Based on the book 'Genetics: Analysis & Principles, 6th edition, by Robert J. Brooker' and the course at the Vrije Universiteit Amsterdam a summary was written that specifically focuses on gene transcription and RNA modification
12.1
The information needed to create a living organism, the chromosomal DNA, is stored in
units called genes; a segment of DNA supposed to make a functional product (RNA or
polypeptide). This information is accessed via transcription, the act or process of making a
copy in the form of a mRNA molecule; RNA synthesis from a DNA template.
Protein-coding/structural genes carry the info for the amino acid sequence of a polypeptide.
When such a structural gene is transcribed into messenger RNA (mRNA), it is then later
translated into the polypeptide chain. One or more polypeptides create a functional protein,
which structure/form determine the traits of an organism. The central dogma of genetics
describes the regular flow: DNA RNA protein/polypeptide, which is the final stop, the
irrevocable end. DNA base sequence defines the beginning and end of a gene along with the
regulation of RNA synthesis. Whether or not a gene is expressed influences the production
of a functional product, it being RNA/protein, along with a particular trait.
Some irregularities in the dogma include the process of RNA replicating itself (e.g. influenza
virus) and the transfer from RNA DNA: the enzyme reverse transcriptase is able to create
of copy of the RNA in the form of DNA, cDNA.
The DNA includes several components essential for transcription:
1. Regulatory sequence: site for the binding of regulatory proteins that affect the rate
of transcription, transcription factors.
2. Promoter: site for RNA polymerase binding and thus starting point of the
transcription.
3. Terminator: signals the end of transcription.
This enables RNA synthesis to occur within a defined location, from promoter to terminator.
RNA is always synthesized based on the template strand of the DNA, the opposite is the
non-template strand; also known as the coding/sense strand for protein coding genes.
Also, the mRNA from the template DNA includes several characteristic aspects:
1. Ribosome binding-site: location for ribosome to bind and start translation.
2. Start codon: specifies the first amino acid in the polypeptide, similar to the ribosome
binding site.
3. Codons: set of three nucleotides coding for one amino acid; the sequence of codons
determine the organization of amino acids in polypeptide.
4. Stop codons: specifies the end of the polypeptide synthesis.
Transcription features three stages:
1. Initiation: the promoter is recognised by transcription factors and initiates RNA
polymerase binding to the promoter.
2. Elongation: as RNA pol. slides along the DNA an open complex is created, since the
double helix needs to be split up for the template strand to be accessed and
transcribed.
3. Termination: this complex causes RNA pol. to dissociate from the DNA and stop
transcription. It thus entails protein-DNA interactions, like transcription factors that
either directly or indirectly bind to the DNA and signal termination.
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