Biology Chapter on Lipids and Proteins

Macronutrients

• Macronutrients are nutrients the body needs in large quantities to supply energy and maintain structure and systems.
• The three main macronutrients are carbohydrates, proteins, and fats.

Carbohydrates

• Carbohydrates are organic compounds composed primarily of carbon, hydrogen, and oxygen (typically in a 2:1 ratio of hydrogen to oxygen).
• They range from simple sugars (3-7 carbon atoms) to complex polymers.
• Carbohydrates are the body's primary energy source—providing 80% to 100% of caloric intake.

Classification of Carbohydrates

• Monosaccharides: Simple sugars; examples include glucose (dextrose), fructose (levulose), and galactose.
  • Glucose is the body's primary fuel source.
  • Fructose is converted to glucose.
  • Galactose is not found freely in foods but is converted to glucose.
  • These are absorbed directly into the bloodstream from the small intestine without digestion.
• Disaccharides: Double sugars; examples include sucrose (table sugar), lactose (milk sugar), and maltose.
  • These must undergo hydrolysis to be broken down into simple sugars before absorption.
• Polysaccharides: Complex sugars; examples include starch, dextrins, cellulose, fiber, and glycogen.
  • Starch is the most important polysaccharide, serving as a main source of energy and found in grains, potatoes, and legumes.
  • Starch converts to glucose during digestion.
  • Dextrins are intermediate breakdown products of starch.
  • Cellulose provides dietary bulk, aids digestion, and stimulates peristalsis. Sources include vegetable stems, leaves, and coverings.
  • Soluble fiber can delay gastric transit and glucose absorption.
  • Insoluble fiber accelerates gastric transit, increases fecal weight, and slows starch hydrolysis.
  • Pectins are non-digestible, gel-like polysaccharides found in fruits; used in jellies to treat diarrhea; bind cholesterol, reducing absorption.
  • Glycogen is also known as animal starch, formed from glucose and stored in liver and muscle tissues. Used for energy production.

Carbohydrate Digestion

• Mouth: Amylase, an enzyme in saliva, begins the breakdown of starch into dextrins and maltose.
• Stomach: No enzymes for carbohydrate digestion; ptyalin (salivary amylase) action may continue a little.
• Small Intestine: Amylopsin, a pancreatic enzyme, breaks down starch further. Intestinal juice contains disaccharidases (sucrase, lactase, maltase) that break disaccharides into monosaccharides in preparation for absorption.

Fats / Lipids

• Fats are organic compounds composed mainly of carbon, hydrogen, and oxygen.
• Fats constitute a class of fat and fat-related compounds called lipids.
• Fats supply a more concentrated source of energy than carbohydrates.
• Fats surround and protect vital organs from shock and injury.
• Fats help maintain body temperature.
• Fats facilitate the absorption of fat-soluble vitamins (A, D, E, K).
• Fats create satiety and delay hunger sensations.

Fat Classification

• Simple Lipids: Neutral fats (e.g. triglyerides).
• Compound Lipids: Combinations of fats and other components (e.g. phospholipids, glycolipids, lipoproteins).
  • Phospholipids consist of fatty acids, phosphoric acids and nitrogenous bases.
  • Glycolipids consist of fatty acids combined with carbohydrates and nitrogenous bases.
  • Lipoproteins are made up of lipids and proteins; found in cell and organelle membranes.
• Derived Fats: Derivatives resulting from fat digestion or other complex products (e.g., glycerol, sterols).
  • Glycerol is a water soluble component of triglycerides, and is inconvertible with carbohydrates.
  • Steroids are a class of fat-related substances containing sterols. They're complex fat-like compounds found in body tissues, especially the brain, nerve tissues, bile, blood and the liver where most cholesterol is synthesized.

Fatty Acids

• Fatty acids are the key refined fuel forms of fats that cells use for energy.
• Saturated fatty acids: no hydrogen can be added; abundant in animals.
• Monounsaturated fatty acids: have a double bond between two carbon atoms.
• Polyunsaturated fatty acids: have two or more double bonds.

Omega-6 / Omega-3 Ratio

• Plants produce omega-3 and omega-6 oils, but omega-6 is more common.
• Humans should consume more omega-3 fatty acids from sources like cod liver oil, mackerel, or fish.

Fat Digestion

• Mouth: Mechanical mastication
• Stomach: Mechanical separation of fats, and some fatty acids. Small amounts of gastric lipase.
• Small Intestine: Emulsification by bile salts. Pancreatic lipase breaks triglycerides into fatty acids and glycerol.

Protein

• Proteins are essential for building and repairing tissues, producing enzymes, and creating hormones.
• Proteins come from the Greek word "protos" meaning primary or first in rank.
• Proteins are vital for the structure and function of all living cells.
• Protein structure is determined by the unique sequence and arrangement of amino acids.

Protein Classification

• Simple Proteins: Amino acids only when hydrolyzed. Examples include albumins, globulins, glutelins and prolamins, albuminoids, histones, protamines.
• Compound Proteins: Combination of simple proteins and a non-protein substance (prostetic group). Examples include nucleoproteins, mucoproteins, glycoproteins, lipoproteins, phosphoproteins, chromoproteins, and metalloproteins.
• Derived Proteins: Products from the hydrolysis of proteins; categorized into primary-derived proteins (denatured proteins) and secondary-derived proteins which are results from partial hydrolysis of proteins (e.g., proteoses, peptones, polypeptides, and peptides).

Protein Digestion

• Mouth: Mechanical mastication
• Stomach: Pepsin breaks down proteins, and activated by the hydrochloric acid.
• Small Intestine: Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidases) break proteins down into peptides and amino acids, absorbed. Intestinal enzymes (aminopeptidase, dipeptidase) further break peptides and dipeptides into amino acids for absorption.

Recommended Daily Protein Intakes

• Daily recommendations for protein intake vary based on age, gender, pregnancy, and lactation.

Protein Sources

• Complete proteins include meat, fish, poultry, eggs, milk, and cheese.
• Incomplete proteins include legumes and nuts.
• Some grains and cereals may also provide some protein.

Protein Energy Malnutrition (PEM)

• PEM is a condition related to insufficient intake of protein and or energy.
• Two forms of PEM include marasmus (long deprivation of food) and kwashiorkor (sudden deprivation of food).