BIOQUI - 27/07/2023

Synthesis of Lipids and Its Importance

Introduction to Lipid Synthesis

• The synthesis of lipids is a complex biochemical process, yet it is presented simply for educational purposes.

• Understanding lipid synthesis is crucial as it has been vital for the survival of the Homo genus over millions of years.

• Efficient fat synthesis has provided energy reserves that have helped humans survive various catastrophic events throughout history.

Health Implications of Lipid Synthesis

• While efficient fat synthesis aids in energy storage, it also contributes to health issues like obesity.

• Obesity can lead to serious health conditions such as atherosclerosis and myocardial infarction.

Structure and Characteristics of Fatty Acids

Components of Fatty Acids

• Fatty acids consist of two main parts: a hydrocarbon chain and a carboxylic acid head.

• The hydrocarbon chain can vary in length from 3 to 24 carbon atoms, influencing its properties.

Properties of Hydrocarbon Chains

• Hydrocarbon chains are hydrophobic due to their non-polar covalent bonds, making them incompatible with polar molecules like water.

• The carboxylic acid group can exist as a carboxylate ion or retain its polar characteristics, allowing fatty acids to interact with both hydrophilic and hydrophobic environments.

Role of Lipids in Membrane Formation

Membrane Structure

• Lipids form cellular membranes through bilayer structures that exhibit amphipathic properties.

• The arrangement allows polar heads to face outward towards water while hydrophobic tails face inward, creating a stable barrier.

Example: Phospholipids

• Phosphatidylcholine is highlighted as one of the most abundant phospholipids in cell membranes, consisting of glycerol, phosphate, choline, and two fatty acid chains.

Types of Fatty Acids and Their Health Impact

Saturated vs. Unsaturated Fatty Acids

• Saturated fatty acids lack double bonds; they generally have higher melting points compared to unsaturated ones.

Understanding Atherosclerosis and Fatty Acids

Overview of Unsaturated Fats

• The discussion begins with a focus on atherosclerosis, highlighting the health benefits of unsaturated fatty acids found in vegetable oils, which generally have lower melting points and remain liquid at room temperature.

Saturated vs. Unsaturated Fats

• An illustration contrasts saturated fats with unsaturated fats, noting that unsaturated fats contain double bonds where hydrogen atoms are positioned on the same side (cis configuration), making them less healthy compared to trans fats.

Essential Fatty Acids

• Essential fatty acids like linoleic acid and arachidonic acid are introduced; linoleic acid has 18 carbons and two double bonds, while arachidonic acid is derived from it and contains 20 carbons with four double bonds.

Dietary Sources of Fatty Acids

• These essential fatty acids must be consumed through diet as they are abundant in both animal and plant fats, ensuring no significant deficiency occurs.

Synthesis of Fatty Acids

• The synthesis process is described as complex and cyclical, primarily utilizing NADPH for reduction during the anabolic pathway to create various chain lengths of fatty acids.

Mechanisms Behind Fatty Acid Elongation

Initial Steps in Synthesis

• The synthesis starts with acetyl-CoA and malonyl-CoA; each cycle elongates the fatty acid by two carbon units using these substrates.

Location of Synthesis

• While fatty acid synthesis occurs in the cytosol, elongation beyond 18 carbons takes place within mitochondria. This distinction emphasizes different cellular environments for various processes.

Role of Carbohydrates in Energy Production

• Carbohydrates convert into glucose through glycolysis, producing pyruvate that transforms into acetyl-CoA inside mitochondria—highlighting how energy availability influences fatty acid synthesis pathways.

Citrate's Role in Transporting Acetyl-CoA

Citrate Conversion Process

• When energy levels are high, citrate accumulates due to inhibited enzymes in the Krebs cycle. Citrate exits mitochondria where it is converted back into oxaloacetate and acetyl-CoA by citrate lyase.

Formation of Malonyl-CoA

• Once outside mitochondria, part of acetyl-CoA converts into malonyl-CoA through an enzymatic reaction involving bicarbonate—this step is crucial for initiating the fatty acid synthesis cycle.

The Complex Nature of Fatty Acid Synthase

Structure and Functionality

• The enzyme complex known as fatty acid synthase consists of multiple catalytic regions that sequentially facilitate the reduction and elongation processes necessary for synthesizing long-chain fatty acids.

Understanding Fatty Acid Synthesis

Overview of Catalytic Activities

• The synthesis process involves two large molecules that collaborate, each with seven catalytic activities aimed at enhancing efficiency and speed in fatty acid synthesis.

• Acetyl-CoA is converted into malonyl-CoA, where acetyl-CoA has two carbons and malonyl-CoA has three. This sets the stage for the subsequent steps in the synthesis process.

Steps in Fatty Acid Elongation

• The initial compounds (malonyl-CoA and acetyl-CoA) bind to a specific region of the enzyme, initiating a series of steps (two through seven) that elongate the fatty acid chain.

