Biochemistry NBME Exam 2024 Well Revised and
Verified Answers Updated
Proteoglycans
Act as molecular sieves in ECM, CT, and cartilage
GAGs are the long polysacc chains attached to core protein
GAG is heavily hydrated and cushions (has "-" charge)
Degraded via lysosomal pathway (defect = MPS)
Glycolipids
A.K.A. sphingolipids
Made with ceramide lipid base
Serine + palmitoyl-CoA => sphingosine (+FFA) => ceramide
Carb part sticks out into ECM (same w/ glycoproteins)
Side chain pKa's
Asp - 3.9 Gln - 4.1 His - 6.0 Cys - 8.5 Tyr -10.5 Lys - 10.5 Arg - 12.5
Lipids
FAs are carboxylic acids classified from C opposite C=O
Prostaglandins from polyunsat FAs like arachadonic acid
Phosphocoline: 2 FFAs + P group on glycerol - a component of sphingomyelin
Proteins
Written N-terminus to C-terminus
Cationic proteins migrate towards cathode ( - charge)
A-helix: carbonyl of a.a. binds w/ N-H of a.a. 4 down chain
Supersecondary str (ex: zing fingers) seen in TFs
PEST: sequence at N-terminus that tags protein for rapid degradation after synthesis by
nonspecific proteases
Hemoglobin
,2 A + 2 B, each with a heme porphyrin ring binding to Fe, which subsequently binds to
O2
Hb curve shifts to right w/ dec pH and inc 2,3-BPG binding to Hb=> unloads O2 better to
tissues
Fetal Hb has no 2,3-BPG binding site => higher affinity for O2
Curve shifts to left when CO binds => harder to unload O2
Collagen
Gly-X-Y, where X usually pro and Y usually hydroxypro
Triple helix formed inside cell, then secreted out and forms fibril
Hydroxylation of pro/lys inside ER requires vit C + O2
Lysyl oxidase deaminates hydroxylysine and lysine to form reactive aldehyde groups,
which cross-link the fibers
OI
Type I collagen malformation
Blue sclera + weak bones
Huntington's
Glu repeats cause malformed and aggregation of protein
A1-antitrypsin deficiency
Causes cirrhosis & emphysema
Marfan's syndrome
From fibrillin defect, causing massive growth and heart defects
Ehler-Danlos
no lysyl hydroxylase in collagen formation
=> hyperextensible skin
Michaelis-Menton
V = (Vmax * [S]) / (Km + [S])
Competitive inhibitors
Vmax same, Km increases
Intersect at Y-intercept on Lineweaver-Burke plot
Noncompetitive inhibitors
, Vmax decreases, Km same
Intersect at X-intercept on Lineweaver-Burke plot
Irreversible inhibitors have same kinetics
Allosteric enzyme
2+ subunits, each with substrate-binding sites that exhibit cooperativity
Allosteric binding can facilitate or inhibit substrate binding
Hemophilia A
Factor VIII deficiency
Creatine kinase
Isozyme with MM, BB, and BM forms
BM makes up 25% of myocardium and indicator of MI
Skeletal m is 99% MM
Carb digestion
Salivary amylase breaks down a-1,4 bonds in starch => dextrin
Intestinal amylase breaks down a-1,4 bonds b/t glucose => oligosaccharides,
disaccharides, and trisaccharides
Enzymes at brush border cleave to mono (a-1,4 + a-1,6)
Pancreatitis
Elevated serum amylase and lactase
Autodigestion of lipids/proteins
Lipid digestion
Occurs in pancreas, where 95% of lipids absorbed
Requires bile and lipase, which breaks down TAG => 2-MAG + FFA => micelles
Micelles release contents into enterocytes, where TAG is reformed using acyl-CoA
synthetase
TAG contributes CM formation, which passes into lymph
Bile salts reabsorbed in terminal ileum
Protein digestion
Digestion begins in stomach via pepsin (activated w/ H+)
Trypsin in intestine activated by enteropeptidase and activates all other proteolytic
