Phyto 2
Lecture 2
3 units of acetate(2carbons)
mevalonic acid (6 carbons)
 This reaction happens in the presence of certain enzymes.
3
 Mevalonic acid pathway consider the main pathway to produce two
important groups of metabolites which are :
1-terpenes
2-steroids (hormones)
 Mevalonic acid pathway is common in animals ,humans and plants.
 Acetate is responsible for production of primary metabolites .
 Glycolysis :is a process responsible for the production of glucose -6p(OH on
position 6 has phosphate group) why?? As a source of energy.
-Now glucose-6p will split to give 2 units of pyruvic acid then to pyruvate,
pyruvate will give glyceraldehyde then to acetate which then will start kreps
cycle .
 During Glycolysis pathway all essential amino acids will produce except the
aromatic amino acids (phynelalanine / tyrosine /tryptophan).
 What we mean by essential amino acids ? we mean that they are part of
protein
 Our bodies don’t produce these essential amino acid ,we take them from
plants .
 Humans and animals depend mainly on plants as a source of protein .
 So, all aliphatic amino acids are produced within glycolysis.
Summary:
 Acetate pathway
primary metabolites.
 Shikimate pathway
aromatic amino acids.
 Mevalonate pathway
production of hormones.
Shikimate +mevalonate
If there is no acetate
comes from acetate.
no shikimate/mevalonate
Acetate produce all amino acids except aromatic amino acids (18 amino acid)
Shikimate produce aromatic amino acids (3 amino acids)
 But, there are thousands of amino acids why they are not essential?
Because they are not a part of protein .
 The fourth and the most important secondary metabolite which produced
from amino acids is alcohol.
Amino acids (from shikimate or acetate)
alcohols.
-so amino acid is the precursor of alcohols.
-amino acids contain nitrogenous group.
So: alcohols are essentially nitrogenous compounds (must contain
nitrogen).
If it hasn’t nitrogen it’s not alcohol .
 Differentiate plant from another one due to the presence of specific
enzymes.
 Example : thyme and mint both have the same building blocks ,both have
the same pathway but they differ in their taste why?? Because of different
enzymes .
 What we mean by enzyme ?
Enzymes found in plants ,animals, humans and microorganisms ,they are
selective and highly specific.
Selective:it reacts only on this compound .
Specific : reacts on specific position on this compound .
Example occurs in our body:
Vitamin D3:
Is vitamin D3 active in our bodies ??
The answer is No , vitamin D3 in order to work must have two important steps
before :
1- Oxidation at position 25 by (hydroxylase enzyme) (this step occurs in the
liver ).
Why this enzyme works on D3?
Because it is selective to D3.
Why this enzyme works on position 25?
Because it is specific at this position .
2-further oxidation by another more specific hydroxylase enzyme (this step
occurs in the kidney ) to give 1,25dihydroxy D3(calcitriol) .
 Production of isoprene:
Mevalonic acid(6 carbons)
isoprene(5 carbons).
by decarboxylation (CO2 will go out)
Isoprene is the first building block which plant utilize to biosynthesize all
terpenes and steroids .
3 acetate
mevalonic acid
-co2
isoprene unit
decarboxylase
Keep in mind that the presence or absence of double bond or any other
functional group is a later step (it comes later on).
-sesterpenes ( 25 c ) doesn’t exist in the nature.
-triterpenes are the component of sex hormones.
-polyterpenes found in rubber.
-they must be attach head to tail or tail to head . and not head to head or tail
to tail.
 These compounds their chemical ,physical and pharmacological
activity is different .
 Monoterpenes /sesquiterpenes are volatile oils (aromatic)
 2 isoprene units can make further junction and cyclization.
Either it still aliphatic or it cyclyze .
For example:
Citral (aldehyde)found in most citras fruits (it is the most expensive compound in
these fruits .
 Menthol (cyclization and addition of OH group as a later step)
 a-Phellandrene:
(eucalyptus) no additional functional groubs.
 Sesquiterpene 15 carbon atoms
Alpha-selinene bi cyclic)‫(موجود في الكرفس‬
 Diterpenes (20 carbons)4 isoprene units
Vitamin A
 Triterpenes (6 isoprene units)
Attachment between the third and fourth isoprene unit is not head to tail or
tail to head it is head to head or tail to tail why??
Because this compound which finally will convert to cholesterol must be
cyclyze at the end ,and if it was head to tail or tail to heat it can’t be cyclize.
Example of triterpenes is squaline (fish oil )(omega 3)
Wood is glucose and starch is glucose but starch can be digest while wood
can’t …why??
Because glucose in wood linked by beta 1-4 linkage which make it easy to
form strong hydrogen bondings.