Rucete ✏ Biology In a Nutshell
1. What Is Protein Synthesis?
Protein synthesis is the process by which cells build proteins using the instructions encoded in DNA.
It consists of four main steps:
- Transcription
- RNA Processing
- Translation
- Folding/modification (not always emphasized in basic summaries)
2. Transcription (DNA → mRNA)
- Occurs in the nucleus.
- RNA polymerase binds to DNA and synthesizes a complementary mRNA strand from the DNA template.
- This process uses base pairing: A→U, T→A, G→C, C→G.
- The result is pre-mRNA.
3. RNA Processing (only in eukaryotes)
- Pre-mRNA is modified to become mature mRNA:
- 5’ cap is added.
- Poly-A tail is added.
- Introns (non-coding sequences) are removed.
- Exons (coding sequences) are spliced together.
4. Translation (mRNA → Protein)
- Occurs in the cytoplasm at the ribosome.
- mRNA binds to a ribosome, where the code is read in codons (groups of three nucleotides).
- Each codon corresponds to one amino acid.
- tRNA molecules carry amino acids to the ribosome:
- Each tRNA has an anticodon that pairs with a codon on the mRNA.
- rRNA (ribosomal RNA) helps form the ribosome and catalyze peptide bond formation.
5. Ribosome Structure
- Composed of two subunits (large and small).
- Has three binding sites:
- A site (aminoacyl): where new tRNA enters
- P site (peptidyl): where the growing polypeptide chain is held
- E site (exit): where empty tRNA exits
6. Summary of Protein Synthesis Flow
DNA → Transcription → pre-mRNA → RNA processing → mRNA → Translation → Polypeptide (Protein)
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Biology in a nutshell