**Ethanol Metabolism in the Liver**This image demonstrates two main pathways of ethanol metabolism, highlighting the processes occurring in the cytosol and mitochondrion.**Cytosol:**- **Pathway 1: Major pathway of ethanol metabolism in the liver** - Ethanol (\( \text{CH}_3\text{CH}_2\text{OH} \)) is converted to acetaldehyde (\( \text{CH}_3\text{CHO} \)) through the action of Alcohol Dehydrogenase (ADH). - This reaction involves the reduction of NAD\(^+\) to NADH, releasing a proton (H\(^+\)).**Pathway 2: Microsomal ethanol oxidizing system (MEOS)** - Ethanol is also metabolized by CYP2E1, generating NADP\(^+\), NADPH, and water (\( 2\text{H}_2\text{O} \)).**Mitochondrion:**- Acetaldehyde (\( \text{CH}_3\text{CHO} \)) is further oxidized to acetate (\( \text{CH}_3\text{COOH} \)) by Aldehyde Dehydrogenase (ALDH). - This reaction also reduces NAD\(^+\) to NADH, adding another proton (H\(^+\)). - Acetate is then converted to water (\( \text{H}_2\text{O} \)).**Note:** Excessive alcohol consumption increases the NADH:NAD\(^+\) ratio in the cytosol of hepatocytes. **Q7: Which mechanisms may be used to reverse a high NADH:NAD⁺ ratio in the cytosol under anaerobic conditions?**This question focuses on the cellular mechanisms that help maintain the balance between reduced (NADH) and oxidized (NAD⁺) forms of nicotinamide adenine dinucleotide, particularly when oxygen is scarce. Understanding these processes is crucial for studying cellular respiration and metabolic pathways during anaerobic conditions.

Alcohol Metabolism -- Alcohol --Alcohol the group of compounds which have a general formula R -OH ,where R= Cn H2n+1 -OH and simple alcohol which is generally called as alcohol Ethyl Alcohol with formula C2 H5 -OH. Most part of the alcohol is metabolized in liver . Alcohol is oxidized in the liver by Alcohol dehydrogenase to acetaldehyde . Absorption of alcohol --Alcohol is readily absorbed by the stomach and intestine. Excretion of alcohol --There occurs only 1% of alcohol or ethyl alcohol excreted through lungs , urine and sweat . Molecules which bind cellular respiration enzymes act as signals giving the enzyme information about cells in energy state . ATP ,ADP and NADH are molecules which regulate cellular respiration enzymes. . Alcohol Dehydrogenase play an important part in alcohol metabolism ,it is an NAD+ dependent cytoplasmic enzyme which oxidizes ethanol to acetaldehyde .Acetaldehyde is further oxidized to acetate by alpha mitochondrial NAD+ dependent enzyme known as aldehyde dehydrogenase . Acetate is converted in to acetyl Co A Some time mutation occur and in the mutant individual alcohol metabolism become slow and even small quantity of alcohol causes alcohol intoxication symptoms . Biochemical alteration in Alcoholism and high ratio of NADH /NAD+--High cytosolic NADH /NADP ratio means a high driving force is very important to obtain high production rates . The metabolism of alcohol specially ethyl alcohol involving the consumption of NAD+ and consequently a high NADH /NAD+ ratio. Following processes occur in altered condition - a- Lactic Acidosis -- High concentration of NADH favors the conservation of pyruvate to lactate which may lead to lactic acidosis . b- Hypoglycemia -- Decreased condition of pyruvate leads to inadequate formation of alpha oxaloacetate lead to gluconeogenesis and finally hypoglycemia . c - Suppression of TCA cycle due to decreased pyruvate ,high NADH . d - Acetyl Co A increased level causes its accumulation in liver and lead to ketogenesis ,fatty acid synthesis ( not oxidation ) also accumulate in liver and result in fatty liver . Mechanism reversing the High ratio of NADH / NAD+ in Cytosol in Anaerobic Condition --- NAD/ NADH ratio under anaerobic condition NAD+ is regenerated when the electrons from NADH molecules are shuttled . The mechanism involve are as follows -- 1- NAD+ After accepting an electron from glucose forms the NADH which transport the electron to mitochondria ,cell take the energy which is stored in electron . 2 - NADH after donating electron to oxygen become NAD+. 3 - NAD+ / NADH redox couple is known as a regulator of cell energy metabolism involves Glycolysis and Mitochondrial phosphorylation . 4 - The enzyme involved in restoring the NAD+ , in glycolysis where glyceraldehyde 3 - phosphate is oxidized to D- glycerate 1,3 bisphosphate in the cytosol. 5 - The process of fermentation results in the reduction of pyruvate to form lactic acid and oxidation of NADH to form NAD+