Transcription And Translation Flashcards
Describe the process of transcription
1) the section of DNA that contains the gene unwinds and unzips under the control of DNA helicase. This breaks the hydrogen bonds between the bases.
2) only one of these two strands of DNA contains the code for the protein to be synthesised. This is the sense strand runs for ‘5 to ‘3. The other strand, the antisense strand, is a complementary copy of the sense strand and does not code for a protein. The antisense strand acts as the template strand during transcription, so that the complementary RNA strand formed carries the same base sequence as the sense strand
3) Free RNA nucleotides will base pair with complementary bases exposed on the antisense strand when the DNA unzips (A-U, C-G uracil bind to adenine on the anti-sense strand)
4) phosphodiester bonds are formed between the RNA nucleotides by RNA polymerase. Transcription stops at the end of the gene and the completed strand of RNA is called mRNA
The mRNA then detaches from the DNA template and laves the nucleus through a nuclear pore
Describe the process of translation
1) the mRNA binds to the small subunit of the ribosome at its start codon
2) a tRNA, (that is carrying an amino acid) with the complementary anticodon binds to the mRNA start codon
3) another tRNA with the anticodon and carrying the corresponding amino acid then binds to the next codon on the mRNA . A maximum of two tRNA strands can be bound at the same time
4) peptide bond form between the amino acids on the tRNAs, the formation of the peptide bonds is catalysed by peptidyl transferase from he rRNA
5) the ribosome then moves along the mRNA release in the first tRNA, this allows for another tRNA to bind to the codon on the mRNA. This is repeated with another amino acid added each ice and keeps repeating until the ribosome reaches the end of the mRNA at a stop codon and the polypeptide is released
The amino acids joined together form the primary structure of the protein
