AA& PROTIENS

Question 1

What distinguishes proteins from carbohydrates and fats?

Answer 1

Presence of nitrogen (~16% of peptide chain)

Question 2

What bond links amino acids together?

Answer 2

Peptide bond (covalent)

Question 3

Define dipeptide, tripeptide, polypeptide

Answer 3

2 AA = dipeptide; 3 AA = tripeptide; many AA = polypeptide

Question 4

Typical length of serum proteins

Answer 4

~100–150 amino acids

Question 5

Primary protein structure

Answer 5

Amino acid sequence linked by covalent bonds

Question 6

Secondary protein structure

Answer 6

Winding of polypeptide chain stabilized by hydrogen bonds

Question 7

Tertiary protein structure

Answer 7

3D folding stabilized by disulfide bonds, H-bonds, electrostatic and hydrophobic interactions

Question 8

Quaternary protein structure

Answer 8

Association of ≥2 polypeptide chains (e.g., hemoglobin)

Question 9

Primary site of plasma protein synthesis

Answer 9

Liver (hepatocytes)

Question 10

Two protein compartments

Answer 10

Intravascular and extravascular

Question 11

Define nitrogen balance

Answer 11

Balance between protein anabolism and catabolism

Question 12

Negative nitrogen balance occurs when

Answer 12

Catabolism > anabolism (burns, fever, starvation)

Question 13

Positive nitrogen balance occurs when

Answer 13

Anabolism > catabolism (growth, pregnancy, recovery)

Question 14

Enzyme deficiency in PKU

Answer 14

Phenylalanine hydroxylase

Question 15

Accumulated substance in PKU

Answer 15

Phenylalanine → phenylpyruvic acid

Question 16

Classic urine odor in PKU

Answer 16

Musty odor

Question 17

PKU newborn screening test

Answer 17

Guthrie bacterial inhibition assay

Question 18

MSUD enzyme defect

Answer 18

Keto acid decarboxylase deficiency

Question 19

Amino acids affected in MSUD

Answer 19

Leucine, isoleucine, valine

Question 20

MSUD hallmark clinical sign

Answer 20

Maple syrup/burnt sugar odor

Question 21

Enzyme deficient in homocystinuria

Answer 21

Cystathionine-β-synthase

Question 22

Elevated amino acids in homocystinuria

Answer 22

Homocysteine and methionine

Question 23

Major complications of homocystinuria

Answer 23

Thrombosis, osteoporosis, lens dislocation

Question 24

What reaction detects free amino acids?

Answer 24

Ninhydrin reaction (purple color)

Question 25

Principle of the ninhydrin reaction

Answer 25

Free α-amino groups produce purple color proportional to concentration

Question 26

Gold standard total protein method

Answer 26

Kjeldahl method

Question 27

Biuret method principle

Answer 27

Cu²⁺ binds peptide bonds → violet color (540 nm)

Question 28

Advantage of dye-binding methods

Answer 28

High sensitivity, easy to perform

Question 29

Refractometry measures protein by

Answer 29

Change in refractive index

Question 30

Major function of albumin

Answer 30

Maintains colloid osmotic pressure

Question 31

Transport substances bound by albumin

Answer 31

Bilirubin, drugs, fatty acids, minerals

Question 32

Albumin decreases in

Answer 32

Liver disease, malnutrition, muscle disorders

Question 33

Albumin increases in

Answer 33

Dehydration

Question 34

Prealbumin clinical significance

Answer 34

Sensitive marker of protein nutrition

Question 35

Alpha-1 antitrypsin function

Answer 35

Inhibits trypsin; acute phase protein

Question 36

Alpha-1 fetoprotein significance

Answer 36

Tumor marker for liver and germ cell cancer

Question 37

Haptoglobin function

Answer 37

Binds free hemoglobin

Question 38

Ceruloplasmin function

Answer 38

Copper transport; oxidation-reduction reactions

Question 39

Disease associated with low ceruloplasmin

Answer 39

Wilson’s disease

Question 40

Transferrin function

Answer 40

Iron transport protein

Question 41

Transferrin increases in

Answer 41

Iron deficiency

Question 42

C-reactive protein significance

Answer 42

Strong acute-phase inflammatory marker

Question 43

pH used in serum protein electrophoresis

Answer 43

pH 8.6

Question 44

Protein that migrates farthest toward anode

Answer 44

Albumin

Question 45

Order of protein migration

Answer 45

Albumin → α1 → α2 → β → γ

Question 46

Formula for globulin

Answer 46

Total protein − albumin

Question 47

Decreased A/G ratio suggests

Answer 47

Liver disease with ↑ gamma globulins

Question 48

A/G ratio formula

Answer 48

Albumin ÷ globulin