Lecture on Protein Synthesis

Overview

Protein synthesis is the process of making proteins, which involves two main steps:

• Transcription: Copying a single gene from DNA into messenger RNA (mRNA).
• Translation: Using the mRNA strand to produce a protein.

Importance of Protein Synthesis

• DNA resides in the nucleus and contains all genetic material in the form of genes.
• Genes are specific sequences of bases, coding for amino acids, which combine to form proteins.
• Ribosomes, where protein synthesis occurs, are located outside the nucleus.
• DNA is too large to leave the nucleus, so a smaller mRNA copy is made to transfer genetic information to ribosomes.

Structure of mRNA

• Differences from DNA:
  • Shorter, as it represents only a single gene.
  • Single-stranded, unlike the double-stranded DNA.
  • Contains uracil (U) instead of thymine (T).

Transcription Process

1. DNA Uncoiling: DNA is uncoiled for easier transcription.
2. Initiation by RNA Polymerase:
   • RNA polymerase binds before the gene starts on the DNA.
   • DNA strands separate ahead of the polymerase, exposing bases.
3. Complementary Base Pairing:
   • RNA polymerase reads DNA bases one by one to form an mRNA strand.
   • Complementary base rules: A pairs with U (instead of T), T with A, G with C, C with G.
4. Completion:
   • RNA polymerase moves along the DNA, creating mRNA.
   • Once the entire gene is transcribed, RNA polymerase detaches.
   • DNA strands rejoin, and the mRNA leaves the nucleus to the ribosome.

Translation Process

• Codons and Amino Acids:
  • mRNA codons (triplets) code for specific amino acids.
  • There are 20 different amino acids, each associated with specific codons.

Steps in Translation

1. Ribosome Binding:
   • mRNA binds with ribosome to initiate protein assembly.
2. Role of tRNA:
   • Transfer RNA (tRNA) brings amino acids to the ribosome.
   • Each tRNA molecule has an anticodon complementary to mRNA codons.
   • Correct amino acids are brought in sequence by matching tRNA anticodons with mRNA codons.
3. Building the Protein:
   • Ribosome links amino acids together in a chain.
   • As tRNA molecules bind and release amino acids, the ribosome assembles the protein.
4. Completion:
   • Ribosome continues until the end of the mRNA.
   • Amino acid chain detaches and folds into a functional protein.

Conclusion

• Protein synthesis is a vital cellular function, efficiently translating genetic instructions from DNA into functional proteins.
• Understanding transcription and translation is crucial for comprehending how genetic information is expressed.