LIFESCI 7C Lecture Notes - Lecture 7: Essential Amino Acid, Digestive Enzyme, Foregut
Week 7
The Human Mirobiome Part 1
The Human Mirobiome Part 2
The Human Mirobiome Part 3
Case 5: The Human Microbiome
● Our body is home to a diversity of bacterial species
○ Not all species have been identified yet, but it’s estimated 10x bacterial cells as human cells in our
bodies
○ Symbiosis between us and them → affects human health in many important ways
■ E.g. intestinal bacteria help break down food and synthesize vitamins
● Each person has a unique collection of bacterial microbial species → variability makes it difficult for scientists to
decipher individual species’ roles in health/desease
○ Three enterotypes/”gut types: -> Ruminococcus, Bacteroides, or Prevotella, each composition
producing different vitamins that may even make a person more, or less, susceptible to certain
diseases; not sure yet what specific enterotype means for a person’s health
○ Enterotype unrelated to gender, BMI, or natioanlity, but influenced by diet!
● All animals have their own microbiomes -- even tiny single-celled ukaryotes
● Symbiotic bacteria provide a variety of benefits to their hosts, some so intimately connected it’s hard to separate
one from the other (e.g. hard to study human bacteria because they can’t grow outside the body)
○ Gets to the point of complete dependence for survival, appearing like organelles rather than
independent organisms (e.g. aphids+ buchnera bacteria) and becoming integral part of cells themselves
40.2 Animal Nutrition and Diet
● Animals acquire energy thorugh food → Animals must acquire food in the form of plants and other animals →
food isn’t just carbs, fats, proteins, but also certain minerals and chemical compounds they cannot synthesize
on their own
Energy balance is form of homeostasis
● energy balance A form of homeostasis in which the amount of energy calories from food taken in equals the
amount of calories used over time to meet metabolic needs.
○ energy intake Sources of energy.
○ energy use The ways in which energy is expended.
● Source of energy: diet
○ 70% of energy used for basic life processes
○ 30% of energy used for physical activity
● Energy imbalance occuring when energy intake does not equal energy used
○ Animal eats more than it needs → positive energy balances → energy stores (like fat deposits) grow over
time → shift in metabolism to anabolic processes that build energy stores
■ Some animals eat more during one part of year and less during another
■ Some animals eat constantly throughout the year by migrating to places w/ food
■ Some animals hibernate or become less active to conserve energy use during iwnter
○ Animals that cannot acquire enough in food are in negative energy balance → undernourished
■ Animals instarvatioin consume its own internal fuel reserves → glycogen/fat stores first, then
protein
● Humans store excess calories in fat bc over evolutionary history food was less abundant and more
unpredictable in availability than it was today
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○ Now we have excessive intake of food calories → increasing problem of obesity
■ Increases risk of diabetes, heart disease, stroke, shorter life-span
○ For most animals, acquiring/storing food efficiently in the body allows for a fuel reserve to meet
seasonal energy requirements
■ Rationing of stored energy → essential part of metabolic and digestive physiology
An animal’s diet must supply nutrients that it cannot synthesize
● essential amino acid An amino acid that cannot be synthesized by cellular biochemical pathways and instead
must be ingested. → most animals can synthesize about half their animo acids
○ Humans unable to synthesize 8 out of 20 animo acids and must attain them through diet, the most
reliable way through meat
● dietary mineral A chemical element other than carbon, hydrogen, oxygen, or nitrogen that is required in the diet
and must be obtained in food; see also minerals. (Mg, P, K, Ca, Fe, Zn, etc)
○ Mg, Zn → enzyme cofactors
○ Ca → neuron, muscle function and building skeletons
○ Fe → binds O in hemoglobins
○ Na, Cl obtained through salt
● vitamin An organic molecule that is required in very small amounts in the diet.
○ Have diverse roles; different animals have different vitamin requirements
○ 13 essential vitamins of h umans
○ Vitamin C deficiency → scurvy (Vitamin C needed for building connective tissue) → bleeding gums, loss
of teeth, slow wond healing
○ Vitamin B (1, 6, 12) deficiency → nervous system disorder and various forms of anemia
○ Vitamin D: essential for absorption of calcium in diet and thus skeletal growth and health → deficiency=>
rickets (bones not mineralized properly)
○ Vitamin E deficiency → sometiems linked to anemia
40.4: Digestion and Absorption of Food
● Food must be isolated in a specialized organelle/compartment so it can be broken down chemically w/o
damaging other organelles/body structures
● intracellular digestion The process in single-celled protists in which food is broken down within cells.
○ Lysosomes w/ hydrolytic enzymes fuse w/ vacuoles containing food particles, mixing the contents →
chemical breakdown → food products of intracellular digestion are available for use by the cell
● extracellular digestion The process in most animals in which food is isolated and broken down outside a cell,
in a body compartment.
○ Breakdown products are taken up into the bloodstream via absorption
■ absorption The direct uptake of molecules by organisms, commonly to obtain food. In
vertebrate digestion, it is the process by which breakdown products are taken up into the
bloodstream.
The digestive tract has regional specializations
● Some animals carry out digestion in an internal cavity; food → mouth→ internal cavity → cells in cavity secret
breakdown enzymes → these same cells absorb breakdown products
● Other animals have elaborate digestive systems that transport food by digestive tube from mouth to anus
○ gut/digestive tract Collectively, the passages that connect the mouth, digestive organs, and anus
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○ Food moved in single direction → particular regions of gut are specialized for different functions, e.g.
mechanical and chemical breakdown of food, absorption of released nutrients, storage and elimination
of waste products
● Three main parts of digestive tract
○ foregut The first part of an animal’s digestive tract, including the mouth, esophagus, and stomach.
■ mouth The first part of the foregut, which receives food.
■ esophagus Part of the foregut; the passage from the mouth to the stomach.
■ stomach/crop The last part of the foregut, which serves as a storage and digestive chamber
○ midgut The middle part of an animal’s digestive tract, including the small intestine.
■ small intestine Part of the midgut; the site of the last part of digestion and most nutrient
absorption.
● Specialized organs secrete enzymes and othe hcemicals that aid breakdowon of
particular macromolecules such as fats and carbs
○ hindgut The last part of an animal’s digestive tract, including the large intestine and rectum.
■ large intestine/colon Part of the hindgut and the site of reabsorption of water and minerals;
■ rectum The part of the hindgut where feces are stored until elimination.
● peristalsis Waves of smooth muscular contraction that move food toward the base of the stomach.
○ Keep substances movign from one end of the tract to the other and prevent backwards movement
Digestion begins in the mouth
● Food is first mechanically broken in the
● w/ jaws, teeth, or insect andibles
● Food is then chemically broken by enzymes that break subunit bonds of large molecules
○ Enzymes require proper chemical environment (specifc pH’s → some neutral, some acidic), different
environments providd by carrying out digestion in differnt compartmnets
○ In mammals, chemical digestion starts in the mouth w/ salivary secretions
■ amylase An enzyme that breaks down starch into smaller subunits.
■ lipase A type of enzyme produced by the pancreas that breaks apart lipids, thus enabling their
more effective digestion.
■
● Swallowing is a complex set of motor
reflexes carried out by several muscles and
structures in the rear of the mouth and
pharynx; once intiated, swallowing reflexes
are involuntary, under autonomic nervous
system
○ mouth
○ pharynx The region of the throat
that connects the nasal and mouth
cavities; in hemichordates, a tube
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