Feeding and Digestion: NutrientsAll animals are ingestive heterotrophs.But the means by which they procure their food are as diverse as the animals themselves.

NutritionNutrition is the process of obtaining the matter necessary for growth and healthy maintenance of the body.The science of Nutrition is the study of

the chemical compounds that compose and maintain the animal body how animals obtain them via synthesis or ingestion

Feeding is the process of obtaining and ingesting foods.Digestion is the enzymatic process of breaking down ingested food particles and molecules into smaller subunits that an animal can distribute throughout its body via the bloodstream.Absorption (a.k.a. assimilation) is the passage of molecules from outside to inside of living tissues.

The inside (lumen) of the GI tract is contiguous with the environment at one or both ends.

The lumen is a passageway through the living tissues, not considered truly part of them.

Feeding intervals vary among species. Humans in industrialized nations usually eat three meals a day Most herbivores graze or browse often throughout the day Large snakes might eat only 3-4 times a year

Nutrition: Building and Maintaining a BodyA typical, healthy human male body is composed of approximately

62% water 16% protein 16% lipid 6% minerals ~ 1.5% nucleic acids 1% carbohydrate

How do animals acquire building blocks of these body components? What is the function/purpose of each component? What problems must animals solve to make enough of their components?

ProteinArguably the most important component of the animal body, protein comprises almost half of the dry weight of an adult animal.Protein functions in animals include

physical structure of much of the body components of many hormones contribute to oxygen transport driving enzymatic reactions

blood clotting in vertebrates components of immune system comprise most of muscle mass

Protein StructureProteins are polymers of amino acids joined by peptide bonds.

o dipeptide - two covalently bonded amino acidso tripeptide - three covalently bonded amino acidso polypeptide - relatively short chain of covalently bonded amino acids

Animals require 20 standard amino acids (22 in some species) to make protein.

Structural ProteinsStructural proteins form animal infrastructure.Examples:

o muscleo collageno silko keratin

Functional ProteinsFunctional proteins are components of biological machinery.Examples:

o muscleo enzymeso channel & transporter

proteinso antibodieso some hormoneso snake venomso hemoglobin

Nitrogen: A Limiting FactorNitrogen comprises about 16% of protein mass.Although it is the most abundant gas in our atmosphere (78%), it can be a limiting factor because it must be fixed by nitrogen-fixing organisms.In habitats where nitrogen is difficult to fix (e.g. acidic bogs), plants have evolved special adaptations to procur nitrogen.Where nitrogen is limiting, herbvivores must compete for nitrogen resources.This limits their population size, which sends ripple effects up the trophic levels.

Essential Amino AcidsPlants can synthesize all the amino acids, vitamins, and other biological molecules they need. Animals cannot.Amino acids that cannot be metabolically synthesized by a particular animal are said to be essential.

must be obtained in the diet. differ slightly among species, usually numbers about 10 in any given species

A conditionally non-essential amino acid is one that is needed for only part of the life cycle

example: Human children cannot make histidine, but healthy adults can. can be manufactured as long as a different nutrient precursor is available

example: Humans can make tyrosine if they have enough methionine precursor.

Amino Acid DeficiencyPlants are the ultimate source of essential amino acids for all animals.Herbivores generally have less trouble procuring essential amino acids than carnivores because they obtain them from

their plant food their intestinal microbiome flora

Animals cannot store amino acids.When an excess of amino acids is consumed

amino terminals are stripped off these are excreted via the renal system as nitrogenous waste the remaining carbon chains are used for other purposes

Consequence: Animals must constantly ingest the essential amino acids they needor they will suffer deficiency of the proteins containing them.Because most proteins contain at least a few residues of most amino acids,animals require all amino acids--essential and non-essential--at all times.If one is missing, the protein cannot be made.

