Introduction to Biochemistry Quiz

Biochemistry Lecture Notes

• Course Theme: Integration of Metabolism, Metabolic Effects of Insulin and Glucagon, The Feed/Fast Cycle, Diabetes Mellitus, Obesity, Nutrition, Vitamins
• Reading Materials: Lippincott's Illustrated Reviews: Biochemistry - 5th Edition, by Harvey and Ferrier, pages 305-371
• Assessment: Written exam, Oral exam
• Insulin, Glucagon and Diabetes Mellitus: Introduction to the pancreas's roles in digestion and hormone production.
  • The pancreas performs digestive functions and secretes insulin and glucagon, both crucial for lipid, protein, and glucose metabolism.
  • Other hormones from the pancreas such as amylin, somatostatin and pancreatic polypeptide also perform a role.
• Pancreas Anatomy: The pancreas consists of acini and islets of Langerhans.
  • Acini secrete digestive juices into the duodenum.
  • Islets of Langerhans secrete insulin and glucagon directly into the bloodstream. Specific cell types in the islets (alpha, beta and delta) produce different hormones (glucagon, insulin and somatostatin respectively)
• Islet Cells: Three major cell types
  • Alpha cells (25%): Produce glucagon
  • Beta cells (60%): Primarily in the middle of the islet; Produce insulin and amylin.
  • Delta cells (10%): Produce somatostatin.
  • PP Cells: Produce pancreatic polypeptide
• Insulin and its Metabolic Effects: Insulin, a small protein, is synthesized in beta cells.
  • It affects carbohydrate, fat, and protein metabolism.
  • Actions in the normal state: affects glucose productions, utilization; protein synthesis, and more.
  • Actions in the insulin-resistance state: hyperglycemia, hyperinsulinemia; increased lipidolysis, increased free fatty acids and glycerol, increased lipogenesis, decreased triglycerides, and more; decreased gluconeogenesis and abnormal protein metabolism and more.
• Insulin and its Effects on Carbohydrate Metabolism:
  • After a meal, insulin promotes rapid uptake, storage, and use of glucose in muscles, adipose tissue, and liver.
• Insulin and Muscle Glucose Uptake:
• Muscle uptake of glucose is enhanced by exercise or by high blood glucose levels, even in the absence of insulin.
• Insulin and Liver Uptake of Glucose:
  • Insulin inhibits liver phosphorylase, the enzyme that breaks down glycogen into glucose so promoting glycogen storage instead.
  • Insulin enhances glucose uptake by increasing glucokinase activity.
  • Insulin promotes glycogen synthesis.
• Glucose Release from the Liver Between Meals: Declining blood glucose levels cause a decrease in insulin secretion, which reverses the effects of glycogen storage and causes glycogen to be split to glucose, then causing the glucose to detach from the phosphate radical.
• Insulin and Fat Metabolism: Insulin promotes conversion of excess glucose into fatty acids for fat storage. This is stored in adipose tissue as triglycerides.
• Lack of Effect of Insulin on Glucose Uptake by the Brain: The brain can use glucose without insulin.
• Effects of Insulin on Other Cells: Insulin increases glucose uptake and use in most body cells; it promotes fat deposition in adipose tissue.
• Insulin Promotes Fat Synthesis and Storage: Insulin promotes glucose utilization and fatty acid synthesis in liver cells, which are then transported via lipoproteins to adipose cells for storage.
• Insulin Deficiency and Fat Use: Lack of insulin causes increased fat breakdown and release of free fatty acids. This causes increased plasma concentrations of cholesterol and phospholipids, which can contribute to atherosclerosis in people with serious diabetes.
• Excess Usage of Fats - Ketosis and Acidosis: Deficiency of insulin causes more acetoacetic acid to be produced in the liver cells but also depresses the utilization of acetoacetic acid in peripheral tissues. High concentrations of acetoacetic acid and Beta-hydroxybutyric acid can cause acidosis and coma.
• Effect of Insulin on Protein Metabolism and Growth:
  • During the few hours after a meal, insulin promotes protein synthesis and storage in tissues.
  • Insulin promotes amino acid uptake into cells, aiding protein synthesis.
• Protein catabolism is also inhibited by insulin.
• Insulin and growth hormone work synergistically to promote growth.
• Insulin Lack and Protein Effects: Insulin deficiency causes protein wastage, which leads to weakness and deranged function in organs.
• Mechanism of Insulin Secretion: Glucose enters beta cells and is phosphorylated to glucose-6-phosphate by glucokinase. A higher level of ATP blocks potassium channels leading to depolarization and opening of calcium channels, promoting insulin release through exocytosis.
• Other Factors Stimulating Insulin Secretion: Increased blood glucose, free fatty acids, amino acids, gastrointestinal hormones (gastrin, cholecystokinin, secretin, GIP), glucagon, growth hormone, cortisol, parasympathetic stimulation (acetylcholine), insulin resistance and obesity, and drugs (sulfonylureas).
• Factors Inhibiting Insulin Secretion: Decreased blood glucose, fasting, somatostatin, adrenergic activity, leptin.
• Role of Insulin (and Other Hormones) in "Switching" Between Carbohydrates and Lipid Metabolism: Blood glucose levels control switching between using carbohydrates and fats for energy. High glucose promotes carbohydrate use, while low blood glucose stimulates use of fats.
• Glucagon and its Functions: Secretion from alpha cells of the islets in response to low blood glucose. Enhances glucose levels (opposed to insulin).
• Glucagon Effects on Glucose Metabolism: Promotes breakdown of liver glycogen, increases gluconeogenesis to increase glucose mobilization for other body organs. Inhibits storage of liver triglycerides.
• Regulation of Glucagon Secretion: Increased blood glucose inhibits glucagon secretion. Elevated blood amino acids stimulate glucagon release. Exercise also stimulates glucagon secretion in a way that's not fully understood yet.
• Somatostatin and Insulin Secretion: It is a peptide hormone from delta cells; decreases the secretion of insulin and glucagon. It also inhibits the motility of the stomach, duodenum, and gallbladder.
• Diabetes Mellitus: A syndrome of impaired carbohydrate, fat, and protein metabolism.
  • Type I: Impaired insulin secretion (often autoimmune-mediated beta cell destruction); requires exogenous insulin.
  • Type II: Insulin resistance, often with initial compensatory hyperinsulinemia; often associated with obesity and can be treated with diet and exercise.
• Clinical Characteristics of Type I and Type II Diabetes: (See Table 78-1) Includes age of onset, body mass, plasma insulin, plasma glucagon, plasma glucose, insulin sensitivity.
• Type I Diabetes and its effects: Loss of insulin production, resulting in chronic high glucose concentrations causing tissue damage (atherosclerosis, end-stage kidney disease etc.), loss of urine glucose causing dehydration, proteins being used instead of glucose for energy.
• Type II Diabetes and its effects: Insulin resistance, chronic high glucose concentrations causing tissue damage, increased risk of heart attacks, stroke, and blindness
• Symptoms of Diabetes: Frequent urination, excessive thirst, sudden weight loss, blurred vision, and slow healing wounds.
• Diagnosis of Diabetes: Fasting blood glucose and insulin levels (normal levels), acetone breath tests. Glucose tolerance tests (normal curve for blood glucose vs. time).
• Treatment of Diabetes:
  • Type I: Exogenous insulin administration, often adjusting doses throughout the day.
  • Type II: Dietary and exercise recommendations, medication to increase insulin sensitivity or to stimulate pancreas insulin production; exogenous insulin administration may be necessary in some cases.
• Insulinonoma (Hyperinsulinism): Excessive insulin production from tumors of the islets of Langerhans.
• Insulin Shock and Hypoglycemia: A harmful syndrome, caused by excess insulin intake. It can cause symptoms like nervousness, sweating, and eventually coma. Treatment involves the immediate administration of glucose intravenously to elevate blood glucose levels.

