Antiparallelism (biochemistry)

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In molecular biology , genetics and biochemistry, antiparallelism is the description for opposing orientations of two sub-areas of a biopolymer .

genetics

In the field of genetics and biochemistry, the term often refers to the orientation of a ribonucleic acid (RNA) or a deoxyribonucleic acid (DNA). In double-stranded (ds) DNA, the two strands are oriented antiparallel, one in the 5 '→ 3' direction and the complementary one in the 3 '→ 5' direction.

The synthesis of nucleic acids under the catalytic action of the polymerases takes place step by step by adding a monomer , the activated nucleotide , to the 3 'end of the growing chain of the oligo- or polynucleotide (a polymer ). The free OH group ( hydroxyl group ) reacts in the 3 'position of the terminal deoxyribose (in the case of DNA) or ribose (in the case of RNA) with the phosphate residue of the nucleoside triphosphate (dNTP or NTP) with elimination of pyrophosphate . This nucleotide is attached by the phosphodiester bond formed. The polymerization, catalyzed by DNA or RNA polymerases , proceeds in the 3 ′ direction. The direction of synthesis of a DNA or RNA strand is therefore 5 '→ 3'.

There are RNA and DNA polymerases that are active independently of a template, such as poly (A) polymerase or deoxyribonucleotidyl transferase . However, the transfer and reproduction of genetic information requires polymerases whose enzymatic activity depends on a template and which use another existing nucleic acid strand as a template when building a new nucleic acid strand . A complementary strand with the corresponding information-carrying sequence of certain nucleotides is built up on the template strand by base pairing, which strand then runs anti-parallel. The 5 '→ 3' synthesized strand is opposite its template 3 '→ 5'.

Polymerases that are dependent on templates of DNA present are, for example, the DNA polymerases involved in replication ; they are needed before a nucleus is divided in order to double the DNA of the chromosomes (duplication) and to be able to pass on the stored genetic information to daughter cells. The RNA polymerases involved in transcription are also DNA-dependent ; they are needed to make the genetic information of certain DNA segments currently available for the cell in the form of RNA. Genetic information for protein biosynthesis is given in the form of mRNA (messenger RNA); it is read on ribosomes and translated during translation . The reading direction here is 5 '→ 3'.

Formations of antiparallel oriented strands or strand sections are also possible with a ribonucleic acid (RNA). They also occur here as a result of complementarily paired bases. As a result, hairpin structures, for example, can be formed as secondary structures of a single RNA strand, in that sections within the strand are attached to one another by base pairing and form an area with a double-stranded formation, the so-called stem area; a single-stranded section in between then forms a so-called loop .

Antiparallelism, based on nucleic acids , is usually the result of complementary base pairings between different strands or different sections of an individual strand. It can occur in both DNA and RNA strands and in two strands of DNA / DNA, DNA / RNA or RNA / RNA.

Proteins

In proteins , the term is used in antiparallel β-sheet domains and refers to the amino acid sequence conventionally defined from the amino terminus to the carboxyl terminus . This means that one area of ​​the opposite β-sheet is arranged at the amino-carboxyl terminal, the opposite is oriented at the carboxyl-amino terminal.

literature

  • Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 6 edition, Spektrum Akademischer Verlag, Heidelberg 2007. ISBN 978-3-8274-1800-5 .
  • Donald Voet, Judith G. Voet: Biochemistry. 3rd edition, John Wiley & Sons, New York 2004. ISBN 0-471-19350-X .
  • Bruce Alberts , Alexander Johnson, Peter Walter, Julian Lewis, Martin Raff, Keith Roberts: Molecular Biology of the Cell , 5th Edition, Taylor & Francis 2007, ISBN 978-0815341062 .