Example: Life Without LysineLysine, a component of many proteins, has an affinity for serotonin receptors.Lysine deficiency has been linked to anxiety disorders in humans suffering lysine insufficiency.Rice is a dietary staple of more than 70% of the world's population. In some cases, rice is almost the only food readily available. Rice, like many grains, lacks lysine.Lysine deficiency is a worldwide problem because of this. Symptoms include

nausea and dizziness anxiety hair loss anemia muscle wasting connective tissue deterioration

Beans do contain lysine.A diet of rice and beans provides complete protein for a human.(Usually, combining a whole grain with any legume, seed, or tree nut will do the same.)This is one instance in which a GMO might come to the rescue, though they haven't yet quite gotten all the bugs out of the system.

LipidsLipids are a diverse class of molecules loosely linked by the presence of saturated or unsaturated fatty acid chains.Lipid functions in animals include

long-term energy storage signaling via activation of G protein-coupled or nuclear receptors cushioning of external body parts cushioning of internal organs and structures insulation in homeotherms/endotherms cell membrane component precursors to many cell products, including some hormones component of cholesterol facilitate prostaglandin manufacture play a role in inflammation store fat-soluble vitamins

Fatty acids with more than one double bond are known as polyunsaturated fatty acids (PUFAs), which is adorable.

Fatty AcidsFatty acids can be identified with a standardized "shorthand" system.For example, linoleic acid (left) can be written as:

18.2ω6in which

18 is the number of carbons in the chain 2 is the number of double bonds in the chain 6 is the position of the first double bond, counting from the CH3

terminal (ω)Linoleic acid is an "omega-6" fatty acid.The first double bond of an "omega-3" is three bonds away from its CH3 terminal.)In humans, several omega-3 fatty acids are essential nutrients.

Alpha-linolenic acid (ALA) iso a precursor for many cellular products (including other

fatty acids)o manufactured by many plantso found in common food items such as

flax seed canola oil walnuts soy beans and soy products

Docosahexaenoic acid (DHA) is

o involved in infant brain and retinal developmento required for normal brain function in adultso preferentially taken up by the brain over other fatty acidso anti-inflammatory (which has a cascade of health

benefits)o manufactured by marine microalgaeo stored in fatty tissue (especially liver) of oily marine fish

(anchovies, herring, etc.) Eicosapentaenoic Acid (EPA) is

o involved in infant brain and retinal developmento required for normal brain function in adultso preferentially taken up by the brain over other fatty acidso anti-inflammatory (which has a cascade of health

benefits)o precursor to other fatty acids, including DHAo manufactured by marine microalgaeo stored in fatty tissue (especially liver) of oily marine fish

(anchovies, herring, etc.)Fish can either manufacture EPA from dietary precursors or obtain it from algae.

Biologically Important LipidsClasses of lipids with biological significance include

triglycerides (fats and oils) - glycerine bound to three fatty acid chains

phospholipids - phosphate group bound to two fatty acid chains

waxes - chains of alkanes or esters derived from alcohols and fatty acids

sterols - diverse group; linked carbon rings

CarbohydratesCarbohydrates are a family of macromolecules providing

fuel for the Krebs Cycle mobile energy source in blood

o glucose (most animals) o trehalose (many insects)

energy storage (short term, compared to fats) aso glycogen (animals, fungi) o amylose and amylopectin (plants)

structural support as o cellulose (plants, Chytrid fungi) o hemicellulose (plants) o chitin (fungi; chitin-bearing animals)

Carbohydrates are polymers of sugars (saccharides) joined by covalent glycosidic bonds.Simple carbohydrates contain one or two sugars:

o monosaccharide - one carbon ring o disaccharide - two carbon rings

Complex carbohydrates are chains of sugars:o oligosaccharide - short polymer of 3 - 10 covalently bonded monosaccharides o polysaccharide - polymer more than 10 covalently bonded monosaccharides (linear or branched)

