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Lecture 18

BIO 102 Lecture 18: Lecture 18-19: Chapter 35 - Nutrition and Digestion

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Quinnipiac University
BIO 102
Jack Kronengold

● Nutrients - substances obtained from the environment that organisms need for their growth and survival ● 6 major categories: ○ Carbohydrates (sugars, starches) ○ Lipids (fats, oils) ○ Proteins ○ Minerals ○ Vitamins ○ Water ● Lips, Carbohydrates and Proteins - supply energy ○ Majority from carbohydrates and lipids ○ These molecules are broken down by digestion to their subunits, which are used during cellular respiration ○ Energy from these subunits is released and is captured in ATP ● Energy content from nutrients is measured in Calories a unit that represents 1,000 calories ○ A calorie is the amount of energy required to raise the temperature of 1 gram of water 1*C ○ About 60% of the caloric energy in food is released as heat; the remaining 40% is captured in ATP ○ The average human burns 70 Calories/hour at rest, and up to 20 Calories/minute during exercise ■ People differ in metabolic rate, the speed at which cellular reactions occur ● Carbohydrates - source of quick energy ○ Include sugars: ■ Glucose (from which cells derive most of their energy) ■ Sucrose (table sugar; glucose + fructose) ■ Polysaccharides (long chains of sugar molecules) ■ Cellulose, starch, and glycogen are all polysaccharides composed of chains of glucose ● Cellulose - the major structural component of plant cell walls, is the most abundant carbohydrate on the planet ○ Only a few animals are able to digest cellulose ● Starch - the principle energy-storage material of plants, and a major source of energy for humans and many other animals ● Glycogen - used by animals for short-term energy storage (“carbo-loading”) ○ Animals (including humans) store glycogen in the liver and muscles ○ Although humans can accumulate hundreds of pounds of fat, most can store less than a pound of glycogen (can power 18 miles of running) ● Fats and oils - the most concentrated energy source ○ Contain over twice as many Calories per unit weight as do carbohydrates or proteins (9 Calories/gram vs 4 Calories/gram) ○ Fat deposits provide insulation for animals living in cold environments, such as seals, whales and walruses ● Essential nutrients - certain raw materials which cannot be synthesized and must be supplied in the diet ● Essential nutrients for humans include certain: ○ Fatty acids ○ Amino acids ○ Minerals ○ Vitamins ○ Water ● Certain Fatty acids are essential in the human diet ○ Fats and oils provide a source of energy, but also provide essential fatty acids ○ Serve as raw materials used to synthesize molecules in a wide range of physiological activities (absorbing fat soluble vitamins, cell division, immune response) ○ Sources: fish oils, canola oil, soybean oil, flaxseed, and walnuts ● Amino Acids - form the building blocks of protein ○ Proteins form muscle, connective tissue, nails and hair ○ They act as enzymes, receptors on cell membranes, and antibodies ○ The human body cannot synthesize 9 (adults) or 10 (infants) of the 20 different amino acids used in the proteins ○ Essential amino acids must be obtained from protein-rich foods: meat, milk, eggs, corn, beans, soybeans ○ Protein deficiency can result in debilitating conditions: kwashiorkor (atrophied muscles) which occurs most frequently in poverty-stricken countries ○ Low blood proteins = low osmotic pressure = leaky capillaries ● Minerals - elements required by the body ○ Minerals are elements that play many crucial roles in animal nutrition and can only be obtained in the diet or dissolved in drinking water ○ Calcium, magnesium, and phosphorus are major constituents of bone and teeth ○ Sodium, calcium, and potassium are needed for muscle contraction and the conduction of nerve impulses ○ Iron is a central component of hemoglobin in the blood, and iodine is found in hormones produced by the thyroid gland ○ Animals also require trace amounts of zinc, copper, and chromium ● Vitamins - play many roles in metabolism ○ Vitamins are organic molecules that animals require in small amounts for normal cell function, growth and development ○ Two categories for human vitamins: water soluble or fat soluble ○ Water Soluble Vitamins ■ Include vitamin C and the nine compounds that make up the B-vitamin complex ■ Not stored in appreciable amounts - they dissolve in watery blood plasma and are filtered out by the kidneys ■ Most water-soluble vitamins act as coenzymes ■ They work in conjunction with enzymes to promote chemical reactions that supply energy ■ Deficiency of the B vitamin niacin can cause swollen tongue, skin lesions of pellagra, nervous disorders ■ folic acid (b vitamin) is required to synthesize thymine, a