PNB Chapter 4

Why do animals require a continuous influx of energy?

To maintain bodies against entropy + provide energy for respiration + circulation + other physiclogical processes

How animals handle need for energy

Almost all animals are heterotrophs, not autotrophs

Varies on whether they are invertebrates or vertebrates

Whether they can survive long periods of hypoxia (abnormally low O,)

What food sources they have available to them

All animal cells require 02, but many can survive periods of hypoxia, and cells can either use anaerobic or aerobic metabolic pathways

All animals must provide

• Pathway for food intake

• A site optimized for mechanical, chemical and enzymatic digestion

• A site for absorption of amino acids, sugars, lipids, minerals, water, small organic molecules

• A pathway for the loss of waste products (in addition to the loss of CO)

Food represents

Energy trapped in the chemical bonds between atoms found in food

Energy was used to form bonds —> that energy can be released + captured when broken

Why is this the case?

Energy can only change its form —> animals must develop strategy to effectively capture energy when those bonds are broken

Amount of energy

Not all chemical compounds have, same structure or complexity —> diff amount of energy provided

Calorie

Unit of energy inherent in chemical bonds

calorie: energy required to raise temp of 1mL of water 1 degree C

Calorie (CAPS): energy required ,to riase temp of 1L of water 1 degree C

Proteins

4.2 Cal/gm

Must lose nitrogen from amino acids

Can feed breakdown products of proteins into glycolysis, citric acid cycle, oxidative phosphorylation

Carbs

4.5 Cal/gm

Generate CO as primary waste product through glycolysis, citric acid cycle, oxidative phosphorylation

Fats

9 Cal/gm

Feed two carbon fragments into glycolysis, citric acid cycle, oxidative phosphorylation

Traits that point to common origin of life on Earth

All animals have enzymatic machinery to generate ATP from glucose by glycolysis, citric acid cycle, oxidative phosphorylation + use ATP as universal energy source within cells

Determining reasonable energy elevel required by most animals

Basal metabolic rate = 70 * (weight in Kg)³^/4

Simplified way to determine minimal energy to keep animal alive

• Reptiles - 0.23 Cal/g/hr

• Mammals - 0.37 Cal/g/hr

• Birds - 0.4 Cal/g/hr

Sun

Primary source of energy captured primarily through photosynthesis

Each minute ~4.2 kilowatt-hours/m² of energy falls on Earth from sun

20 days: energy carried by sunshine = all energy stored in coal, natural gas, oil on planet

Efficiency of photosynthesis: dependent on wavelength of light

Light used for photosynthesis only about 45% of sunlight —> allows for approx 11% of available sunlight being captured by photosynthesis

Geothermal vents

On ocean floor, provide energy in form of H2S (hydrogen sulfide) +

high temperatures (750°F/hot enough to melt lead)

Properties of geothermal vents

• Temperatures up to 860'F - ranging from 140°F to 860'F compared to normal 40°F of seawater

• High pressures than prevent water boiling

• Extremely acidic water - pH around 2.8

• No sunlight

• Rich source of H2S —> provides 174 Cal/mol compared to 686 Cal/mol for glucose

• Presence of extremeophilic bacteria that use HyS as an energy source, which are then eaten by animals.

Early life from geothermal vents

Suggested by many scientists

High abundance of NH3 + CH4 needed for amino acid synthesis, plenty of heat, presence of many organic molecules

Problem: high heat

Radioactive Decay of Metals

Depths of Mponeng gold mine in South Africa: bacterium Candidatus Desulforudis audaxviator grows effectively in absence of light or any other energy source than energy provided by radioactive decay of metals.

