Translation

 Background knowledge

• The complete mRNA leave the nucleus and goes into the  cytoplasm
• polypeptide= many proteins
• The goal of translation is to create proteins

Act I
Initiation:



tRNA forms a complex with the with the ribosomal sub units
 this complex then binds with mRNA at the 5' cap and scans the mRNA

transfer RNA brings amino acids that correspond to the codons on mRNA
tRNA recognizes these codons by the anticodon loop attached to it
The starter codon is AUG which corresponds with the amino acid Methionine , the anticodon loop for it is UAC

Elongation
The polypeptide becomes longer one amino acid at a time
The first tRNA carrying the starter amino acid AUG goes to the P site
when the next tRNA brings the amino acid the previous tRNA goes to the E site

Termination
The codons UCC, UCA, UCG, UCU have no corresponding tRNA sequence so this process stops
Now the termination proteins release the ribosome from the mRNA, the polypeptide chain is released

Transcription

ACT I

• Transcription factors attach to the TATA box also known as the promoter
• The sequences before the TATA box are known as upstream, after the TATA box is known as downstream

• Transcription factors that bind to the the TATA box help attract RNA polymerase 2
• Once  RNA Polymerase 2 binds to transcription factors a transcription initiation complex is created and RNA starts transcribing
• A DNA strand can be transcribed  by several RNA polymerase 2, at a time

Act II

• The double stranded DNA is separated at certain points by RNA polymerase 2 
• The strand being transcribed is the template strand ( antisense) the other strand is the coding strand( sense) 
• The  RNA polymerase 2 binds RNA nucleotides to the template base pairs
• As the RNA strands grow they trail off from each polymerase and the DNA strands reform a helix 
• The RNA strand and template strand are anti-parallel
• Genes are read 3'-5' which creates a 5'-3' RNA molecule
• In RNA there is ''U'' instead of ''T" in the base pairs e.g A=U , T=A

Act III

• The terminator signals the end of transcription, it is the sequence AAUAAA
• At the end of the pre-mRNA molecule that was just synthesized a G cap is added to then of 5' and a Poly(A) tail is added at the end of the 3' 
• Introns (junk sequences that must be removed)
•  Extrons ( sequences that must be expressed) 
• The  spliceosome loops and cuts out the introns 
• It is composed of proteins and  snRNP
•  Every snRNPs has  a small nuclear RNA molecule/ snRNA
• The spliceosome also joins the exons, to create a mRNA molecule
• A messenger RNA has now been synthesized from the DNA strands