CELL PROCESSES

Unit 2- Cell Processes                                                                                                      Kriti Chopra

Protein Synthesis

TRANSCRIPTION

1. The cell gets a message to make a certain quantity of specific protein. 

2. A portion of the DNA molecule unwinds, exposing the gene responsible for the protein.

3. Nucleotides, with the help of enzymes , move along one strand of the exposed gene and form a molecule of m-RNA. U pairs with A in the RNA.

4. Multiple copies of m-RNA are made according to the quantity of the order.  They leave the nucleus and enter the cytoplasm through nuclear pores.

5. An m-RNA binds with a ribosome so that the m-RNA can be read by the ribosome.

6. The message is read three nucleotide bases at a time. Each codon or triplet code stands for a specific amino acid activated by an enzyme.

TRANSLATION

7. The transfer RNA molecule has TWO ends.  One end has specific binding site for particular amino acid. The other end has a sequence of three nucleotides, the anticodon that can base pair with a codon.

8. The appropriate molecule of t-RNA attaches to and carries activated amino acid to the ribosome. And anticodon base pair with codon in order to bring the specific amino acid to the correct place.

9. A second transfer RNA picks up another activated amino acid and brings it to the ribosome, matching the anticodon to codon.

TERMINATION

10. First t-RNA releases its amino acid to the second transfer RNA and leaves the site. ( They form peptide bonds using ATP.

11. The second t-RNA releases its “load” of amino acids to the third t-RNA and leaves sight,

12. This process repeats itself until the entire message is read through