DNA Transcription and Translation

Introduction

• Understanding DNA transcription and translation is key to knowing how genetic material in a single cell leads to the development of an organism.
• These processes convert the genetic code into proteins, essential for organismal development.

Key Terminology

• Gene: A portion of the chromosome that codes for proteins.
• mRNA (messenger RNA): Carries genetic information from DNA to the ribosome.
• tRNA (transfer RNA): Brings amino acids to the ribosome during protein synthesis.
• Codon: A set of three nucleotides on the mRNA that corresponds to a specific amino acid.

DNA Transcription

1. Initiation:

   • Enzymes use one DNA strand as a template to produce mRNA.
   • RNA polymerase binds to the promoter sequence with the help of transcription factors.
   • DNA strands separate: the template (antisense) strand and nontemplate (sense) strand.

2. Elongation:

   • RNA polymerase synthesizes mRNA from 5' to 3', utilizing the antisense strand.
   • RNA is synthesized with ribose sugar and uracil instead of deoxyribose and thymine.
   • DNA is re-zipped as RNA polymerase moves along.

3. Termination:

   • Reaches the end of the gene, RNA polymerase releases the newly synthesized mRNA.

RNA Processing

• Modifications occur after transcription before the mRNA exits the nucleus.

DNA Translation

1. Introduction:

   • Occurs in the cytoplasm at the ribosome.
   • mRNA codons direct the sequence of amino acids in a protein.

2. Codon Reading and tRNA:

   • 64 possible codons coding for 20 amino acids, with redundancy but no ambiguity.
   • Start codon: AUG (methionine), Stop codons: UAA, UAG, UGA.

3. Initiation:

   • Small ribosomal subunit binds to mRNA and initiator tRNA.
   • Large ribosomal subunit forms the complete initiation complex.

4. Elongation:

   • tRNA enters ribosome and matches codon with anticodon, adding amino acids to the chain.
   • Ribosome shifts, allowing new tRNA entry and elongation continues.

5. Termination:

   • Stops when a stop codon is encountered.
   • Completed polypeptide is released for folding and modification.

Conclusion

• DNA transcription and translation convert genetic information into functional proteins, vital for cellular and organismal function.
• This process is fundamental to understanding how DNA codes for life.