MLT GlobeChemistry: Proteins & electrophoresis – page 3
125 Chemistry MCQs on Proteins & electrophoresis with answers and explanations.
Which proteins make up most of the alpha-2 globulin band on serum protein electrophoresis?
Haptoglobin and alpha-2-macroglobulin (with ceruloplasmin) form the alpha-2 band. Transferrin and C3 are in the beta region; alpha-1 antitrypsin dominates alpha-1.
In intravascular hemolysis, serum haptoglobin is usually:
Haptoglobin binds free hemoglobin and the complex is quickly cleared by macrophages (CD163), so levels fall. Haptoglobin does rise in inflammation, which can mask mild hemolysis.
In multiple myeloma, the 'CRAB' features stand for hypercalcemia, renal insufficiency, anemia and:
CRAB = Calcium raised, Renal failure, Anemia and Bone (lytic) lesions. These end-organ features separate active myeloma from MGUS and smoldering myeloma.
A patient with severe vomiting has total protein 8.6 g/dL (86 g/L) and albumin 5.4 g/dL (54 g/L); both return to normal after IV fluids. The cause of the high values was:
Loss of plasma water concentrates all proteins, so total protein and albumin rise together and correct with rehydration. True hyperalbuminemia from disease almost never occurs.
Specific serum proteins such as IgG, IgA, IgM, C3 and C4 are most commonly measured in routine laboratories by:
Antibody–antigen complexes scatter light (nephelometry) or reduce transmitted light (turbidimetry) in proportion to the protein concentration. Electrophoresis cannot measure individual proteins specifically.
Which is the most abundant protein in normal human plasma?
Albumin makes up roughly 55–60% of total plasma protein, more than any other single protein.
Routine serum protein electrophoresis on agarose separates proteins into how many main fractions?
The five classic fractions are albumin, alpha-1, alpha-2, beta and gamma globulins.
Which protein is present in plasma but absent from serum?
Fibrinogen is converted to fibrin and removed in the clot, so serum lacks it. The other proteins remain in serum.
On serum protein electrophoresis, most immunoglobulins migrate in which fraction?
Immunoglobulins, especially IgG, make up most of the gamma region, which moves least toward the anode at pH 8.6.
C-reactive protein is best described as:
CRP is a positive acute-phase protein synthesised by hepatocytes, mainly in response to IL-6. It rises quickly in infection and inflammation.
The approximate reference interval for total serum protein in adults is:
Adult total serum protein is roughly 6–8 g/dL (60–80 g/L), with exact limits varying slightly between laboratories. Albumin alone is about 3.5–5.0 g/dL.
Bence Jones protein in urine consists of:
Bence Jones proteins are free monoclonal kappa or lambda light chains, small enough to pass the glomerulus; they are typical of multiple myeloma.
Which amino acid most strongly favours formation of an α-helix?
Alanine's small, uncharged side chain fits the helix well. Proline's rigid ring breaks helices, and glycine is too flexible.
Why can atoms around a peptide bond not rotate freely?
Electron delocalisation between the carbonyl and amide nitrogen makes the peptide unit planar and rigid. Urea disrupts non-covalent bonds, not peptide bonds.
Which statement about protein secondary structure is correct?
Proline's fixed angle and glycine's flexibility suit tight β-turns. β-Sheets can be parallel or antiparallel, and α-helices are stabilised by backbone hydrogen bonds within one chain.
The carbon skeleton of glutamate, and through it proline and arginine, comes from which TCA-cycle intermediate?
Reductive amination or transamination of α-ketoglutarate gives glutamate, the parent of glutamine, proline and arginine. Oxaloacetate gives aspartate.
Which statement about protein separation by column chromatography is correct?
More column length gives more interactions with the stationary phase and better separation. The packed matrix is stationary; in gel filtration large proteins are excluded from pores and elute first.
Most amino acids give a purple colour with ninhydrin. Which amino acid gives a yellow colour instead?
Proline has a secondary (imino) amine, so it forms a yellow product rather than Ruhemann's purple. Glycine, lysine and arginine have primary α-amino groups and give purple.
When a protein is hydrolysed in 6 mol/L HCl, glutamine and asparagine are:
Acid hydrolysis removes the side-chain amide nitrogen as ammonium, so amino acid analysis reports Glx and Asx. The amino acids are not decarboxylated or hydroxylated.
Which amino acid residue most strongly disrupts an α-helix when it occurs within the chain?
Proline's ring locks the backbone and its nitrogen has no hydrogen for helix hydrogen bonding, so it acts as a helix breaker. Alanine, leucine and methionine favour helix formation.