Explain question number 26 to 34 in full detail with the exam-oriented MBBS with flow chart and diagram only.

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Here is the complete, exam-oriented MBBS answer for Questions 26-34 with flowcharts and diagrams:

MBBS BIOCHEMISTRY - Questions 26 to 34

Complete Exam-Oriented Guide with Flowcharts & Diagrams

Q26. Oxidative Phosphorylation (OxPhos)

Definition

Oxidative phosphorylation is the process by which energy released during oxidation of NADH and FADH2 by the electron transport chain (ETC) is used to synthesize ATP from ADP + Pi via the enzyme ATP synthase.

FLOWCHART: Mechanism of Oxidative Phosphorylation

NADH / FADH2  (from TCA cycle, fatty acid oxidation, glycolysis)
        |
        ▼
┌─────────────────────────────────────────────────────────────┐
│              ELECTRON TRANSPORT CHAIN (ETC)                  │
│  (Inner Mitochondrial Membrane)                              │
│                                                              │
│  NADH ──► Complex I ──► CoQ ──► Complex III ──► Cyt c ──►  │
│                                                   Complex IV │
│  FADH2 ─────► Complex II ──────►CoQ                   ──►  │
│                                               O2 → H2O      │
└─────────────────────────────────────────────────────────────┘
        |
        ▼
  Protons pumped from MATRIX → INTERMEMBRANE SPACE
  (at Complexes I, III, IV)
        |
        ▼
  Electrochemical Gradient (Proton Motive Force = Δp)
        |
        ▼
  Protons flow BACK into matrix through ATP SYNTHASE (Complex V)
        |
        ▼
  ADP + Pi ──────────────────► ATP

DIAGRAM: The 5 Complexes

┌────────────────────────────────────────────────────────────────────┐
│  INTERMEMBRANE SPACE  ←H+  ←H+        ←H+            H+ →        │
│  ─────────────────────────────────────────────────────────────────│
│  Complex I   Complex II   Complex III   Complex IV   Complex V     │
│  NADH-CoQ    Succinate-   CoQ-Cyt c    Cyt c-O2     ATP           │
│  Oxidored.   CoQ Oxidored oxidored.    Oxidase(CcO)  Synthase      │
│  [NADH DH]   [SDH]       [Cyt bc1]    [CcO]         [F0F1-ATPase] │
│  ─────────────────────────────────────────────────────────────────│
│  MATRIX       H+→         H+→          H+→            ← H+        │
│  (NADH)      (FADH2)                              ADP+Pi → ATP     │
└────────────────────────────────────────────────────────────────────┘

Net ATP Yield:

1 NADH = 2.5 ATP
1 FADH2 = 1.5 ATP

Chemiosmotic Theory (Mitchell's Hypothesis)

Electron Flow
     |
     ▼
Proton pumping (H+) out of matrix
     |
     ▼
Electrochemical gradient (Proton Motive Force = ΔΨ + ΔpH)
     |
     ▼
H+ flows back in through ATP synthase pore (F0 subunit)
     |
     ▼
Conformational change in F1 subunit → ATP synthesis
     |
     ▼
ATP released into mitochondrial matrix

INHIBITORS OF OXIDATIVE PHOSPHORYLATION

Type	Example	Site of Action
ETC Inhibitors	Rotenone (insecticide)	Complex I
	Amytal (barbiturate)	Complex I
	TTFA	Complex II
	Antimycin A	Complex III
	Cyanide (CN-)	Complex IV
	Carbon Monoxide (CO)	Complex IV
	Azide (N3-)	Complex IV
ATP Synthase Inhibitors	Oligomycin	Complex V (F0)
Uncouplers	DNP (2,4-dinitrophenol)	Bypasses ATP synthase
	FCCP	Bypasses ATP synthase
	Thermogenin (UCP-1)	Brown adipose tissue

Flowchart: Uncoupling vs Inhibition

ETC Inhibitors              Uncouplers
      |                          |
      ▼                          ▼
Block electron flow       Allow proton re-entry
      |                   BYPASSING ATP synthase
      ▼                          |
↓ATP + ↓ O2 consumption    ▼
                      ↓ATP but ↑ O2 consumption
                      (energy released as HEAT)

INHERITED DISORDERS OF OXIDATIVE PHOSPHORYLATION (OXPHOS Diseases)

