PLANTS AND ANIMALS PHYSIOLOGY
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BIO 101
LECTURES
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WHAT IS PHYSIOLOGY?
▪ Physiology is the study of vital
functions and processes in living
organisms
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PHYSIOLOGY IN PLANTS
▪ Seed dormancy and germination
▪ Plant growth and development
▪ Photosynthesis
▪ Absorption and distribution of nutrients
▪ Flowering, fruit formation
▪ Other internal processes
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PHYSIOLOGY IN ANIMALS
▪ Reproduction and fœtal development
▪ Digestion and absorption of nutrients
▪ Growth and development
▪ Formation and distribution of enzymes, proteins, hormones,
carbohydrates
▪ Functoning of organs and other structures
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Physiological processes
▪ All physiological processes in Plants and
animals are mediated by ENZYMES
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What then are ENZYMES?
▪ Enzymes are biological molecules that
increase the rates of biochemical reactions in
living organisms
▪ In other words, enzymes are biological
catalysts!
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Nature of ENZYMES
▪ Enzymes are linear chains of polypeptides,
containing between 82 to 2500 amino acid residues.
▪ This chain folds to produce a 3-dimensional, globular
structure.
▪ Therefore, enzymes are called globular proteins
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Nature of ENZYMES cont’d
▪ This folding of the enzyme polypeptide creates a unique
“pocket” or “groove” on the surface of the enzyme.
▪ Into this groove, a complementary shaped substrate
molecule can fit.
▪ This pocket or groove in an enzyme is called the active
site.
ENZYME ACTIVE SITE
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The Nature of ENZYMES
▪ Most enzymes are protein.
▪ A few other enzymes are not proteins, but RNA-
based biomolecules
▪ An example of an RNA-based enzyme is
Ribonucleoprotein.
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ENZYMES
▪ Some enzyme proteins function alone.
▪ Other enzyme proteins require a non-protein component before
functioning.
▪ These non-protein components are called Cofactors
▪ Enzyme proteins alone, without their cofactors, are termed
Apoenzymes or Apoproteins.
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COFACTORS
▪ INORGANIC ▪ ORGANIC (tightly bound to
its apoenzyme). Prosthetic
▪ Metal ions e.g K+, Fe2+, group e.g Biotin
Fe3+, Cu2+, Zn2+,
Mn2+, Mg2+, Ca2+,
Mo3+. ▪ ORGANIC (loosely bound to
its apoenzyme). Coenzyme
e.g Riboflavin (FAD),
Thiamine, Folic acid, NAD,
NADP.
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ENZYME NOMENCLATURE
▪ The International Enzyme Commission
approved a system by which all enzymes are
names.
▪ The system is based on the type of reaction
catalysed by the enzyme.
▪ All enzymes fall into six (6) major classes.
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CLASSES OF ENZYMES
▪ Enzymes in this group
catalyse oxidation and
reduction reactions.
▪ That is, the transfer of
▪ EC 1. hydrogen or oxygen atoms
Oxidoreductases between biomolecules.
▪ Examples are oxidases,
dehydrogenases,
peroxidases.
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CLASSES OF ENZYMES
▪ Catalyse the transfer of
a functional group e.g
methyl, phosphate group
▪ EC 2 from one molecule to
another.
TRANSFERASES
▪ An example is
Hexokinase
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CLASSES OF ENZYMES
▪ Catalyse hydrolysis
reactions.
▪ The breakdown of large
molecules by addition of
▪ EC 3 HYDROLASES water molecules.
▪ Examples esterases,
glycosidases,
proteases, lipases.
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CLASSES OF ENZYMES
▪ Enhance the addition of a
group to a double bond
▪ Or enhance the removal of
two groups from nearby
atoms to create a double
▪ EC 4 LYASES
bond.
▪ Examoles are aldolases and
dehydratases.
