In
biochemistry
Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
, two
biopolymers are antiparallel if they run
parallel
Parallel is a geometric term of location which may refer to:
Computing
* Parallel algorithm
* Parallel computing
* Parallel metaheuristic
* Parallel (software), a UNIX utility for running programs in parallel
* Parallel Sysplex, a cluster of ...
to each other but with opposite
directionality (alignments). An example is the two
complementary
A complement is something that completes something else.
Complement may refer specifically to:
The arts
* Complement (music), an interval that, when added to another, spans an octave
** Aggregate complementation, the separation of pitch-class ...
strands of a
DNA double helix
A double is a look-alike or doppelgänger; one person or being that resembles another.
Double, The Double or Dubble may also refer to:
Film and television
* Double (filmmaking), someone who substitutes for the credited actor of a character
* ...
, which
run in opposite directions alongside each other.
Nucleic acids
Nucleic acid molecules have a
phosphoryl {{unreferenced, date=May 2015
A phosphoryl group is the chemical ion or radical: P+O32−, containing phosphorus and oxygen. (The correct chemical name for this −PO32− group is phosphonato, and phosphono for −PO3H2; as ''phosphoryl'' in ch ...
(5') end and a
hydroxyl
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...
(3') end. This notation follows from
organic chemistry nomenclature, and can be used to define the movement of enzymes such as
DNA polymerase
A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create ...
s relative to the DNA strand in a non-arbitrary manner.
G-quadruplexes
G-quadruplex
In molecular biology, G-quadruplex Nucleic acid secondary structure, secondary structures (G4) are formed in nucleic acids by sequences that are rich in guanine. They are helical in shape and contain guanine tetrads that can form from one, two o ...
es, also known as G4 DNA are secondary structures found in nucleic acids that are rich in
guanine
Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is c ...
. These structures are normally located at the
telomere
A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Although there are different architectures, telomeres, in a broad sense, are a widespread genetic feature mos ...
s (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. The structure of these G-quadruplexes can be determined by a cation.
DNA replication
In DNA, the 5'
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
is located at the top of the
leading strand
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...
, and the 3' carbon is located at the lower section of the
lagging strand
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritance ...
. The
nucleic acid sequences are complementary and parallel, but they go in opposite directions, hence the antiparallel designation.
The antiparallel structure of DNA is important in
DNA replication
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...
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
Okazaki fragments are short sequences of DNA nucleotides (approximately 150 to 200 base pairs long in eukaryotes) which are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA ...
.
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. The four base pairs are:
adenine
Adenine () ( symbol A or Ade) is a nucleobase (a purine derivative). It is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The three others are guanine, cytosine and thymine. Its deri ...
,
guanine
Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is c ...
,
cytosine
Cytosine () ( symbol C or Cyt) is one of the four nucleobases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an ...
, and
thymine
Thymine () ( symbol T or Thy) is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidi ...
, where adenine complements thymine, and guanine complements cytosine.
Transcription
Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including:
Genetics
* Transcription (biology), the copying of DNA into RNA, the fir ...
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.
Polypeptides
Polypeptides have an
N-terminus
The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the ami ...
and a
C-terminus
The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...
, 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
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
sub-unit is the basis for
directionality notation in polypeptides; a given
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
can be represented as its set of unique
amino acid abbreviations within an N-terminus and a C-terminus.
Beta sheet
Many proteins may adopt a
beta sheet as part of their
secondary structure
Protein secondary structure is the three dimensional conformational isomerism, form of ''local segments'' of proteins. The two most common Protein structure#Secondary structure, secondary structural elements are alpha helix, alpha helices and beta ...
. In beta sheets, sections of a single polypeptide may run side-by-side and antiparallel to each other, to allow for
hydrogen bonding between their
backbone chain
In polymer science, the polymer chain or simply backbone of a polymer is the main chain of a polymer. Polymers are often classified according to the elements in the main chains. The character of the backbone, i.e. its flexibility, determines the ...
s. 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.
References
{{DEFAULTSORT:Antiparallel (Biochemistry)
Biochemistry