Key Concept: Mitochondrial DNA (mtDNA) is maternally inherited and encodes 13 subunits of ETC + ATP synthase

Flowchart: OXPHOS Diseases

Mutation in mtDNA or nuclear DNA
              |
              ▼
Defective ETC complex subunit
              |
              ▼
↓ ATP production + ↑ Reactive Oxygen Species (ROS)
              |
        ┌─────┴──────┐
        ▼             ▼
Muscle/Nerve      End-organ
Cell death        damage

Disease	Defect	Features
MELAS	Complex I/III; ND1/tRNA mutation	Mitochondrial Encephalomyopathy, Lactic Acidosis, Stroke-like episodes
MERRF	tRNA(Lys) mutation	Myoclonic Epilepsy with Ragged Red Fibers
Leber's Optic Neuropathy (LHON)	Complex I subunit	Sudden blindness in young males
Leigh Syndrome	Complex I/IV	Subacute necrotizing encephalopathy in infants
Kearns-Sayre Syndrome	Large mtDNA deletion	Ophthalmoplegia + Retinal degeneration

Ragged Red Fibers on Gomori Trichrome stain = pathognomonic of mitochondrial myopathies

Q27. Free Radicals and Oxidative Stress

Definition

A free radical is any atom or molecule that has one or more unpaired electrons in its outer orbital, making it highly reactive.

FLOWCHART: Generation of Free Radicals

O2 (molecular oxygen)
     |  (1 electron reduction)
     ▼
Superoxide radical (O2•-)  ← Mitochondria, NADPH oxidase, XO
     |  (SOD + H+)
     ▼
Hydrogen peroxide (H2O2)   ← Less reactive
     |  (Fenton reaction: Fe2+ or Cu+)
     ▼
Hydroxyl radical (•OH)     ← MOST REACTIVE / MOST DAMAGING
     |
     ▼
Lipid peroxidation / DNA damage / Protein oxidation

Important Free Radicals

Radical	Symbol	Source
Superoxide	O2•-	ETC leak, NADPH oxidase
Hydroxyl	•OH	Fenton/Haber-Weiss
Nitric oxide	NO•	NOS enzyme
Peroxynitrite	ONOO-	NO• + O2•-
Lipid peroxy radical	LOO•	Lipid peroxidation chain

OXIDATIVE STRESS IN PATHOGENESIS OF DISEASES

                  ┌──── Excess ROS ────┐
                  |                    |
                  ▼                    ▼
         DNA Damage              Protein Oxidation
              |                        |
              ▼                        ▼
         Mutations               Enzyme inactivation
              |                        |
              ▼                        ▼
           Cancer                  Cell death
                  |
                  ▼
         Lipid Peroxidation
              |
              ▼
       Membrane damage

Disease	Mechanism of ROS involvement
Atherosclerosis	LDL oxidized by ROS → foam cell formation
Diabetes mellitus	Hyperglycemia → glycation → ROS → microvascular damage
Cancer	ROS → DNA mutation → oncogene activation
Alzheimer's disease	Amyloid β generates ROS → neuronal death
Parkinson's disease	Dopamine oxidation → •OH → substantia nigra damage
Ischemia-reperfusion	Xanthine oxidase → burst of O2•- on reperfusion
Aging	Cumulative mtDNA damage by ROS
Inflammation	PMNs produce O2•- via respiratory burst (NADPH oxidase)
Radiation injury	Ionizing radiation splits H2O → •OH

Q28. Antioxidants

Definition

Antioxidants are substances that prevent or reduce oxidative damage by scavenging, quenching, or preventing the formation of free radicals.

CLASSIFICATION OF ANTIOXIDANTS

                    ANTIOXIDANTS
                         |
           ┌─────────────┴────────────┐
           ▼                          ▼
     ENZYMATIC                   NON-ENZYMATIC
           |                          |
    ┌──────┴──────┐          ┌────────┴──────────┐
    ▼             ▼          ▼                    ▼
   SOD          CAT      ENDOGENOUS          EXOGENOUS
   GPx          TRX    (Glutathione,       (Vitamin C,
   GRx                  Uric acid,          Vitamin E,
                         Bilirubin,          Carotenoids,
                         Coenzyme Q)         Polyphenols)

