1. How DNA Makes Protein / Protein Synthesis
Starting Facts
A section of DNA that codes for a polypeptide (a gene) has it´s bases in the correct order.
Aa´s are in the body because we have eaten protein and after digestion, the aa´s were absorbed from the small intestine into our blood. Cells that needed them took them in.
3 stages
Transcription, aa activation, translation

2. Transcription
The order of bases in a gene is changed into a mRNA molecule
Where ? In nucleus
How ?
DNA unwinds and unzips (H bonds between complementary bases break).
In the nucleus there are free mRNA bases floating around. With the help of RNA polymerase they come in and temporarily complementary base pair with the exposed DNA bases. (N.B an exposed A on the DNA will have U (uracil) pair with it).
When the gene has been transcribed, the temporary H bonds break. mRNA moves away and out through the nuclear pores and into the cytoplasm.
The DNA zips up and winds up (to protect itself)

4. Aa activation
This is when tRNA becomes loaded /activated with it´s correct aa.
Where ? - in the cytoplasm
How ?
It´s correct aa matches the 3 bases at the bottom of the tRNA, it´s anticodon.
This is all catalysed by a specific enzyme and ATP energy is used.

6. 3) Translation
This converts the mRNA into a line of aa´s that are in the correct order.
Where ? In the cytoplasm
How ?
a) The first 3 bases, codon, of mRNA is held by a ribosome.
b) The correct tRNA, carrying the correct aa comes along and temporarily forms H bonds during complementary base pairing.
c) The ribosome is also holding the second codon, it´s complementary tRNA comes along and the anticodon forms H bonds with it´s codon, during cbp.
d) The first aa detaches from it´s tRNA and goes and bonds to the 2nd aa.
The ribosome moves along and this process continues until the whole mRNA has been translated.
After each tRNA has left it´s aa there to join the aa line, it goes away and will get activated /loaded up again with another aa that is correct.

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