Radioactive-decay support of bacterial colony can in turn support growth of animals as found in geothermal vents

• Subsurface realm has twice volume of oceans + thought to be home to 1030 cells - one of biggest, diverse, oldest habitats on planet

Radiation from unstable elements —> splits water into H2 + chemically reactive peroxides (OOH)

The oriental hornet

Outer cuticle absorbs sunlight to generate energy

• Composed of of brown and yellow banded segments that sandwich layer of yellow pigment - xanthopterin

  • Brown segment: grating-like structure that effectively captures light onto deeper cuticle

  • Yellow band: oval-shaped bumps that increase collection surface area

• Bands are antireflective + light trapping structure

• Absorption of light onto colored bands develops voltage difference —> used by proteins to generate ATP

• Only example of an animal directly capturing energy in sunlight like plant

But gains most calories from consumption of other insects

Molecular H2 and CO in seawater

Recent discoveries: atmospheric trace gases are major energy source for growth + survival of aerobic bacteria in aquatic ecosystems

• H2 and CO: ubiquitous, very diffusible, yield enough energy by oxidation —> supports growth of bacteria (then consumed by animals)

• Especially important energy source in deep oceanic environments with little or no sunlight: concentration is 15- and 2000-fold higher for H2 and CO, respectively compared to atmosphere

• Bacteria express need dehydrogenases + other enzymes to oxidize gases + capture enough bond energy to grow slowly

Animal Requirements

all animals must ingest, idgest, absorb nutrients and lose wastes

Abilities to find and consume food

• Ability to detect food by smell (or chemotaxis), taste, sight, contact.

  • Requires in many cases: nose, eyes, color vision, sense of smell, sense of taste, equally complex nervous system to detect + process information

  • Color vision: ripe food are different color than unripened food.

• Able to bring food into space (hollow tube or cavity) where food can be digested + nutrients can be absorbed

  • Conditions: optimized (pH, presence of ions, etc.) for digestion + absorption

• Space were non-digestible portions of food + other fat-soluble waste products can be lost from body

  • Allows for loss of non-digestible bits of food + hydrophilic waste products that cannot be lost through urine

Steps

1) Feeding: bringing food inside body

2) Digestion: converting large complex molecules into individual building blocks

3) Absorption: bringing needed molecules, ions, water into cells to make available for entire body

• Dependent on specific proteins and/or channels —> bring things inside cells\

4) Waste: providing place fro intestinal flora to survive, grow, provide benefit + for waste products to leave body

What factors affect whether an animal is capable of eating a food source?

• size of food

• shape of food

• taste of food

Filter feeders

Can support large body sizes

Some animals (copepods, amphipods, sponges, bivalves, fish, sharks, whales, flamingos, etc.) filter food from either fresh or salt water

Food particles (phytoplankton, krill, etc.): very small + low density

• Small individually, but estimated 400 million tonnes of Antarctic krill in the Southern Ocean

Filter feeder examples

• Whales: filter large amounts of water to overcome water's low food density

  Chesapeake oysters: strain sea water over gills, capable of filtering 50 gallons/day of seawater

• Fish - basking sharks, manta rays, via filtering of water

• Tunicates - via endocytosis of food trapped on cilia or by
  mucus

• Sea cucumbers - via endocytosis of food trapped on tentacles

• Crustaceans - krill, crabs, barnacles, via filtering of water

• Mammals - Baleen whales, via filtering of water

• Bivalves - oysters, shellfish, via filtering of water.

• Sponges - via endocytosis of food particles trapped on flagella

• Cnidarians - Jellyfish, via filtering and endocytosis

• Birds - Flamingos ingest mud and silty water + separate food particles

Is it possible to survive by removing organic molecules from seawater?

Organic molecules are at even lower concentrations than phytoplankton + need to be taken up by active transport

• Uncommon source of food, but bivalves and polychaetes use active transport to remove organic molecules from seawater - not primary source of energy

Baleen whales

Some of the largest animals on Earth

Filter feeders

Baleen composed of keratin - replaces upper jaw teeth

Water brought into mouth in large volumes, pushed past baleen (efficient filter to trap food), swallowed

Teeth

Optimized for diet type

What challenges are faced by large food masses?