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CLASSES OF ENZYMES
▪ Catalyse Isomerization
changes within a single
molecule
▪ That is, the rearrangement of
atoms in a molecule without
▪ EC 5 ISOMERASES
changing their chemical
formula
▪ Examples are epimerases
and racemerases.
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CLASSES OF ENZYMES
▪ Catalyse formation of
covalent bonds between two
molecules.
▪ energy of catalysis is
▪ EC 6 LIGASES OR obtained from the cleavage or
SYNTHETASES breakdown of a nucleoside
triphosphate (ATP, GTP).
▪ Examples are DNA ligase,
chelatases
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ENZYME CODE
▪ Each enzyme class has subclasses
▪ Enzyme code is a four-digit code or number preceeded by EC
▪ The first three digits define the reaction catalysed.
▪ The fourth digit is a unique identifier (serial number).
▪ Each enzyme is also given a systemic name defining the
reaction catalysed.
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ENZYME CODE
▪ EC = Enzyme Commission
▪ 2 = Enzyme major class
(Transferase)
▪ 7 = Enzyme subclass (a
Phosphotransferase)
EC 2711
▪ 1 = Phosphotransferase with
a hydroxyl group as acceptor
▪ 1 = D-glucose as phosphoryl
group acceptor
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PROPERTIES OF ENZYMES
▪ Most enzymes are proteins
▪ Enzymes are biological catalysts
▪ Enzyme reactions are reversible
▪ The concentration of an enzyme affects its activity.
▪ Enzymes are thermolabile (45 degrees Centigrade maximum)
▪ Enzymes are sensitive to pH
▪ Enzyme reactions are specific.
▪ Most enzymes require cofactors to work.
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THE PHYSIOLOGY OF DIGESTION IN
MAMMALS
▪ Digestion in Mammals is made possible by the gut
▪ The gut is a long tube stretching from the mouth to
the anus.
▪ Four sections of the gut are important in Digestion.
▪ These are the Mouth, the Stomach and accessories,
the Small Intestine, and the Large Intestine.
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Digestion Processes
▪ Digestion breaks down large, ingested food particles into small
forms that can be absorbed and used by the body.
▪ It requires both mechanical and chemical digestion.
▪ Digestion occurs on the mouth, Stomach, and Small Intestine.
▪ Secretions from accessory organs like the pancreas, gall
Bladder and liver also aid in the digestion process.
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The Mouth
▪ Provides both mechanical and chemical digestion.
▪ Functions optimally with the pH of 6.7 and 7.0.
▪ Digestion of carbohydrates starts in the mouth.
▪ Salivary glands in the mouth secret alpha-amylase to digest
carbohydrates.
▪ An example of alpha-amylase is Ptyalin, which converts starch into
maltose and isomaltose.
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The Stomach
▪ Has a pH of between 0.8 to 3.5
▪ Proteins are digested in the stomach into polypeptides and
oligopeptides.
▪ This is effected by the enzyme pepsin, which functions optimally
at a pH of 2.0 to 3.0
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The Stomach
▪ Minor digestion of lipids into fatty acids and monoacylglycerols
also occurs in the stomach.
▪ This is made possible by the action of the enzyme lipase.
▪ Lipase is secreted by the Chief Cells in the oxyntic glands of
the body of the stomach.
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The Small Intestine
▪ Has an optimum pH of 6 to 7.
▪ Is separated from the stomach by the pylorus.
▪ Has three parts: the duodenum, the jejenum, and the ileum.
▪ Produces digestive enzymes, and with those of the pancreas and
liver, help in absorption of nutrients into the bloodstream.
▪ Has mucosal folds, villi, and microvilli to help in the absorption of
nutrients.
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The Large Intestine
▪ Functions to absorb water and salts from already digested material.
▪ Has micro-organismes which release vitamins from their action
▪ Consists of the Cecum and Colon.
▪ The colon is divided into ascending colon, descending colon,
transverse colon, Sigmoid colon, and rectum.
▪ The large intestine empties through the anus.