• In this cyclic process, fatty acids grow by two carbon units per cycle, utilizing reduced phosphates at various stages.

Cycle Details for Palmitic Acid

• The overall process is cyclical; for palmitic acid (16 carbons), there are seven cycles of elongation.

• Each cycle adds two carbons except for the first step which incorporates both malonyl-CoA and acetyl-CoA.

Formation of Triglycerides

• Once formed, fatty acids (12 to 24 carbons long) undergo esterification with glycerol to create triglycerides, which are crucial energy storage forms in adipocytes.

• Glycerol consists of three carbon atoms and alcohol groups where fatty acids attach via their carboxylic acid groups.

Clinical Implications: Obesity

• Obesity is highlighted as a significant global health issue linked to excessive fat accumulation in tissues such as the liver and vascular walls.

• Factors contributing to obesity include economic changes leading to increased food availability across various social levels.

Health Risks Associated with Obesity

• Excessive fat can lead to serious conditions like hepatic steatosis and atherosclerosis due to lipid accumulation within blood vessels.

• Atherosclerosis develops from chronic inflammation caused by macrophages attempting to clear accumulated lipids, resulting in foam cell formation.

Parameters for Assessing Obesity

Obesity and Its Impact on Children

Understanding Body Mass Index (BMI) and Obesity Categories

• The classification of body mass index (BMI) is outlined:

• Overweight: BMI of 25 to 30

• Obesity: BMI of 30 to 35

• Severe obesity: BMI of 35 to 40

• Morbid obesity: BMI over 40

Rise in Childhood Obesity

• Observations indicate a significant number of children attending school are obese, often accompanied by overweight parents. This trend highlights the early onset of childhood obesity.

Biological Implications of Obesity

• The increase in adipocytes (fat cells) during childhood leads to permanent changes that make weight loss more challenging later in life.

Contributing Factors to Weight Gain

• Key contributors include:

• High consumption of sugary drinks, with examples like Coca-Cola containing excessive sugar.

• In Northern countries, measures are being taken to limit large bottle sizes and increase taxes on sugary beverages to reduce consumption among children.

Fast Food and Sedentary Lifestyle

• Fast food consumption, characterized by high carbohydrates and fats, along with a sedentary lifestyle, significantly contributes to rising obesity rates among children.

• WHO statistics reveal alarming projections for childhood obesity, estimating that by 2025 there will be around 70 million obese children globally.

Psychological Effects of Obesity

• Young individuals face severe psychological issues related to body image; feelings of rejection and low self-esteem are common among those struggling with weight.

Recommendations for Healthy Eating Habits

• Suggestions include:

• Avoiding oversized portions typically seen at buffets.

• Emphasizing appropriate serving sizes and promoting fruits and vegetables as staples in meals.

• A strong recommendation against sugary sodas is made; water should be the primary beverage choice instead.

Dietary Adjustments for Healthier Choices

• Research indicates that consuming artificial sweeteners may alter gut microbiota, which could have health implications worth exploring further.

• It’s advised to limit not just carbohydrates but also unhealthy fats found in fried foods while still allowing lean meats as part of a balanced diet.

Meal Frequency and Portion Control

• Smaller meals eaten more frequently can help manage hunger better than larger meals.

Importance of Physical Activity

• Regular physical activity is crucial; engaging in moderate exercise for about forty minutes daily can significantly aid weight management alongside dietary changes.

Hydration's Role in Weight Management

• Drinking water before meals can promote satiety by distending the stomach, helping control appetite effectively.

Caution Against Quick-Fix Diet Solutions

Understanding Weight Loss: A Sustainable Approach

The Importance of Time and Lifestyle Changes

• Significant weight loss requires time and a reasonable diet; extreme short-term diets are ineffective as they lead to rapid weight regain.

• Emphasizing a lifestyle change is crucial, focusing on balanced meals with lean meats and salads while minimizing carbohydrates.

• Daily exercise is essential for sustained weight loss over months, along with support groups and professional guidance when challenges arise.

Medical Interventions for Obesity

• For morbid obesity, surgical options like gastric bypass create a small stomach pouch that connects directly to the intestine, reducing food absorption.

• Other surgical methods include gastric bands that limit food intake and biliopancreatic diversion surgeries aimed at altering digestion processes.

Pharmacological Options in Weight Management

• Current medications do not offer miraculous solutions; some drugs like amphetamines suppress appetite but carry risks of dependency.

• Antidepressants may also be used in specific cases for their appetite-suppressing effects, though their efficacy can be limited.

Mechanisms Affecting Lipid Absorption

• Low-density lipoproteins transport lipids throughout the body; certain medications can inhibit lipid absorption in the intestines.

• Acetylcysteine has been noted to block cholesterol absorption within the intestines.

Neurological Influences on Eating Behavior