Version 2012-III |
Amino Acids |
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Amino acids (AA)
are in general any organic compounds containing carboxylic (-C00H)
and amine (-NH2) functional groups. From among vast number of AAs,
most important are L-alpha-amino acids - headstones of all proteins
and thus key in natural sciences. |
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The basic characteristics of AA |
Aliphatic
chain
structure |
Particular AA is defined by the structure of
side aliphatic chain (the R in molecule picture) determining its major
properties. |
| Chirality |
All alpha-AA but glycine occurs in two mirror
forms (L and D optical isomers - antipodes). With few exceptions L-isomers
vastly prevail in proteins formation. |
| Hybridism |
As AA contain both carboxylic and amine group,
they are both acid and base at the same time. This fact is important
for AA polar solution (in water for instance) and key role plays pH
value. |
At certain pH value (AA-specific) the negative
and positive charges of functional groups are equal and molecule acts
as neutral one. Under described conditions – isoelectric point – the
molecule is called Zwitterion (from German Zwitter - hybrid) and has
very low solubility and could be often isolated from solution as precipitate. |
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Biogennous role |
The AA could be metabolized in following ways by living organisms:
- Growth - peptide and protein synthesis
- Functionality - formation of
non-protein molecules
- Gaining energy by oxidation of AA
Essential and non-essential AA can be defined from the point of view
of particular living organism. Essential are those AA, which could be synthesised
inside the organisms body and the only source to obtain them is a food
or – in case of corals for instance – seawater.
Growth – peptide and protein synthesis
Protein synthesis is in fact a kind of polymerization, where various
AA reacts and forms molecular chain via Peptide bond: |
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Reaction needs an energy supply and is not occurring directly. Entire
process is determined by genetic code and mediated by RNA or in smaller
extent by enzymes. Resulting protein is defined by the sequence and number
of particular AA.
Functionality – non-protein molecules synthesis
AA acts here as the precursors of important non-protein molecules, such
as neurotransmitters, porphyrins, nucleotides, hormones etc. Some marine
animals, for example cone snails, are able to convert L-isomers of AA to
D-isomers, which acts against other organisms as violent poisons and thus
are perfect anti-predator weapons. Even the only difference between isomers
is a mirror structure, biological effect is dramatically dissimilar. |
Utilisation of free amino acids |
Rate of AA adsorption by invertebrates |
There are following AA resources for marine invertebrates available:
- Self-synthesis
- Particulate organic food
- Seawater
Natural seawater contains
smaller amount of free dissolved AA and their direct biological utilisation
has been studied among many marine invertebrates with relatively definite
results valid for absolute majority of investigated subjects:
Marine organisms adsorb free AA from seawater rapidly and in substantial amount
Graph shows the rate of selected AA adsorption by sea mollusc Spinula
solidissima during 24-hours exposure in % of initial AA concentration: |
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Following table shows average rate of selected AA adsorption by
particular groups of animals after 16 - 24-hours exposure in % of initial
AA concentration. Adsorption rates correspond to the way of food uptake
and are significant especially for seawater-filter feeders. |
Sponges |
64% |
Sipunculidae (peanut worms) |
36% |
Cnidarians |
34% |
Moluscs |
47% |
Ribbonlike worms |
58% |
Arthropods (e.g. barnacles) |
1% |
Bryozoans (moss animals) |
70% |
Echinoderms (e.g. starfish) |
64% |
Annelids (segmented worms) |
57% |
Chordates (e.g. sea squirt) |
32% |
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AA-impact on symbiosis of corals and Zooxanthellae |
Large number of Anthozoans (sea anemones and corals) harbours in
their cells symbiotic dinoflagellates - Zooxanthellae. Symbiotic coexistence
lies in linked metabolism of carbon, nitrogen and phosphorus above all:
- Zooxanthellae
provide their hosts
- in the form of carbon compound as the products
of photosynthesis - with:
- Up to 90% of its total energy budget
- Substances
needed for growth
- Hosts provides Zooxanthellae with:
- Living space
and shelter
- Nutrition
- in fact waste metabolic products containing
phosphorus and nitrogen
- Continuous CO2 (carbon dioxide) supply
for photosynthesis
A question for scientific research is what hosts
chemical factor initializes and controls the process of photosynthetic
products release from the cells of Zooxanthellae to those of hosts.
One of related scientific works investigated this problem on Pocillopora
damicornis coral species. A set of free amino acids has been determined
as a host factor, which:
- initializes selective release of photosynthetic
products for hosts needs
- increases the ability of carbon fixation
by Zooxanthellae
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It has been found the free AA plays important role of signal molecules
for biologic processes. |
Literature |
UPTAKE OF AMINO ACIDS BY MARINE INVERTEBRATES, Grover C. Stephens and Robert A, Schinslw University of Minnesota and Marinc Biological Laboratory, Woods Hole, Massachusetts.
Free amino acids exhibit anthozoan "host factor" activity: They induce the release of photosynthate from symbiotic dinoflagellates in vitro RuTH D. GATES*t, OVE HOEGH-GULDBERGt, MARGARET J. MCFALL-NGAI§, KARL Y. BIL'*, AND LEONARD MUSCATINE* *Biology Department, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90024-1606; *Department of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia; and §Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-0371 |
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