Prokaryotic Protein Synthesis
Two steps:
- Transcription
- Translation
Eukaryotic Protein Synthesis
Three steps:
- Transcription
- RNA processing
- Translation
Key Player in Transcription: RNA Polymerase
- Unwinds the DNA in order for the copying to occur.
- Makes an RNA copy of DNA.
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Word derivation:
- Poly: many
- mer: segments
- ase: enzyme
- A polymerase is an enzyme that adds many segments together. In this case, it adds many nucleotides together to make RNA.
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Comparison to DNA polymerase:
- DNA polymerase is the key molecule in DNA replication.
- DNA polymerase did not unwind the DNA; helicase did.
What Is a Gene?
- A chromosome is basically a long piece of DNA that has many genes.
- A gene is a strand of DNA with a promoter on one end and terminator on the other.
- The part of the gene that is going to be transcribed is called the transcription unit.
The Transcription Process
Step 1: Initiation
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RNA polymerase attaches to the promoter.
- The position of the promoter tells the RNA polymerase which strand to copy.
- RNA polymerase unwinds the DNA.
Step 2: Elongation
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RNA nucleotides are added to make a mRNA copy of the template strand.
- The nucleotides are added to the 3' end of the ribose sugar.
- Therefore, RNA polymerase copies in the 5' → 3' direction.
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RNA review (compared to DNA):
- Is single-stranded.
- Uses uracil instead of thymine.
- Uses ribose sugar instead of deoxyribose.
Step 3: Termination
- mRNA detaches from the template when it reaches the termination point.
- Transcription is completed!
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Remember:
- Prokaryotic mRNA is ready to make proteins.
- Eukaryotic mRNA has to be processed before it can make proteins.
