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BTEC APPLIED SCIENCE: UNIT 11 - Learning Aim A
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DNA and Protein Synthesis. At a grade Distinction
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Unit 11Genetics and genetic engineering
M1: discuss the functional role of nucleic acids in DNA in the stage of protein synthesis
Triplet codes: a triple codon is a DNA or an RNA molecule that code for a specific amino acid by using
a sequence of three following nucleotide. Some codons are used to stop or start a signal for
translation. And the triple code that consists of three nucleotide is used to identify a single amino
acid.
Codon: Codons are units of genetic information made up of trinucleotides in DNA or RNA that code
for a specific amino acid or stop signals. There are 64 unique codons of which 3 act as a stop signal
and the other 61 are used to identify the amino acid.
Anticodon: An anticodon is a three nucleotide base sequence that is like a matching codon in a
messenger RNA {mRNA} sequence and is located at one end of a transfer RNA {tRNA} molecule.
Degenerated code: Degenerated code is a system of codes where different words all have the same
meaning. Because there are several situation where different codons defines the same amino acid,
so the genetic code is degenerated
Non overlapping: A non overlapping code means that two or more similar letter are not used for two
different codons. In other word that the production of more than one codon cannot include a single
nucleotide.
The process of protein synthesis:
Transcription:
, is the process of making messenger RNA from a DNA (in the nucleus)
1. DNA helicase breaks the hydrogen bonds between the DNA helix
2. RNA nucleotides base pair (by forming temporary hydrogen bonds) with the exposed DNA
template strand
3. RNA polymerase forms phosphodiester bonds between adjacent RNA nucleotides
4. RNA polymerase moves along the DNA rewinding the DNA as it moves along
In eukaryotes, transcription produces pre-mRNA; which must splice (removal of non-coding
regions called introns) to form mRNA.
Processing mRNA:
In this process the mRNA is not mature yet so it must go through more process before that leaves
the nucleus
1. Introns which are areas of the mRNA that do not code for the protein, are removed during
splicing. So, exons are the only parts of the remaining mRNA that really code for the protein.
The ribonucleoprotein that is formed by association of both (RNA and protein) are tiny
proteins that are required for the splicing process and contain RNA in the nucleus.
Endonucleases are involved in the repair of DNA. The AP endonuclease enzyme catalyses the
exclusive cutting of DNA at AP sites, so preparing DNA for subsequent repair, repair synthesis, and
DNA ligation. For example, when depurination takes place, a deoxyribose sugar is left with a missing
base.
2. Elongation that is the matching between the codons on the mRNA and the anticodons on
the tRNA, the tRNA starts to add amino acids to the expanding polypeptide as it enters the
ribosome. Then the tRNA exit the ribosome when this transfer is completed. The ribosome
then moves one codon down the mRNA and a new tRNA with the correct amino acid enters
after the polypeptide increases as the process is repeated.
3. In the termination a stop codon marks the end of the mRNA coding and the elongation
phase. And instead of a tRNA a protein know as a release factor is what the stop codon
needs this protein will force the complex of the mRNA ribosome the tRNA and the
polypeptide to dissolve and release each of the components.
Amino acid activation:
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