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TRANSLATION

The first step: Understanding THE GENETIC CODE

Recall how the DNA strand consists of long streams of nitrogenous bases, which can be arranged in an infinite number of ways: AATCGCCTTACCA...or whatever! This GENETIC CODE is a triplet code: each three bases represent one amino acid. There are TWENTY AMINO ACIDS which form all the proteins in living things. Each one has different chemical properties, and the specific order of the amino acids in a protein determines

As you might guess, with 20 amino acids being arranged in protein strands ranging from 1000 amino acids long to HUNDREDS OF THOUSANDS of amino acids long, there is a nearly infinite variety of protein possible!

Armed with this information, let's return now to the Genetic Code and draw a piece of newly made mRNA, fresh off the DNA.

The code is

e.g. - a "U" in the center position always encodes a hydrophobic ("water fearing") aa. A change (mutation) at the two outer positions will not change that.

e.g. - negatively charged aa's (e.g. aspartate, glutamate) always begin with GA. A mutation in the 3rd position will not change that.

This is evidence that a triplet code not only allows for more diversity, but is also "safer" than a couplet code in case of mutations.

TRANSLATION is the process by which the mRNA transcript triplet "language" is translated into a different language: that of protein.

The PLAYERS in TRANSLATION

In this drama, there are many players: ...and DNA is the producer, sitting back in his trailer smoking cigars while everyone else runs around like maniacs doing the work.

Recall that protein, like nucleic acid, is a POLYMER (chain of repeating subunits) composed of AMINO ACIDS in sequence designated by the DNA which encodes its manufacture.

The general structure of an amino acid is:

The identity of "R" determines the physical properties of the amino acid.

Amino acids (sometimes called simply "aa's") are linked via PEPTIDE BONDS to form the primary structure of the polypeptide (= protein).

The primary structure, in turn, determines the secondary, tertiary, and to a great extent, the quaternary structure of the final protein.

  • Globular proteins - compact, highly coiled. (e.g., enzymes, antibodies)
  • Fibrous proteins - elongate (Tend to be structural, as in hair, muscle, etc.)
  • An ENZYME is a biological protein catalyst: It facilitates and speeds up a chemical reaction that would otherwise take much longer to happen, if it happened at all.

  • Enzymes not only play important roles in translation, but are also the products of translation, since they are proteins.
  • And translation is effected not only by proteins, but by three different kinds of RNA: messenger (mRNA), transfer (tRNA) and riobosomal (rRNA).

    TWO MORE IMPORTANT PLAYERS IN THE TRANSLATION DRAMA: tRNA and rRNA

  • We've seen mRNA and how it's made
  • There are two more types of RNA also involved in translation:

    TRANSFER RNA (tRNA)

    What is tRNA, and how is it different from mRNA?

    Why does tRNA to fold in its special way?

    The PROCESS of TRANSLATION

    STEP ONE: AMINO ACID ACTIVATION

    RIBOSOMAL RNA (rRNA)

    Who is rRNA?

    rRNA is one of the main components of the RIBOSOME, which is also composed of specific types of protein

  • A "Svedberg" unit of relative sedimentation in a centrifuge column of Cesium chloride. It's a unit we use to describe the size of ribosome parts.
  • rRNA and ribosomal proteins are assembled into ribosome components in the nucleus, then shuttled out into the cytoplasm, where they will make protein.
  • Ribosomes are complex assemblages of proteins and rRNA, and they differ slightly across species (more notably between prokaryotes and eukaryotes).

    Once we have ...we're ready for TRANSLATION: the process of making protein directly from the mRNA template strand, which was made from the DNA.

    STEP TWO: PROTEIN SYNTHESIS