Animals need mechanical methods (teeth, jaws, beaks) to chew, tear or scrape food into their mouths

Mouths/oral cavity also specialized in shape + size of jaw, number of teeth, shape of tongue

Jaws and teeth: designed to mechanically break down food into smaller particles + mix particles with saliva

Saliva: starts enzymatic digestion + aids in swallowing of food into esophagus

Types of teeth

Different types of teeth optimized for diet type + either tearing or grinding of food Carnivores: canine teeth + slashing carnassial molars

Herbivores: large molar with replaceable ridges - helps grind plant material

Some animals: teeth replaced as wear themselves out

• Polyphyodont teeth: replaced (shark teeth(

• Diphyodont: not replaced

Teeth common among vertebrates vs Invertebrates: analogous structure to jaws and teeth (radula)

Tongues

Vertebrate tongue: sensory organ, also moves food within mouth

Hagfish: tongue with keratinized teeth

Invertebrates: no equivalent to vertebrate tongue

Some insects: proboscis - elongated tube —> shares some of properties of vertebrate tongue

Advantages and disadvanrages of eating large food mass at one time

Makes feeding less frequent + less dangerous

Digestive system must be able to store + digest large food mass over long period of time - requires large digestive tract

Liquid digestion

Highly specialized digestive process

Commonly blood feeders - hematophagy

• Blood: rich in proteins + lipids - can be taken without great effort

• Preferred form of feeding for worms, nematodes, lamprey, vampire bats, vampire finches, hood mockingbirds, tristan thrush, oxpeckers

• Have both mouth parts (specialized hollow needle) + anti-clotting agents to penetrate vascular structure of hosts

Effective way to transmit bacteria + other infectious agents between animals

Parasites: commonly liquid feeders + vectors that transmit diseases (tick and Lyme)

Mammals: begin as liquid feeders - dependence on breast milk (wide range of protein, fat, carbohydrates)

• Protein: 1%-15% in humans and rabbits

• Fats: 1%-50% in donkeys and seals

• Carbohydrates: 1%-7%

Milk: nutritious food for newborns but expensive to produce

Digestive Tracts

Tube: food enters one end and waste products leave out the other end

• Foregut (esophagus)

• Midgut (stomach)

• Hindgut (intestinal tract)

Some invertebrates: cavity-style digestive tract, most: digestive tract that is very similar in structure to the vertebrate digestive tract

Size and structure of digestive tract is informative of types of food eaten by animals

Basic types of digestive tracts found in animals

Batch reactors: cavities with one entrance - digestion, absorption, waster-generation occur in same place

• uncommon, only found in invertebrates

Plug-flow reactors: tubes - where digestion, fermentation, absorption, waste generation occurs in different areas

• Found in all vertebrates + many invertebrates

Continuous flow stirred tank reactors: found in ruminants and termites

• Ideal for the digestion of cellulose

Diet Types

Diets are specialized for animals

Divided into following groups based on preferred diet:

• Herbivores - plants

• Carnivores - animal flesh

• Omnivores - plants and animals

• Cucinovores - cooked food

No animal is universal digester

Differences in diets ad the structure and length of the digestive tract

More difficult to digest plant material than animal flesh —> requires longer digestive tract in hindgut herbivores + different size and shape of stomach in carnivores - where protein digestion occurs

Cooking of human food: reduces need for a long hindgut + changes shape and functioning of the mouth and teeth + makes humans uniquely only cucinovore

Digestive tract wall

Invertebrate and vertebrate digestive tract wall: number of similarities, independent of length and preferred diet type

• Single layer of polarized epithelium (apical + basal membranes are anatomically + functionally differentiated)

  • Large surface area —> result of villi (folds) + microvilli (Fick's law)

• Similar secretions of fluids (saliva, acidic, alkaline) + enzymes (proteases, carbohydrases, lipases, nucleases, etc.) into tract or cavity

• Similar absorptive processes (type and number of transporters) are present

  • Ex: GLUT family of glucose facilitated transporters are found in both + amino acid transporters

Simplest digestive tract in invertebrates

Evolved different types of digestive systems based on diets

Simplest: digestive tract with single opening for ingestion of food + expulsion of waste - gastrovascular cavity (commonly found in flatworms, comb jellies, coral, jelly fish and sea anemones)

