MLT GlobeChemistry: Proteins & electrophoresis – page 2
125 Chemistry MCQs on Proteins & electrophoresis with answers and explanations.
Glutelins, plant storage proteins such as glutenin, are found mainly in:
Glutelins and prolamins are the main storage proteins of wheat, rice and other cereals and form gluten. Milk is rich in caseins, eggs in albumins.
Adjacent strands of a β-pleated sheet are held together by:
Backbone hydrogen bonds link neighbouring strands, whether parallel or antiparallel. Disulfide bridges can cross-link chains but do not define the sheet; glycosidic bonds join sugars.
Ninhydrin produces a purple colour with release of CO2 when it reacts with:
Ninhydrin oxidatively deaminates and decarboxylates free α-amino acids, forming Ruhemann's purple. Peptide bonds are detected by the biuret reaction instead.
Which amino acid has no chiral carbon and is therefore optically inactive?
Glycine's side chain is a hydrogen atom, so its α-carbon carries two identical groups. Threonine has two chiral centres; serine and valine have one.
Which protein does NOT take part in cell–cell adhesion?
Cytochrome c is a mitochondrial electron carrier (also released in apoptosis). Cadherins, integrins and neural cell adhesion molecules mediate cell–cell or cell–matrix attachment.
Which amino acid gives pyruvate directly in a single transamination?
ALT transfers alanine's amino group to alpha-ketoglutarate, leaving pyruvate. This is the basis of the glucose–alanine cycle. Leucine and lysine are ketogenic.
In serum protein electrophoresis at pH 8.6, which fraction migrates farthest toward the anode?
At pH 8.6 serum proteins are negatively charged and move to the anode. Albumin has the most negative charge for its size and moves farthest; the order is albumin, alpha-1, alpha-2, beta, gamma.
A near-absent alpha-1 band on serum protein electrophoresis in a young adult with emphysema suggests deficiency of:
Alpha-1 antitrypsin makes up most of the alpha-1 band. Its deficiency leaves proteases unchecked in the lung (early emphysema) and can cause liver disease.
The biuret method for total serum protein is based on which reaction?
In biuret, Cu2+ in alkaline medium binds peptide bonds (at least two per molecule) to give a violet colour read near 540 nm. Nitrogen conversion to ammonium is the Kjeldahl method, not biuret.
A hand refractometer is used to estimate total protein in serum. The method measures:
Refractometry measures refractive index, which rises with the concentration of dissolved solids, mostly protein. Absorbance at 280 nm is a separate ultraviolet method.
A woman with systemic lupus erythematosus has a broad, diffuse increase across the entire gamma region on electrophoresis. This is best described as:
A wide, smooth gamma increase reflects many plasma-cell clones making different immunoglobulins, typical of chronic inflammation, autoimmune disease or chronic infection. A monoclonal protein gives a narrow, sharp band.
Immunofixation shows a sharp band in the IgA lane and a band at the same position in the kappa lane. The correct interpretation is:
A heavy-chain band and a light-chain band at the same mobility indicate one monoclonal immunoglobulin, here IgA kappa. A free light chain would show a band only in the kappa lane.
The upper reference limit for total protein excretion in urine of a healthy adult is about:
Healthy adults excrete less than about 150 mg of protein per day, much of it uromodulin and small amounts of albumin. Levels near 1500 mg/day are clearly pathologic.
Nephrotic-range proteinuria in an adult is generally defined as urine protein greater than:
Nephrotic syndrome features proteinuria above about 3.5 g/day (per 1.73 m²), with hypoalbuminemia, edema and hyperlipidemia. Lower amounts indicate proteinuria but not the nephrotic range.
The usual reference interval for total protein in lumbar cerebrospinal fluid of an adult is about:
Adult lumbar CSF protein is roughly 15–45 mg/dL, less than 1% of serum protein (6–8 g/dL). Neonates have higher normal values.
Which plasma protein decreases during the acute-phase response?
Transthyretin, albumin and transferrin are negative acute-phase proteins and fall during inflammation. CRP, fibrinogen and haptoglobin are positive acute-phase reactants.
A 19-year-old with liver disease and a neurological tremor has low serum ceruloplasmin. This most suggests:
Wilson disease (ATP7B defect) impairs copper incorporation into ceruloplasmin, so serum ceruloplasmin is usually low, with liver and neurological disease. Hemochromatosis is an iron disorder.
What is the main physiological function of albumin?
Albumin is the most abundant plasma protein and provides about 80% of plasma oncotic pressure, holding water in the vessels. It also transports bilirubin, fatty acids, calcium and drugs.
The primary structure of a protein is:
Primary structure is the linear amino acid sequence joined by peptide bonds. Helices and sheets are secondary, 3D folding is tertiary, and subunit arrangement is quaternary structure.
A peptide bond links:
A peptide (amide) bond forms between the α-carboxyl of one amino acid and the α-amino group of the next, releasing water. Linked cysteine sulfhydryls form disulfide bonds.