DETAILED CLASSIFICATION TABLE

Category	Antioxidant	Mechanism
Enzymatic	Superoxide Dismutase (SOD)	2O2•- + 2H+ → H2O2 + O2
	Catalase (CAT)	2H2O2 → 2H2O + O2
	Glutathione Peroxidase (GPx)	H2O2 + 2GSH → GSSG + 2H2O
	Glutathione Reductase (GRx)	GSSG + NADPH → 2GSH + NADP+
Non-Enzymatic - Endogenous	Reduced Glutathione (GSH)	Tripeptide; regenerated by HMP shunt
	Uric acid	Scavenges •OH and HOCl
	Bilirubin	Lipid peroxidation scavenger
	Albumin	Binds copper ions
	Coenzyme Q (CoQ10)	Quenches free radicals in membranes
Non-Enzymatic - Exogenous	Vitamin C (Ascorbate)	Scavenges O2•-, •OH; regenerates Vit E
	Vitamin E (α-Tocopherol)	Lipid peroxyl radical scavenger
	Beta-Carotene (Vit A precursor)	Singlet oxygen quencher
	Selenium	Component of GPx
	Flavonoids/Polyphenols	Metal chelation, radical scavenging

GLUTATHIONE CYCLE (KEY EXAM DIAGRAM)

H2O2 + 2GSH ──── GPx ────► GSSG + 2H2O
                              |
                              ▼
                         GRx + NADPH
                              |
                              ▼
                    2GSH + NADP+
                              ↑
                         NADPH supplied
                         by HMP SHUNT

Exam Tip: G6PD deficiency → ↓NADPH → ↓GSH → ↑oxidative stress → Hemolytic anemia

Q29. Aerobic Glycolysis

Definition

Glycolysis is the anaerobic/aerobic breakdown of glucose (6C) to pyruvate (3C) in the cytoplasm, yielding a net 2 ATP (substrate level) + 2 NADH.

FLOWCHART: 10 Steps of Glycolysis

GLUCOSE (6C)
     │  Hexokinase/Glucokinase + ATP → ADP   [Step 1 - IRREVERSIBLE]
     ▼
Glucose-6-phosphate (G6P)
     │  Phosphoglucose isomerase
     ▼
Fructose-6-phosphate (F6P)
     │  Phosphofructokinase-1 (PFK-1) + ATP → ADP  [Step 3 - IRREVERSIBLE, RATE-LIMITING]
     ▼
Fructose-1,6-bisphosphate (F-1,6-BP)
     │  Aldolase
     ▼
DHAP ←──── (interconvert) ────► Glyceraldehyde-3-P (G3P)
                                        │ (×2 from here)
                                        │  G3P Dehydrogenase + NAD+→ NADH
                                        ▼
                               1,3-Bisphosphoglycerate (1,3-BPG)
                                        │  Phosphoglycerate Kinase + ADP→ATP  [Substrate-level]
                                        ▼
                               3-Phosphoglycerate (3PG)
                                        │  Phosphoglycerate Mutase
                                        ▼
                               2-Phosphoglycerate (2PG)
                                        │  Enolase (inhibited by FLUORIDE)
                                        ▼
                               Phosphoenolpyruvate (PEP)
                                        │  Pyruvate Kinase + ADP → ATP   [Step 10 - IRREVERSIBLE]
                                        ▼
                                   PYRUVATE (3C)
                                        │
                           ┌────────────┴──────────────┐
                           ▼                            ▼
                   AEROBIC                         ANAEROBIC
               (Mitochondria)                   (Cytoplasm)
                      │                              │
                      ▼                              ▼
               Acetyl-CoA                         LACTATE
               (via PDH)                     (Lactate dehydrogenase)
                      │
                      ▼
                  TCA Cycle

ENERGETICS OF GLYCOLYSIS

Step	ATP Used/Produced	Type
Hexokinase	-1 ATP	Investment
PFK-1	-1 ATP	Investment
PGK (×2)	+2 ATP	Substrate-level
Pyruvate kinase (×2)	+2 ATP	Substrate-level
G3P-DH (×2)	+2 NADH	Oxidative (5 ATP in aerobic)
Net (anaerobic)	+2 ATP
Net (aerobic)	+2 ATP + 2 NADH = ~7 ATP

