Glycolysis enzymes are located in the cytosol of cells.  Pyruvate enters the mitochondrion to be metabolized further

Mitochondrial compartments: The mitochondrial matrix contains Pyruvate Dehydrogenase and enzymes of Krebs Cycle, plus other pathways such as fatty acid oxidation. 

Pyruvate Dehydrogenase catalyzes oxidative decarboxylation of pyruvate, to form acetyl-CoA

FAD (Flavin Adenine Dinucleotide) is a derivative of the B-vitamin riboflavin (dimethylisoalloxazine-ribitol). The flavin ring system undergoes oxidation/reduction as shown below. Whereas NAD⁺ is a coenzyme that reversibly binds to enzymes, FAD is a prosthetic group, that is permanently part of the complex. 

FAD accepts and donates 2 electrons with 2 protons (2 H):

Thiamine pyrophosphate (TPP) is a derivative of  thiamine (vitamin B₁). Nutritional deficiency of thiamine leads to the disease beriberi. Beriberi affects especially the brain, because TPP is required for carbohydrate metabolism, and the brain depends on glucose metabolism for energy

Acetyl CoA, a product of the Pyruvate Dehydrogenase reaction, is a central compound in metabolism. The "high energy" thioester linkage makes it an excellent donor of the acetate moiety

For example, acetyl CoA functions as:

• input to the Krebs Cycle, where the acetate moiety is further degraded to CO₂.
• donor of acetate for synthesis of fatty acids, ketone bodies, and cholesterol.

ATPs  formed in TCA cycle from one molecule of Pyruvate

1. 3ATP            7. 3ATP          5. 3 ATP                     

 8. 1 ATP         9. 2 ATP          11.3 ATP         Total =15 ATP.

 ATPS formed from one molecule of Acetyl CoA =12ATP

ATPs formed from one molecule of glucose after complete oxidation

One molecule of glucose -->2 molecules of pyruvate

['By glycolysis] ->8 ATP

2 molecules of pyruvate [By TCA cycle] -> 30 ATP

Total = 38 ATP

LIPOPROTIENS

Lipoproteins Consist of a Nonpolar Core & a Single Surface Layer of Amphipathic Lipids

The nonpolar lipid core consists of mainly triacylglycerol and cholesteryl ester and is surrounded by a single surface layer of amphipathic phospholipid and cholesterol molecules .These are oriented so that their polar groups face outward to the aqueous medium. The protein moiety of a lipoprotein is known as an apolipoprotein or apoprotein,constituting nearly 70% of some HDL and as little as 1% of Chylomicons. Some apolipoproteins are integral and cannot be removed, whereas others can be freely transferred to other lipoproteins.

There  re five types of lipoproteins, namely chylomicrons, very low density lipoproteins(VLDL)  low density lipoproteins (LDL), high density Lipoproteins (HDL) and free fatty acid-albumin complexes.

Glycogen Metabolism

The formation of glycogen from glucose is called Glycogenesis

Glycogen is a polymer of glucose residues linked mainly by a(1→ 4)  glycosidic linkages. There are a(1→6) linkages at branch points. The chains and branches are longer than shown. Glucose is stored as glycogen predominantly in liver and muscle cells

Glycogen Synthesis

Uridine diphosphate glucose (UDP-glucose) is the immediate precursor for glycogen synthesis. As glucose residues are added to glycogen, UDP-glucose is the substrate and UDP is released as a reaction product. Nucleotide diphosphate sugars are precursors also for synthesis of other complex carbohydrates, including oligosaccharide chains of glycoproteins, etc.

UDP-glucose is formed from glucose-1-phosphate and uridine triphosphate (UTP)

glucose-1-phosphate + UTP → UDP-glucose + 2 P_i

Cleavage of PPi is the only energy cost for glycogen synthesis (1P bond per glucose residue)

Glycogenin initiates glycogen synthesis. Glycogenin is an enzyme that catalyzes glycosylation of one of its own tyrosine residues.

