We present here in a very condensed way the elements of genetic information transfer. This article is based on various - much more detailed - articles of the German Wikipedia and The Sequence Onotolgy.
1. Gene¶
A gene is a section on the DNA.
The genes in DNA contain the information for the production of RNA (ribonucleic acids).
Protein-coding genes encode mRNA (messenger RNA). The mRNA contains the information for the construction of proteins.
The sequence of bases determines the sequence of amino acids in the protein. In each case, three nucleotides lying next to each other form a codon, with the help of which a specific amino acid to be incorporated into a protein can be clearly determined.
2. DNA (deoxyribonucleic acid)¶
A double-stranded concatenation of 4 possible nucleotides.
DNA is mostly located in the cell nucleus as chromosomes (nuclear DNA = nDNA) and carries the hereditary information in almost all living organisms. A small part of the DNA is located in the mitochondria (cellular power plants) as mitochondrial DNA (mtDNA).
Model of a DNA. CC BY-SA 3.0
3. RNA (ribonucleic acid)¶
A mostly single-stranded concatenation of 5 possible nucleotide species.
RNA is the carrier of genetic information in certain viruses. There is RNA that passes on (hereditary) information (coding RNA) and RNA that does not.
in 2017 and 2018 alone, 2000 new forms of RNA were discovered each year. PubMed finds about 250,000 newly published scientific articles for the search term RNA in the years 2014 to 2018. For comparison: for the keyword ADHD (English for ADHD there were just under 11,500).
3.1. Coding RNA (mRNA)¶
mRNA copies the information contained in a gene, conveys it to the ribosome, where protein biosynthesis takes place by means of this information.
Shapes:
- NSD transcript
- Capped mRNA
- Consensus mRNA
- Edited mRNA
- Specimen mRNA
-
MRNA with frameshift
- Monocistronic mRNA
- Polyadenylated mRNA
- Polycistronic mRNA
- Recoded mRNA
- Trans spliced mRNA
3.2. Non-coding RNA (ncRNA)¶
There are many types of non-coding RNA. They can change the expression of genes.
Forms of non-coding RNA:
- AsRNA (antisense RNA)
- Regulates gene expression
- Is transcribed from the coding DNA strand and not from the template DNA strand. Is therefore complementary to mRNA.
- CircRNA (circular RNA)
- Binds to miRNA. Is thereby involved in the regulation of cellular processes, such as proliferation or apoptosis (cell death)
- Class I RNA
- Class II RNA
- EnhancerRNA
- Could have regulatory function
- Guide RNA
- HnRNA (heterogeneous nuclear RNA)/ pre-mRNA (precursor mRNA)
- Precursor of the mature mRNA
- LncRNA (long non-coding RNA)
- Longer than 200 nucleotides
-
MiRNAs (microRNAs)
- Closely related to siRNAs
- Regulate cellular processes such as proliferation and cell death with
- PiRNA (Piwi-interacting RNA)
- 26-31 nucleotides long
- Form complexes with PIWI proteins involved in epigenetic and posttranscriptional silencing in germ cells
- Riboswitches
- Serve the gene regulation
- Ribozymes
- Catalytically active RNA molecules
- Catalyze chemical reactions, just as enzymes do
- RRNA (ribosomal RNA)
- Does not carry genetic information (like tRNA)
- Is involved in the assembly of the ribosome
- Is also catalytically active when the peptide bond is linked
- RRNA cleavage RNA
- RasiRNA (repeat associated small interfering RNA)
- RNase MRP RNA
- Essential for the catalytic activity of RNase MRP.
RNase MRP is an enzymatically active ribonucleoprotein that participates in the initiation of mitochondrial DNA replication in mitochondria and is involved in precursor rRNA processing in the nucleus, where it splices the internal transcribed spacer 1 between 18S and 5.8S rRNAs.
- RNase P RNA
- ScRNA (small cytoplasmic RNA)
- ScaRNA (small cajal body-specific RNA)
- Are found in the Cajal Bodies
- Subclass of snoRNA
- Control the modification (methylation and pseudouridylation) of RNA polymerase II-transcribed spliceosomal RNAs U1, U2, U4, U5, and U12.
- ScaRNA1 (small cajal body-specific RNA 1, ACA35)
- Appears to be involved in the pseudouridylation of U2 spliceosomal RNA at residue U89
- ShRNA
- SiRNA (small interfering RNA)
- Arises in a cell signaling pathway known as RNAi (RNA interference)
In this process, dsRNA (double-stranded RNA) is split into many smaller siRNAs by the enzyme Dicer and incorporated into RISC (RNA-induced silencing complex, an enzyme complex). By means of the contained RNA fragments, RISC binds to DNA (e.g. to gene regions) or to mRNA and can thus “switch them off”.