REGULATION OF GLYCOLYSIS

                    HIGH ENERGY STATE          LOW ENERGY STATE
                    (↑ATP, ↑citrate)           (↑AMP, ↑ADP, ↑F-2,6-BP)
                            │                            │
                            ▼                            ▼
                    INHIBIT PFK-1                  ACTIVATE PFK-1
                    INHIBIT HK                     ACTIVATE PFK-1
                    INHIBIT PK                     ACTIVATE PK
                    → Glycolysis ↓                 → Glycolysis ↑

Enzyme	Activators	Inhibitors
Hexokinase/Glucokinase	Glucose	G6P (HK), insulin (GK)
PFK-1 (rate-limiting)	AMP, ADP, F-2,6-BP, Pi	ATP, Citrate, H+
Pyruvate Kinase	F-1,6-BP (feedforward)	ATP, Acetyl-CoA, Alanine; phosphorylation by glucagon

INHIBITORS OF GLYCOLYSIS

Inhibitor	Enzyme Inhibited	Mechanism
Iodoacetate	G3P Dehydrogenase	Alkylates -SH group
Fluoride	Enolase	Chelates Mg2+; used in blood collection
2-Deoxyglucose	Hexokinase	Competitive analog of glucose
Arsenate	PGK	Replaces Pi in 1,3-BPG formation

Q30. Rapaport-Leubering Cycle & 2,3-BPG

Overview

The Rapaport-Leubering (RL) cycle is a shunt in glycolysis that occurs exclusively in red blood cells (RBCs). It produces 2,3-bisphosphoglycerate (2,3-BPG), which is a critical regulator of hemoglobin oxygen affinity.

FLOWCHART: Rapaport-Leubering Cycle

Glucose
   |
   ▼ (Glycolysis)
1,3-Bisphosphoglycerate (1,3-BPG)
   |                    |
   | PGK (normal        | Bisphosphoglycerate mutase (BPGM)
   | glycolysis)        | [Rapaport-Leubering Shunt]
   ▼                    ▼
3-Phosphoglycerate    2,3-Bisphosphoglycerate (2,3-BPG)
   |                    |
   ▼                    | 2,3-BPG phosphatase
   ...                  ▼
   Pyruvate           3-Phosphoglycerate ──► re-enters glycolysis

Key point: The RL cycle BYPASSES the PGK step - so 1 ATP is lost per cycle

SIGNIFICANCE OF 2,3-BPG

      Low O2 in tissues
             |
             ▼
      ↑ 2,3-BPG synthesis (by BPGM)
             |
             ▼
      2,3-BPG binds to deoxyhemoglobin
      (central cavity, β-chains)
             |
             ▼
      Stabilizes T-state (tense/deoxy form)
             |
             ▼
      ↓ O2 affinity of Hb
             |
             ▼
      O2 released to tissues (RIGHT shift of O2 dissociation curve)

Condition	2,3-BPG Level	Effect
Altitude	↑	Right shift → more O2 to tissues
Anemia	↑	Compensatory O2 delivery
Stored blood (blood bank)	↓	Left shift → poor O2 delivery
HbF (fetal)	Low affinity for 2,3-BPG	Left shift → captures O2 from mother
Pyruvate kinase deficiency	↑	Right shift → partial compensation

Q31. Krebs Cycle (TCA Cycle / Citric Acid Cycle)

Location: Mitochondrial matrix

Substrate entry: Acetyl-CoA (2C unit)

FLOWCHART: 8 Steps of Krebs Cycle

            Acetyl-CoA (2C)
                 │
                 ▼ Citrate Synthase
            CITRATE (6C)  ←─────── OAA (4C) ←─────────────────┐
                 │                                               │
                 ▼ Aconitase (Fluoroacetate inhibits)           │
           Isocitrate (6C)                                      │
                 │                                               │
                 ▼ Isocitrate DH [NAD+→NADH; CO2↑] ← RATE-LIMITING
           α-Ketoglutarate (5C)                                  │
                 │                                               │
                 ▼ α-KG DH complex [NAD+→NADH; CO2↑] (Arsenite inhibits)
           Succinyl-CoA (4C)                                     │
                 │                                               │
                 ▼ Succinyl-CoA Synthetase [ADP→ATP / GTP]      │
             SUCCINATE (4C)                                      │
                 │                                               │
                 ▼ Succinate DH (SDH) [FAD→FADH2] (Malonate inhibits)
             FUMARATE (4C)                                       │
                 │                                               │
                 ▼ Fumarase                                      │
              MALATE (4C)                                        │
                 │                                               │
                 ▼ Malate DH [NAD+→NADH]                        │
               OAA (4C) ─────────────────────────────────────────┘

