ammonia
10
(aspartic and glutamic acid); (2) basic amino acids, containing an excess of
basic nitrogen (e.g., histidine, arginine, lysine); (3) neutral amino acids, containing one amino and one carboxyl group, which may be subdivided
according to whether the radical of the restgroup in the general formula represents an aliphatic (e.g., glycine, serine, leucine), an aromatic (phenylalanine, tyrosine), a sulfur (cysteine, methionine, cystine) or heterocyclic (e.g.,
tryptophan, proline) nucleus. Amino acids are soluble in water, except cystine and tyrosine, and insoluble in alcohol and ether (except proline). They
form crystalline salts with metallic bases and with mineral acids. Many taste
sweet (glycine, alanine, serine, and proline), others are tasteless (tryptophan
and lecrine) or bitter (arginine). Fundamental constituents of living matter;
hundreds to thousands of amino acids are combined to make each protein
molecule. There are about 25 amino acids known to be constituents of proteins, and synthesized by autotrophs, such as most green plants. Certain "essential" amino acids must be obtained from the environment by heterotrophs.
Other "nonessential" amino acids are not necessarily required from the
environment, since organisms can synthesize them themselves.
NH2
I
R - e - eOOH
I
H
Amino acids
ammonia gaseous compound (NH 3 ), which in solution in water is partially present as ammonium ion (NH 4 +). In freshwater systems as well as in the marine
environment, it is a basic nutrient for phytoplankton growth. In the decomposition of organic compounds (manure), ammonia and ammonium ions
are major end products, which can be transported through the atmosphere
over considerable distances. Ammonia can be oxidized microbiologically to
nitrate (nitrification), and thus is a source of "acid rain". ~nitrogen cycle.
ammonification is the formation of ammonia from decomposing nitrogenous
organic compounds, ~nitrogen cycle.
ammonites (Ammonoidea) extinct order of the class Cephalopoda (phylum
Mollusca) with coiled external shells with complex suture lines. They have
been extinct since the Cretaceous.
Amoebida (amebas, amoebas) order of the phylum Rhizopoda (kingdom
Protoctista), naked single-celled uninucleate organisms with a lobed cell-surface forming the pseudopodia (feet), that live in the sea, freshwater or on
land in moisture. Amoebida change constantly in shape, and crawl over the
substrate with pseudopodia. Some species reach several mm in length.
Example: Amoeba.
10
(aspartic and glutamic acid); (2) basic amino acids, containing an excess of
basic nitrogen (e.g., histidine, arginine, lysine); (3) neutral amino acids, containing one amino and one carboxyl group, which may be subdivided
according to whether the radical of the restgroup in the general formula represents an aliphatic (e.g., glycine, serine, leucine), an aromatic (phenylalanine, tyrosine), a sulfur (cysteine, methionine, cystine) or heterocyclic (e.g.,
tryptophan, proline) nucleus. Amino acids are soluble in water, except cystine and tyrosine, and insoluble in alcohol and ether (except proline). They
form crystalline salts with metallic bases and with mineral acids. Many taste
sweet (glycine, alanine, serine, and proline), others are tasteless (tryptophan
and lecrine) or bitter (arginine). Fundamental constituents of living matter;
hundreds to thousands of amino acids are combined to make each protein
molecule. There are about 25 amino acids known to be constituents of proteins, and synthesized by autotrophs, such as most green plants. Certain "essential" amino acids must be obtained from the environment by heterotrophs.
Other "nonessential" amino acids are not necessarily required from the
environment, since organisms can synthesize them themselves.
NH2
I
R - e - eOOH
I
H
Amino acids
ammonia gaseous compound (NH 3 ), which in solution in water is partially present as ammonium ion (NH 4 +). In freshwater systems as well as in the marine
environment, it is a basic nutrient for phytoplankton growth. In the decomposition of organic compounds (manure), ammonia and ammonium ions
are major end products, which can be transported through the atmosphere
over considerable distances. Ammonia can be oxidized microbiologically to
nitrate (nitrification), and thus is a source of "acid rain". ~nitrogen cycle.
ammonification is the formation of ammonia from decomposing nitrogenous
organic compounds, ~nitrogen cycle.
ammonites (Ammonoidea) extinct order of the class Cephalopoda (phylum
Mollusca) with coiled external shells with complex suture lines. They have
been extinct since the Cretaceous.
Amoebida (amebas, amoebas) order of the phylum Rhizopoda (kingdom
Protoctista), naked single-celled uninucleate organisms with a lobed cell-surface forming the pseudopodia (feet), that live in the sea, freshwater or on
land in moisture. Amoebida change constantly in shape, and crawl over the
substrate with pseudopodia. Some species reach several mm in length.
Example: Amoeba.