Additional notes (Nutrition and Biochemistry)

• Obesity: Accumulation of excess body fat; it is defined as 20% above the standard weight for a given age, sex, and race. It is the most common problem related to overnutrition.
• Pathological Types of Obesity:
  • Hyperplastic: Lifelong increased number of fat cells.
  • Hypertrophic: Increased size of fat cells.
• Importance of Obesity: Obesity increases the risk of several diseases, including cardiovascular disorders (HTN, atherosclerosis, angina, varicose veins), liver problems (fatty liver, cholecystitis, cholelithiasis). Metabolic problems (Gout, DM-II). Gynecological disorders (Amenorrhea, oligomenorrhea. Endometrial Carcinoma).
• Assessment of Obesity: Calculation of the Body Mass Index (BMI) to estimate the relative risk of an overweight or obese state.
  • BMI: Calculation of weight (kg)/height(m)^2
• Types of Obesity:
  • Exogenous: Caused by consuming more calories than expenditure through reduced physical activity.
  • Endogenous: Caused by different underlying conditions such as hormonal imbalances, genetic predisposition.

Additional Notes (Vitamins)

• General Characteristics of Vitamins: Vitamins are organic components. They are required in very small quantities. They are not synthesized by the body for proper function.
• Classification of Vitamins: Fat-soluble (A, D, E, K) and Water-soluble (C and B complex).
• Vitamin A: Group of unsaturated nutritional compounds (retinol/retinal/retinoic acid, and carotenoids). Daily requirement depends on age (infants, men, women, pregnant, and lactating). It plays vital roles like vision, gene transcription, immune function, embryonic development, bone metabolism, and more.
• Vitamin D: Group of fat-soluble secosteroids. (Cholecalciferol and ergocalciferol). It is made in the skin or ingested and requires 2 hydroxylations in the body by the liver and the kidneys to be biologically active. Crucial for Calcium balance.
• Vitamin E: A group of compounds that include tocopherols and tocotrienols. They are naturally occurring antioxidants. Daily requirement depends on age.
• Vitamin K: A group of structurally similar fat-soluble vitamins. It is crucial for blood clotting and plays a role in oxidative phosphorylation. Synthesis can occur in the intestines. Daily requirement depends on age.
• Water-Soluble Vitamins (B-Complex and C): Several B types that play crucial roles in energy-releasing mechanisms, protein, glucose and fat metabolism, and more. Water-soluble vitamins are not stored in significant quantities so they need to be ingested daily in proper amounts.

Test your knowledge on the fundamental principles of biochemistry with this quiz. Explore the essential concepts such as the role of enzymes, the building blocks of proteins, and the energy currency of the cell. This quiz will help you reinforce your understanding of the biochemical processes that sustain life.