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Transcription and Translation - Coggle Diagram
Transcription
and
Translation
Transcription
An mRNA copy of a gene is made from DNA. In eukaryotes, this takes place in the nucleus. In prokaryotes, this takes place in the cytoplasm.
1) RNA polymerase attaches to DNA
2) Complementary mRNA is formed
3) RNA polymerase moves down the DNA strand
4) RNA polymerase reaches a stop signal
When a stop signal is reached, RNA polymerase stops making mRNA and detaches from the DNA. In eukaryotes, mRNA moves out of he nucleus via a nuclear pore and attaches to a ribosome in the cytoplasm.
The enzyme moves along the DNA, assembling the mRNA strand. One passed, the hydrogen bonds form again between the DNA strands.
RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand (only one DNA strand acts as a template). Free bases are attracted to the exposed bases. Complementary base pairing means the mRNA strand ends up being a complementary copy of the DNA (uracil instead of thymine). Once RNA nucleotides are paired with their base on the DNA strand, RNA polymerase joins adjacent nucleotides with a phosphodiester bond, forming an mRNA strand (this makes 5' end of mRNA first moving down RNA).
Attaches at the start codon. In eukaryotes a DNA helicase is attached to the RNA polymerase and breaks the hydrogen bonds between the two polynucleotide strands. In prokaryotes the RNA polymerase separates the DNA strands.
Splicing takes place between the Pre-mRNA and mRNA stages (before mRNA leaves the nucleus), where introns are removed by enzymes leaving only the exons/coding parts of the gene.
Translation
Occurs in ribosomes in the cytoplasm of BOTH eukaryotes and prokaryotes, and involves amino acids joining together to make a polypeptide chain (protein synthesis).
The mRNA attaches to a ribosome and the tRNA molecules carry specific amino acids to it
tRNA + amino acid (with an anticodon complementary to the first codon on mRNA) attaches to the mRNA by base pairing
A second tRNA + amino acid attaches to the next codon in the same way
The two amino acids are then joined by a peptide bond by the ribosome (ATP provides energy), and the first tRNA molecule moves away leaving the amino acid
A third tRNA molecule then binds to the next codon on the mRNA, and the ribosome moves along the mRNA so the next amino acid can bind
This continues until there is a stop signal
DNA
transcription
mRNA
translation
Protein