✨ USMLE STEP 1: BIOCHEMISTRY
CHAPTER 3 - ENDOCRINE SYSTEM
PILLAR 1 CORE NOTES
Core Instructions for Rankers: Master these high-yield board-style hormone
signaling pathways and feedback loops. Mapped directly to the physiological
vocabulary of elite molecular boards.
🎯 Section 1: Intracellular Hormone Signaling
Mechanisms
⚡ 1. The cAMP Secondary Messenger Cascade:
Hormone Targets: ACTH, LH, FSH, TSH, ADH (V2 Receptor), GHRH,
Glucagon, HCG, Calcitonin, and PTH .
➡️
Molecular Mechanism: Hormone binding activates Gs-protein stimulates
➡️ ➡️
Adenylyl Cyclase converts ATP to cAMP activates Protein Kinase A
➡️
(PKA) phosphorylates functional cellular proteins .
✨ USMLE STEP 1: BIOCHEMISTRY CHAPTER 3 - ENDOCRINE SYSTEM 1
, • ⚡ 2. The IP3 / DAG Gq-Protein Cascade:
Hormone Targets: GnRH, TRH, GHRH, Angiotensin II, ADH (V1 Receptor), and
Oxytocin .
➡️
Molecular Mechanism: Hormone binding activates Gq-protein stimulates
➡️
Phospholipase C (PLC) cleaves PIP2 into IP3 and DAG . IP3 induces
immediate calcium release from the endoplasmic reticulum, while DAG
activates Protein Kinase C (PKC) .
✨ USMLE STEP 1: BIOCHEMISTRY CHAPTER 3 - ENDOCRINE SYSTEM 2
,✨ USMLE STEP 1: BIOCHEMISTRY CHAPTER 3 - ENDOCRINE SYSTEM 3
, ⚡ 3. The Intracellular Receptor (Steroid/Thyroid) Pathway:
Hormone Targets: Progesterone, Estrogen, Testosterone, Cortisol,
Aldosterone, T3/T4, and Vitamin D .
Molecular Mechanism: Lipophilic hormones diffuse directly across the cell
➡️ ➡️
membrane bind to cytoplasmic or nuclear receptors transformation of
➡️
the receptor complex binds to specific Hormone Response Elements
(HRE) on DNA to directly alter transcription and protein synthesis .
🎯 Section 2: Tyrosine-Kinase and cGMP Receptor
Signaling Pathways
⚡ 1. The Receptor Tyrosine Kinase (RTK) Map-Kinase Cascade:
Hormone Targets: Insulin, IGF-1, FGF, PDGF, and EGF .
Molecular Mechanism: Binding induces receptor dimerization ➡️
➡️
autophosphorylation of intracellular Tyrosine residues recruits IRS-1➡️
triggers the downstream Ras-MAPK pathway to directly activate nuclear
transcription factors for cell growth and protein synthesis .
✨ USMLE STEP 1: BIOCHEMISTRY CHAPTER 3 - ENDOCRINE SYSTEM 4
CHAPTER 3 - ENDOCRINE SYSTEM
PILLAR 1 CORE NOTES
Core Instructions for Rankers: Master these high-yield board-style hormone
signaling pathways and feedback loops. Mapped directly to the physiological
vocabulary of elite molecular boards.
🎯 Section 1: Intracellular Hormone Signaling
Mechanisms
⚡ 1. The cAMP Secondary Messenger Cascade:
Hormone Targets: ACTH, LH, FSH, TSH, ADH (V2 Receptor), GHRH,
Glucagon, HCG, Calcitonin, and PTH .
➡️
Molecular Mechanism: Hormone binding activates Gs-protein stimulates
➡️ ➡️
Adenylyl Cyclase converts ATP to cAMP activates Protein Kinase A
➡️
(PKA) phosphorylates functional cellular proteins .
✨ USMLE STEP 1: BIOCHEMISTRY CHAPTER 3 - ENDOCRINE SYSTEM 1
, • ⚡ 2. The IP3 / DAG Gq-Protein Cascade:
Hormone Targets: GnRH, TRH, GHRH, Angiotensin II, ADH (V1 Receptor), and
Oxytocin .
➡️
Molecular Mechanism: Hormone binding activates Gq-protein stimulates
➡️
Phospholipase C (PLC) cleaves PIP2 into IP3 and DAG . IP3 induces
immediate calcium release from the endoplasmic reticulum, while DAG
activates Protein Kinase C (PKC) .
✨ USMLE STEP 1: BIOCHEMISTRY CHAPTER 3 - ENDOCRINE SYSTEM 2
,✨ USMLE STEP 1: BIOCHEMISTRY CHAPTER 3 - ENDOCRINE SYSTEM 3
, ⚡ 3. The Intracellular Receptor (Steroid/Thyroid) Pathway:
Hormone Targets: Progesterone, Estrogen, Testosterone, Cortisol,
Aldosterone, T3/T4, and Vitamin D .
Molecular Mechanism: Lipophilic hormones diffuse directly across the cell
➡️ ➡️
membrane bind to cytoplasmic or nuclear receptors transformation of
➡️
the receptor complex binds to specific Hormone Response Elements
(HRE) on DNA to directly alter transcription and protein synthesis .
🎯 Section 2: Tyrosine-Kinase and cGMP Receptor
Signaling Pathways
⚡ 1. The Receptor Tyrosine Kinase (RTK) Map-Kinase Cascade:
Hormone Targets: Insulin, IGF-1, FGF, PDGF, and EGF .
Molecular Mechanism: Binding induces receptor dimerization ➡️
➡️
autophosphorylation of intracellular Tyrosine residues recruits IRS-1➡️
triggers the downstream Ras-MAPK pathway to directly activate nuclear
transcription factors for cell growth and protein synthesis .
✨ USMLE STEP 1: BIOCHEMISTRY CHAPTER 3 - ENDOCRINE SYSTEM 4
