Biochemistry NBME 2024 LATEST EXAM QUESTIOS AND ANSWERS
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Course
Biochemistry NBME
Institution
Biochemistry NBME
Biochemistry NBME 2024 LATEST
EXAM QUESTIOS AND ANSWERS
Translation - ANSWER mRNA codon read 5->3, so tRNA
anticodon is 3->5
20 aminoacyl-tRNA synthetases (1 per a.a.) bring a.a to tRNA,
using ATP to bind a.a. to the enzyme
Met-tRNA is sitting in P-site on small subunit when...
Biochemistry NBME 2024 LATEST
EXAM QUESTIOS AND ANSWERS
Translation - ANSWER ✔ mRNA codon read 5->3, so tRNA
anticodon is 3->5
20 aminoacyl-tRNA synthetases (1 per a.a.) bring a.a to tRNA,
using ATP to bind a.a. to the enzyme
Met-tRNA is sitting in P-site on small subunit when AUG codon
recognizes it, allowing large subunit to join
Next aminoacyl-tRNA comes into A site, peptide bond forms
(using peptidyl transferase, an ribozyme) as existing chain
transfers onto A site a.a., and then both complexes shift so new
chain in P site
EF-1 required for A site binding and EF-2 needed for shift
More than 1 ribosome can be attached to mRNA (polysome)
C-terminus a.a. translated first
Operon (bacteria) - ANSWER ✔ 1 polycistronic mRNA encodes
for all proteins of a pathway
Operator is region of DNA near promoter that determines whether
or not DNA will be transcribed
Co-repressor binds to repressor, activating => no transcription
Inducer binds to repressor, inactivating it => transcription
Lac operon induced in absence of glucose b/c cAMP high =>
cAMP-CAP can bind to TF and allow RNA pol to bind
Cancer - ANSWER ✔ Mutations in GFs (GH, PDGF, FGF), GFRs
(TK receptors), signal transducers (ras, abl, src), TFs, and cell
cycle regulators (CDK) can cause oncogene formation
Tumor-suppressor genes are opposite, where mutation reduces
their activity, causing cancer
,Ex: TGF-B (reduce CDK activity), NF-1/GAP (reduce ras activity),
Rb, p53 (induced when DNA is damaged to prevent cell from
entering S phase until DNA is fixed or cell apoptosis)
Apoptosis - ANSWER ✔ Caspaces activated by cytokines, TNF,
Fas ligand
p53 => stim of Bax gene => apoptosis
CytC escapes into cytosol from mit via Bax channel => apop
CytC normally kept inside mit by bcl-2
Mechanisms of oncogenesis - ANSWER ✔ Pt mutation: p53, ras
Insertional activation: myc oncogene translocated downstream of
constiutively active Ig promoter => Burkitt lymphoma
Chimeric protein activation: Philadelphia chromosome creative
from fusion of bcr and c-abl genes => superactive TKR
Gene amplification: HER2/neu
Carcinogens - ANSWER ✔ Initators: direct damage to
macromolecules, but not enough to form tumor by itself
Promoters: stim growth of cells exposed to initiators
UV => thymidine dimers
X-Ray/Gamma => radical formation
DNA Viruses: HPV destroys p53, EBV stim bcl-2 to help protect
oncogenic cells against apoptosis
Tumor growth - ANSWER ✔ Tumors cause angiogenesis
(VEGF) in hypoxic conditions to supply themselves w/ nutrients
Use MMPs and cys/ser proteases to break basement membrane
and invade bloodstream
Proteoglycans - ANSWER ✔ 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 - ANSWER ✔ 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 - ANSWER ✔ Asp - 3.9 Gln - 4.1 His - 6.0 Cys -
8.5 Tyr -10.5 Lys - 10.5 Arg - 12.5
Lipids - ANSWER ✔ 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 - ANSWER ✔ 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 - ANSWER ✔ 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 - ANSWER ✔ Gly-X-Y, where X usually pro and Y
usually hydroxypro
Triple helix formed inside cell, then secreted out and forms fibril
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