Biologically Significant Plant PolysaccharidesGreen Plant Structural Polysaccharides

celluloseo unbranched polymer of glucoseo form via Beta 1,4 glycosidic bondso most animals lack enzymes to catabolize Beta 1,4 glycosidic bondso the most abundant organic molecule on earth

hemicelluloseo branched polymer of glucoseo shorter (fewer monomers) than cellulose

Green Plant Storage Polysaccharideso amylose

helical glucose polymers of 500 to 20,000 monomers form via Alpha 1,4 glycosidic bonds animal amylases (e.g., in saliva) can break Alpha 1,4 glycosidic

bondso amylopectin - branched glucose polymers of between one and two

million monomers Most animals lack the enzymes to digest these. Herbivores employ a complex intestinal microbiome of protists and bacteria

that manufacture cellulases.

Biologically Significant Animal PolysaccharidesAnimal Structural Polysaccharide

chitino polymer of N-acetylglucosamine (a glucose derivative)o differs from cellulose in substitution of a carbon and nitrogen

containing amyl group for the hydroxyl group (OH) found in cellulose.

Chitinases found in bacteria and fungi can break down chitin.

Animals lack intestinal chitinase. Animals with chitinous cuticle/exoskeleton produce

chitinases in the epithelium. second most abundant organic molecule on earth

Animal Storage Polysaccharideglycogen

highly branched polymer of glucose form via Alpha 1,4 glycosidic bonds In vertebrates

manufactured/accumulated in response to insulin broken down into glucose in response to

glucagon

Nutrient Energy ValuesProteins, Carbohydrates, and Lipids to not provide the same energy to animals ingesting and digesting them. Lipids have the highest energy density (9.3 - 9.5 kcal/g) Mixed carbohydrates have the lowest energy density (4.0 - 4.1 kcal/g) Protein energy density (net) varies with nitrogen excretion product:

4.85 kcal/g in ammonia producers 4.77 kcal/g in urea producers 4.85 kcal/g in uric acid producers

MineralsOf course, C H O N are not the only elements comprising living organisms.Minerals are inorganic regulators required for various metabolic functions.Minerals do not provide energy, but they are involved in the Krebs Cycle.Minerals function in

maintenance of osmotic pressure regulation of pH cell membrane permeability normal function of muscle and nerve cells structural components of the skeleton component of hemoglobin (iron) component of thyroxin (iodine) acting as enzyme cofactors the list goes on!

About 40% of proteins are metalloproteins that contain one or more mineral atoms. Animals must ingest minerals to provide these important functional atoms.

Macrominerals are needed in relatively larger quantities. calcium phosphorus magnesium sodium potassium chloride sulfur

Microminerals are needed in relatively smaller quantities. iron manganese copper iodine zinc cobalt fluoride selenium

Minerals are essential nutrients: organisms cannot synthesize chemical elements. (derp)

VitaminsMany vitamins are essential nutrients.Essential vitamins differ among species. Plants have no essential vitamins: They can synthesize all the vitamins they need. Vitamins are small organic molecules needed in very small quantities for normal animal function. Many act as coenzymes in a variety of biochemical reactions.Others are precursors for components of vital biological molecules such as visual pigments.

Ever wonder why everyone tells you carrots are good for your vision?

Carrots are loaded with carotenoid pigments, notably β-carotene. Carotenoids serve as light-capturing antenna pigments in plant photosystems. Animals cannot manufacture Vitamin A (retinol) de novo They can partially break down β-carotene molecule to yield retinol's precursor. Retinol serves as the light-capture component in rhodopsins, the visual pigments in animal photoreceptors.

Evolution as opportunism:Animals would not have been able to evolve visual systems as we know them today if they had not ingested the light-capturing molecules manufactured by plants.

A better success story than lysine-enriched GMO rice is Golden Rice, genetically modified to produce beta-carotene, precursor to vitamin A.

(Vitamin A deficiency is estimated to be the cause of death of 670,000 children under the age of five every year.)