DNA Replication and Protein Synthesis

Refer to notes on Organic Macromolecules for Structure of Nucleic Acids (DNA and RNA) and Proteins before commencing these notes.

DNA Replication

Genes (the chemicals of heredity) are composed of DNA. Whenever new cells are made in either meiosis or mitosis, then new genes made of DNA are produced for the new cells.
DNA Replication means the duplication of DNA that is identical to the original double-stranded DNA.
This replication of DNA must be exact, or a mutation of an incorrect sequence of nucleotides will occur.

DNA Replication occurs in 3 steps:
1. The 2 bases forming each rung of the 'ladder' snap apart. This is caused by an enzyme that passes along the strands, 'unzipping' it.
2. Spare nucleotides (in the nucleus of the cell) attach themselves to the 'broken rungs' to repair the break. Each repairing nucleotide is identical to the one broken.
3. As each 'broken rung' is repaired, two 'ladders' form, that is 2 identical strands of DNA. The 'repairing' is really the process of replication.

There are 2 processes in protein synthesis:
1. Transcription (DNA makes all 3 forms of RNA in the nucleus)
2. Translation (DNA plus all 3 forms of RNA together make proteins at the ribosome in the cytoplasm)

Transcription (DNA makes all 3 forms of RNA in the nucleus)
Translation (DNA plus all 3 forms of RNA together make proteins at the ribosome in the cytoplasm)

One strand of the DNA double helix is used to make mRNA (which travels to the 'ribosome workbench'), tRNA (which collects its specific amino acid for the protein), and rRNA (which forms much of each ribosome where proteins are made).
The complete process is still unclear.

mRNA has many codon sequences consisting of 3 nucleotides, each of which codes for a particular amino acid to build up the protein.
mRNA which is a long single strand lies across a ribosome.
Meanwhile, tRNA has an 'opposite' or complementary anticodon sequence, and searches the cytoplasm for the specific amino acid which is specifically coded for by each tRNA's anticodon.
Each tRNA brings each of the many amino acids to the mRNA at the ribosome.
After each amino acid is linked in turn to the growing protein, the tRNA dissociates itself from the amino acid and the mRNA.
There are both start codons and stop codons. Start codons initiate the making of a protein. Stop codons terminate the making of a protein and release it into the cytoplasm.