Physiological regulation of glycogen metabolism

Both synthesis and breakdown of glycogen are spontaneous. If glycogen synthesis and phosphorolysis were active simultaneously in a cell, there would be a futile cycle with cleavage of 1 P bond per cycle

To prevent such a futile cycle, Glycogen Synthase and Glycogen Phosphorylase are reciprocally regulated, both by allosteric effectors and by covalent modification (phosphorylation)

Glycogen catabolism (breakdown)

Glycogen Phosphorylase catalyzes phosphorolytic cleavage of the →(1→4) glycosidic linkages of glycogen, releasing glucose-1-phosphate as the reaction product.

Glycogen (n residues) + P_i → glycogen (n-1 residues) + glucose-1-phosphate

The Major product of glycogen breakdown is glucose -1-phosphate

Fate of glucose-1-phosphate in relation to other pathways:

Phosphoglucomutase catalyzes the reversible reaction:

Glucose-1-phosphate → Glucose-6-phosphate

ZINC

The enzyme RNA polymerase, which is required for transcription, contains zinc and it is essential for protein bio synthesis.

Deficiency in Zinc leads to poor wound healing, lesions of skin impaired spermatogenesis, hyperkeratosis, dermatitis and alopecia

Pepsin

• Primary enzyme for protein degradation in stomach
• Optimal pH: 1.5-2.0 (acidic)
• Secreted as inactive pepsinogen
• Cleaves proteins into smaller peptides

Histone

• Protein rich in basic amino acids (lysine and arginine)
• Packages DNA in chromosomes
• Forms nucleosomes with DNA
• Types: H1, H2A, H2B, H3, H4

Casein

• Example of phosphoprotein
• Major protein in milk
• Contains phosphate groups attached to serine residues
• Forms micelles in milk

Antibodies (Immunoglobulins)

• Structure composed of 2 long (heavy) & 2 short (light) peptide chains
• Y-shaped structure
• Connected by disulfide bonds
• Variable regions bind to antigens
• Constant regions determine antibody class

Insulin Receptors

• Tetrameric glycoprotein
• Consists of 2 α and 2 β subunits
• α subunits: Extracellular, insulin-binding
• β subunits: Transmembrane, tyrosine kinase activity
• Essential for glucose homeostasis

Collagen

• Contains triple helix structure
• Most abundant protein in mammals
• Composed of three polypeptide chains (tropocollagen)
• Amino acid sequence: Gly-X-Y (where X is often proline, Y is often hydroxyproline)
• Provides structural support to tissues

Protein electrophoresis is a laboratory technique used to separate proteins based on their size, charge, or other physical properties. It plays a vital role in diagnosing and monitoring various diseases, especially those involving abnormal protein production or structure.

Types of Protein Electrophoresis

1. SPE (Serum Protein Electrophoresis)

• Principle: Separation of serum proteins based on their charge.

• Major Fractions:

  • Albumin

  • Alpha-1 globulin

  • Alpha-2 globulin

  • Beta globulin

  • Gamma globulin

• Clinical Applications:

  • Multiple Myeloma: Detects monoclonal spike (M-protein) in gamma region.

  • Chronic Infections: Polyclonal increase in gamma globulins.

  • Nephrotic Syndrome: Decreased albumin, increased alpha-2 globulin.

  • Liver Disease: Altered albumin and beta-gamma bridging.

2. Hemoglobin Electrophoresis

• Principle: Separation of hemoglobin variants based on charge differences.

• Common Hemoglobins:

  • HbA, HbA₂, HbF, HbS, HbC, HbE

• Clinical Applications:

  • Thalassemia: Elevated HbA₂ or HbF levels.

  • Sickle Cell Disease: Presence of HbS.

  • Hemoglobinopathies: Differentiates variants like HbC, HbE, etc.

3. SDS-PAGE (Sodium Dodecyl Sulfate–Polyacrylamide Gel Electrophoresis)

• Principle: Proteins are denatured and separated by molecular weight.

• SDS: Imparts uniform negative charge, eliminating charge-based separation.

• Clinical Applications:

  • Protein Purification: Identifies specific proteins in research and diagnostics.

  • Genetic Disorders: Detects abnormal or truncated proteins.

  • Muscular Dystrophies: Analyzes dystrophin protein expression.

  • Cancer Research: Studies tumor markers and oncogenic proteins.