32 topics with concise breakdowns: definitions, key facts, and lecture questions.
Carbohydrates are the primary energy source for the brain and erythrocytes. In this section, we examine the complete pathway of carbohydrates in the body: from gastrointestinal digestion and the function of transport proteins (GLUT) to complex intracellular cascades. You will learn how the cell burns glucose via glycolysis, stores it as glycogen in the liver and muscles, and synthesizes it anew through gluconeogenesis.
We will bridge fundamental formulas with clinical practice. You will understand the biochemical basis of lactose intolerance, the mechanisms of glycogen storage diseases and lactic acidosis, and analyze why alcohol causes hypoglycemia. Special attention is paid to the pentose phosphate pathway and the critical role of glutathione in protecting erythrocytes from oxidative stress.
What are the most frequent exam questions? Primarily irreversible reactions and key enzymes of glycolysis and gluconeogenesis. Make sure to learn the mechanisms of hormonal regulation (insulin, glucagon, adrenaline), methods for maintaining normal blood glucose levels, and the glucose-lactate cycle (Cori cycle).
Why are carbohydrates not digested in the stomach?
Gastric juice lacks enzymes that break down carbohydrates. Additionally, the acidic environment of the stomach inactivates salivary $\alpha$-amylase, which began hydrolysis in the oral cavity.
How does glucose penetrate from the blood into tissue cells?
Transport is carried out via facilitated diffusion. This process requires special carrier proteins (GLUT), which operate without direct expenditure of cellular energy.
Why cannot glucose leave the cell back into the blood?
Upon entering the cell, it undergoes phosphorylation. The resulting glucose-6-phosphate loses its ability to cross cell membranes, finding itself in a peculiar energetic "trap".
Why does the body store glucose specifically as a complex polymer rather than in free form?
Free glucose readily dissolves in water and drastically increases intracellular osmotic pressure. This would cause a rapid influx of water into the cell and its rupture (osmotic shock). Polymeric granules are insoluble and do not affect osmosis.
What is the difference between phosphorolysis and hydrolysis?
During phosphorolysis, inorganic phosphate ($H_3PO_4$) rather than a water molecule is used to break the chemical bond between glucose residues. Due to this, the cleaved fragment is immediately converted into a phosphorylated product (glucose-1-phosphate).
Why does glycogen break down without hormonal participation during moderate muscular work?
AMP accumulates in muscles due to ATP hydrolysis. AMP acts as a potent allosteric activator of the less active dephosphorylated form of glycogen phosphorylase.
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