REPLICATION

1. Before a cell divides, the bonds between the complementary bases break in short sections of the double-stranded DNA molecules, and the complementary strands separate from one another (UNWINDING/ UNZIPPING)

• Each split in the molecule is called a REPLICATION FORK

2. At the forks, each separated strand serves as a template for the synthesis of a new complementary strand

3. In a process directed by enzymes, free nucleotide units that are present in the nucleus link to complementary bases on each of the DNA strands

4. The sugars and phosphates of the new nucleotides bond together to form the backbones of both new strands

• The process of DNA replication begins with one double-stranded DNA molecule and ends with 2 double stranded DNA molecules

• Each double strand contains one strand from the parent molecule + a new complementary strand assembled from free nucleotides

• Each of the new double stranded molecules is identical to the other and is also identical to the original parent molecule

PROTEIN SYNTHESIS

TRANSCRIPTION

1.Protein synthesis begins once the double-stranded DNA molecule unzips

2.Double helix uncoils

3. Nucleotides from the mRNA find the appropriate pair by using the single stranded DNA as blueprint

* Soon mRNA nucleotides are joined into a long chain

4. Once the chain has been fused, the mRNA molecule moves away from the parent DNA strand

* The 2 strands of the original DNA rejoins

• THE PROCESS OF TRANSCRIPTION IS COMPLETE

• ss mRNA molecule moves through the nuclear membrane & carries the nitrogen base code to the ribosomes in the cytoplasm

TRANSLATION

1. mRNA attaches itself to the ribosome much like a ribbon

2. An initiator codon turns on the protein synthesis

3. tRNA picks up amino acids that are circulating within the cytoplasm and shuttles them to the mRNA

4. The amino acid is held in place against one end of the clover-leaf-shaped molecule

* The other end of the tRNA molecule has a plug-shaped structure with 3 nitrogen bases exposed (ANTICODON)

• Each kind of tRNA molecule has a specific anticodon

5. The mRNA moves along the ribosome much like a typewriter ribbon

6. A new codon of mRNA is then exposed for fitting with another tRNA anticodon

7. The amino acid carried by the tRNA molecules are fused into long-chain proteins on the ribosome

8. The sequencing of the amino acid is determined by the message carried from the nucleus by the mRNA molecule

9. Once the protein molecule has been built, a terminator codon turns the synthesis off and the process of translation is complete