Protein Synthesis Cram Notes

Key Concepts in Protein Synthesis

Overview of DNA and Protein Synthesis

• RNA Structure:

  • A-T and C-G pairing in DNA.

  • In RNA (which has uracil - U instead of thymine), A pairs with U and C pairs with G.

  • DNA is located in the nucleus and serves as a blueprint for proteins.

• Function of Proteins:

  • Proteins are essential for cellular structure and function, acting as enzymes, structural components, and signaling molecules.

  • Proteins are synthesized based on the information encoded in DNA.

Steps in Protein Synthesis

1. Transcription

• Definition: The process of copying a segment of DNA into mRNA (messenger RNA).

• Process:

  • RNA polymerase enzyme binds to the DNA and separates the strands.

  • The DNA strand serves as a template for mRNA synthesis. The base pairing occurs:

  • A-U (in RNA), U-A, C-G, G-C.

  • Result: mRNA molecule is synthesized and moves from the nucleus to the cytoplasm.

2. Translation

• Definition: The process where the mRNA is translated into a polypeptide (protein).

• Key Components:

  • Ribosomes:

  • Composed of ribosomal RNA (rRNA) and proteins.

  • Contains A, P, and E sites:

    • A site: binds new aminoacyl-tRNA.

    • P site: holds the tRNA with the growing polypeptide chain.

    • E site: where tRNA exits after delivering its amino acid.

  • tRNA (transfer RNA):

  • Has an anticodon that pairs with the mRNA codon and carries a specific amino acid.

  • Structure includes a cloverleaf shape with an amino acid attached to the 3' end.

• Process:

  • Initiation:

  • mRNA, ribosomal subunits, and initiator tRNA come together at the start codon (AUG).

  • Elongation:

  • The ribosome facilitates successive tRNA binding to the mRNA, causing peptide bonds to form between amino acids and elongating the polypeptide chain.

  • Codon recognition, peptide bond formation, and translocation occur.

  • Termination:

  • A release factor binds to the A site when a stop codon is reached (UAA, UAG, UGA), leading to the release of the polypeptide chain.

mRNA Code

• Codons:

  • Codons are sequences of three nucleotides (triplets) that correspond to specific amino acids.

  • Redundant nature of the genetic code allows multiple codons to encode the same amino acid (mutation insurance).

  • Important codons include:

  • Start codon: AUG (Methionine)

  • Stop codons: UAA, UAG, UGA

tRNA Loading and Amino Acid Activation

• Amino Acid Activation:

  • An enzyme called aminoacyl-tRNA synthetase attaches the appropriate amino acid to its corresponding tRNA, utilizing ATP.

• Function:

  • Activates the amino acid for incorporation into the growing polypeptide chain at the ribosome.

Summary of Transcription and Translation

• In transcription:

  • mRNA is synthesized in the nucleus and is processed (capping, polyadenylation).

  • Introns (non-coding sequences) are removed, and exons (coding sequences) are joined.

• In translation:

  • mRNA is translated in the cytoplasm into a functional polypeptide, forming the basis for cellular function and structure.