ENERGETICS OF ONE TURN OF KREBS CYCLE

Product	Quantity	ATP Equivalent
NADH	3	3 × 2.5 = 7.5 ATP
FADH2	1	1 × 1.5 = 1.5 ATP
GTP/ATP	1	1 ATP
Total		~10 ATP per turn
For 1 glucose (×2)		~20 ATP from TCA

REGULATION OF TCA CYCLE

LOW ENERGY (↑ADP, ↑AMP, ↑NAD+, ↑Ca2+)
         │
         ▼
    ACTIVATE:
    • Isocitrate DH (rate-limiting)
    • α-KG DH complex
    • Citrate synthase
    • PDH complex
         │
         ▼
    ↑ TCA cycle flux → ↑ ATP

HIGH ENERGY (↑ATP, ↑NADH, ↑Succinyl-CoA, ↑Citrate)
         │
         ▼
    INHIBIT above enzymes → ↓ TCA cycle

INHIBITORS OF TCA CYCLE

Inhibitor	Enzyme	Notes
Fluoroacetate (Rat poison)	Aconitase	"Lethal synthesis" - fluorocitrate formed
Arsenite / Heavy metals	α-KG DH, PDH	Inhibits lipoic acid
Malonate	Succinate DH	Competitive inhibitor

ANAPLEROTIC REACTIONS (TCA replenishment)

Pyruvate carboxylase: Pyruvate + CO2 → OAA
Glutamate dehydrogenase: Glutamate → α-KG
Propionyl-CoA metabolism → Succinyl-CoA

Q32. Gluconeogenesis

Definition

Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors. It occurs mainly in the liver (90%) and kidney (10%).

GLUCONEOGENIC PRECURSORS

       LACTATE ──────── LDH ──────────────────►┐
       ALANINE ─── Alanine aminotransferase ───►│
      GLYCEROL ─── Glycerol-3-P → DHAP ─────►  │
 GLUCOGENIC AA ─── → α-KG, OAA, Succinyl-CoA ►  │
    PROPIONATE ─── Succinyl-CoA ─────────────►  │
                                                 ▼
                                          GLUCOSE-6-P
                                                 |
                                                 ▼
                                          GLUCOSE (blood)

FLOWCHART: 3 UNIQUE STEPS OF GLUCONEOGENESIS (Bypass steps)

PYRUVATE
   |
   | ①  Pyruvate Carboxylase (mitochondria)
   |    [ATP + CO2; Biotin cofactor; ACTIVATED by Acetyl-CoA]
   ▼
OXALOACETATE (OAA)
   |
   | ②  PEPCK (Phosphoenolpyruvate Carboxykinase)
   |    [GTP → GDP + CO2]
   ▼
PHOSPHOENOLPYRUVATE (PEP)
   |
   ▼ (Reverse of glycolysis steps 9→4)
FRUCTOSE-1,6-BISPHOSPHATE
   |
   | ③  Fructose-1,6-Bisphosphatase (F1,6-BPase)
   |    [Inhibited by AMP, F-2,6-BP]
   ▼
FRUCTOSE-6-PHOSPHATE
   |
   ▼ (Phosphoglucose isomerase)
GLUCOSE-6-PHOSPHATE
   |
   | ④  Glucose-6-Phosphatase (ER membrane; liver + kidney only)
   ▼
GLUCOSE → Released into blood

REGULATION OF GLUCONEOGENESIS

GLUCAGON (fasting state) / CORTISOL
         │
         ▼
  ↑ Pyruvate carboxylase (by ↑Acetyl-CoA)
  ↑ PEPCK (gene transcription ↑)
  ↑ F-1,6-BPase (↓ F-2,6-BP due to ↓PFK-2)
         │
         ▼
  ↑ GLUCONEOGENESIS (maintains blood glucose)

INSULIN (fed state)
         │
         ▼
  ↓ PEPCK gene expression
  ↓ F-1,6-BPase (↑F-2,6-BP → inhibits F1,6-BPase)
         │
         ▼
  ↓ GLUCONEOGENESIS

