mRNA - Has a sequence of codons that specifies the amino acid sequence of the polypeptide
tRNA - Carry the corresponding amino acid to their codon. Has anticodon of three bases that binds to a complementary codon on mRNA
Ribosomes - Act as a binding site for mRNA and tRNA. Catalyzes the peptide bonds of the polypeptide. Small subunit binds to mRNA. Large subunit has binding sites for tRNAs and catalyzes the peptide bonds between amino acids
1. DNA double helix must unwind.
2. Two strands need to seperate or "unzip" (enzyme Helicase is responsible for this)
3. Free floating nucleotides form complementary pairs with nucleotides of both the DNA strands.
4. Nuceotides which have formed complementary base pairs with nucleotides of the OLD strand now join to each other to form a NEW strand of DNA. (enzyme DNA polymerase is responsible for this)
Result: Two identical DNA double helices, each consisting of one "old" strand and one "new" strand. (Semi convervative)
RNA Polymerase binds to a site on the DNA at the start of a gene
RNA Polymerase separates the DNA strands and synthesizes a complementary RNA copy from the antisense DNA strand
Transcription occurs in a 5' to 3' direction: RNA Polymerase adds the 5' end of the free nucleotide to the 3' end of the growing mRNA molecule
Covalently bonds ribonucloside triphosphates that align opposite their exposed complementary partner [uses energy from the clevage of the other phosphate groups to join them together]
- Once RNA sequence has been synthesized:
- RNA detaches from DNA
- Double helix reforms
- Transcription occurs in the nucleus then mRNA moves to the cytoplasm where Translation can occur
After the mRNA leaves the nucleus it enters the cytoplasm.
2. The location of translation occurs in the ribosomes in the cytoplasm
3. Ribsomes attach themselves to the mRNA (Ribosomes are also composed of RNA - rRNA)
4. Each ribosome covers an area of three codons on the mRNA.
5. the first tRNA carrying an amino acid will come in and the anti-codon exposed on the tRNA will have complementary binding with the codon of the mRNA in the A SITE of the ribosome.
6.Ribosome moves, first tRNA is now in the P site on the ribosome.
7. the second tRNA with it's own anti-codon (therefore carrying a specific amino acid) will complementary bind to the second codon on the mRNA filling the A site in the ribosome.
8. The second amino acid will attach to the first (formation of a peptide bond by a condensation reaction)
9. The first amino acid will be released from the first tRNA. The chain is beginning to form.
10. The ribosome will move again, and the first tRNA will now be in the E site of the ribosome. The second tRNA will be in the P site and a new tRNA will enter site A, continuing the process.
11. As the ribosome keeps moving, the anti-codon of the FIRST tRNA will dissociate from the first codon of the mRNA in the E-site of the ribosome.
12. This process continues until a STOP codon is reached.
13. the STOP and START codons do not code for an amino acid, but terminate and begin translation. mRNA is convereted into amino acid sequence using tRNA
And we're done with this subtopic! yay!
Written by Venetia (Biology)