Enzymes, Carbohydrates, and Spectrophotometry: A Review
Enzymes: Proteinaceous Catalysts
Enzymes are proteinaceous substances involved in biochemical reactions. They are proteins formed from amino acids. When the number of amino acids is between -100 and +100, they are called polypeptides. The linear sequence of amino acids, known as the primary structure, is unique for each protein and dictates its function.
Enzymes can only bind to a specific substrate, forming a reversible enzyme-substrate complex. They are used as reagents in clinical chemistry because they are very specific; each enzyme reacts with a specific substrate quantitatively. Another catalytic function is to accelerate or decelerate a chemical reaction.
Spectrophotometric Techniques
Spectrophotometry is used in two main types of analysis:
Endpoint Analysis
In endpoint analysis, the substance being analyzed is transformed into a measurable substance after the chemical reaction is complete. This is commonly used in clinical analysis.
Kinetic Analysis
Kinetic analysis determines changes in the substances under analysis during the chemical reaction by making measurements at time intervals.
Carbohydrates: Energy Sources
Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They are soluble in water and classified according to the number of carbon atoms or the functional groups they contain. Monosaccharides are the basic units that combine to form polysaccharides.
Glucose is a form of energy storage and consumption. It is absorbed in the small intestine and converted into a polysaccharide called glycogen, which accumulates inside the cells of the liver and muscles as an energy reserve. The body obtains energy from glycogen through hydrolysis, a process called glycolysis.
Glycemia: Blood Glucose Levels
Glycemia refers to the blood glucose level, which remains constant in a healthy individual during fasting periods, controlled by hormonal regulation. The hormones glucagon and insulin maintain this stability.
- Insulin, synthesized in the pancreas when glucose levels are high, causes a decrease in blood glucose and promotes glycogen synthesis.
- When glucose levels are low (below 70-110 mg/L), hypoglycemia occurs. High glucose levels indicate hyperglycemia and may indicate diabetes.
Types of Diabetes
- Type 1: Typically occurs in young individuals and involves no insulin production due to autoimmune destruction of pancreatic beta cells.
- Type 2: Typically occurs in adults and is caused by a deficiency in insulin production or tissue resistance to insulin.
- Gestational Diabetes: Occurs during pregnancy (around 24-28 weeks) due to metabolic stress as the mother’s body provides energy for the fetus.
Symptoms of Diabetes
- Polyuria: High urine output
- Polydipsia: Increased thirst
- Polyphagia: Increased appetite
Hyperlipidemias: Lipids and Lipoproteins
Hyperlipidemias involve lipids, a set of molecules with different structures that are partially or totally insoluble in water. They need to bind to proteins, forming transportable lipoproteins, to circulate in the body.
Lipoprotein Classification by Density
- Chylomicrons: Transport triglycerides from the intestine to the liver.
- VLDL (Very Low-Density Lipoproteins): Synthesized in the liver and transport triglycerides.
- LDL (Low-Density Lipoproteins): Transport cholesterol from the liver to tissues, where it is used to produce hormones and vitamins. High LDL cholesterol is associated with heart attacks and arteriosclerosis.
- HDL (High-Density Lipoproteins): Transport cholesterol from tissues to the liver, where it is excreted as bile in feces (good cholesterol). HDL acts as a protector against heart disease by stabilizing fat molecules like triglycerides and cholesterol.
Atherosclerosis
Atherosclerosis is the accumulation of fat and fibrous tissue in the inner layers of arteries, impeding blood flow. Cholesterol plays a significant role in this slow process, leading to vascular problems such as heart attacks and strokes.
Spectroscopy and Spectrophotometry
Spectroscopy measures the amount of energy that passes through a substance in solution when a known wave of energy is applied. The amount of energy that does not pass through the substance is known as absorbance.
A spectrophotometer consists of a lamp, collimator, lever, sample holder, and detector.
Lambert’s Law
Lambert’s Law establishes the relationship between the intensity of light transmitted by a substance and the thickness of the tray, along with the substance’s concentration. The formula is: A = abc, where:
- A = Absorbance
- a = Absorption coefficient
- b = Path length (cm)
- c = Concentration (moles/L)
Dry Chemistry
Dry chemistry is a technique using dehydrated reagents on solid supports, such as strips, to control blood sugar in patients. The strip is introduced into a sample container, and after a few seconds, the sample is compared with a color chart marketed for this purpose. The water from the sample rehydrates the reagents.