Amino acids and its different structures.ppt

This ppt briefs about aminoacid

1. Amino acids
Plants are able to generate all 20 amino acids necessary for
protein synthesis by themselves
The building blocks of proteins are amino acids.
An amino acid contains an amino group (-NH2), a carboxylic
acid group (-COOH), and a side chain (R). The carbon at the
center is called the alpha-carbon

2. Amino acids are grouped according to the characteristics
of the side chains:
Aliphatic - alanine , glycine, isoleucine, leucine, proline, valine

Aromatic - phenylalanine, tryptophan, tyrosine
Acidic - aspartic acid, glutamic acid
Basic - arginine, histidine, lysine
Hydroxylic - serine, threonine
Sulphur-containing - cysteine, methionine
Amidic (containing amide group) - asparagine, glutamine

3. Of the 20 standard proteinogenic amino acids, 10 are called
essential amino acids because the human body cannot
synthesize them from other compounds at the level needed
for normal growth, so they must be obtained from food.
However, the situation is a little more complicated since
cysteine, tyrosine, histidine and arginine are semi essential
amino acids in children, because the metabolic pathways
that synthesize these amino acids are not fully developed.
The amounts required also depend on the age and health of
the individual, so it is hard to make general statements about
the dietary requirement for some amino acids

4. Essential amino acids
•Failure to obtain enough of even 1 of the 10 essential
amino acids, those that we cannot make, results in
degradation of the body's proteins—muscle and so forth
—to obtain the one amino acid that is needed.
•Unlike fat and starch, the human body does not store
excess amino acids for later use—the amino acids must
be in the food every day.

6. N2 fixation and assimilation
•Plants take up nitrogen as nitrate, in smaller
amounts also as ammonium ions.
• A few species, mainly of the leguminosa family, live
in symbiosis with nitrogen-fixing bacteria that are
able to reduce atmospheric nitrogen to ammonia.
•All other plants reduce nitrate (NO3-).

7. Global nitrogen economy

8. Reduction of inorganic nitrogen
There are two significant pathways:
Main pathway (99% of N entering biosphere)
NO
3
-
+ 2H
+
+ 2e
-
------> NO
2
-
+ H
2
O nitrate reductase (NR)
NO
2
-
+ 8H
+
+ 6e
-
------> NH
4
+
+ 2 H
2O nitrite reductase (NiR)
Second pathway (1% of N entering biosphere)is by nitrogen fixation
N
2
+ 8H
+
+ 8e
-
------> 2 NH
3
+ H
2
dinitrogenase reductase
and dinitrogenase
NR and NiR are found in bacteria, algae, and plants. There exist a number of
distinct types of NR and Nir enzymes.
Nitrogen fixation by dinitrogenase reductase and dinitrogenase occurs only
in certain bacteria.

9. •In a first step, nitrate is reduced to nitrite (NO2-). The
reducing agent is NADH + H+ that is gained during
glycolysis, the respective enzyme nitrate reductase.
• This reaction occurs in the cytosol and couples
glycolysis and nitrate reduction and has the advantage
that the NAD+ necessary for the progress of glycolysis.
•In the second step, nitrite is reduced to ammonium by
nitrite reductase, an enzyme that is located in plastids.
•Each type of plastid has its own assimilatory nitrite
reductase. In photosynthetic tissues, reduced ferredoxin
functions as the electron donor that is produced in
photosynthesis

10. •Free ammonium ions are toxic to plant cells and are
rapidly incorporated into organic compounds.
•The most important quantitative way in green plants
is the reductive amination of alpha-ketoglutarate to
produce glutamate catalyzed by the NADP+-
dependent glutamate dehydrogenase.
• Glutamate is accordingly the amino acid generated
first.

