Lecture Notes: Protein Synthesis and Gene Expression

Cell Structure and Function

• Cell: Basic unit of all living tissue.
• Nucleus: Contains the genome in human cells.
  • 23 pairs of chromosomes in humans.
  • Chromosomes contain DNA strands.
  • DNA is tightly packed around proteins called histones.

DNA and Genes

• Genes: Sections of DNA with instructions for protein synthesis.
• Transcription: Process of copying a gene into messenger RNA (mRNA).
  • RNA polymerase enzyme initiates transcription.
  • mRNA is synthesized as a complementary strand to the DNA.
  • mRNA undergoes processing before it can be used (removal/addition of RNA sections).

Translation and Protein Synthesis

• Translation: Occurs in the cytoplasm, converting mRNA into proteins.
  • Ribosomes: Protein factories that bind to mRNA.
  • tRNA (transfer RNA): Carries amino acids to ribosome.
  • mRNA is read in codons (triplets of bases).
  • tRNA anticodon pairs with mRNA codon, adding amino acids to the chain.
  • Protein chain folds into a specific 3D shape.

Stages of Protein Synthesis

1. Initiation

• RNA polymerase binds to the promoter region of DNA.
• RNA polymerase unwinds DNA and starts mRNA synthesis.

2. Elongation

• RNA polymerase adds nucleotides to the growing mRNA strand.
• mRNA includes exons (coding) and introns (non-coding).
  • Introns are removed through splicing by the spliceosome.

3. Termination

• RNA polymerase reaches the terminator, completing mRNA synthesis.

Post-Transcriptional Modifications

• mRNA processing includes splicing out introns and adding a 5' cap and 3' poly-A tail.
• Mature mRNA exits the nucleus, entering the cytoplasm.

Protein Synthesis Stages

1. Initiation

• Small ribosomal subunit binds to mRNA.
• tRNA matches anticodon to start codon.
• Large ribosomal subunit forms initiation complex.

2. Elongation

• Amino acids are added to the growing polypeptide chain.
• tRNA brings amino acids to the A site, forming peptide bonds at the P site.
• Process repeats until stop codon is reached.

3. Termination

• Stop codon signals release factor to bind, releasing polypeptide.
• Ribosomal subunits and tRNA dissociate.

Gene Expression

• Involves transcription and translation processes.
• Regulated by promoter regions and gene regulatory sequences.

Purpose and Application

• Proteins are essential for physiological functions and processes like digestion.
• mRNA transports genetic information for protein synthesis.
• Ribosomes and tRNA work together to synthesize proteins from genetic instructions.
• The genetic code is translated into proteins that make up the body's structure and function.

Conclusion

• Protein synthesis showcases the central dogma of molecular biology: DNA → RNA → Protein.
• The processes ensure the accurate and efficient production of proteins necessary for life.