Antiparallel (biochemistry)

Source: Wikipedia, the free encyclopedia.

In

run in opposite directions
alongside each other.

Nucleic acids

hydroxyl (3') end. This notation follows from organic chemistry nomenclature, and can be used to define the movement of enzymes such as DNA polymerases
relative to the DNA strand in a non-arbitrary manner.

G-quadruplexes

The different types of topologies in G-quadruplex, propeller, lateral, and diagonal.

G-quadruplexes, also known as G4 DNA are secondary structures found in nucleic acids that are rich in guanine.[1] These structures are normally located at the telomeres (the ends of the chromosomes). The G-quadruplex can either be parallel or antiparallel depending on the loop configuration, which is a component of the structure. If all the DNA strands run in the same direction, it is termed to be a parallel quadruplex, and is known as a strand-reversal/propeller, connecting adjacent parallel strands. If one or more of the DNA strands run in opposite direction, it is termed as an anti-parallel quadruplex, and can either be in a form of a lateral/edgewise, connecting adjacent anti-parallel strands, or a diagonal, joining two diagonally opposite strands.[2] The structure of these G-quadruplexes can be determined by a cation.

DNA replication

Main article:
DNA Replication

In DNA, the 5'

lagging strand. The nucleic acid sequences are complementary and parallel, but they go in opposite directions, hence the antiparallel designation.[3] The antiparallel structure of DNA is important in DNA replication because it replicates the leading strand one way and the lagging strand the other way. During DNA replication, the leading strand is replicated continuously whereas the lagging strand is replicated in segments known as Okazaki fragments
.

Anti-parallelism in biochemistry

The importance of an antiparallel DNA double helix structure is because of its hydrogen bonding between the complementary nitrogenous base pairs. If the DNA structure were to be parallel, the hydrogen bonding would not be possible, as the base pairs would not be paired in the known way.[4] The four base pairs are: adenine, guanine, cytosine, and thymine, where adenine complements thymine, and guanine complements cytosine. Transcription would be another problem if the DNA structure were to be parallel, making no sense of the information being read from the DNA. This would further lead to the production of incorrect proteins.[5]

Polypeptides

Polypeptides have an N-terminus and a C-terminus, which refer to the ends of the polymer in a way that reflects the direction in which the polymer was synthesized. The chronological sequence of each amino acid sub-unit is the basis for directionality notation in polypeptides; a given protein can be represented as its set of unique amino acid abbreviations
within an N-terminus and a C-terminus.

Beta sheet

Antiparallel and parallel beta sheet

Many proteins may adopt a

backbone chains. Beta sheets can also be either a parallel or anti-parallel secondary structure. However, an anti-parallel beta sheet is significantly more stable than a parallel structure due to their well aligned H-bonds, which are at a 90° angle.[6]

References

  1. PMID 28362374
    .
  2. PMID 17012276
    .
  3. ^ Benson G. "Anti-Parallel Strands". K*Nex DNA Modeling. Boston University. Archived from the original on 22 October 2019. Retrieved 12 December 2011.
  4. ^ PhD, Kenneth P Mitton. "Re: Why are the two strands of a DNA molecule antiparallel?". www.madsci.org. Retrieved 2017-04-06.
  5. ^ "why is DNA antiparallel? Can it be parallel?". biology.stackexchange.com. Retrieved 2017-04-06.
  6. ^ "Secondary structure of Proteins". www.chembio.uoguelph.ca. Archived from the original on 2017-04-02. Retrieved 2017-04-01.
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