11. NH4+ formed as a result of nitrate reduction or N2 fixation is
1st incorporated into amino acids via the glutamine synthetase (GS) reaction:

15. 22.2 Biosynthesis of amino acids
Glycolytic, citric acid, and
pentose phosphate Int.
Gln and Glu are N sources
20 common amino acid pathways
(bacterial)
Amino acids based on the precursor
grouped in to 5 families

17. Overview of amino acid biosynthesis

19. Lysine biosynthesis
Condensation rxn

22. Threonine biosynthesis

23. Methionine biosynthesis

25. Non-Protein amino acids
•Of the thousands of known non-protein amino acids (NPA),
about 300 occur in plants.
•They are found mostly in a small number of families, such as
the Leguminosae, Cucurbitaceae, Sapindacae, Aceraceae and
Hippocastenaceae.
•Many of these NPA are structurally similar to the components of
common proteins.
•The incorporation of NPAs into proteins may be associated with
autoimmune diseases in humans.Play role as defensive agents

26. Non-protein amino acids
About 700 amino acids are known, at least 300 from plants
Three major routes for origin
a)modification of existing (often protein) amino acid
b) modification of an existing pathway
c) novel pathways
Found mostly in a small number of families Fabaceae or
Leguminosae seeds of Cucurbitaceae, Sapindaceae,
Aceraceae, Hippocastanaceae and microbes

27. Best characterised NPN are
•L-Canavanine (Arginine analog)
•L-Canaline (Ornithine analog)

29. L-Arginine (top), L-Canavanine (bottom

30. •In the seeds of jack bean (Canavalia ensiformis), massive
accumulation of this toxic secondary metabolite has been
established.
•Canavanine storage in the seeds of such plants can
account for more than 10% of the seed dry matter.
•The preponderance of seed canavanine, its depletion
during growth of the seedlings, its extreme toxicity to
actual (insects, rodents) and serendipitous (humans) seed
predators, and its high nitrogen content all point to the
conclusion that the plant has constructed a compound that
is simultaneously a storage compound and a major seed
defence. This strategy is commonplace in legume seeds
with a variety of secondary compounds.

32. •Bruchid beetle can feed on canavanine
•In addition to canavanine and canaline
catabolic activities , this insect also
possesses an arginyl-tRNA synthetase which
will not recognise L-Canavanine
•The tobacco bud worm, Heliothis virescens,
a distinct insect pest is resistant to
Canavanine (contain canavanine hydrolase in
the gut)

33. Canaline
•Powerful antimetabolite reacts with pyridoxal
phosphate moiety of vitamin B6 containing
enzymes to form a covalently bound oxime
that inactivates the enzyme
•Also function as lysine antagonist

34. Toxic amino acid present in leaves and seeds of tropical legume
Leucaena leucocephala
Toxic effect is due to
mimosine and its
break down product
di hydroxy pyridine
Interferes with
tyrosine metabolism

35. Selenium-containing amino acids
• selenium often replaces S in amino acids
• Associated with high selenium in soils
• These are toxic since incorporated in the place of
S- containing amino acids resulting protein is active
• But low level of Se is essential
• Killed yeast containing Se amino acid are fed to live
stocks

36. Sulfur-containing amino acids in onion
and garlic
•alliin S-allylcysteine sulfoxide
•breaks down to ammonia, sulfuric acid, hydrogen
sulfide and low molecular weight carbonyl
compounds
•anticancer effects

37. Lathyrus and Vicia species
lathyrism neurotoxins-skeletal deformity and rupture of aorta
Osteolathyrism
Toxin is β-amino propio nitrile
NC-CH2-CH2-NH2
Interferes with the cross linking of lysine residues in collagen
Neurolathyrism
Toxin is β-N-oxalyl α- β- diamino propionic acid and β-
cyanoalanine (analog to glutamine-nuro tramsmittor)
Attack nerve cells and lead to weakness and paralysis of the legs
Most common in man and rarely seen in animals

38. neurolathyrism
neurodegeneration
Toxin

39. Azetidine-2-carboxylic acid - often toxic because it replaces
proline
3,4-Dihydroxyphenylalanine- DOPA ... related to dopamine
relationship to Parkinson's Disease
5-Hydroxytryptophan
similar to serotonin
5-hydroxytryptophan can cross blood brain barrier whereas
serotonin cannot
6-10% hydroxytryptophan in Griffonia simplicifolia