enzymes (endo- and exopeptidases)
Verified Answers Updated
Proteoglycans
Act as molecular sieves in ECM, CT, and cartilage
GAGs are the long polysacc chains attached to core protein
GAG is heavily hydrated and cushions (has "-" charge)
Degraded via lysosomal pathway (defect = MPS)
Glycolipids
A.K.A. sphingolipids
Made with ceramide lipid base
Serine + palmitoyl-CoA => sphingosine (+FFA) => ceramide
Carb part sticks out into ECM (same w/ glycoproteins)
Side chain pKa's
Asp - 3.9 Gln - 4.1 His - 6.0 Cys - 8.5 Tyr -10.5 Lys - 10.5 Arg - 12.5
Lipids
FAs are carboxylic acids classified from C opposite C=O
Prostaglandins from polyunsat FAs like arachadonic acid
Phosphocoline: 2 FFAs + P group on glycerol - a component of sphingomyelin
Proteins
Written N-terminus to C-terminus
Cationic proteins migrate towards cathode ( - charge)
A-helix: carbonyl of a.a. binds w/ N-H of a.a. 4 down chain
Supersecondary str (ex: zing fingers) seen in TFs
PEST: sequence at N-terminus that tags protein for rapid degradation after synthesis by
nonspecific proteases
Hemoglobin
,2 A + 2 B, each with a heme porphyrin ring binding to Fe, which subsequently binds to
O2
Hb curve shifts to right w/ dec pH and inc 2,3-BPG binding to Hb=> unloads O2 better to
tissues
Fetal Hb has no 2,3-BPG binding site => higher affinity for O2
Curve shifts to left when CO binds => harder to unload O2
Collagen
Gly-X-Y, where X usually pro and Y usually hydroxypro
Triple helix formed inside cell, then secreted out and forms fibril
Hydroxylation of pro/lys inside ER requires vit C + O2
Lysyl oxidase deaminates hydroxylysine and lysine to form reactive aldehyde groups,
which cross-link the fibers
OI
Type I collagen malformation
Blue sclera + weak bones
Huntington's
Glu repeats cause malformed and aggregation of protein
A1-antitrypsin deficiency
Causes cirrhosis & emphysema
Marfan's syndrome
From fibrillin defect, causing massive growth and heart defects
Ehler-Danlos
no lysyl hydroxylase in collagen formation
=> hyperextensible skin
Michaelis-Menton
V = (Vmax * [S]) / (Km + [S])
Competitive inhibitors
Vmax same, Km increases
Intersect at Y-intercept on Lineweaver-Burke plot
Noncompetitive inhibitors
, Vmax decreases, Km same
Intersect at X-intercept on Lineweaver-Burke plot
Irreversible inhibitors have same kinetics
Allosteric enzyme
2+ subunits, each with substrate-binding sites that exhibit cooperativity
Allosteric binding can facilitate or inhibit substrate binding
Hemophilia A
Factor VIII deficiency
Creatine kinase
Isozyme with MM, BB, and BM forms
BM makes up 25% of myocardium and indicator of MI
Skeletal m is 99% MM
Carb digestion
Salivary amylase breaks down a-1,4 bonds in starch => dextrin
Intestinal amylase breaks down a-1,4 bonds b/t glucose => oligosaccharides,
disaccharides, and trisaccharides
Enzymes at brush border cleave to mono (a-1,4 + a-1,6)
Pancreatitis
Elevated serum amylase and lactase
Autodigestion of lipids/proteins
Lipid digestion
Occurs in pancreas, where 95% of lipids absorbed
Requires bile and lipase, which breaks down TAG => 2-MAG + FFA => micelles
Micelles release contents into enterocytes, where TAG is reformed using acyl-CoA
synthetase
TAG contributes CM formation, which passes into lymph
Bile salts reabsorbed in terminal ileum
Protein digestion
Digestion begins in stomach via pepsin (activated w/ H+)
Trypsin in intestine activated by enteropeptidase and activates all other proteolytic
enzymes (endo- and exopeptidases)
