M2C Unit 2 Lesson 3

What is Km?

describes affinity (opposite trend), the substrate concentration at which velocity equals ½ Vmax.

What is Vmax?

The maximum reaction velocity when the enzyme is saturated with substrate; high Vmax = fast reaction

Pyruvate translocase transports pyruvate from where to where in symport with H+?

cytosol to mitochondria

Pyruvate dehydrogenase converts pyruvate to what?

Acetyl CoA

Where is Pyruvate converted into Acetyl CoA?

In the mitochondria

Pyruvate dehydrogenase complex (PDH complex) is a multienzyme complex containing?

3 enzymes + 5 coenzymes + other proteins

What is E1 in the Pyruvate dehydrogenase complex (PDH complex)?

pyruvate dehydrogenase

What is E2 in the Pyruvate dehydrogenase complex (PDH complex)?

dihydrolipoamide acetyltransferase

What is E3 in the Pyruvate dehydrogenase complex (PDH complex)?

dihydrolipoamide dehydrogenase

What are the cosubstrates of the PDH complex?

NAD+ and CoA-SH

What are the prosthetic groups of the PDH complex?

TPP, lipoamide and FAD

What is the regulator of the PDH complex?

ATP

What acts as a “swinging arm” to transfer the two carbon unit from the active site of E1 to the active site of E3?

Lipoamide (on E2)

Enzyme converting Oxaloacetate + Acetyl-CoA → Citrate?

Citraite Synthase

Enzyme converting Citrate → Isocitrate?

Aconitase

Enzyme converting Isocitrate → alpha-Keto gluterate

Isocitrate dehydrogenase

Enzyme converting alpha-KG → Succinyl CoA

alpha-KG dehydrogenase complex

Enzyme converting Succinyl CoA → Succinate

Succinyl CoA synthase

Enzyme converting Succinate → Fumerate

Succinate dehydrogenase

Enzyme converting Fumerate to Malate

Fumerase

Enzyme converting Malate to Oxaloacetate

Malate dehydrogenase

For each acetyl CoA which enters the cycle, how many molecules of CO2 are released?

two

For each acetyl CoA which enters the cycle, what coenzymes are reduced?

NAD+ and Q

For each acetyl CoA which enters the cycle, how many GDP (ADP) are phosphorylated?

One

What is E1 in the a-Ketoglutarate dehydrogenase complex?

a-ketoglutarate dehydrogenase (with TPP)

What is E2 in the a-Ketoglutarate dehydrogenase complex?

succinyltransferase (with flexible lipoamide prosthetic group)

What is E3 in the a-Ketoglutarate dehydrogenase complex?

dihydrolipoamide dehydrogenase (with FAD)

Each acetyl CoA entering the cycle nets:

__ NADH

__QH2

___GTP (or __ ATP)

3

1

1 (1)

Total # of ATP prodiced through just 1 cycle of TCA?

10 ATP

1 NADH yields how many ATP?

2.5 ATP

1 QH2 yields how many ATP?

1.5 ATP

1 acetyl CoA yields how many ATP?

10 ATP

1 glucose makes how many ATP through Glycolysis and TCA?

32 ATP

Does CoA-SH activate or inhibit E2 of PDH complex?

activate

Does acetyl-CoA activate or inhibit E2 of PDH complex?

inhibit

Does NAD+ activate or inhibit E3 of PDH complex?

activate

Does NADH activate or inhibit E3 of PDH complex?

inhibits

When PDH complex is phosphorylated it is (active/inactive)?

inactive

When PDH complex is dephosphorylated it is (active/inactive)?

active

What enzyme dephosphorylates PDH complex?

Pyruvate dehydrogenase phosphatase (PDP)

What is Pyruvate Dehydrogenase complex deficiency?

Impaired conversion of pyruvate to acetyl-CoA, causing energy deficits and metabolic disturbances.

Pyruvate Dehydrogenase complex deficien symptoms.

• Neurological symptoms: Developmental delay, hypotonia, ataxia, seizures, and intellectual disability.

• Lactic acidosis: Due to the buildup of pyruvate, which is shunted to lactate.

• Progressive neurodegeneration: Brain abnormalities, particularly in the basal ganglia and brainstem.

Diagnosis for:

• Elevated lactate and pyruvate levels in blood and cerebrospinal fluid.

