1. 2.7 DNA Replication, transcription and translation
Molecular Biology
2.7 DNA Replication, transcription and translation

2. DNA to Protein Synthesis
The function of most genes is to specify the sequence of amino acids in a particular polypeptide.
Two processes are needed to produce a polypeptide using the base sequence of a gene.
Transcription
Translation

3. Transcription
Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
The enzyme RNA polymerase binds to a site on the DNA at the start of a gene
The RNA polymerase separates the double strand of DNA and pairs up RNA nucleotides with complementary bases.

4. Transcription
The RNA polymerase forms covalent bonds between the nucleotides
Transcription stops at the end of the gene. The completed mRNA is released.

5. Transcription
The completed mRNA has a base sequence that is complementary to the template DNA strand.
Note: Uracil replaces Thymine
Complete the transcription portion of the practice sheet

6. Translation Translation is synthesis of polypeptides on ribosomes
Ribosomes are complex structures that consist of a small and large sub-unit with binding sites for each of the molecules used in translation.

7. Translation
The amino acid sequence of polypeptides is determined by mRNA according to the genetic code

8. Translation
Codons of three bases on mRNA correspond to one amino acid in a polypeptide
“Genetic Code” = The translation “dictionary” that enables the cellular machinery to convert the base sequence on mRNA into the amino acid sequence

9. Translation There are 20 amino acids and only 4 nucleotide bases.
Living organisms use a triplet code with 3 bases coding for an animo acid.
The sequence of 3 bases on the mRNA = CODON
Examine the list of codons

10. Translation
There are 3 “stop” codons that code for the end of translation.
Different codons can code for the same amino acid.
The code is “degenerate”

11. Translation
Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA
The amino acids are carried on tRNA
The tRNA has a 3 base ANTICODON complementary to the mRNA codon
Complete the translation portion of the worksheet