- SiRNAs are involved in various cellular processes and diseases.
- SnRNA (small nuclear RNA)
- Are found in the cell nucleus
- Responsible for splicing hnRNA at the spliceosome.
- SnoRNA (small nucleolar RNA)
- Are found in the nucleolus
- Closely related to scaRNAs
- Small regulatory ncRNA
- SRP RNA
- TRNA (transfer RNA)
- Does not encode genetic information
- Auxiliary molecule in protein biosynthesis
- Takes up single amino acid from cytoplasm and transports it to ribosome
- TRNA is encoded by a specific RNA gene
- TasiRNA
- Telomerase RNA
- Telomeric transcript
- Three prime overlapping ncRNA
- Vault RNA
- Y RNA
4. Nucleotides¶
Nucleotides each consist of a base, a sugar and a phosphate:
- Base (five possible bases)
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T)
- Uracil (U) (in DNA only thymine instead)
- Sugar
- Ribose (D-ribofuranose) or
- Deoxyribose (2-deoxy-D-ribofuranose)
- Phosphate
- At least one phosphate group
5. Proteins (proteins)¶
Proteins are necessary for the biological development of a living being and for cell metabolism.
Human proteins can be formed from 21 different α-amino acids. The α-amino acids chain together through peptide bonds to form a polymer (polypeptides). These polypeptides unfold in the aqueous environment to form the native protein.
The biosynthesis of proteins takes place in all cells at the ribosomes by means of mRNA, which transmits the blueprint of proteins as genetic information.
The sequence of the bases of the mRNA encodes in triplets (codons) the sequence of the (proteinogenic) amino acid. After translation, the side chains of some amino acids incorporated in the protein can still be changed.
One study found a correlation of ADHD with the proteins lysosomal Pro-X carboxypeptidase and alpha-2-antiplasmin in blood plasma.
6. Amino acids (aminocarboxylic acids)¶
Amino acids are chemical compounds with an amino group (contains nitrogen) and a carboxylic acid group (contains carbon) that are found in all living things.
Amino acids are the building blocks of proteins (albumen).
They primarily serve to build up body tissue and are the final stages in the breakdown of protein.
Essential amino acids cannot be produced by an organism itself and must therefore be taken in through food.
Amino acids can be differentiated according to various categories:
6.1. Types amino acids¶
6.1.1. After structure¶
- Amino acids by structure
- Α-amino acids (2-aminocarboxylic acids, e.g. glycine)
- Β-amino acids (3-aminocarboxylic acids, e.g. β-alanine)
- Γ-amino acids (4-aminocarboxylic acids, e.g. γ-aminobutyric acid = GABA)
6.1.2. Amino acids by function¶
- Proteinogenicity
Proteinogenicity means that the amino acid serves as a building block of proteins
- Proteinogenic amino acids
- Α-amino acids, which are the building blocks of proteins, in humans 21 different
Name / abundance in proteins / essential:
- Alanine (9.0 %)
- Arginine (4.7 %) partial essential
- Asparagine (4.4 %)
- Aspartic acid (5.5%)
- Cysteine (2.8%) essential for children and pregnant women
- Glutamine (3.9%)
- Glutamic acid (6.2 %)
- Glycine (7.5 %)
- Histidine (2.1 %) partially essential
- Isoleucine (4.6%) essential
- Leucine (7.5%) essential
- Lysine (7.0 %) essential
- Methionine (1.7%) essential
- Phenylalanine (3.5%) essential
- Proline (4.6 %)
- Pyrrolysine (non-canonical, only in bacteria)
- Selenocysteine (non-canonical)
- Serine (7.1 %)
- Threonine (6.0 %) essential
- Tryptophan (1.1%) essential
- Tyrosine (3.5%) essential for children and pregnant women
- Unknown amino acid (unclear if amino acid)
- Valine (6.9%) essential
- Non-proteinogenic amino acids
- Naturally occurring (= biogenic / organogenic) amino acids
- More than 400 non-proteinogenic amino acids with biological functions
- D-amino acids (rare) are special subgroup
- Synthetically produced / theoretically possible amino acids
- Considerably larger number
-
Neurotransmitter
- Some amino acids act as neurotransmitters
- As well as some degradation products of amino acids
- Hormones
- Tissue Mediators
6.1.3. Amino acids by formation¶
- Naturally occurring (= biogenic / organogenic)
- Synthetically produced