component of DNA - deficiency impairs cell division throughout the body ○ Fat Soluble Vitamins ■ A,D,E and K - have a variety of functions ■ Can be stored in body fat and may accumulate in the body over time ■ Vitamin A - used to synthesize the light-capturing molecule in the retina of the eye ■ Vitamin D - required for bone formation; its deficiency can lead to bone deformities such as rickets ■ Vitamin E - antioxidant, neutralizing free radicals that form in the body ■ Vitamin K - helps to regulate blood clotting ● Human body is about 60% water ○ Person can survive longer without food than without water ○ All metabolic reactions occur in a watery solution, and water participates directly in hydrolysis reactions that break down proteins, carbohydrates, and fats ○ Water is the principal component of saliva, blood, lymph, interstitial fluid, and the cytosol within each cell ● Digestion is the process that physically grinds up food and then chemically breaks it down into simpler molecules ● The animal digestive system consists of a series of compartments in which food is processed, and organs that produce secretions that aid in digestion ● All digestive systems perform five tasks: ○ Ingestion - food is brought into the digestive tract through an opening, usually called a mouth ○ Mechanical digestion - the food is physically broken down into smaller pieces with a greater surface area than larger particles, allowing digestive enzymes to work more efficiently ○ Chemical digestion - digestive chemicals and enzymes break down large food molecules into smaller subunits ○ Absorption - the small subunits are transported out of the digestive tract through cells lining the digestive tract to the blood for use by body cells ○ Elimination - indigestible materials are expelled from body ● Sponges - digestion occurs within single cells ○ Lack a digestive system and rely exclusively on intracellular digestion ○ This limits their food to microscopic particles ○ Sponges circulate seawater through pores in their bodies ○ Specialized collar cells engulf food particles in the water and ingest them by phagocytosis, forming a food vacuole ○ The food vacuole fuses with a lysozome, a membrane enclosed packet of digestive enzymes ○ The digested food molecules are absorbed into the cell cytoplasm ○ Indigestible material is expelled ● Simplest digestive system: a chamber with one opening (gastrovascular cavity) ○ All animals (except sponges) have evolved a chamber within the body in which food is broken down by enzymes outside the cells (extracellular digestion) ○ A sac with one opening is the simplest digestive system, and is found in the cnidarians, such as sea anemones, hydra, and sea jellies ○ How the gastrovascular cavity works: ■ The animals stinging tentacles capture prey and push the prey through the mouth into the gastrovascular cavity ■ Gland cells lining the cavity secrete enzymes that begin digesting the prey ■ Nutritive cells lining the cavity then absorb the nutrients and also engulf partly digested food particles by phagocytosis ■ Further digestion is intracellular, within food vacuoles in the nutritive cells ● Most animals have tubular digestive systems with specialized compartments ○ These systems are one-way tubes that begin with a mouth and end with an anus ○ Specialized regions within the tube: ■ Physically grind up the food ■ Enzymatically break it down and absorb the nutrients ■ Expel the wastes through the anus ○ Earthworm ■ Ingests soil that passes through the esophagus (muscular tube leading from the mouth to the crop [an expandable sac where food is stored]) ■ Food is released into the gizzard, where sand grains and muscular contractions grind it into smaller particles ■ In the intestine, enzymes digest food particles into small molecules that are absorbed ■ Undigested organic matter is expelled through the anus ● Major organs of the vertebrate digestive system: ○ Mouth ○ Esophagus ○ stomach ○ Small Intestine ○ Large Intestine ○ Some vertebrates have other specialized chambers depending on their diet ● Birds ○ Lack teeth and swallow their food whole ○ Their stomachs grind food ○ The food passes through a muscular esophagus and enters the crop, which stores and moistens the food ○ The food then enters the stomach which has 2 chambers ■ The first chamber secretes protein-digesting enzymes ■ The second chamber (thick walled muscular chamber) grinds the food ○ Food then enters the gizzard, where the food is ground further ○ Then to the small intestine where it is further digested and the nutrients are absorbed ● Specialized stomachs with microbiomes allow ruminants to digest cellulose ○ Ruminant animals (including cows, sheep, goats and camels) can obtain energy from cellulose ○ Ruminants have multiple
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