacrylamide gel electrophoresis.

Question 8

Describe the process of a SDS-PAGE test.

Answer 8

Separates proteins according to size. Electrical current applied, proteins are negatively-charged so move along gel. Can be transferred to thin membrane and detected using secondary antibodies.

Question 9

What is the difference between immunohistochemistry and immunocytochemistry?

Answer 9

Immunohistochemistry = uses enzymatic colour-changing reaction to detect proteins in fixed tissue samples.

Immunocytochemistry = uses enzymatic colour-changing reaction to detect proteins in cells.

Question 10

Describe the urea cycle.

Answer 10

Ammonium ion + bicarbonate ion -> carbamoyl phosphate

Carbamoyl phosphate + ornithine -> citrulline

Citrulline + aspartate -> argininosuccinate

Argininosuccinate - fumarate -> arginine

Arginine -> urea

Question 11

What equation relates rate of product formation with enzyme affinity?

Answer 11

Rate of substrate formation (change in conc. / time) = Max rate of formation at saturating substrate conc. / substrate conc. at 0.5 max rate + substrate conc.