• Genetic testing for mutations in PDHA1, PDHB, or other PDH complex genes

• Enzyme activity assays to measure PDH function in cultured fibroblasts or muscle biopsies

Pyruvate Dehydrogenase complex deficiency

Pyruvate Dehydrogenase complex deficiency treatment

• Ketogenic diet

• Dichloroacetate (DCA) to stimulate pyruvate

  dehydrogenase phosphatase, enhancing PDH activity.

• Thiamine (Vitamin B1) supplementation in cases where

  PDH function is partially responsive to thiamine

Arsenic Poisoning cause

Occurs due to exposure to arsenic-containing compounds, which can be found in contaminated water, pesticides, and industrial processes.

Mechanism of Toxicity for Arsenic Poisoning

• Disruption of Oxidative Phosphorylation

• Oxidative Stress and DNA Damage

• Inhibition of PDC

How does Arsenic Poisoning inhibit PDC?

1. Arsenic binds to lipoic acid, a cofactor for PDH, α-ketoglutarate dehydrogenase, and branched-chain ketoacid dehydrogenase.

2. This disrupts the TCA cycle, leading to impaired ATP production and lactic acidosis.

How does Arsenic Poisoning lead to disruption of Oxidative Phosphorylation?

1. Arsenic mimics phosphate (Pi) and replaces it in ATP synthesis, forming unstable arsenate esters that hydrolyze easily.

2. This leads to decreased ATP production and cellular energy failure.

How does Arsenic Poisoning lead to Oxidative Stress and DNA Damage?

• Arsenic generates reactive oxygen species (ROS), causing mitochondrial damage, lipid peroxidation, and apoptosis.

Clinical manifestations of Acute Arsenic Poisoning

• Severe gastrointestinal symptoms: Vomiting, rice-water diarrhea, abdominal pain.

• Cardiovascular collapse: Hypotension, arrhythmias, and shock.

• Neurological symptoms: Seizures, delirium, and coma.

Clinical manifestations of Chronic Poisoning of Arsenic

• Skin changes: Hyperpigmentation, palmar and plantar keratosis, Mee's lines (white bands on nails).

• Neuropathy: Stocking-glove distribution paresthesia, weakness.

• Cancer risk: Increased risk of lung, skin, bladder, and liver cancers.

• Bone marrow suppression: Anemia, leukopenia.

Diagnosis of Arsenic Poisining

• Blood and urine arsenic levels (acute exposure).

• Hair and nail arsenic analysis (chronic exposure).

• Metabolic acidosis with high lactate (due to PDH inhibition).

Arsenic Poisining treatment

• Immediate decontamination (remove source of arsenic).

• Chelation therapy: Dimercaprol (BAL) or DMSA (succimer) binds arsenic and promotes excretion.

• Penicillamine may be used in chronic cases.

• Supportive care: IV fluids, correction of electrolyte imbalances, and

symptom management.

What is Vitamin B1 deficiency (Beriberi)?

• Vitamin B1 (Thiamine) is an essential water-soluble vitamin involved in carbohydrate metabolism and energy production.

• Deficiency leads to beriberi, a condition that primarily affects the nervous and cardiovascular systems.

Causes of Thiamine Deficiency

• Poor dietary intake (e.g., polished rice, alcoholics, malnutrition)

• Increased demand (e.g., pregnancy, lactation, hyperthyroidism, fever, sepsis)

• Malabsorption (e.g., chronic diarrhea, bariatric surgery)

• Excessive loss (e.g., dialysis, diuretics)

• Alcoholism (impairs absorption and utilization)

What is Dry Beriberi?

(Neurological Manifestations)

1. Peripheral neuropathy: Symmetrical, affecting legs more than arms.

2. Paresthesia, numbness, muscle weakness, foot drop.

3. Wernicke-Korsakoff Syndrome (in alcoholics):

   1. Wernicke encephalopathy: Confusion, ataxia, ophthalmoplegia.

   2. Korsakoff syndrome: Amnesia, confabulation, psychosis.

What is Wet Beriberi?

(Cardiovascular Manifestations)

1. High-output heart failure due to vasodilation.

2. Edema, tachycardia, dyspnea, cardiomegaly.

3. Can lead to shock and death if untreated.

What is Infantile Beriberi?

(in breastfed infants of thiamine-deficient mothers)

1. Heart failure, aphonia, vomiting, convulsions.

2. Can be fatal if not treated immediately

Alcoholism is a major risk factor for berberi, often leading to what?

Wernicke-Korsakoff syndrome