Substrate	Entry point	Tissue
Lactate (Cori cycle)	Pyruvate	Liver
Alanine (Glucose-alanine cycle)	Pyruvate	Liver
Glycerol	DHAP	Liver
Amino acids (glucogenic)	Multiple TCA intermediates	Liver
Propionate (odd-chain FA)	Succinyl-CoA → OAA	Liver

Q33. HMP Shunt (Pentose Phosphate Pathway)

Location: Cytoplasm

Main purpose: NADPH production + Ribose-5-P production

FLOWCHART: HMP Shunt Pathway

GLUCOSE-6-PHOSPHATE (G6P)
        │
        │  ①  G6P Dehydrogenase (G6PD)  ←── RATE-LIMITING STEP
        │     [NADP+ → NADPH]
        ▼
6-PHOSPHOGLUCONO-δ-LACTONE
        │
        │  ②  Lactonase
        ▼
6-PHOSPHOGLUCONATE
        │
        │  ③  6-Phosphogluconate DH
        │     [NADP+ → NADPH + CO2]
        ▼
RIBULOSE-5-PHOSPHATE (5C)
        │
        ├──────────────────────────────────────────────┐
        ▼                                              ▼
RIBOSE-5-P                                   XYLULOSE-5-P
(nucleotides, NAD+, FAD, CoA)
        │
        └──── (Non-oxidative phase: Transketolase + Transaldolase)
              ▼
         Fructose-6-P and Glyceraldehyde-3-P
         (re-enter glycolysis)

SIGNIFICANCE OF HMP SHUNT

              HMP SHUNT PRODUCES:
              │
              ├─► NADPH (×2 per glucose)
              │       │
              │       ├─► Glutathione reduction (GPx system)
              │       ├─► Fatty acid synthesis (FAS)
              │       ├─► Cholesterol synthesis (HMG-CoA reductase)
              │       ├─► Steroid synthesis (P450 enzymes)
              │       └─► Respiratory burst (NADPH oxidase)
              │
              └─► RIBOSE-5-PHOSPHATE
                      │
                      └─► Nucleotide synthesis (ATP, GTP, NAD+, FAD, CoA)
                          RNA and DNA synthesis

ASSOCIATED DISORDERS

Disorder	Deficient Enzyme	Clinical Features
G6PD Deficiency	G6P Dehydrogenase	Hemolytic anemia (precipitated by oxidant drugs, fava beans, infections); Heinz bodies; X-linked recessive
Transaldolase Deficiency	Transaldolase	Liver cirrhosis, hepatosplenomegaly
Chronic Granulomatous Disease (CGD)	NADPH Oxidase	Recurrent catalase-positive infections (Staph, Aspergillus); defective respiratory burst

G6PD Deficiency - Exam Flowchart

G6PD Deficiency
      │
      ▼
↓ HMP shunt → ↓ NADPH
      │
      ▼
↓ Reduced Glutathione (GSH)
      │
      ▼
Oxidative stress in RBCs (triggered by drugs/infection)
      │
      ▼
Denatured Hb → Heinz bodies
      │
      ▼
RBC membrane damage
      │
      ▼
Hemolysis (Intravascular/Extravascular)

Drugs causing hemolysis in G6PD: Primaquine, Dapsone, Sulfamethoxazole, Nitrofurantoin, Chloramphenicol

Q34. Glycogen Metabolism

GLYCOGEN SYNTHESIS (Glycogenesis)

GLUCOSE
  |  Hexokinase/Glucokinase (ATP)
  ▼
Glucose-6-P
  |  Phosphoglucomutase
  ▼
Glucose-1-P
  |  UDP-glucose pyrophosphorylase (UTP → PPi)
  ▼
UDP-Glucose  ← the "active form" of glucose
  |  Glycogen Synthase (RATE-LIMITING)
  |  [adds to α1→4 chain; INHIBITED by glucagon/epinephrine; ACTIVATED by insulin, G6P]
  ▼
Glycogen chain (α1→4 linkages)
  |  Branching enzyme (adds α1→6 branches)
  ▼
GLYCOGEN (branched structure)

GLYCOGEN DEGRADATION (Glycogenolysis)