• Gastrovascular cavities: blind-ended tubes or cavities with single opening

• Cells lining wall of cavity secrete digestive enzymes that digest food —> engulfed by same cells as example of intracellular digestion

• No division of labor - entire structure carries out digestion + absorption

More complex digestive tract

Shares many traits with vertebrate digestive tract

Hollow tube: food entering one end (mouth) + exiting other end (anus)

• Each region of canal has specialized function - digestion or absorption

• Effectively same design of typical vertebrate digestive tract, but vertebrate digestive tracts have some unique adaptations

Crop

Adaptations shared between vertebrate and inertebrate digestive tract

Key trait of enzymatic digestion of food: process takes tiem

• Food stored in crop to provide additional time while food is being digested in stomach

• Common in birds, some dinosaurs, snails/slugs, earthworms, leeches, insects

Gizzard

Aids with digestion

Found in birds, dinosaurs, reptiles, earthworms, fish, crustacean

Uses strong muscular contractions to force particles of stone or grit to abrade particles of food

Some invertebrates: contain chitinous plates or teeth in lieu of small stones

Gizzard + teeth in jaw both carry out mechanical digestion —> partially digested food enters stomach to finish chemical + enzymatic digestion

Different functions in different regions of the digestive tract

Chemical and enzymatic digestion commonly separated from mechanical digestion

Absorption separate from digestion

Dramatically increases efficiency of each step + overall increase in complexity

Foregut/esophagus

Connection between mouth + midgut

Modified to include crop

Common for foregut to be physically attached to the lungs in vertebrates

Stomach

Vertebrate midgut contains

Chemical + enzymatic digestion of proteins

Single stomach or multiple stomachs (ruminants)

Some animals also have cecum: additional place for digestion

Very hostile environment for most prokaryotes with exception of Heliobactor pylori Stomach wall contains Ht/Nat proton pumps that increase HCl concentration to pH of ~ 1.0

Structure of stomach: indication of different type of diet an animal eats

All vertebrates + many invertebrates have

Invertebrates commonly have direct connection between their digestive tract and renal system

Hindgut

Small and large intestinal tracts

Can be meters in length

Plays important role in digestion and absorption + provides suitable site for growth of bacterial symbiotic species

Approximately 90% of digestion occurs in small intestine + 99% absorption

Large intestine: commonly involved in water + solute absorption + site of microbiome

Common accessory organs: liver, pancreas - provide essential secretions of salts, buffers, enzymes

Intracellular vs Extracellular Digestion

Sponges and clams: internalize food particles within cells —> digest particles - intracellular digestion

• Limits food particle size that has to be smaller than cell

Vertebrates: intracellular digestion in phagocytosis of dead cells + bacteria by macrophages

Majority of animals exploit extracellular digestion of food particles

Advantages: food particles can be much larger than cells, digestion can be carried out in specialized areas - stomach, gizzard, or crop with specialized secretions

• Requires cells lining digestive tract to be able to transport nutrients + need molecules through active + passive transport processes

Protein Metabolism

All animals require continuous influx of proteins because animals do not store amino acids

Proteins normally recycled and replaced —> forces animals to deal with ammonia as waste product

Digestion of protein always occurs in stomach (midgut) - has specialized conditions of high acidity, acid-insensitive proteases, protective layer of acid-resistant mucus

Peptide bond: strong bond - takes time and specialized conditions to break bond

All essential animo acids common to all animals + all are produced by plants

Lipid Metabolism

All animals must also ingest lipids but not same lipids

Structural variability of essential animal lipids

Great deal of variability in percentage of daily caloric + nutritional requirements satisfied by lipids

Not all animals can digest the same lipids

Bumblebees express wax lipases allowing them to digest waxes

• Wax esters: excellent example of need for animals to possess specific enzymatic activities in order to utilize material as food

Carbohydrate Metabolism

All animals can consume carbohydrates especially glucose

All animal cells have ability to carry out glycolysis, citric acid cycle, oxidative phosphorylation

Exceptions in terms of metabolism of other sugars, mammals express lactase to digest lactose found in breast milk

