DNA replication

The process of making pre-mRNA using part of the DNA as a template.

• DNA helicase (enzyme) separates the 2 strands to expose the nucleotide bases.
• The nucleotides bases from the template strand, pair with complementary nucleotides from the pool present in the nucleus.
• The enzyme RNA polymerase moves along the strand and joins the nucleotide together to form mRNA.
• The DNA strand rejoins it.
• Once the RNA polymerasereaches a stop codon, it detaches and the production of pre-mRNA is complete.

The process of removing introns and joining extrons together

mRNA molecules are too large to diffuse out of the nucleus, so once they have been spliced they leave via the nuclear pore.

• Ribosome becomes attached to the starting codon of mRNA
• tRNA with complementary anticodon, moves to ribosome and pair with codon.
• The tRNA carries a specific amino acid
• Step 2 and 3 happen again (with next codon).
• The ribsome moves along the mRNA, bringing together 2 tRNA molecules at any one time.
• The 2 amino acids are joined by peptide bond.
• As the ribosome move onto the third codon the first tRNA molecule is released from its amino acid.
• Builds up a peptide chain.
• Continues until ribosome reaches a stop codon.