GLYCOGEN
  |  Glycogen Phosphorylase (RATE-LIMITING; uses Pi, not water)
  |  [Activated by: glucagon, epinephrine, AMP, Ca2+]
  |  [Inhibited by: insulin, ATP, G6P]
  ▼
Glucose-1-P (from α1→4 bonds)
  |  Phosphoglucomutase
  ▼
Glucose-6-P
  |  (in liver/kidney) Glucose-6-phosphatase
  ▼
FREE GLUCOSE → Blood

Note: Debranching enzyme releases glucose from α1→6 branch points (as FREE glucose)

REGULATION OF GLYCOGEN METABOLISM - MASTER FLOWCHART

                    GLUCAGON / EPINEPHRINE
                             │
                             ▼
                      Adenylyl Cyclase
                             │
                      ↑ cAMP (ATP → cAMP)
                             │
                             ▼
                        PKA (active)
                       /            \
                      ▼              ▼
           Phosphorylase kinase    Glycogen Synthase
               (active)              (inactive, phosphorylated)
                   │
                   ▼
       Glycogen Phosphorylase
           (active, b→a)
                   │
                   ▼
           GLYCOGENOLYSIS ↑
           GLYCOGENESIS ↓


                    INSULIN
                      │
                      ▼
               Phosphodiesterase ↑ (breaks cAMP)
               Protein phosphatase ↑ (dephosphorylates)
                      │
                      ▼
           Glycogen Phosphorylase (inactive)
           Glycogen Synthase (active)
                      │
                      ▼
           GLYCOGENESIS ↑ / GLYCOGENOLYSIS ↓

GLYCOGEN STORAGE DISEASES (GSDs) - HIGH YIELD TABLE

Type	Name	Deficient Enzyme	Organ	Clinical Features
Type I	von Gierke	Glucose-6-phosphatase	Liver, Kidney	Severe fasting hypoglycemia, hepatomegaly, lactic acidosis, hyperlipidemia
Type II	Pompe	Lysosomal α1→4 Glucosidase (Acid Maltase)	Heart, Muscle	Cardiomegaly, hypotonia; infantile form fatal
Type III	Cori / Forbes	Debranching enzyme	Liver, Muscle	Milder hypoglycemia, hepatomegaly
Type IV	Andersen	Branching enzyme	Liver	Cirrhosis, hepatosplenomegaly
Type V	McArdle	Muscle Phosphorylase	Muscle	Exercise intolerance, myoglobinuria, no rise in blood lactate with exercise
Type VI	Hers	Liver Phosphorylase	Liver	Mild hypoglycemia
Type VII	Tarui	Phosphofructokinase-1 (PFK-1)	Muscle, RBC	Exercise intolerance + hemolytic anemia

Mnemonic for GSDs:

"Very Poor Carbohydrate Metabolism Has Always Troubled People" Von Gierke, Pompe, Cori, McArdle, Hers, Andersen, Tarui, Phosphofructokinase

EXAM SUMMARY TABLE - HIGH YIELD POINTS

Q	Topic	MOST TESTED Fact
26	OxPhos	Cyanide blocks Complex IV; MELAS is most common OXPHOS disease; DNP is uncoupler
27	Free Radicals	•OH is most damaging; Fenton reaction uses Fe2+; ROS → LDL oxidation → atherosclerosis
28	Antioxidants	SOD → H2O2 → Catalase → H2O; GPx needs selenium; G6PD provides NADPH for GSH
29	Glycolysis	PFK-1 is rate-limiting; Fluoride inhibits Enolase; Net 2 ATP (anaerobic)
30	2,3-BPG	Made only in RBCs; Right shifts ODC; Low in stored blood; HbF ignores it
31	TCA Cycle	Isocitrate DH is rate-limiting; Fluoroacetate = rat poison (aconitase); 10 ATP per turn
32	Gluconeogenesis	4 unique enzymes; G6Pase absent in muscle; Biotin for pyruvate carboxylase
33	HMP Shunt	G6PD is rate-limiting; NADPH for fatty acid synthesis; G6PD def → hemolysis
34	Glycogen	Pompe = lysosomal acid maltase (Type II); McArdle = no lactate rise; von Gierke = G6Pase

Sources: Basic Medical Biochemistry - A Clinical Approach 6e (Lieberman & Peet); Lippincott Illustrated Reviews Biochemistry 8e

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