Not all animals possess needed enzymes to digest complex carbohydrates to tri-, di- or monosaccharides

Glucose: excellent fuel source but does not supply nitrogen needed for protein synthesis

Symbiotic relationships

Close and long-term biological interaction between two different organisms of same or different species

Parasitic (one benefits at the expense of other)

Mutualistic (both benefit)

Commensalistic (one benefits without negatively affecting the other)

Ruminants

Not all animals can break chemical bonds found within food

Fermentation: prokaryote-mediated breakdown of food particles)

• common process in animals

Mammals like cattle or sheep can cause breakdown of cellulose within their foreguts through symbiotic process by providing ideal environment for growth of microorganisms that express cellulase gene - vary in location + process by which they breakdown plant material

Hindgut fermentation

Seen in animals with simple, single-chamber stomach (horses, rhinos, rodents, rabbits and koalas)

Microbial fermentation: occurs in large intestine + cecum, requires prokaryotes that express cellulase gene

• Generally have larger + more complex cecum + large intestine + GI tract that averages 10-15 times body length

• Cecum: located after small intestine - limits amount of further digestion + absorption that can occur after fermentation

Foregut fermentation

Occurs in mammals known as ruminants - ferment cellulose plant material in specialized stomach, prior to protein digestion

Commonly regurgitate plant material (cud) to rechewed and increasing mechanical breakdown of plant cell walls

• Cattle, goats, sheep, giraffes, yaks, deer, antelope, kangaroos

Four compartments of ruminant stomach

• Rumen: primary site of microbial fermentation

• reticulum: separation of fine food particles from larger partially digested food particles fermentation

• omasum: receives chewed and fermented cud and absorbs small organic acids produced by fermentation

• abomasum: true stomach that acts to diget mostly microbial proteins

  • Stomach where microbes are digested

Rumen and reticulum: essentially fermentation vat - microbes breakdown cellulose material into acetic, propionic, butyric acids

Microbial flora

Cellulolytic (expressing cellulase)

• breaks glycosidic B(1→4) linked D-glucose molecules

Xylanolytic (expressing xylanase)

• breaks down the linear polysaccharide ß-1,4-xylan into xylose

Pectinolytic species (expressing pectinase)

• breaks down pectin - polysaccharide found in plant cell walls

Nutrition

Nutrient absorptive processes in animals are universal

Not all food is just used for fuel - complex mixture of minerals, organic molecules + other components —> some animals breakdown as fuel for ATP production, other components play other critical roles

Nutrients: vitamins, minerals, other organic compounds

Dietary requirements varies dramatically in terms of nutrient need

Vitamins

Cofactors in metabolism which cannot be synthesized by animals + must be consumed from plants or from flesh of other animals

Needed by both vertebrates and invertebrates + demonstrates common origin of all animals evolutionarily

Many critical components needed for glucose metabolism

Minerals

All animals composed of same 26 elements - 96% of all elements are carbon, hydrogen, oxygen and nitrogen, approx 4% comprised of elements calcium, potassium, phosphate, sodium, chloride, sulphur, magnesium

Common trace elements: cobalt, nickel, copper, vanadium, chromium, manganese, and molybdenum —> parts of enzymes, proteins or vitamins

Billions of years of evolution has given rise to animals - during this process minerals that stabilize cellular structures + pay critical physiological roles are same in all animals

Ex:

• Nickel - active center of hydrogenases

• Chromium - needed for Insulin action

• Vanadium - part of the respiratory proteins of sea squirts

• Cobalt - part of the B-complex vitamins

Poisons

Plants commonly cannot move —> commonly produce poisons or alkaloids that are insecticidal (ex: cocaine, strychnine, curare, nicotine)

• Makes themselves less attractive to animal predators + similar compounds produced by snakes, spiders, bees, wasps, bombardier beetles

Compounds:

• Tannins- bitter and astringents, precipitate proteins, makes digestion difficult

• Oils - cannabis, act as irritants

• Oxalicacid - calcium percipitation

• Enzyme inhibitors + hormone mimics