Tufa

Tufa is a variety of limestone, formed by the precipitation of carbonate minerals from ambient temperature water bodies. Geothermally heated hot springs sometimes produce similar (but less porous) carbonate deposits known as travertine. Tufa is sometimes referred to as (meteogene) travertine; care must be taken when searching through literature to prevent confusion with hot spring (thermogene) travertine. Calcareous tufa should not be confused with tuff, a porous volcanic rock with parallel etymological origins that is sometimes called "tufa".

Classification and features

Modern and fossil tufa deposits abound with wetland plants; as such many tufa deposits are characterised by their large macrobiological component and are highly porous. Tufa forms either in fluvial channels or in lacustrine settings. Ford and Pedley (1996) provide a review of tufa systems worldwide.

Fluvial deposits

Deposits can be classified by their depositional environment (or otherwise by vegetation or petrographically). Pedley (1990) provides an extensive classification system, which includes the following classes of fluvial tufa:

Tufa (disambiguation)

Tufa may refer to:

EF-Tu

EF-Tu (elongation factor thermo unstable) is one of the prokaryotic elongation factors. Elongation factors are part of the mechanism that synthesizes new proteins by translation at the ribosome. Individual amino acid links are added to the protein chain by transfer RNA (t-RNA). Messenger RNA (mRNA) carries a codon that codes for each amino acid. t-RNA carries the amino acid and an anticodon for that amino acid. The ribosome creates a protein chain by following the mRNA code and selecting the next t-RNA and its amino acid.

The prokaryotic factor EF-Tu helps the aminoacyl-tRNA move onto a free site on the ribosome. In the cytoplasm, EF-Tu binds an aminoacylated, or charged, tRNA molecule. This complex enters the ribosome.

There are 3 tRNA attachment sites on the ribosome: aminoacyl (A), peptidyl (P) and exit (E). The tRNA complex first binds to the A site, then moves to the P site, and is released at the E site.

The tRNA anticodon domain associates with the mRNA codon domain in the ribosomal A site. If the codon-anticodon pairing is correct, EF-Tu hydrolyzes guanosine triphosphate (GTP) into guanosine diphosphate (GDP) and inorganic phosphate. This creates a conformational change in EF-Tu that causes EF-Tu to dissociate from the tRNA of the ternary complex (and therefore leave the ribosome). The aminoacyl-tRNA then fully enters the A site, where its amino acid is brought near the P site's polypeptide and the ribosome catalyzes the covalent transfer of the polypeptide onto the amino acid . The tRNA on the P site (without peptide) moves to the E site and is then released.